NOTICES OF THE PROCEEDINGS AT THE MEETINGS OF THE MEMBERS OF THE Eo^al Xustttution of #teat Btttaitt, WITH ABSTRACTS OF THE DISCOURSES DELIVERED AT THE EVENING MEETINGS. VOLUME XIII. 1890—1892. LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, STAMFOKD STREET AND CHARING CROSS. 1893. ?patron. HER MOST GRACIOUS MAJESTY QUEEN VICTOKIA. Uice^^Patron antj i^onorarg i^emter. HIS ROYAL HIGHNESS THE PEINCE OF WALES, E.G. F.K.S. President — The Duke of Northumberland, E.G. D.C.L. LL.D. Treasurer — Sir James Crichton-Browne, M.D. LL.D. F.E.S. — V.P. Honorary Secretary — Sir Frederick Bramwell, Bart.| D.C.L. LL.D. F.R.S. M. Inst. G.E.— V.P. Managers. 1892-93. Sir Frederick Abel, K.C.B. D.C.L. Captain W. de W. Abney, C.B. R.E. D.C.L. F.R.S. George Berkley, Esq. M. Inst. C.E. Shelford Bidwell, Esq. M.A. F.R.S. Joseph Brown, Esq. C.B. Q.C. Arthur Herbert Church, Esq. M.A. Sir Andrew Clark, Bart. M.D. LL.D. F T? S Sir ' Douglas Galton, K.C.B. D.C.L. LL.D. F.R.S.— F.P. The Right Hon. Lord Halsbury, M.A. D.C.L. F.R.S.— F.P. William Huggins, Esq. D.C.L. LL.D. F.R.S.— F.P. David Edward Hughes, Esq. F.R.S.— V.P. The Right Hon. Lord Kelvin, D.C.L. LL.D. Pres. R.S.— F.P. Hugo MiiUer, Esq. Ph.D. F.R.S. John Rae, M.D. LL.D. F.R.S. William Chandler Roberts- Austen, Esq. C.B. F.R.S. Visitors. 1892-93. Thomas Buzzard, M.D. F.R.C.P. Michael Carteighe, Esq. F.CS. Andrew Aiuslie Common, Esq. F.R.S. F.R.A.S. James Farmer, Esq. J.P, Robert Hannah, Esq. George Herbert, Esq. Donald William Charles Hood, M.D. F.R.C.P. James Mansergh, Esq. M. Inst. C.E. Lachlan Mackintosh Rate, Esq. M.A. John Callander Ross, Esq. Arthur William RUcker, Esq. M.A. F.R.S. Sir David Salomons, Bart. M.A. F.R.A.S. F.CS. John Bell Sedgwick, Esq. J.P. F.R.G.S. John Isaac Thornycroft, Esq. INI. Inst. C.E. Robert Wilson, Esq. M. Inst. C.E. professors. Honorary Professor of Natural Philosophy— J OUN Tyndall, Esq. D.C.L. LL.D. F.R.S. &c. Professor of Natural Philosophy— The Right Hon. Lord Rayleigh, M.A. D.C.L. LL.D. F.R.S. &c. Fullerian Professor of Chemistry— J A-ii^s Dewar, Esq. M.A. LL.D. F.R.S. &c. FuUerian Prof essor of Physiology — Victor Horsley, Esq. F.R.S. B.S. F.R.C.S. Honorary Librarian— Mr. Benjamin Vincent. Keeper of the Library and Assistant Secretary— Mr. Henry Young. Clerk of Accounts and CoUector—Mr. Henry C. Hughes. Assistants in the Laboratories— Mr. R. N. Lennox, Mr. J. W. Heath, and Mr. G. Gordon. Ateistant in the Library ^Mr. Herbert C. Fyfe. CONTENTS. 1890. Page Jan. 24. — Professor Dewar — The Scientific Work of Joule 1 „ 31. — Sir Frederick Abel— Smokeless Explosives .. 7 Feb. 3.— General Monthly Meeting 24 „ 7. — Henry B. Wheatley, Esq. — The London Stage in Elizabeth's Eeign.. .. .. .. ,. 27 „ 14. — Professor J. A. Fleming — Problems in the Physics of an Electric Lamp .. .. .. .. 84 „ 21. — Shelford Bidwell, Esq. —Magnetic Phenomena .. 50 „ 28. — Professor C. Hubert H. Parry — Evolution in Music .. .. .. .. .. .. 56 March 3.— General Monthly Meeting 69 „ 7. — Francis Gotoh, Esq. — Electrical Relations of the Brain and Spinal Cord .. .. .. .. 183 5, 14. — Professor T. E. Thorpe — The Glow of Phosphorus 72 „ 21. — Professor G. F. Fitzgerald — Electromagnetic Radiation .. ,. .. .. .. .. 77 „ 28. — The Right Hon. Lord Rayleigh — Foam.. .. 85 April 7.— General Monthly Meeting .. .. .. .. 97 „ 18. — Sir Frederick Bramwbll, Bart. — Welding by Electricity^ 186 40143 !▼ CONTENTS. 1890. Page April 25. — The Right Hon. Sir John Lubbock, Bart. M.P. — The Shapes of Leaves and Cotyledons .. .. 102 May 1.— Annual Meeting .. .. .. .. .. 112 „ 2. — Walter H. Pollock, Esq. — Theophile Gautier (no Abstract) .. .. ,. ., ., 113 „ 6.— General Monthly Meeting 113 „ 9. — R. Brudenell Carter, Esq. — Colour- Vision and Colour-Blindness .. .. .. .. ..116 „ 16. — Professor Raphael Meldola — The Photographic Image .. .. .. .. .. .. 131: „ 23. — Professor A. C. Haddon — Manners and Customs of the Torres Straits Islanders .. .. .. 145 „ 30. — A. A. Common, Esq. — Astronomical Telescopes .. 157 June 2.— General Monthly Meeting 173 „ 6. — Professor W. Botd Dawkins — The Search for Coal in the South of England 175 „ 13. — Professor Silvanus P. Thompson — The Physical Foundation of Music .. .. .. .. 206 July 7.— General Monthly Meeting 197 Nov. 3. — General Monthly Meeting 199 Dec. 1.— General Monthly Meeting 203 1891. Jan. 23.— The Right Hon. Sir Edward Fry — British Mosses .. .. 237 „ 30. — Professor J. W. Judd — The Rejuvenescence of Crystals 250 Yg\), 2.— General Monthly Meeting 258 ^j 6. — The Right Hon. Lord Ratleigh — Some Applica- tions of Photography ., .. .. .. 261 CONTENTS. V 1891. Page Feb. 13. — Peofessor A. Schuster — Recent Total Solar Eclipses 273 „ 20. — Edward Emanuel Klein, M.D. — Infectious Dis- eases, their Nature, Cause, and Mode of Spread 277 „ ' 27. — Percy Fitzgerald, Esq. — The Art of Acting (no Abstract) , 293 March 2.— General Monthly Meeting ,. 293 „ 6. — Professor J. A. Fleming — Electromagnetic Pepul- sion .. .. .. 296 „ 13.— Felix Semon, M.D.— The Culture of the Singing Voice 317 „ 20. — Professor Victor Horsley — Hydrophobia (no Abstract) .. .. ,. .. .. .. 342 April 6.— General Monthly Meeting 342 ,j 10. — Sir William Thomson — Electric and Magnetic Screening .. .. .. ,. .. .. 345 „ 17. — Professor A. W. Etjcker — Magnetic Rocks .. 417 „ 24. — The Rev. Canon Ainger — Euphuism — past and present (no Abstract) .. .. .. .. 420 May 1. — Annual Meeting .. .. .. .. .. 356 „ 1. — James Edmund Harting, Esq. — Hawks and Hawking .. .. .. .. .. .. 357 „ 4.— General Monthly Meeting .. 362 5, 8. — Professor W. Ramsay — Liquids and Gases .. 365 „ 15. — Professor G. D. Livein^} — Crystallisation .. 375 „ 22. — Professor J. A. Ewing — The Molecular Process in Magnetic Induction .. .. .. .. 387 „ 29. — David Gill, Esq. — An Astronomer's Work in a Modern Observatory .. .. ., .. 402 June 1. — General Monthly Meeting .. .. .. .. 420 VI CONTENTS. 1891. Page June 2. — (Extra Evening.^ Charles Waldstein, Esq. — The Discovery of " The Tomb of Aristotle " . . 423 „ 5. — St. George J. Mivart, Esq. — The Implications of Science ,. .. .. .. .. .. 428 „ 12. — Professor Harold Dixon — The Rate of Explosion in Gases .. .. .. .. .. .. 443 Faraday Centenary Lectures. „ 17. — I. By The Right Hon. Loud IIayleigh „ 26. — II. By Professor Dewar ., July 6. — General Monthly Meeting .. Nov. 2. — General Monthly Meeting .. Dec. 7. — General Monthly Meeting .. 462 481 451 454 458 1892. Jan. 22. — The Right Hon. Lord Ratleigh — The Composi- tion of Water (no A&s/rac/) .. .. .. 489 ,j 29. — Sir George Douglas, Bart. — Tales of the Scottish Peasantry .. .. .. .. .. .. 489 Peb. 1.— General Monthly Meeting 498 „ 1. — Special General Meeting .. .. .. .. 501 J, 4. — (Extra Evening.) Nikola Tesla, Esq. Currents of High Potential and of High Frequency .. 637 5. — Professor Roberts-Austen — Metals at High Tem- peratures .. .. .. .. .. .. 502 12.~G. J. Stmons, Esq. — Rain, Snow, and Hail (wo Abstract) .. .. .. .. .. .. 518 ,, 19. — Professor Percy F. Frankland — Micro-organisms in their relation to Chemical Change .. .. 619 26. — Sir David Salomons, Bart. — Optical Projection.. 534 March 4. — Professor L. C. Miall — The Surface-film of "Water and its relation to the Life of Plants and Animals .. .. .. .. .. .. 510 CONTENTS. VU 1892. Page Marcli 7.— General Monthly Meeting 550 „ 11. — F. T. PiGGOTT, Esq. — "Japanesque" .. .. 554 „ 18. — George Du Maurier, Esq. —Modern Satire in Black and White (no Abstract) .. .. .. 564 „ 25. — John Evans, Esq. — Posy-rings (no Abstract) .. 564 April 1. — Professor Oliver Lodge — The Motion of the Ether near the Earth . .. ,. .. 565 „ 4.— General Monthly Meeting .. .. .. .. 581 ,j 8. — Professor W. E. Ayrton — Electric Meters, Motors, and Money matters {no Abstract) .. 583 ^^ 29.— B. W. EicHARDSON, M.D.— The Physiology of Dreams .. .. .. .. .. .. 584 May 2 —Annual Meeting 600 „ 6. — Captain Abney — The Sensitiveness of the Eye to Light and Colour .. .. ,. .. .. 601 „ 9.— General Monthly Meeting 612 „ 13. — WifiLiAM HuGGiNS, Esq. — The New Star in Auriga 615 „ 20.— J. Wilson Swan, Esq. — Electro-metallurgy .. 625 „ 27. — Sir J. Crichton-Browne — Emotional ExjDression 653 June 3.— LuDWiG MoND, Esq. — Metallic Carbonyls . . .. 668 „ 10. — Professor Dewar — Magnetic Properties of Liquid Oxygen .. .. .. .. .. ,. 695 „ 13.— General Monthly Meeting 681 July 4. — General Monthly Meeting .. .. ,. .. 684 Nov. 7.— General Monthly Meeting 687 Dec. 5. — General Monthly Meeting .. ., .. .. 692 Index to Volume XIII. .. .. .. .. 700 ( viii ) PLATES. Page Applications of Photography .. .. .. .. 263,265 Crystallisation .. .. .. .. .. ,. 386 Spectra of Sirius and a Aurigae .. .. .. .-. 408 Apparatus for Liquefaction and Solidification of Gases .. 483 Apparatus employed at the Faraday Centenary Lecture by Professor Dewar .. .. .. .. .. 484 Spectra of New Star in Auriga, Plates I. and II. .. .. 618 iSogal fingtitution of ffireat Brit WEEKLY EVENING MEETING^ Friday, Jcanuaiy 24, 1890. Sir Frederick Abel, C.B. D.C.L. F.R.S. Vice- in the Claair. Professor Dewar, M.A. F.R.S. 3LB.L The Scientific Work of Joule. (Abstract.) Prof. Dewar commenced by remarking that the Royal Institution had been so closely identified with the great workers in physical science that it was impossible to allow the work of Joule, whose researches had produced as marked a revolution in Physical Science as Darwin's in Biology, to pass without recognition in the present series of Friday Evening Discourses. Sir William Thomson, as Joule's friend and fellow-worker to the last, had been invited to undertake the duty, and had agreed to do so ; but at the last moment had been compelled to decline by reason of important official duties in Scotland, and the task had consequently devolved upon him. Having given a brief account of Joule's parentage, early life, and education, Prof. Dewar reviewed, as fully as time would permit, his scientific work, which extended over about forty years, and was repre- sented by 115 original memoirs. The first period (1838 to 1843) was distinguished as that in which Joule educated himself in experimental methods, chiefly in connection with electricity and electro-magnetic engines. This work led him in 1840 to his first great discovery, the true law governing the relation between electric energy and thermal evolution, which enabled him later on to account for the whole dis- tribution of the current, not only in the battery in which it is pro- duced, but in conductors exterior to it. Joule was thus led to take up the study of electrolysis. Faraday had already made the discovery that electrolytic bodies could be split up into equivalent proportions by the passage of the same electric current ; Joule saw that there would be great difiiculty in finding out the distribution of the current energy, and accounting for the whole of it. After a laborious research he succeeded in showing that during electrolytic action there was an absorption of heat equivalent to the heat evolved during the original combination of the constituents of the compound body. The prose- cution of his electrical researches rapidly brought Joule on the road to his great discovery of the Mechanical Equivalent of Heat, it being clear from a foot-note to a paper dated 18th February, 1843, that he already had well in hand the study of the strict relations between chemical, electrical, and mechanical effects. In working out these laws, it was to be remarked that Joule — in common with most inventors and seekers after new scientific truths — chose perhaps the most difficult means that could have been selected ; Vol. XIII. (No. 84.) b 2 Professor Dewar [Jan. 24, and in looking back at his work in the light of present knowledge, it seemed simply astounding that he should have succeeded so com- pletely as he did. The original coil used by Joule for the mechanical determination of heat (kindly lent for the occasion by Prof. Eiicker) was shown, and the course of the experiment explained. The vast difficulties which Joule had to overcome in order to prove that there was a definite, permanent, and persistent relation between the amount of mechanical energy expended and the heat pro- duced were commented on ; the thermal efiects being produced not directly but through the medium of an electric current varying in intensity, and calculations having to be made not only for these fluctuations, but for the effects of radiation, the movement of the air, and other indirect complications. The very small increment of heat to be measured obliged Joule to use thermometers of great delicacy, and these he had to devise and construct himself. One of the thermometers so used was exhibited. Working in this way, Joule was able by the end of July, 1843, to state definitely that the amount of heat capable of increasing the temperature of a pound of water by 1° F. was equal to, and might be converted into, a mechanical force capable of raising 838 lbs. to the height of one foot. Soon afterwards he attained almost identical results by a more direct method — the friction of water passing through small tubes — which gave him 770 foot pounds per unit of heat. It was impossible, said the lecturer, to thoroughly appreciate Joule's work without glancing at the early history of the subject ; and when one did so it was amazing to find how near men of the stamp of Eumford, Davy, and Young had been to Joule's great dis- covery, and yet missed it. Count Eumford was the first to clearly define the relation between the constant production of heat and loss of movement by frictional motion. He proved that the amoimt of heat produced by friction was continuous, and apparently unlimited ; but he did not think of measuring the relation between the mechanical enerfry expended and the amount of heat produced. Alluding to the results obtained from this apparatus, the lecturer said that Count Eumford might have shown that in his exj)eriments the heat pro- duced was proportional to the time of working, and so obtained a result capable of being expressed in horse-power. The value so deducted from Eumford's experiments is not far removed from Joule's first number. The experiments commenced by Count Eumford were carried on by Davy, at that time working with Beddoes at Bristol ; and led to one of the most remarkable essays on heat of that period, which disposed for ever of the theory of the separate existence of caloric. Taking two pieces of ice on a cold day, Davy mounted them so that they could be rotated against each other with frictional pressure, the effect being that the pieces of ice were melted, and the water so produced had a much higher specific heat than the original ice. To guard against the possibility of heat being conveyed to the frictional 1890.] on The Scientific Work of Joule. 3 apparatus by the suiToimding air, Davy made an experiment in vacuo, isolating the apparatus by means of ice ; and found that under such conditions sufficient heat could be produced to melt wax placed in the receiver. The lecturer here showed an exj^eriment illustrating the production of water by the friction of two pieces of ice in vacuo, under conditions of temperature much more severe than those of Davy's experiment. Following Davy, Young devoted a great deal of attention to the subject, and by 1812 he and Davy had quite changed their opinions, and had adopted the view that heat and motion were convertible effects. Having by July 1843 assured himself of the principle of his dis- covery, Joule now devoted himself to the elaboration of methods of working, modifying and repeating experiments in various ways, but always approaching nearer and nearer to exactness, as shown by the following Table of results : — Joule's values of the Mechanical Equivalent op Heat. Kilogramme metres. Magneto-electric currents 1843 460 Friction of water in tubes „ 424 * 6 Diminution of heat produced in a battery current when the current produces work „ 499 Compression of air 1845 443*8 Expansion of air „ 437 • 8 Friction of water „ 488*3 „ „ „ 1847 428-9 „ „ „ 1850 423-9 ,, „ mercury „ 424*7 „ „ iron ■. „ 425*2 Heat developed in Daniel's cell „ 419 - 5 „ „ in wire of known absolute resistance .. .. 1867 429*5 Friction of water in calorimeter 1878 423-9 Prof. Dewar here exhibited and explained the action of the original calorimeter used by Joule. It was seen to consist of a set of vanes which were made to revolve in water by the falling of known weights through a definite and known height, the heat produced being due (after making the necessary deduction for the friction due to the momentum of the weights) entirely to the friction of the fluid. It was found that whatever fluid was employed, the same definite results were obtained : — a production of heat in the liquid bearing a constant relation to the unit of mechanical energy expended. The extreme delicacy of Joule's apparatus, and the marvellous accuracy of his observations were shown by the fact that working with weights of 29 lbs. each, and repeating each observation 20 times, the total increase of temperature did not exceed half a degree Fahrenheit. In contrast to this the lecturer showed, by means of apparatus kindly lent by Prof. Ayrton, the method now employed for repeating Joule's work and arriving at substantially the same results b}' much simpler means B 2 4 Professor Dewar [Jan. 24, While continuing to work intermittently at his great discovery, Joule employed himself in the following years in elaborate investiga- tions bearing uj)on the point of maximum density of water, specific gravity, and atomic volumes. An illustration of his method of deter- mining maximum density was given by means of two large cylinders filled with water and connected by a narrow channel in which was placed a floating indicator. It was shown that the slightest variation in density of the water of either cylinder — variations far beyond the scope of the most delicate thermometer — set up currents which were immediately detected by the movement of the indicator, and that by this means it was quite possible to ascertain the exact temperature at which water attained its maximum density. Joule's determinations of atomic volumes were marvellous at the time they were made, and were still interesting. Illustrations of his work in this direction were given by means of a solution of sugar, which was seen to occupy j)ractically the same space as was occupied by an amount of water exactly equivalent to that combined in the carbohydrate. The carbon hypothetically combined with the water to form the sugar appearing to make no sensible difference to the volume ; and in contrast to this was seen the enormous difference in volume brought about by dissolving two equal portions of soda car- bonate, one portion being ordinary hydrated crystals and the other portion being anhydrous, in equal volumes of water. Joule's last great research was carried out conjointly with Sir William Thomson, and occupied nearly ten years of laborious enquiry. Its chief object was to prove that in compressing a gas the amount of heat produced is equivalent to the work done, and independent of the mere fact of the approach of the particles. But Joule was desirous of amplifying the enquiry, and in fact the work might be divided into three sections : (1) the study of gases passing through narrow apertures'; (2) the velocity attained by bodies passing through the air ; and (3) the temperature ultimately attained by such moving bodies. With respect to 2 and 3, it was shown that a body rotating in the air at the rate of about 150 to 180 feet per second increased in temperature by nearly 1° F., and that this increase of temperature was definite for a given velocity, and independent of the size of the moving mass and the density of the gaseous medium. With regard to (1) the relation of gaseous pressure and volume to temperature, the researches of Eegnault had already shown that the simple law of Marriotte and Boyle could not stand by itself; and Joule sought to modify it by the study of gases passing through very small tubes or porous bodies. The investiga- tions were carried out at Manchester on a large scale, and were assisted by a Government grant. Steam engines were employed to maintain a current of gas at a constant temperature and pressure through loug coils of pipe placed in water tanks. They proved that any difference of temperature in the gas brought about in its passage through the porous body must be due to work done by it, and that this difference of temperature varied for different gases, according to their constitution. 1890.] on The Scientific Work of Joule. 5 Working under the same conditions, hydrogen was shown to be reduced a small amount in temperature, air somewhat more (about 0'3^), and carbonic acid a much greater amount. A repetition of Joule and Thomson's experiment was shown by means of a 100 feet coil of lead pipe, compressed hydrogen, air, and carbonic acid gas being employed, and the original results verified in each case. The effect of this research was to enable Joule and Thomson to formulate a great im- provement on the gaseous laws ; for instead of the product of the volume and pressure being strictly proportional to the absolute tem- perature, as it had been hitherto believed to be, they found that a new term was involved, which is equivalent to a constant divided by the absolute temperature and multiplied by the volume. In conclusion, Prof. Dewar read the following letter, which he had received from Sir Lyon Playfair in response to his request for some reminiscences of Joule : — Dear Dewar, 20^/i Jan., 1890. You ask for some of my memories of Joule from 1842 to 1845, when I was Professor of Chemistry at the Royal Institution in Manchester. The great Dalton died in the autumn of 1844, and had long been President of the Manchester Philosophical Society. He naturally gave impulse to the study of science in that town, where there was an active band of young workers in research. Joule was, even then, foremost among these ; and the names of Binney, Williamson, Schunck, Angus Smith, Young, and others show that the spirit of scientific inquiry was active. We were also stimulated by the fact that Baron Liebig and Bunsen came to pay me visits during that time ; they were men to excite research. Joule was a man of singular simplicity and earnestness. We used to meet at each other's houses at supper, to help the progress of our work by discussion. Joule was an earnest worker, and was then engaged on his experiments on the mechanical equivalent of heat. He took me to his small laboratory to show me his experiments, and I of course quickly recognised that my young friend the brewer was a great philosopher. We jointly worked upon questions of far less importance than his great central discovery, but he was equally interested. I was very anxious that he should devote his life to science, and persuaded him to become candidate for the Professorship of Natural Philosophy at St. Andrews. He was on the point of securing this, but his slight personal deformity was an objection in the eyes of one of the electors ; and St. Andrews lost the glory of having one of the greatest discoverers of our age. When Joule first sent an account of his experiments to the Royal Society, the paper was referred, among others, to Sir Charles Wheat- stone, who was my intimate personal friend. Wheatstone was an eminently fair man and a good judge, but the discovery did not then recommend itself to his mind. For a whole Sunday afternoon we walked on Barnes Common, discussing the experiments and their 6 Professor Dewar on The Scientific Worh of Joule. [Jan, 24, consequences, if true, to science. But all my arguments were insufficient to convince my friend ; and I fear that then the Eoyal Society did not appreciate and publish the researches. I write from memory only, for I know that, later, no society or institution honoured Joule more than the Eoyal Society and its members. Not for one moment, however, did Joule hesitate in the accuracy of his experiments or his conclusions. He once suggested to me that we might take a trip together to the Falls of Niagara, not to look at its beauties, but to ascertain the dijSference of temperature of the water at the top and bottom of the fall. Of course the change of motion into heat was a necessary consequence of his views. No more pleasant memory of my life remains than the fact that, side by side, at my lectures in the Eoyal Institution, used to sit the illustrious Dalton, with his beautiful face, so like that of Newton, and the keenly intelligent Joule. I can give no other explanation than the fact of organic chemistry being then a new science that two philosophers of such eminence should come to the lectures of a mere tyro in science. I used to look upon them as two types of the highest progress in science. Newton had introduced law, order, and number into the movements of masses of matter in the universe ; Dalton introduced the same into the minute masses which we call atoms; and Joule, with a keen insight into the operations and correlation of forces, connected them together and showed their mutual equi- valence. I do not know whether these memories are of any use to you, but, such as they are, they are at your disposal for your lecture on the friend of my youth. Yours sincerely, Lyon Playfair. 1890.] Sir Frederick Ahel on Smokeless Explosives. 7 WEEKLY EVENING MEETING, Friday, January 31, 1890. Sir Feederick Bramwell, Bart. D.C.L. F.R.S. Honorary Secretary and Vice-President, in the Chair. Sir Frederick Abel, C.B. D.C.L. D.Sc. F.RS. V.P.B.L Sirtokeless Explosives. The production of smoke which attends the ignition or explosion of gunpowder is often a source of considerable inconvenience in con- nection with its application to naval or military purposes, its employ- ment in mines, and its use by the sportsman, although occasions not unfrequently arise during naval and military operations when the shroud of smoke produced by musketry or artillery fire, has proved of important advantage to one or other, or to both, of the belligerents during different periods of an engagement. Until within the last few years, however, but little, if any, thought appears to have been given to the possibility of dispensing with or greatly diminishing the production of smoke in the applica- tion of fire-arms, excepting in connection with sport. The inconve- nience and disappointment often resulting from the obscuring effects of a neighbouring gun-discharge, or of the first shot from a double- barrel arm, led the s^^ortsman to look hopefully to gun-cotton, directly after its first production in 1846, as a probable source of greater comfort and brighter prospects in the pursuit of his pastime and in his strivings for success. A comparison between the chemical changes attending the burning, explosion, or metamorphosis of gun-cotton and of gunpowder, serves to explain the cause of the production of smoke in the latter case, and the reason of smpkelessness in the case of gun-cotton. Whilst the products of explosion of the latter consist exclusively of gases, and of water which assumes the transparent form of highly- heated vapour at the moment of its production, the explosive sub- stances classed as gunpowder, composed of mixtures of saltj)etre, or another nitrate of a metal, with charred wood or other carbonised vegetable matter, and with variable quantities of sulphur, furnish pro- ducts, of which very large proportions are not gaseous, even at high temperatures. Upon the ignition of such a mixture, these products are in part deposited in the form of a fused residue, which constitutes the fouling in a fire-arm, and are in part distributed, in an extremely fine state of division, through the gases and vaj)ours developed by the explosion, thus producing smoke. In the case of gunpowder of ordinary composition, the solid pro- ducts amount to over fifty per cent, by weight of the total products 8 Sir Frederick Ahel [Jan. 31, of cxj)losion, and the dense white smoke which it produces, consists in part of extremely finely divided potassium carbonate which is a component of the solid products, and, to a great extent, of potassium sulphate produced chiefly by the burning of one of the important solid products of explosion, potassium sulphide, when it is carried in a fine state of division into the air by the rush of gas. With other explosives, which are also smoke-producing, the formation of the smoke is due to the fact that one or other of the products, although existing as vaj)our at the instant of its develop- ment, is immediately condensed to a cloud composed of minute liquid particles, or of vesicles, as in the case of mercury vapour liberated upon the explosion of mercuric fulminate, or of the aqueous vapour produced upon the ignition of a mixture of ammonium nitrate and charcoal, or ammonium nitrate and picric acid. Until within the last half-dozen years, the varieties of gunpowder which have been applied to war purposes in this and other countries have exhibited comparatively few variations in chemical composition. The proportions of charcoal, saltpetre, and sulphur, employed in their production, exhibit slight diiferences in difi'erent countries, and tbese, as well as the character of the charcoal used, its sources and method of production, underwent but little modification for very many years. The same remark applies to the nature of the successive operations pursued in the manufacture of black powder for artillery purposes in this and other countries. The replacement of smooth-bore guns by rifled artillery, which followed the Crimean war, and the increase in the size and power of guns consequent upon the application of armour to ships and forts, soon called for the pursuit of investigations having for their object the attainment of means for variously modifying the action of fired gunj)owder, so as to render it suitable for the different calibres of guns, whose full power could not be effectively, or in some instances safely, develoj^ed by the use of the kind of gunj)owder previously employed indiscriminately in artillery of all known calibres. In order to control the violence of explosion of gunpowder, by modifying the rapidity of transmission of explosion from particle to particle, or through the mass of each individual j)article, of which the charge of a gun is composed, the accomplishment of the desired results was, in the first instance, and indeed throughout practical investigations extending over many years, sought exclusively in modifications of the size and form of the individual masses composing a charge of powder, and of their density and hardness ; it being considered that, as the proportions of saltpetre, charcoal and sulphur, generally emjiloyed in the production of gunpowder, very nearly correspond to those required for the development of the greatest chemical energy by those incorporated materials, it was advisable to seek for the attainment of the desired results by modifications of the physical and mechanical characters of gunpowder, rather than by any modification in the proportions and chemical characters of its ingredients. 1890.] on Smokeless Explosives. 9 The varieties of powder, which, as the outcome of careful practi- cal and scientific researches in this direction, have been introduced into artillery-service from time to time, and some of which, at any rate, have proved fairly efficient, have been of two distinct types. The first of these, produced by breaking up more or less highly-pressed cakes of black powder into grains, j)ebbles, or boulders, of approxi- mately uniform size and shape, the sharp edges and rough surfaces being afterwards removed by attrition (reeling and glazing), are simply a further development of one of the original forms of granu- lated or corned powder, represented by the old F. G., or small-arms, and L. G., or cannon-powder. Gunpowders of this class, ranging in size from about 1000 pieces to the ounce, to about six pieces to the pound, have been introduced into artillery-service, and certain of them, viz. E. L. G. (rifle large grain), which was the first step in advance upon the old cannon-powder (L. G.) ; pebble-powder (P), and large j^ebble or boulder-powder (P 2), are still employed more or less extensively in some guns of the present day. The other type of powder has no representative among the more ancient varieties ; it has its origin in the obviously sound theoretical view that uniformity in the results furnished by a particular powder, when employed under like conditions, demands not merely identity in regard to composition, but also identity in form, size, density, and structure of the individual masses composing the charge used in a gun. The practical realisation of this view should obviously be attained, or at any rate approached, by submitting equal quantities of one and the same mixture of ingredients, presented in the form of powder of uniform fineness and dryness, to a uniform pressure for a fixed period in moulds of uniform size, and under surrounding con- ditions as nearly as possible alike. The fulfilment of these conditions would, moreover, have to be supplemented by an equally uniform course of proceeding in the subsequent drying and other finishing processes to which the powder-masses would be submitted. The only form of powder, introduced into our artillery-service for a brief period, in the production of which these conditions were adhered to as closely as possible, was a so-called pellet powder, which consisted of small cylinders, having semi-perforations with the object of increasing the total inflaming surface of the individual masses. Practical experience with this powder, and with others prepared upon the same system, but with much less rigorous regard to uni- formity in such details as state of division and condition of dryness of the powder before its compression into cylindrical or other forms, showed that uniformity in the ballistic properties of black powder could be as well and even more readily secured by the thorough blending or mixing together of batches presenting some variation in regard to density, hardness, or other features, as by aiming at an approach to absolute uniformity in the characters of each individual mass composing a charge. 10 Sir Frederick Abel [Jan. 31, At the time that our attention was first actively given to this subject of the modification of the ballistic proj^erties of powder, it had already been to some extent dealt with in the United States by Kodman and Doremus, and the latter was the first to propose the application, as charges for guns, of powder-masses produced by the compression of coarsely grained powder into moulds of prismatic form. In Russia the first step was taken to utilise the results arrived at by Doremus, and to adojjt a prismatic powder for use in guns of large calibre. Side by side with the development and perfection of the manu- facture of prismatic powder in Russia, Germany, and in this country, new experiments on the production of powder-masses suitable, by their comparatively gradual action, for employment in the very large charges required for the heavy artillery of the present day, by the powerful compression of mixtures of more or less finely broken up powder-cake into masses of greater size than those of the i)ebble, pellet, and j^rism powders, were actively pursued in Italy, and also by our own Government Committee on Explosives, and the outcome of very exhaustive practical investigations were the very efficient Fossano powder, or poudre progressif, of the Italians, and the boulder and large cylindrical powders known as P^ and C^, produced at \A'altham Abbey, which scarcely vied, however, wdth the Italian powder in the uniformity of their ballistic properties. Researches carried out by Captain Noble and the lecturer some years ago with a series of gunpowders differing considerably in com- position from each other, indicated that advantages might be secured in the production of powders for heavy guns by so modifying the proportions of the constituents (e. g. by considerably increasing the proportion of charcoal and reducing the proportion of sulphur) as to give rise to the production of a much greater volume of gas, and at the same time to diminish the heat developed by the explosion. These researches served, among other purposes, to throw con- siderable light upon the cause of the wearing or erosive action of powder-explosions upon the inner surface of the gun, which in time produces so serious a deterioration of the arm that the velocity of projection and accuracy of shooting suffer very greatly, an effect the extent of which increases in an increasing ratio to the size of the guns, in consequence, obviously, of the large increase in the weight of the charges fired. Several causes undoubtedly combine to bring about the wearing away of the gun's bore, which is especially great where the products of explo.sion, wliile under the maximum pressure, can escape between the projectile and the bore. The great velocity with which the very highly heated gaseous and liquid (fused solid) products of ex- plosion sweep over the heated surface of the metal gives rise to a displacement of the particles composing it, which increases as the surface becomes roughened by the first action upon the least compact portions of the metal, and thus opposes greater resistance ; at the 1890.] on Smokeless Explosives. 11 same time, the effect of the high temperature to which the surface is raised is to reduce its rigidity and power of resisting the force of the gaseous torrent, and lastly some amount of chemical action upon the metal, by certain of the highly heated non-gaseous products of explosion, contributes towards an increase in the erosive effects. A series of careful experiments made by Captain Noble with powders of different composition, and with other explosives, afforded decisive evidence that the explosive agent which furnished the largest pro- portion of gaseous products, and the explosion of which was attended by the development of the smallest amount of heat, exerted least erosive action. It is probable that important changes in the composition of powders manufactured by us for our heavy guns would have resulted from those researches, but in the meantime, two eminent German gunpowder manufacturers had occupied themselves independently, and simultaneously, with the important practical question of pro- ducing some more suitable powder for heavy guns than the various new forms of ordinary black powder, the rate of burning of which, especially when confined in a close chamber, was, after all, reduced only in a moderate degree by the increase in the size of the masses, and by such increase in their density as it was practicable to attain. The German experimenters directed their attention not merely to an alteration of the proportions of the powder ingredients, but also to a modification in the character of charcoal employed, and the success attending their labours in these directions led to the practically simultaneous production, by Mr. Heidemann at the Westphalian Powder Works, and Mr. Diittenhofer at the Eottweil Works near Hamburg, of a prismatic powder of cocoa-brown, colour, consisting of saltpetre in somewhat higher proportion, of sulphur in much lower proportion, than in normal black powder, and of very slightly burned charcoal, similar in composition to the charcoal (cJiarhon roux) which Violette, a French chemist, first produced in 1847 by the action of superheated steam upon wood or other vegetable matter, and which he proposed for employment in the manufacture of sporting powder. These brown prismatic powders (or " cocoa-powders," as they were termed from their colour), are distinguished from black powder not only by their appearance, but also by their very slow combustion in open air, by their comparatively gradual and long-sustained action when used in guns, and by the simple character of their products of explosion as compared with those of black powder. As the oxidising ingredient, saltpetre, is contained, in brown or cocoa powder, in larger proportion relatively to the oxidisable components sulj)hur and char- coal than in black powder, these become fully oxidised, while the products of explosion of the latter contain, on the other hand, larger proportions of unoxidised material, or of only partially oxidised pro- ducts. Moreover, there is produced upon the explosion of brown powder a relatively very large amount of water-vapour, not merely because the finished powder contains a larger proportion of water than 12 Sir Frederick Abel [Jan. 31, black powder, but also because the very sliglilly cbarred wood or straw used in the brown powder is much richer in hydrogen than black charcoal, and therefore furnishes by its oxidation a considerable amouut of water. The total volume of gas furnished by the brown powder (at 0" C. and 760 mm. barometer) is only about 200 volumes per kilogramme of powder, against 278 volumes furnished by a normal sample of black powder, but the amount of water-vapour furnished upon its explosion is about three times that produced from black powder, and this would make the volume of gas and vapour developed by the two powders about equal if the heat of its explosion were the same in the two cases ; the actual temperature produced by the explosion of brown powder is, however, somewhat the higher of the two. Although the smoke produced upon firing a charge of brown powder from a gun appears at first but little different in denseness to that of black powder, it certainly disperses much more rapidly, a difference which is probably due to the speedy absorption, by solution, of the finely divided potassium salts by the large proportion of water- vapour distributed throughout the so-called smoke. This class of powder was substituted with considerable advantage for black powder in guns of comparatively large calibre ; nevertheless it became desirable to attain even slower or more gradual action in the case of the very large charges required for guns of the heaviest calibres, such as those which propel shot of about 2000 lbs. weight. Accordingly, the brown powder has been modified in regard to the proportions of its ingredients to suit these conditions, while, on the other hand, powder intermediate with respect to rapidity of action between black pebble powder and the brown powder, has been found more suitable than the former for use in guns of moderately large calibre. The recent successful adaptation of machine guns and compara- tively large quick-firing guns to naval service, more especially for the defence of ships against attack by torpedo boats, &c., has rendered the provision of a powder for use with them, which would produce comparatively little or no smoke, a matter of very considerable importance, inasmuch as the efficieocy of such defence must be greatly diminished by the circumstance that, after a very brief use of the guns with black powder, the objects against which their fire is destined to operate, become more or less completely hidden from those directing them, by the dense veil of powder-smoke produced. Hence much attention has been directed during the last few years to the production of smokeless, or nearly smokeless powders for naval use in the above directions. At the same time, the views of many military authorities regarding the importance of dispensing with smoke in land engage- ments has also created a demand, the apparent urgency of which has been increased by various circumstances, for a smokeless powder suitable for field artillery and small arms. The properties of ammonium nitrate, of which the products of de- composition by heat are, in addition to water-vapour, entirely gaseous, 1890.] on Smokeless Explosives. 13 have rendered it a tempting material to work upon in the hands of those who have striven to produce a smokeless powder, but its deliques- cent character has been the chief obstacle to its application as a com- ponent of an explosive agent susceptible of substitution for black powder for service purposes. A German chemical engineer, F. Gans, conceived that, by incor- porating charcoal and saltpetre with a particular proportion of ammonium nitrate, he had produced an explosive material which did not partake of the hygroscopic character common to other ammonium- nitrate mixtures, and that, by its explosion, the potassium in the saltpetre formed a volatile combination with nitrogen and hydrogen, a potassium amide, so that, although containing nearly half its weight of potassium salt, it would furnish only volatile products. The views of Mr. Gans regarding the changes which his so-called amide powder undergoes upon explosion were not borne out by existing chemical knowledge, while the powder compounded in accordance with his views proved to be by no means smokeless, and was certainly not non-hygro- scopic. Mr. Heidemann has, however, been successful, by modifications of Gans's prescription and by application of his own special experience in j)owder-manufacture, in producing an ammonium nitrate powder possessed of remarkable ballistic properties, furnishing comparatively little smoke, which speedily disperses, and exhibiting the hygroscopic characteristics of ammonium nitrate preparations in a decidedly less degree than any other hitherto prepared. The powder, while yielding a very much larger volume of gas and water-vapour than black or brown powder, is considerably slower than the latter ; the charge required to produce equal ballistic results is less, while the chamber- pressure developed is lower, and the pressures along the chase of the gun are higher, than in the case of brown powder. The ammonium nitrate powder contains, in its normal, dried condition, more water than even brown powder ; it does not exhibit any great tendency to absorb moisture from an ordinarily dry or even a somewhat moist atmosphere, but if the amount of atmospheric moisture approaches saturation, it will rapidly absorb water, and when once the process begins it continues rapidly, the powder masses becoming speedily quite pasty. The charges for quick-firing guns are enclosed in metal cases, in which they are securely sealed up ; the powder is therefore prevented from absorbing moisture from the external air, but it has been found that if the cartridges are kept for long periods in ships' magazines, in which, Irom their position relatively to the ship's boilers, the temperature is more or less elevated, sometimes for considerable periods, the expulsion of water from some portions of the powder-masses composing the hermetically sealed charge, and its consequent irregular distribution, may give rise to a want of uniformity in the action of the powder, and to the occasional development of high pressures. Although, therefore, this ammonium- nitrate powder may be regarded as the first successful advance towards the production of a comparatively smokeless artillery-powder, it is 14 Sir Frederick Abel [Jan. 31, not uniformly well adapted to the requirements which it should fulfil in naval service. Attention was fiirst seriously directed to the subject of smokeless powder by the reports received about four years ago of remarkable results stated to have been obtained in France with such a powder for use with the magazine rifle (the Lebel) which was being adapted to mili- tary service. These Reports were speedily followed by others, descrip- tive of marvellous velocities obtained with small charges of this powder, or some modifications of it, from guns of very great length. As in the case of melinite, the fabulously destructive effects of which were much vaunted at about the same time, the secret of the precise nature of the smokeless powder was so well preserved by the French au- thorities, that surmises could only be made on the subject even by those most conversant with these matters. It is now well known, however, that more than one smokeless explosive has succeeded the original powder, the perfection of which was reported to be beyond dispute, and that the material now adopted for use in the Lebel rifle bears, at any rate, great similarity to j^reparations which have been made the subject of j)atents in this country, and which are still experi- mental powders in other countries. So far as smokelessness is concerned, no material can surpass gun- cotton pure and simple ; but, even if its rate of combustion in a fire- arm could be controlled with certainty and uniformity, although only used in very small charges, such as are required for military rifles, its application as a safe and reliable propulsive agent for mili- tary and naval use is attended by so many difficulties, that the non- success of the numerous attempts, made in the first twenty-five years of its existence, to apply it in this direction, is not surprising. Soon after its discovery by Schonbein and Bottger in 1816, en- deavours were made to apply gun-cotton wool, rammed into cases, as a charge for small arms, but with disastrous results. Subsequently von Lenk, who made the first practical approach to the regulation of the explosive power of gun-cotton, j)roduced small arm cartridges by superposing layers of gun-cotton threads, these being closely plaited round a core of wood. Von Lenk's system of regulating the rapidity of burning of gun-cotton, so as to suit it either for gradual or violent action, consists, in fact, in converting coarse or fine, loosely or lightly twisted, threads or rovings of finely carded cotton into the most explosive form of gun-cotton, and of arranging these threads or yarns in different ways so as to modify the mechanical condition i. e. the compactness and extent and distribution of enclosed air-spaces, of the mass of gun-cotton composed of them. Thus, small arm car- tridges were composed, as already stated, of compact layers of tightly plaited, fine gun-cotton thread ; cannon cartridges were made up of coarse, loose gun-cotton yarn wound very compactly upon a core ; charges for shells consisted of very loose cylindrical hollow plaits (like lamp wicks) along which fire flashed almost instantaneously ; and mining charges were made in the form of a very tightly twisted 1890.] on Smokeless Explosives. 15 rope with a hollow core. While the two latter forms of gun-cotton always burned with almost instantaneous rapidity in open air, and with highly destructive effects if they were strongly confined, the tightly wound or plaited masses burned slowly in air, and would frequently exert their explosive force so gradually when con- fined in a firearm, as to produce good ballistic results without appre- ciably destructive eifect upon the arm. Occasionally, however, in consequence of some slight unforeseen variation in the compactness of the material, or in the amount and disposition of the air-spaces in the mass, very violent action would be produced, showing that this system of regulating the explosive. force of gun-cotton was quite unreliable. Misled by the apparently promising nature of the earliest results which von Lenk obtained, the Austrian Government embarked, in 1862, upon a somewhat extensive application of von Lenk's gun-cotton to small arms, and provided several batteries of field guns for the use of this material. The abandonment of these measures for applying a smokeless explosive to military purposes soon followed upon the attain- ment of unsatisfactory results, and was hastened by the occurrence of a very destructive explosion at gun-cotton stores at Simmering, near Vienna, in 1862. It was at about this time that the attention of the English Govern- ment, and through them of the lecturer, was directed to the subject of gun-cotton, the Austrian Government having communicated details regarding improvements in its manufacture accomplished by von Lenk, and results obtained in the extended experiments which had been carried out on its application to the various purposes above indicated, according to the system devised by that officer. One of the results of the lecturer's researches, subsequently carried on at Wool- wich and Waltham Abbey, was his elaboration of the system of manufacture and employment of gun-cotton which has been in exten- sive use at the government works with little if any modification for over eighteen years, and has been copied from us by France, Germany, and other countries. By reducing the partially purified gun-cotton- fibre to pulp as in the ordinary process of making paper, com- pleting its purification when in that condition, and afterwards convert- ing the finely-divided explosive into highly compressed homogeneous masses of any desired form and size, very important improvements were effected in its stability, its uniformity of composition and action, and its adaptability to practical uses, a great advance being made in the exercise of control over the rapidity of combustion or explosion of the material. No success had attended the experiments instituted in England with wound cannon cartridges of gun-cotton-threads made according to von Lenk's plan ; on the other hand a number of results which at first sight appeared very promising, were obtained at Woolwich in 1867-8 with bronze field-guns and cartridges built up of compressed gun-cotton-masses arranged in different ways (with varied air-spaces, &c.) with the object of regulating the rapidity of explosion of the 16 Sir Frederick Abel [Jan. 31, charge. But altlioiigli the attainment of high velocities with com- paratively small charges of the material, unaccompanied by any indi- cations of injury to the gun, was frequent, it became evident that the fulfilment of the conditions essential to safety to the arm were exceedingly difficult to attain with certainty ; they aj)peared indeed to be altogether beyond absolute control, even in so small a gun as the twelve-pounder. Military authorities not being, in those days, alive to the advantages which might accrue from the employment of an entirely smokeless explosive in artillery, the lecturer received no encouragement to persevere with experiments in this direction, and the same was the case with respect to the possible use of a smokeless explosive in military small arms, with which, however, far more pro- mising results had at that time been obtained at Woolwich. Abel's system of preparing gun-cotton was no sooner elaborated than its application to the production of smokeless cartridges for sporting purposes was achieved with considerable success by Messrs. Prentice of Stowmarket. The first gun-cotton cartridge, which found considerable favour with sportsmen, consisted of a roll of felt-like paper composed of gun-cotton and ordinary cotton, and produced from a mixture of the pulped materials. Afterwards a cylindrical pellet of slightly compressed gun-cotton pulp was used, the rapidity of exj)losion of which was retarded, while it was at the same time protected from absorption of moisture, by impregnation with a small proportion of india-rubber. Neither of these cartridges afi'orded promise of suffi- cient uniformity of action to fulfil military requirements, but after a series of experiments which the lecturer made with compressed gun- cotton arranged in various ways, very promising results were attained, especially with the Martini-Henry rifle and a charge of pellet-form, the rapidity of explosion of which was regulated by simple means. A sporting powder which was nearly smokeless had, in the mean- time, been produced by Colonel Schultze, of the Prussian Artillery, from wood cut up into very small cube-like fragments, converted into a mild form of nitro-cellulose after a jn-eliminary purifying treatment, and impregnated with a small portion of an oxidising agent. Sub- sequently the manufacture of the Schultze powder was considerably modified ; it was converted into the granular form and rendered con- siderably more uniform in character and less hygroscopic, and it then bore considerable resemblance to the E.G. powder, a granulated nitro- cotton powder, produced, in the first instance, at Stowmarket, and consisting of a less highly nitrated cotton than gun-cotton (trinitro- cellulose), incorporated in the pulped condition with a somewhat considerable proportion of the nitrates of potassium and barium, and converted into grains through the agency of a solvent and a binding material. Both of these powders produced some smoke when fired, though the amount was small in comparison with that from black powder. They did not compete with the latter in regard to accuracy of shooting, when used in arms of precision, but they are interesting as being the forerunners of a variety of so-called smokeless powders, 1890.] on Smokeless Explosives. 17 of which gun-cotton or some form of nitro-cellulose is the basis, and of which those of Johnson and Borland, and of the Smokeless Powder Company, are the most prominent in this country. In past years, both camphor and liquid solvents, such as acetic ether and acetone, for gun-cotton, and mixtures of ether and alcohol for nitro-cotton, have been ap])lied to the hardening of the surfaces of compressed masses or granules of those materials, by von Forster and others, with a view to render them non-porous, and in the E.G. powder manufacture the latter solvent was thus applied to harden the powder-granules. In the Johnson-Borland powder, camphor is applied to the same purpose ; in smokeless powders of French and German manufacture acetic ether and acetone have been used, and the solvent has been applied, not merely to harden the granules or tablets of the ex- plosive, but to convert the latter into a homogeneous horn-like material. Much mystery has surrounded the nature and origin of the first smokeless powder adopted, apparently with undue haste, by the French Government, for use with the Lebel magazine rifle. A few particles of the Vieille powder, or Poudre B, were seen by the lecturer about two years ago, and very small specimens appear to have fallen into the hands of the German Government about that time. They were in the form of small yellowish-brown tablets of about 0*07 inch to 0 • 1 inch square, of the thickness of stout notepaper, and had evi- dently been produced by cutting up thin sheets of the material. They appeared to contain, as an important ingredient, picric acid (the basis of " melinite ") a substance extensively used as a dye, and obtained by the action of nitric acid, at a low temperature, upon carbolic acid and cresylic acid, constituents of coal tar. Originally produced by the action of nitric acid upon indigo, and afterwards by similar treat- ment of Botany Bay gum, it was first known as carbazotic acid, and is one of the earliest of known explosives of organic origin. When sufficiently heated, or when set light to, it burns with a yellow smoky flame, and even very large quantities of it have been known to burn away somewhat fiercely, but without exploding. Under certain con- ditions, however, and especially if subjected to the action of a power- ful detonator, it explodes with very great violence and highly destructive effects, as pointed out by Sprengel in 1873, and recent experiments at Woolwich have shown that it does this even, as in the case of gun-cotton, when it contains as much as 15 per cent, of water. It is no longer a secret that picric acid at any rate forms the basis of the much-vaunted and mysterious explosive for shells for which the French Government were said to have paid a very large sum of money, and the destructive effects of which have been described as nothing less then marvellous. M. Turpin patented, in 1875, the use of picric acid alone as an explosive for shells and for other engines of destruction, and whether or not his claims to be the inventor of melinite are valid, there appears no doubt that his patent in France was the starting-point of the development and adop- tion of that explosive. Vol. XIII. (No. 84.) c 18 Sir Frederick Ahel [Jan. 31, The attention thus dinicted in France to the properties of picric acid appears to have given rise to experiments resulting in its employment as an ingredient of the first smokeless powder {Foudre B) adopted for the French magazine rifle. The idea of employing picric acid preparations as explosive agents for propulsive purposes originated with Designolle about twenty years ago, but no useful results attended the experiments with the particular mixtures proposed by him. It is certain that the recent adaptation of that substance in France was of a different character, and that, promising as were the results of the new smokeless powder, of which it appears to have formed an ingredient, and a counterpart of which was made the subject of experiments at Woolwich about three years ago, its deficiency in the all-essential quality of stability must have been, at any rate, one cause of its abandonment in favour of another form of smokeless powder, which there is reason to believe is of more simple character. In Germany, the subject of smokeless powder for small arms and artillery was being steadily pursued in secret, while the sensational reports concerning Pottdre B were spread about in France, and a small-arm powder giving excellent results in regard to ballistic properties and uniformity, was elaborated at the Rottweil powder- works, and appears to have been adopted into the German service for a time, but its first great promise of success seems to have failed of fulfilment through defects in stability. Reference has already been made to the conversion of gun-cotton (trinitrocellulose), and to mixtures of it with less explosive forms of nitrated cotton (or cellulose of other description), by the action of solvents, into horn-like materials. These are in the first instance obtained in the form of gelatinous masses, which, prior to the complete evaporation, or removal in other ways, of the solvent, can be pressed or squirted into wires, rods, or tubes, or rolled or spread into sheets ; when they have become hardened, they may be cut up into tablets, or into strips or pieces of size suitable for conversion into charges or cartridges. Numerous patents have been secured for the treatment of gun-cotton, nitro-cotton, or mixtures of these with other substances, by the methods indicated ; but in this direction the German makers of the powder just now referred to seem to have secured priority. Experi- ments were made about a year and a half ago with powder produced in this way at Woolwich, and the Wetteren Powder Company in Belgium has also manufactured so-called paper powders, or horn-like preparations, of the same kind, which were brought forward as counterparts of the French small arm- and artillery-smokeless powder. Mr. Alfred Nobel, to whom the mining world is so largely indebted for the invention of dynamite, and of other very efficient blast- in^ agents of which nitro-glycerine is the basis, was the first to apply the latter explosive agent, in conjunction with one of the lower pro- ducts of nitration of cellulose, to the production of a smokeless powder. This powder bears great resemblance to one of the most interesting of 1890.] on Smokeless Explosives. 19 known violent explosive agents, also invented by Mr. Nobel, and called by him blasting gelatine, in consequence of its peculiar gelatinous character. When the nitro-cotton is impregnated and allowed to digest vrith nitro-glycerine, it loses its fibrous nature and becomes gelatinised while assimilating the nitro-glycerine, the two substances furnishing a product which has almost the character of a compound. By macerating the nitro-cotton with from 7 to 10 per cent, of nitro- glycerine, and maintaining the mixture warm, the whole soon becomes converted into a plastic material from which it is very difficult to separate a portion of either of its components. This preparation, and certain modifications of it, have acquired high importance as blasting agents more powerful than dynamite, and possessed of the valuable property that their prolonged immersion in water does not separate from them any appreciable proportion of nitro-glycerine. In the earlier days of the attempted application of blasting gelatine to military uses, in Austria, when endeavours were there made to render the material less susceptible of accidental explosion on active service (as by the penetration of bullets or shell fragments into transport wagons containing supplies of the explosive), this result was achieved by Colonel Hess by incorporating with the components a small proportion of camphor, a substance which had then, for some time past, played an important part in the technical application of nitro-cotton to the production of the remarkable substitutes for ivory, horn, &c., known as Xylonite. By incorporating with nitro-glycerine a much larger proportion of nitro-cotton than used in the production of blasting gelatine, and by employing camphor as an agent for pro- moting the union of the two explosives, as well as, apparently, for deadening the violence, or reducing the rapidity of explosion of the product, Mr. Nobel has obtained a material of almost horn-like character, which can be pressed into pellets or rolled into sheets while in the plastic condition, and which compares favourably with the gun-cotton preparations of somewhat similar physical characters just referred to, as regards ballistic properties, stability and uni- formity, besides being almost absolutely smokeless. The retention in its composition of some proportion of the volatile substance camphor, which may gradually be reduced in amount by evaporation, renders this explosive liable to undergo some modification in its ballistic properties in course of time ; it is believed that this point has been dealt with by Mr. Nobel, and accounts from Italy speak favourably of the results of trials of his powder in small arms, while Mr. Kru|)p is reported to be carrying on experiments with it in guns of several calibres. The Government Committee on Explosives, in endeavouring to remedy the above defect of Nobel's original powder, were led by their researches to the preparation of other varieties of nitro-glycerine- powder, which, when applied in the form of wires or rods, made up into sheaves or bundles, have given, in the service small-bore rifle, excellent ballistic results. The most promising of them, which c 2 20 Sir FredericJc Ahel [Jan. 31, fulfils, besides, the conditions of smokelessness and of stability, so far as can be guaranteed by tbe application of special tests of exposure to elevated temperatures, &c., is now being submitted to searching experiments with the view of so applying it in the arm as to over- come certain difficulties attending the employment, in a very small- bore rifle, of an explosive developing much greater energy than the black-2)owder charge, which therefore gives very considerably higher velocities even with much smaller charges, and consequently heats the arm much more. Thus, the service black-powder charge furnishes, with the small-bore rifle, an average (and variable) velocity of 1800 f.s., together with pressures ranging from 18 to 20 tons per square inch ; on the other hand, with considerably less of the explosive referred to, there is no difficulty in securing a very uniform velocity of about 2200 f.s. with pressures not exceeding 17 tons, while velocities as high as 2500 f.s. are obtainable with pressures not greater than the maximum allowed with the black-powder charge. It is obvious, from what has already been said respecting the causes of the erosive action of powder in guns, that comparatively considerable erosive effects would be expected to be produced by powders of high energy as compared wdth black powder. Moreover, the freedom of the products of explosion from any solid substances, and consequently the absence of any fouling or deposition of residue in the arm, causes the heated surfaces of the projectile and of the interior of the barrel to remain clean, and in a condition, therefore, very favourable to close adherence together. If to these circumstances be added the fact that the behaviour of the smokeless powder has to be adapted to suit an arm, a cartridge, and a projectile originally designed for use with black powder, it will be understood that the devisino" of an explosive which shall be practically smokeless, suffi- ciently stable, and susceptible of perfectly safe use in the arm under all service conditions, easy of manufacture and not too costly, is, after all, but a small part of the difficult problem of adapting a smokeless powder successfully to the new military rifle — a problem which, however, appears to be on the near approach to satisfactory solution. The experience already acquired in guns ranging in calibre from 1 • 85 inches to 6 inches, with the smokeless powder devised for use in our service, has been very promising, and indicates that the difficulties attending its adaptation to guns designed for black powder are likely to prove coi.siderably less than in the case of the small arm. But here again, the circumstances that much smaller charges are required to furnish the same ballistics as the service black-powder charges, and that the comparatively gradual and sustained action of the new powder gives rise to lower pressures in the chamber of the gun, and higher pressures along the chase, demonstrate that the full utilisation of the ballistic advantages, and the increase in the power of guns of a given calibre and weight, with the new form of powder, are only attainable by some modifications in the designs of the guns — such aa 1890.] on Smokeless Explosives. 21 a reduction in size of the charge-chamber, and some additions to the strength, and perhaps, in some cases, of the length, of the chase. When, however, the smokeless powder has been adapted with success in all respects to artillery, from small machine guns to guns of comparatively heavy calibre, and when its ballistic advantages have been fully utilised in guns of suitable design, it will remain to be determined how far such a powder — undeniably of much more sensitive constitution than black powder, or any of its modifications — will withstand, unchanged and unharmed, the various vicissitudes of climate, and the service storage-conditions in ships and on land in all parts of the world, — a condition essential to its adaptability to naval and military use, and especially to the service of our Empire ; and whether sufficient confidence can be placed in its stability for lont^ periods under these extremely varied conditions to warrant the neces- sary freedom from apprehension of possible danger, emanating from within the material itself, to allow of its being substituted for black powder wherever its use may present advantages. Possible it might be, that the storage, with perfect safety, of such a powder in ships, forts, or magazines might demand the adoption of precautionary measures which might place some comparatively narrow limits upon the extent of its practicable service applications ; even then, however, an imperative need for the introduction of special arrangements to secure safety and immunity from deterioration may be of small importance as compared with the great advantages which the provision of a thoroughly efficient smokeless powder may secure to the possessor of it, especially in naval warfare. That the opinions respecting the importance of such advantages are founded upon a sound basis, one can hardly doubt, after the views expressed by several of the highest military and naval authorities, although opinions as to their extent may differ very considerably even among such authorities. The accounts furnished from time to time from official and private sources of the effects observed, at some considerable distance, by witnesses of practice with the smokeless powders successively adopted in France, have doubtless been regarded by military authorities as warranting the belief that the employment of such powders must effect a great revolution in the conduct of campaigns. Not only have the absence of smoke and flame been dwelt upon as important factors in such a revolution, but the recorders of the achievements of smoke- less powder — whose descriptions have doubtless been to some extent influenced by the vivid pictures already presented to them of what they should anticipate — have even been led to make such explicit assertions as to the noiselessness of these powders, that hio^h military authorities have actually been thereby misled to pourtray, by vivid word-painting, the contrast between the battles of the future and the past;— to imagine the terrific din caused by the discbarge of several hundred field-guns and the roar of musketry in the ^n-eat battles of the past, giving place to noise so slight that distant troops 22 Sir Frederick Ahel [Jan. 31, will no longer receive indications where their comrades are engaged, while sentries and advanced posts will no longer be able to warn the main body of the approach of an enemy by the discharge of their rifles, and, that battles might possibly be raging within a few miles of columns on the march without the fact becoming at once apparent to them. It is somewhat difficult to conceive that, in these comparatively enlightened days — an acquaintance with the first principles of physical science having for many years past constituted a preliminary condi- tion of admission to the training establishments of the future warrior — the physical impossibility of such fairy tales as appear to be considered necessary in France for the delusion of the ordinary public, would not at once have been obvious. Yet, even in professional publications in Germany, where we are led to expect that the judgment of experts would be comparatively unlikely to be led astray through lack of scientific knowledg^e, we have, during the earlier part of last year, read, in articles upon the influence of smokeless powder upon the art of war (based evidently upon the reports received from France), such passages as these : — " The art of war gains in no way as far as sim- plicity is concerned ; on the contrary, it appears to us that the absence of so important a mechanical means of help as noise and smoke were to the commander, requires increased skill and circum- spection in addition to the qualities demanded by a general " " The course of a fight will certainly be mysterious, on account of the relative stillness with which it will be carried on." In an amusing article, in imitation of the account of the Battle of Dorking, which appeared in the ' Deutsche Heeres Zeitung,' of April last, the consternation is described with which a battalion receives the information from a wounded fugitive from the outposts that the enemy's bullets have been playing havoc among them, without any visible or audible indications as to the quarter of attack. Later in the year, and especially since the manceuvres before the German and Austrian Emperors, when the employment of the new smokeless powder was the event of the day, the absurdity of the assertions as to the noiselessness of the new powders became a theme for strong observations in the German service papers ; the assumed existence of a noiseless powder was ridiculed as a thing equally impossible with a recoil-less powder ; the violence of the report, or explosion, produced upon the discharge of a firearm being in direct relation to the volume and tension of the gaseous matter projected into the surrounding air. The circumstance that blank ammunition was alone used in the smokeless powder exhibition at the German manoeuvres may have served to lend some support to the assertions as to comparatively little noise made by the powder — the report of blank cartridges being slight, on account of the small and lightly confined charges used. It is said that the sound of practice with blank ammunition at the German manoeuvres, was scarcely recognised at a distance of 100 metres. In a recently published pamphlet on the results of employment of the 1890.] on Smokeless Explosives. 23 latest German smokeless powder in the manoeuvres, it is stated, on the other hand, that the difference between the violence of the report of the new powder and of black powder is scarcely perceptible ; that it is sharper and more ringing, but not of such long duration. This description accords exactly with our own experience of the reports produced by different varieties of smokeless powder, and of the lecturer's earlier experience with gun-cotton charges fired from rifles and field guns. The noise produced by the latter was decidedly more ringing and distressing to the ear in close proximity to the gun, but also of decidedly less volume, than the report of a black-powder charge, when heard at a considerable distance from the gun. As regards smokelessness : the present German service powder is not actually smokeless, but produces a thin, almost transparent, bluish cloud which is immediately dissipated. Independent rifle-firing was not rendered visible by the smoke produced at a distance of 300 metres, and at shorter ranges the smoke presented the appearance of a puff from a cigar. The most rapid salvo-firing during the operations near Spandau did not have the effect of obscuring those firing from distant observers. That, in future warfare, if smokeless or nearly smokeless powders have maintained their position as safe and reliable propelling agents for small arms and field artillery, belligerents of both sides will be alike users of them, there can be no doubt. The consequent absence of the screening effect of smoke — which, on the one hand, removes an important protection and the means of making rapid advances or sudden changes of position in comparative safety, and, on the other hand, secures to both sides the power of ensuring to the fullest extent accuracy of shooting, and of making deadly attack by indi- vidual fire through the medium of cover, with comparative immunity from detection — can scarcely fail to change more or less radically many of the existing conditions under which engagements are fought. As regards the naval service, it is especially and, at present at any rate, exclusively for the new machine- and quick-firing guns that a smokeless powder is wanted ; for such service the advantages which would be secured by the provision of a reliable powder of this kind can scarcely be over-estimated, and their realisation within no distant period may, it is believed, be anticipated with confidence. [F. A. A.] 24 General Monthly Meeting. [Feb. 3, GENERAL MONTHLY MEETING, Monday, February 3, 1890. Sir James Crichton Browne, M.D. LL.D. F.E.S. Treasurer and Vice-President, in tlie Chair. F. W. Fison, Esq. M.A. (Oxon.) F.C.S. Dr. C. A. Martius, The Right Hon. Earl Russell, William Schooling, Esq. F.R.A.S. were elected Members of the Royal Institution. The Special Thanks of the Members were returned for the following Donation to the Fund for the Promotion of Experimental Research : — Professor Dewar, 50Z. The decease of Sir William Withey Gull, Bart. M.D. D.C.L. F.R.S. M.B.I, on January 29th, was announced from the Chair. The following Resolution passed hj the Managers at their Meeting this day was read : — Resolved: — That the Managers of the Koyal Institutioa of Great Britain desire, at this, their first Meeting after the death of Sir William Withey Gnll, to place on record in their minutes their sense of the great loss sustained by the death of one who, for nearly thirty years, had been a Member of the Institution ; who had occupied the Chair of Fullerian Professor of Physiology, and who, quite recently, had been one of their colleagues on the Board of Management, and who had, on every occasion, shown the deep interest he took in the Institution, and in the welfare of all connected with it. The Managers further desire to be permitted to offer to Lady Gull the expression of their most sincere sympathy and condolence with her in her bereavement. Fesohed : — That the Honorary Secretary do send to Lady Gull a copy of this Resolution. The following resolution passed by the Managers at their Meeting this day was read : — Resolved : — That the thanks of the Managers of the Institution be given to the National Telephone Company for the great assistance which they rendered to Professor Riicker in illustrating his Course of Christmas Lectures, by so kindly enabling him to show the operations of the Telephone as actually employed for exchange work. Resolved: — That the Honorary Secretary do send to the Company a copy of this Resolution. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FROM The Governor-General of India — Geological Survey of India : Records, Vol. XXII. Part 4. 4to. 1889. The Lords of the Admiralty— ^diwiicul Almanack, 1893. 8vo. 1889. 1890.] General Monthly Meeting. 25 Accademia del Lincei, Reale, Roma — Atti, Serie Quarta : Kendiconti. 2^ Semes- tre, Vol. V. Fasc. 5-10. 8vo. 1889. Agricidtural Society of England, Royal — Journal, Second Series, Vol. XXV. Part 2. 8vo. 1889. Asiatic Society of Bengal — Journal, Vol. LVIII. Part I. No. 1 ; Part 11. Nos. 1 and 2. 8vo. 1889. Proceedings, 1889, Parts 1 to 6. 8vo. Modern Vernacular Literature of Hindustan. By G. A. Grierson. 8vo, 1889. Astronomical Society, Royal — Monthly Notices, Vol. L. Nos. 1, 2. 8vo. 1890. Ateneo Fewe^o— Kevista Mensile, 1888-9. 8vo. Bankers, Institute o/— Journal, Vol. X. Part 10 ; Vol. XI. Part 1. 8vo. 1889-90. Batavia Observatory — Magnetical and Meteorological Observations, 1888, Vol. XI. 4to. 1889. Kainfall in East Indian Archipelago, 1888. 8vo. 1889. Birmingham Philosophical Society — Proceedings, Vol. VI. Part 2, 8vo. 1889. British Architects, Royal Institute of — Proceedings, 1889-90, Nos. 4-7. 4to. Canada, Geological and Natural History Survey of — Annual Eeports, &c. 1887-8. 8vo. 1889. Canadian Institute — Proceedings, 3rd Series, Vol. VII. Fas. 1. 8vo. 1889. Chemical Industry, Society of — Journal, Vol. VIII. Nos. 11, 12. Svo. 1890. Chemical Society — Journal for Dec. 1889 and Jan. 1890. 8vo. Civil Engineers^ Institution — Proceedings, Vol. XCVIII. Svo. 1889. Corporation of City of London — Catalogue of the Guildhall Library. Svo. 1889. Cracovie, V Academic des Sciences — Bulletin, 1889, Nos. 10-12. Svo. Crisp, Frank, Esq. LL.B. F.L.S. &c. M.R.I, (the Editor)— 5 ouxndl of the Koyal Microscopical Society, 1889, Part 6. Svo. Dawson, G. M. Esq, D.Sc F.G.S. (the Author) — Earlier Cretaceous Rocks of N.W. Canada. Svo. 1889. Ore Deposit of Treadwell Mine, Alaska. Svo. 1889. Glaciation of British Columbia. Svo. 1889. East India Association — Journal, Vol. XXII. No. 1. Svo, 1889. Editors — American Journal of Science for Dec. 1889 and Jan. 1890. Svo. Analyst for Dec. 1889 and Jan. 1890. Svo. Athenaeum for Dec. 1889 and Jan. 1890. 4to. Chemical News for Dec. 1889 and Jan. 1890. 4to. Chemist and Druggist for Dec. 1889 and Jan. 1890. Svo. Electrical Engineer for Dec 1889 and Jan. 1890. fol. Engineer for Dec. 1889 and Jan. 1890. fol. Engineering for Dec. 1889 and Jan. 1890. fol. Horological Journal for Dec. 1889 and Jan. 1890. Svo. Industries for Dec. 1889 and Jan. 1890. fol. Iron for Dec. 1889 and Jan. 1890. 4to. Ironmongery for Dec. 1889 and Jan. 1890. Murray's Magazine for Dec. 1889 and Jan. 1890. Svo. Nature for Dec. 1889 and Jan. 1890. 4to. Photographic News for Dec. 1889 and Jan. 1890. Svo. Revue Scientifique for Dec. 1889 and Jan. J 890. 4to. Telegraphic Journal for Dec. 1889 and Jan. 1890. Svo. Zoophilist for Dec. 1889 and Jan. 1890. 4to. Electrical Engineers, Institution of — Journal, Nos. 82, S3. Svo. 18S9. Florence Biblioteca Nazionale Centrale — BoUetino, Nos. 94-97. Svo. 1889. FranMin Institute — Journal, Nos, 768, 769. Svo. 1889. Geographical Society, Royal — Proceedings, New Series, Vol. XI. No. 12 ; Vol. XII. Nos. 1, 2. 1889-90. Geological Institute. Imperial, Vienna — Verhaudlungen, 1889, Nos. 13-17. Svo. Glasgow Fhilosopjhical Society — Proceedings, Vol. XX. Svo. 1889. Iron and Steel Institute— J onvnsl for 1889, Vol. II. Svo. 1889, John Hopkins University — University Circulars, Nos. 76, 77. 4to. 1SS9-90. Junior Engineering Society — Address. Svo. 1889. 26 General Monthly Meeting. [Feb. 3, Kew Observatory — Report, 1889. Svo. Latzina, M. F. {the Compiler) — Censo General de la Ciudad de Buenos Aires, Tome II. Svo. 1889. Linnean Society— J onrn^i], Nos. 123, 172. Svo. 1889-90. Manchester Geological Society — Transactions, Vol. XX. Parts 11-13. 8vo. 1889. Manchester Steam Users' Association — Boiler Explosions Act, 1882. Report, Nos. 284-350. 4to. 1889. Mechanical Enqineers' Institution — Proceedings, 1889, No. 3. Svo. Meteorological 'Office— Weekly Weather Reports, Nos. 48-52. 4to. 1889. Quarterly Weather Report, 1880, Part 1. 4to. 1889. Meteorological Society, Royal — Quarterly Journal, No. 72. Svo. 1889. Meteorolo'j;ical Record, No. 34. Svo. 1889. Middlesex ffospital—Bepovt for 1888. Svo. 1889. Ministry of Public Works, Borne — Giornale del Genio Civile, Seria Quinta, Vol. lil. Nos. 10, 11. And Disegni. fol. 1889. New Yorli Academy o/>Sc/euces— Transactions, Vol. VIII. Parts 5-8. Svo. 1890. North of England Institute of Mining and Mechanical Engineers — Transactions, Vol. XXXVIII. Part 4. Svo. 1890. Numismatic Society — Chronicle and Journal, 1889, Part 4. Svo. 1889. Odontological Society of Great Britain — Transactions, Vol. XXII. Nos. 2, 3. New Series. Svo. 1889. Pennsylvania Geological Survey — Annual Report, 1887. Svo. 1889. Dictionary of Fossils. Vol. I. A-M. Svo. 1889. Pharmaceutical Society of Great Britain — Journal, Dec. 1889 and Jan. 1890. Svo. Calendar, 1890, Svo. Photographic Society — Journal, Vol. XIV. Nos. 3, 4. Svo. 1889. Relfe Bros. Messrs. (the Publishers) — Modern Thought and Modern Thinkers. By J. F. Charles. 12mo. 1889. Rio de Janeiro Observatory — Revista, Nos. 10-12. Svo. 1889. Royal Historical and Archxological Association of Ireland — Journal, Vol. IX. (4tli Series), No. 80. Svo. 1889. Royal Society of Edinburgh — Proceedings, Vol. XV. ; Vol. XVI. Parts 1 to 7. Svo. 1889. Royal Society of London — Proceedings, No. 284. Svo. 1889. Saxon Society of Sciences, Royal — Philologisch-historischen Classe : Abhandlung. Band XI. No. 5. Svo. 1889. Berichte, 1889, Nos. 2, 3. Svo. 1889. Scottish Society of Arts, iio?/aZ— Transactions, Vol. XII. Part 3. Svo. 1889. Society of Architects — Proceedings, Vol. II. No. 4. Svo. 1890. Society of Arts — Journal for Dec. 1889 and Jan. 1890. Svo. Statistical Society— J owrnal, Vol. LII. Part 4. Svo. 1889. St. Petersbourg Acadentie Imperiales dcs Sciences — Memoii'es, Tome XXXVII. No. 2. 4to 1889. Bulletin, Tome XXXIII. No. 2. 4to. 1889. Sweden Royal Academy of Sciences — Handlingar, Band XX. XXI. and Atlaa 4to. 1882-87. Bihang, Band IX.-XIII. Svo. 1883-8. Ofversigt, Band XLI.-XLV. Svo. 1884-8. Lefnadsttckningar, Band II. Heft 3. Svo. 1885. Forteckning (Table des Matieres), 182G-1883. Svo. 1884. United Service Institution, Royal — Journal, No. 151. Svo. 1889. Vereins zur Beforderung des Gewerbfleisses in Preussen — Verhandlungen, 1889: Heft 9-12. 4to. Victoria Ivsfitnfe — Transactions, No. 91. Svo. 1889. Wriijht & Co. Messrs. J. (the PM^Zis/ters)— Deformities of Children. By W. Pye. Svo. 1890. 1890.] Mr. H. B, Wheatley on London Stage in EUzahetlis Beign. 27 WEEKLY EVENING MEETING, Friday, February 7, 1890. John Eae, M.D. LL.D. F.E.S. Vice-President, in the Chair. Henry B. Wheatley, Esq. F.S.A. The London Stage in ElizabetJCs Beign. As the words "stage" and "drama" are sometimes used synony- mously, it is necessary to state at the outset that the subject of the discourse is the material stage which grew up in this reign, and not the Elizabethan drama. During the first eighteen years of Eliza- beth's reign the growth of the drama was but gradual, and the appliances for the acting of plays were but little different from what they had been in the previous reigns, while in 1576 a great change occurred, and the first playhouse was erected in the fields to the west of the highway at Shoreditch. It was called the Theatre, and the name alone seems to make it certain that this was the first special building for the purpose ; but mention must be made of two statements which seem to militate against this view. The Rev. William Harrison, an Elizabethan divine, wrote a descrijjtion of England, which was published with Holinshed's ' Chronicles,' and a chronology of the world, which is still in MS. In the latter work, under date 1572, Harrison writes "Plaies are banished for a time out of London," on account of the plague ; and, he adds, " would to God these common plaies were exiled for altogether as seminaries of impietie and their theatres pulled down. It is an evident token of a wicked time when plaiers waxe so riche that they can build such houses." It is possible that this was written after 1572, and after the Theatre was built ; but there was evidently a certain looseness of writing respecting places where plays were acted as playhouses. Thus, in the 1631 issue of Howes's edition of Stow's ' Annales' we read that Whitefriars theatre of 1629 was " the 17th stage or common play house which hath been new made within the space of three score years within London and the suburbs." Now sixty years from 1629, takes us back to 1569 ; but in these seventeen playhouses are includedl inns, St. Paul's Singing-school, &c., which cannot be considered as distinct buildings for the performance of plays. A modern instance may be cited in the use of the dormitory of Westminster School for the Latin play ; for the time being it would not be improper to style it a theatre or playhouse, although the dormitory soon loses all appearance of its late use. After considering the bearing of Harrison's and Howes's words, I think we must come to the con- clusion that the general opinion as to the Theatre being the first 28 Mr. Eenry B. Wheatley [Feb. 7, building erected as a playhouse is correct. It is worth while to stop for a moment to ask what was the meaning attached to the word theatre when it was first introduced. To us it means a pLace of amusement specially devoted to the drama, but this was not, I think, the meaning which was conveyed to the populace of London in 1576 ; a theatre was probably understood as a place for the exhibition of spectacles. This opinion is corroborated by a passage in Barclay's ' Argenis ' (lib. 4, cap. xiii.), where we read of " shoutes in a theatre at the fall of a sword bearer," and we know that fencing was commonly exhibited at these early playhouses. The Theatre had a short life of twenty-three years, and it never seems to have taken a very high standing. The Curtain, which was situated close by the Theatre, and was built in the year 1577, was a much more distinguished playhouse. Marlowe was an actor there, and Shakespeare was associated with it in his early career. The two theatres in Shoreditch remained alone for a few years. Plays w^ere occasionally acted in Blackfriars and "Whitefriars, but another theatre was not erected until the Eose was built on the Bankside. This playhouse is shown in Norden's Plan of London in 1593, which is the earliest representation of an English theatre known to exist.* There can be no doubt that the evils connected with the theatres were very considerable, and the Lord Mayor and Aldermen threw every obstacle in the way of the players. First of all they would have no theatres built within the city walls. Some inn-yards where plays had been acted were within, but no new building was allowed. Then they threw obstacles in the way of those outside, and if the erection of a new building w^ere sanctioned, an old one was usually at the same time condemned. This was the case with the Fortune which replaced the Curtain, as the Globe replaced the Theatre when the lease of the latter expired. The Lords of the Council took a rather different view of the situation. They aj)proved of the closing of theatres during times of sickness ; but in view of the Queen's very strong predilection for the stage, they did not allow the city authorities to go quite so fast as they wished. The very interesting volume printed by the Corporation of London, which gives an account of the contents of the Bememhraiicia contaius note of several letters from the Lord Mayors, and the Lords of the Council on this matter. In November 1581, the Lords of the Council directed the Lord Mayor to allow plays to be acted, and give this reason — " in order to relieve the poor players, and to encourage * A diagram wns exliibited which showed the space -within the cit}' walls unoccupied by any theatre, and the relative positions of tlie theatres outside the walls. On the north of the river were the Theatre and tlie Cnrtain, the Ked Bull at Clerkenwell, and the Fortune in Barbican. The Blacktriars theatre was opened in 1590, and was within the walls, but Blackfriars was outside the city jurisdiction. On the south side were the Swan at Paris Garden, the Globe, tlie Rose, and the Bear Garden (afterwards the Kope), all on the Bankside. At Newington Butts was another theatre, of which we know little or nothing. 1890.] on the London Stage in Elizabeths Beign. 29 their being in readiness with convenient matters for Her Highness's solace this next Christmas." The Middlesex Justices were often troubled with complaints of disturbances at theatres, and the valuable volumes edited by Mr. Cordy Jeaffreson and published by the Middlesex County Kecord Society, contain some important notices of the early stage, more particularly a remarkable document respecting the Theatre. We have representations of the outsides of several of the early theatres, and the reason why we have these is because they formed picturesque objects on the banks of the river, and it suited the artists who took views of London from the most attractive point, viz. the south side of the river, to show them in their positions. The Theatre and the Curtain, the Fortune and the Red Bull, the Blackfriars and the Newington theatres were not such prominent objects, and were not represented. None of the theatres were thought to be worthy of being drawn for their own particular interest. Until 1888 we had no representation of a Shakespearian play- house, but in that year the world was enriched by the publication of a contemporary view of the inside of the Swan theatre, which had been found in a MS. at Utrecht. The late Dr. P. A. Tiele, University Librarian at Utrecht, found this curious drawing in liis Library, with a short description in the hand-writing of Arend van Buchell, and purporting to be taken down or copied from the observations of John De Witt. This was published to the world in 1888, by Dr. Gaedertz, who added a careful commentary in which he showed that De Witt must have been in England in the year 1596, when the Swan was a new building.* In this same year, 1888, 1 had the honour of reading a paper on the subject before the New Shakspere Society, and certain difficulties which arose were found to be insoluble without esort to the MS. Dr. Furnivall, therefore, appealed for the loan of this, and in due course it was deposited for a time at the British Museum under the care of Dr. Garnett. The difficulties were then solved, and we are all greatly indebted to the authorities for this liberal instance of international courtesy .f This drawing of the interior of the Swan theatre shows about a third of the round of the entire amphitheatre, and the movable stage which was used for the acting of plays and cleared away when the centre .was required for bull-baiting, bear-baiting, and other sports. This stage stands upon legs and does not appear to be raised many feet above the" arena. At the back is an erection with doors from which issued the actors, and above are the private boxes. This erection is inscribed " Mimorum ^des." Over the uppermost gallery is a roof inscribed " Tectum." The stage and the arena are open to * 'Zur Kenntais der altenglischen Buhne, nebst andern Beitragen zur Shakespeare-Literatur, von Karl Theodor Gaedertz,' Bremen, 1888. t A reproduction of the original drawing will accompany the paper in the next part of the New Shakspere Society's Transactions. 30 Mr. Henry B. Wheatley [Feb. 7, the sky. At the top of the building is the little turret which is shown in the exterior of most of the Bankside theatres, and from it flies the flag with the sign of the house — the " Swan." The trumpeter who announced to the outside world that the performance was about to commence is shown on a slight platform. Round the building are the galleries alternately, three with seats and two for standing room, styled respectively " sedilia " and " portions," the latter are repre- sented as a species of colonnade, and probably access to the " sedilia " was obtained from the " portions." The standing room in front of the stage is inscribed " arena," and to the left is a portion of space inscribed " orchestra " ; near by are a few steps marked " ingressus," which gave access to the first tier of" sedilia." No other stairs are shown, but we obtain some insight into the mode of entering the galleries from a paper of agreement for the new building of the Bear G-arden in 1613, which is printed in the third volume of the Variorum edition of Shakespeare (1821). From this it appears that the Swan was taken as a model for the new theatre, and from the agreement we learn that there were two staircases to lead to the galleries. Gilbert Katherens, described as a carpenter, was to build the Bear Garden, " of suche large compasse, forme, wideness and height, as the plaie house called the Swan in the libertie of Paris Garden, in the saide parishe of St. Saviour's now is. And shall also builde two steare cases without and adjoining to the saide playe house, in suche convenient places as shal be most fitt and convenient for them to stande uppon, and of suche largnes and height as the steare cases of the saide playe house called the Swan now are or be." It will be seen that this view throws great light upon the evolu- tion of the English stage. We know that the form of the Bankside theatres was circular, but we do not know for certain whether the theatres on the north side of the river were also round. The words of De Witt which accompany the sketch would imply that they were alike, for he writes (in Latin) : — " There are in London four amphitheatres of beauty worth seeing. ... Of these the two most excellent are those on the other side of the Thames towards the south, named after the signs that hang out, the Rose and the Swan. The two others are outside the town towards the north." We are here in a realm of conjecture ; but we have some few lines of guidance. Was the word theatre used in its strictly classical sense, as Milton writes (' Samson Agonistes ') — " The building was a spacious theatre, Half round, on two main pillars vaulted high." or was the building really an amphitheatre ? * * Hentzner, in the account of his visit to this country in 1598, describes the amphitheatre on the Bantside, used exclusively for the baiting of bulls and bears, as a Theatre. (^Itinerarium, 1629, p. 196.) 1890.] on the London Stage in Elizabeth's Beign. 31 The Italians had before this time erected theatres which were copied from the classical stage, and it might be imagined that James Burbage, when about to build a special house for theatrical entertain- ments, would have followed some such model, but there is no evidence whatsoever that he did so. Mr. Halliwell Phillipps believed (I do not know on what authority) that the Curtain, our second London theatre, was round ; indeed, he believed it to be the " wooden 0 " of Henry V. (in opposition to the claims of the ever-memorable Globe). The chief reasons for supposing that almost all the Elizabethan theatres were round, are (1) because the early theatres were not intended exclusively for dramatic entertainments, but were used for fencing, tumbling, bear-baiting &c., and the circular form is much more convenient for sports in an arena; (2) because it is highly probable that the Bankside buildings were copied from something that went before ; (3) because this shape is frequently alluded to by the dramatists, and the word " Eound " is used by them as the name of a theatre. Thus, in Brome's City Wit (printed in 1653), one of the characters, Sarpego, who delivers the prologue says — " Some in this i^ound may have both seen't and heard Ere I, that bear its title, bore a beard." The Fortune theatre, near St. Giles's, Cripplegate, according to the Indenture dated January 1599-1600, was built on the same plan as the Globe, which had just been erected, with the exception that the auditorium was square instead of round. This was found to be in- convenient, so that when the Fortune was rebuilt in 1622, it was made round. The only other view of the interior of an early London theatre which we possess, is that of the Red Bull, in the reign of Charles II., in which we find the same expedient as to the stage, so that we may safely come to the conclusion that, whether square or round, the same system was adopted with regard to the plan of the stage. This form had the advantage of being convenient for all kinds of entertainment. If it were general, it is clear that the influence of the classical stage upon the foundation of the modern stage was practically non-existent, and also there is sufficient evidence to allow us to set aside the popular notion that the modern theatre has grown out of the old inn-yard. I fail to see any solid ground or basis for this view, and the only point in its favour seems to be that the pit was frequently called the yard — and this can be otherwise explained. If we agree that the original form of the theatre was a round, with a movable stage in the centre, it follows that when the time came for the building to be devoted exclusively to dramatic entertainments, the stage would naturally be brought back to the portion of the round which had become useless by reason that any would-be spectators placed there could see nothing, and the modern theatre at once stands confessed as a circus flattened at one side — an evolution from the amphitheatre. 32 Mr. Henry B. Wheatley [Feb. 7, It will be seen that with a movable stage placed in the centre of an amphitheatre, effective scenery was practically an impossibility. At the Restoration, however, scenery came into general use, and one reason for this was that the stage having been completely crushed during the Commonwealth an entirely new era then commenced. The different kinds of dramatic entertainment, which had been hitherto kept distinct, were united by Davenant and others, and scenery which had been previously confined to masques was adopted for other plays. Women, who had long before acted in masques, now took their place upon the public stage. The history of the drama is continuous, but that of the stage is in two parts, divided by the period of the Commonwealth. The history of the modern stage does not go farther back than the period of the Restoration. There are two other points connected with the early theatres which require some slight notice — these are size and outside appear- ance. With regard to the first, De Witt states that the Swan theatre would seat 3000 persons, which is a rather startling statement, as the ordinary caj)acity of these theatres was to hold about a thousand. Although the Swan was evidently a larger build- ing than most of the other theatres, it is not easy to believe that its size was so much greater as these figures would necessitate. It is necessary however for us to enlarge our ideas as to the number of the sightseers. Although the population of London in Elizabeth's reign was small when compared with what it is now% it was very considerable for the period, and I think it will be found that the attendants at theatres formed a much larger percentage of the population than they do now. It is not necessary to enlarge upon this point here, but mention may be made of the large number of watermen who were employed upon the Thames, and were fully engaged in taking the sightseers from one side of the river to the other. When, in James I.'s reign, the theatres on the Bankside fell into decay and Blackfriars theatre and other playhouses on the northern side of the river were alone fashionable places of resort, the watermen suffered severely by reason of their loss of custom. To retrieve their position they made a most astonishing demand. In 1613 Taylor, the water poet, was chosen by the Company of Watermen to present their petition to the King. This petition set forth the watermen's services to Queen Elizabeth and the advantages to the State of favouring them. On this foundation they based their extravagant claim that the players might not have a playhouse in London or in Middlesex within four miles of the city on that side of the Thames. If the players were made to return to the Bankside the watermen expected a return of their former prosperity. The substance of Taylor's statement is, that the theatres were first chiefly to the north of London and the Thames ; that they were afterwards transferred to the south, on the Bankside in Southwark, and then again removed to the north. During the time they were at Bankside the traffic on the river so greatly increased that the additional 1890.] on the London Stage in Elizabeth's Beign. 33 number of watermen with their families between Windsor and Gravesend amounted to something like 20,000 persons, and that when they were moved back again to the north they drew every day from 3000 to 4000 persons who used to go by water. Eeckoning a waterman's family at five persons, the number of watermen between Windsor and Gravesend at the height of this traffic would be 8000. This statement as to numbers is very remarkable, and shows that the sightseers of London in Elizabeth's reign were a considerable body.* It is worthy of notice that changes in the habits of the English took place very rapidly even in the time of Queen Elizabeth. When the theatres were first established the visitors went to them on horseback, later on they took boat to Southwark, and in the last years of the reign, when Blackfriars theatre was fashionable, coaches had become numerous. As to the exterior, De Witt distinctly says that it was cased with flint, and this assertion has been doubted chiefly because Hentzner said that the theatres on the Bankside were all of wood. I don't think that we can reject the testimony of one who was apparently a careful observer, on the strength of a general statement such as that of Hentzner. [Enlarged representations of the Swan, the Bear Garden, and the Globe, taken from views of the Bankside, were shown in diagrams on the wall]. These views of the theatres on the Bankside are but small in the originals, and too much stress must not be laid upon their appearance, but I think a difference between the look of the Swan and the Bear Garden on the one side, and of the Globe on the other may be noted. We know that the first Globe theatre was made of wood, but the other two look as if they might have been cased with stone or built up with brick. [H. B. W.] * In order to have some basis of comparison, my friend Mr. Danby P. Fry drew out a theoretical section which makes the arrangement of the seats easier to understand. This drawing was enlarged in a diagram on the wall. He has cal- culated that the height of the building would be about 50 feet, and this number is arrived at thus : — The uppermost gallery of seats is taken as 8 feet in height and the other two as 10 feet, the two rows of porticus at 7 feet each, and the orchestra as 7 feet. To estimate the size of the round is more difficult ; but sup- posing there to have been eleven rows of seats, that is, three rows in the upper- most gallery and four rows in each of the iower galleries, in order to seat 3000 persons, 273 must have been seated in each row, and this would necessitate a round of more than two-thirds the size of Drury Lane theatre. If we suppose De Witt to mean auditors generally, and not merely those seated, a much smaller circle would supply the need, because we could then count in all those standing in the portions and the arena. If the building was arranged to hold 3000 persons when used as an amphitheatre, it would not probably accommodate more than 2000 when the stage was placed in its position, and a portion of the round was thereby made useless for spectators. Vol. XIII. (No. 84.) ' - d 34 Professor J. A. Fleming [Feb. 14 WEEKLY EVENING MEETING, Friday, February 14, 1890. William Crookes, Esq. F.E.S. Vice-President, in tbe Chair. Professor J. A. Fleming, M.A. D.Sc. M.B.I. Problems in the Physics of an Electric Lamp, More tban eigbty years ago Sir Humphry Davy provided the terminal wires of his great battery of 2000 pairs of plates with rods of carbon, and, bringing their extremities in contact, obtained for the first time a brilliant display of the electric arc* The years that have fled away since that time have seen all the marvellous develop- ments of electro-magnetic engineering, have placed in our possession the electric glow-lamp, and brought the art of electrical illumination to a condition in which it progresses each year with giant strides. In addition to the importance attaching to their ever-increasing industrial use, there are many questions of purely scientific interest which present themselves to our minds when we proceed to examine the actions that take place when a carbon conductor is rendered incandescent in a high vacuum, or when an electric arc is formed between two carbon poles. It is to a very few of these physical problems that I desire to direct your attention to-night, but more especially to one which is particularly interesting from the bearing which it has on the general nature of electric discharge. We know as a very familiar fact that if we attempt to raise the temperature of a carbon conductor enclosed in a vacuum beyond a certain limit, not far removed from the melting point of platinum, the carbon begins to volatilise with great rapidity. If an electric glow- lamp has passed through its carbon more than a certain strength of current, the glass bulb speedily becomes darkened by a deposit of this volatilised carbon condensed upon it ; and experience shows us that we cannot raise the temperature of that carbon beyond a definite point without causing this waste of the conductor to become very rapid. In the highly rarefied atmosphere within the bulb of a glow- lamp, the carbon, when at its normal incandescence, must be con- * Sir Humpliry Davy laid a request before the managers of the Royal Insti- tution on July lith, 1808, that they would set on foot a subscription for the purchase of a large galvanic battery. The result of this suggestion was that a galvanic battery of 2000 pairs of copper and zinc plates were sot up in the Royal Institution, and one of the earliest experiments performed with it was the pro- duction of the electric arc between carbon poles, on a large scale. It is probable, however, tliat Davy had produced the light on a small scale some six years before and, according to Quctelet, Curtet observed the arc between carbon points in 1802. See Dr. Paris' ' Life of Sir H. Davy.' 1890.] on Prohle^ns in the Physics of an Electric Lamp. 35 sidered to be projecting off molecules of carbon in all directions, partly in virtue of purely thermal actions, but probably also in con- sequence of certain electrical effects to be presently discussed. This scattering of the material of the carbon conductor takes place with disadvantageous rapidity from an industrial point of view at and beyond a certain temperature,* but it exists as well at much lower temperatures than that which is found to determine the practical limit of durability. A curious appearance is found in many incan- descent lamps which have been " over-run," which shows us that this projection of carbon molecules from the hot conductor is not, perhaps, best described by calling it a vaporisation of its substance, but that the surface molecules are shot off in straight lines, and that they reach the glass envelope without being hindered to any great extent by the molecules of the residual air. If an electric current is passed through an otherwise uniform carbon conductor, which possesses at any one place a specific resist- ance higher than that of the remaining portion, the current, in accordance with a well-known law, there develops a higher tempera- ture, and the molecular scattering at that spot may in consequence be greatly exaggerated. It may be that the detrition of the con- ductor at that locality will be so great as to cut it through after a very short time. When the carbon has the form of a simple horse- shoe loop, and when this molecular scattering takes place from some point in the middle of one branch, the molecular projection makes itself evident by producing a " molecular shadow " of the other leg upon the interior of the glass. I will project upon the screen an image of the carbon horseshoe loop taken from an old glow-lamp, and you will be able to see that the filament has been cut through at one place. At that position some minute congenital defect caused the carbon to have a higher resistance, the temperature at that point when it was in use became excessive, and an intensified molecular scattering took place from that locality. On examining the glass bulb from which it was taken, we find that the glass has been everywhere darkened by a deposit of the scattered carbon except along one narrow line (see Fig. 1), and that line is in the plane of the carbon loop and on the side opposite to the point of rupture of the filament.f I may illustrate to you by a very simple experiment the way in which that "shadow" has been formed.- Here is a p| -shaped rod: this shall represent the carbon conductor in the lamp ; this sheet of cardboard placed behind it, the side of the glass receiver. I have affixed a little spray-producer to one side of the loop, and from that * When the rate of expenditure of energy in the carbon conductor is raised until it reaches a value of about 500 watts, or 360 foot-pounds per second per square inch of radiative surface, a limit of useful temperature has been reached for economical working, under the usual present conditions of steam-engine- driven dynamos and modern glow-lamps. t The writer desires to express bis indebtedness to the Editor of the 'Electrician ' for the loan of the blocks illustrating tliis abstract. D 2 36 Professor J, A. Fleming [Feb. 14, point blow out a spray of inky water. Consider the ink spray to represent the carbon atoms shot off from the overheated spot. We see that the cardboard is bespattered on all points except along one line where it is sheltered by the opposite side of the loop. We have thus produced a " spray shadow " on the board (Fig. 2). The Fig. 1. Fig. 2. r^ Glow-lamp, having the glass bulb blackened by deposit of carbon, show- ing the molecular scattering which has taken place from the point a on the filament, and the shadow or line of no deposit produced at h. " Spray shadow " of a rod thrown on cardboard screen to illustrate formation of molecular shadow in glow lamps. existence of these molecular shadows in incandescent lamps leads us therefore to recognise that the carbon atoms must be shot off in straight lines, or else obviously no such sharp shadow could thus be formed. This phenomenon confirms in a very beautiful manner the deductions of the Kinetic theory of gases. I may remind you that at the ordinary temperature and pressure the mean free path of a mole- cule of air is deduced to be about four one-milliouths of an inch. This is the average distance which such a gaseous molecule moves over before meeting with a collision against a neighbour which changes the direction of its path. Let the air be rarefied, as in these bulbs, to something like a millionth of the ordinary atmospheric pressure, and the mean free path is increased to several inches. The space within the bulb — though from one point of view densely popu- lated with molecules of residual air — is yet, as a fact, in such a con- dition of rarefaction that a carbon molecule projected from the conductor can move over a distance of three or four inches on an 1890.] on Problems in the Physics of an Electric Lamp, 37 average without meeting with interference by collision with another molecule, and the facts revealed to us by these shadows show that this must be the case. I have also at hand some Edison lamps in which these " molecular shadows " are finely shown, but in these cases the deposit on the interior of the bulb is not carbon but copper, because the molecular scattering has here taken place by excessive temperature developed at the copper clamps by which the carbon filament is attached to the platinum wires. The theory, however, is the same. The deposit of copper shows a fine green colour by transmitted light in the thinner portions. One curious lamp also before me had by an accident an aluminium plate volatilised within the bulb. The glass receiver has in consequence been covered with a mirror-like deposit of aluminium, which on the thinner portions shows a fine blue colour by transmitted light, and a silvery lustre by reflected light. This lamp also shows a fine " molecular shadow." These facts prepare us to accept the view that when a glow-lamp is in operation the highly rarefied residual air in the interior of the bulb is being traversed in all directions by multitudinous carbon atoms projected off from the incandescent carbon conductor. I now wish to pass in review before you some facts which indicate that these carbon atoms carry with them electric charges, and that they are charged, if at all, with negative electricity. I may preface all by saying that much of what I have to show you will be seen to be closely related to the phenomena studied by Mr. Crookes in his splendid and classical researches on radiant matter. Our starting-point for this purpose is a discovery made by Mr. Edison in 1884, and which received careful examination at the hands of Mr. Preece in the following year,* and by myself more recently. Here is the initial experiment. A glow-lamp having the usual horseshoe-shaped carbon (see Fig. 3) has a metal plate held on a platinum wire sealed through the glass bulb. This plate is so fixed that it stands up between the two sides of the carbon arch without touching either of them. We shall illuminate the lamp by a continuous current of elec- tricity, and for brevity's sake speak of that half of the loop of carbon on the side by which the current enters it as the positive leg, and the other half of the loop as the negative leg. The diagram in Fig. 4 shows Fig. 3. Glow-lamp having insulated metal middle plate M sealed into bulb to exhibit " Edison effect." * Mr. Preece's interesting paper on this subject is published in the ' Proceedings' of the Royal Society for 1885, p. 219. See also ' The Electrician,' April 4th, 1885, p. 436. 38 Professor J. A. Fleming [Feb. 14, the position of the plate with respect to the carbon loop. There is a distance of half-an-inch, or in some cases many inches, between either leg of the carbon and this middle plate. Setting the lamp in action, I connect a sensitive galvanometer between the middle plate and the Fig. 4. Fig. 5. Sensitive galvanometer connected be- tween the middle plate and positive electrode of a glow-lamp, showing current flowing through it when the lamp is in action (" Edison eflect "). Mode of connection of galvanometer G to middle plate if and carbon horse- shoe'shaped conductor Cin the ex- periment of the " Edison effect." negative terminal of the lamp, and you see that there is no current passing through the instrument. If, however, I connect the terminals of my galvanometer to the middle plate and to the positive electrode of the lamp, we find a current of some milliamperes is passing through it. The diagrams in Fig. 5 show the mode of connection of the galvanometer in the two cases. This effect, which is often spoken of as the " Edison effect," clearly indicates that an insulated plate so placed in the vacuum of a lamp in action is brought down to the same potential or electrical state as the negative electrode of the carbon loop. On examining the direction of the current through the galvanometer we find that it is equivalent to a flow of negative electricity taking place through it from the middle plate to the posi- tive electrode of the lamp. A consideration of this fact shows us that there must be some way by which negative electricity gets across the vacuous space from the negative leg of the carbon to the metal plate, whilst at the same time a negative charge cannot pass from the metal plate across to the positive leg. Before I pass away from this initial experiment, I should like to call your attention to a curious effect at the moment when the lamp is extinguished. Connecting the galvano- meter as at first, between the middle plate and the negative electrode 1890.] on Problems in the Physics of an Electric Lamp. 39 Fig. 6. of the lamp, we notice that though made highly sensitive the galyano meter indicates no current flowing through it whilst the lamp is in action. Switching off the current from the lamp produces, as you see, a violent kick or deflection of the galvanometer, indicating a sudden rush of current through it. In endeavouring to ascertain further facts about this effect one of the experiments which early suggested itself was one directed to determine the relative effects of different portions of the carbon con- ductor. Here is a lamp (see Fig. 6) in which one leg of the carbon horse- shoe has been enclosed in a glass tube of the size of a quill, which shuts in one-half of the carbon. The bulb contains, as before, an insulated middle plate. If we pass the actuating current through this lamp in such a direction that the covered or sheathed leg is the positive leg, we find the effect existing as before. A galvanometer connected between the plate and positive ter- minal of the lamp yields a strong current, whilst if connected between the negative terminal and the middle plate there is no current at all. Let us, however, reverse the current through the lamp so that the shielded or enclosed leg is now the negative one, and the galvanometer is able to detect no current, whether connected in one way or the other. We establish, therefore, the conclusion that it is the negative leg of the carbon loop which is the active agent in the production of this " Edison effect," and that if it is enclosed in a tube of either glass or metal, no current is found flowing in a galva- nometer connected between the positive terminal of the lamp and this middle collecting plate. Another experiment which confirms -this view is as follows: — This lamp (see Fig. 7) hns a middle plate, which is provided with a little mica flap or shutter on one side of it. When the lamp is held upright the mica shield falls over and covers one side of the plate, but when it is held in a horizontal position the mica shield falls away from the front of the plate and exposes it. Using this lamp as before we find that when the positive leg of the carbon loop is opposite to the shielded face of the plate, we get the " Edison effect " as before in any position of the lamp. Reversing the lamp current and making that same leg the negative one, we find that when the lamp is so held the metal plate is shielded by the interposition of the mica, and the Glow-lamp having negative leg of carbon enclosed in glass tube T, the " Edison effect" thereby being annulled or greatly diminished. 40 Professor J. A. Fleming [Feb. 14, galvanometer current is very much less tlian when the shield is shaken on one side and the plate exposed fully to the negative leg. At this stage it will perhaps be most convenient to outline briefly the beginnings of a theory proposed to reconcile these facts, and leave you to judge how far the sub- PjQ 7 sequent experiments confirm this hypothesis. The theory very briefly is as follows: — From all parts of the incandescent carbon loop, but chiefly from the negative leg, car- bon molecules are being projected which carry with them, or are charged with, negative electricity. I will in a few moments make a Glow-lamp having mica shield S interposable between middle plate M and negative leg of carbon, thereby diminishiug the "Edison effect." suggestion to you which may point to a possible hypothesis on the manner in which the molecules ac- quire this negative charge. Sup- posing this, however, to be the case, A Q— ^ and that the bulb is filled with 7 \^ these negatively-charged mole- ^— H-\ cules, what would be the result of introducing into their midst a con- ductor such as this middle metal plate which is charged positively ? Obviously, they would all be attracted to it and discharge against it. Suppose the positive charge of this conductor to be continually renewed, and the negatively- charged molecules continually supplied, which conditions can be obtained by connecting the middle plate to the positive electrode of the lamp, the obvious result will be to produce a current of electricity flowing through the wire or galvanometer, by means of which this middle plate is connected to the positive electrode of the lamp. If, however, the middle plate is connected to the negative electrode of the lamp, the negatively-charged molecules can give up no charge to it, and produce no current in the interpolated galvanometer. We see that on this assumption the effect must necessarily be diminished by any arrangement which prevents these negatively-charged molecules from being shot oif the negative leg or from striking against the middle plate. Another obvious corollary from this theory is that the " Edison effect " should be annihilated if the metal collecting plate is placed at a distance from the negative leg much greater than the mean free path of the molecules. Here are some experiments which confirm this deduction. In this bulb (Fig. 8) the metal collecting plate, which is to be connected through the galvanometer with the positive terminal of the lamp, is placed at the end of a long tube opening out of and forming part of 1890.] on Problems in the Physics of an Electric Lamp. 41 tbe bulb. We find the " Edison effect " is entirely absent, and that the galvanometer current is zero. We have, as it were, placed our target at such a distance that the longest range molecular bullets Fig. 8. 6 0 Collecting plate placed at end of a tube, 1 8 in. in length, opening out of the bulb. cannot hit it, or, at least, but very very few of them do so. Here again is a lamp in which the plate is placed at the extremity of a tube opening out of the bulb, but bent at right angles (Fig. 9). We Fig. 9 ly 0 Collecting plate placed at end of an elbow tube opening out of the bulb. find in this case, as first discovered by Mr. Preece, that there is no "Edison effect." Our molecular marksman cannot shoot round a corner. None of the negatively-charged molecules can reach the plate, although that plate is placed at a distance not greater than would suffice to produce the effect if the bend were straightened out. Following out our hypothesis into its consequences would lead us to 42 Professor J. A. Fleming [Feb. 14, conclude that the material of which the plate is made is without influence on the result, and this is found to be the case. Many of the foregoing facts were established by Mr. Preece as far back as 1885, and I have myself abundantly confirmed his results. We should expect also to find that the larger we make our plate, and the nearer we bring it to the negative leg of the carbon, the greater will be the current 23roduced in a circuit connecting this plate to the positive terminal of the lamp. I have before me a lamp with a large plate placed very near the negative leg of the carbon of a lamp, and we find that we can collect enough current from these molecular charges to work a telegraph relay and ring an electric bell. The current which is now working this relay is made up of the charges collected by the plate from the negatively-charged carbon molecules which are projected against it from the negative leg, across the highly perfect vacuum. I have tried experiments with lamps in which the collecting plate is placed in all kinds of positions, and has various forms, some of which are here, and are represented in the diagrams before you ; but the result may all be summed up by saying that the greatest effects are produced when the collecting plate is as near as possible to the base of the negative end of the loops, and, as far as possible, encloses, without touching, the carbon conductor. Time will not permit me to make more than a passing reference to the fact that the magnitude of the current flowing through the galvanometer when connected between the middle plate and the positive terminal of the lamp often "jumps" from a low to a high value, or vice versa, in a remarkable manner, and that this sudden change in the current can be produced by bringing strong magnets near the outside of the bulb. Let us now follow out into some other consequences this hypothesis that the interior of the bulb of a glow-lamp when in action is pojju- lated by flying crowds of carbon atoms all carrying a negative charge of electricity. Suppose we connect our middle collecting plate with some external reservoir of electric energy, such as a Leyden jar, or with a condenser equivalent in capacity to many hundreds of Leyden jars, and let the side of the condenser which is charged positively be first placed in connection through a galvanometer with the middle plate (see Fig. 10), whilst the negative side is placed in connection with the earth. Here is a condenser of two microfarads capacity so charged and connected. Note what happens when I complete the circuit and illuminate the lamp by passing the current through its filament. The condenser is at once discharged. If, however, we repeat the same experiment with the sole difference that the nega- tively charged side of the condenser is in connection with the middle plate then there is no discharge. The experimental results may be regarded from anotlier point of view. In order that the condenser may be discharged as in the first case, it is essential that the negatively charged side of the condenser shall be in connection with some part of the circuit of the incandescent carbon loop. This ex- 1890.] on Problems in the Physics of an Electric Lamp, 43 Fig. 10. Charged condenser C discharged by middle plate 3f, when the positively charged side of condenser is in connection with the plate and other side to earth e. periment with the condenser discharged by the lamp may be then looked upon as an arrangement in which the plates of a charged con- denser are connected respec- tively to an incandescent carbon loop and to a cool metal plate, both being enclosed in a highly vacuous space, and it appears that when the incandescent con- ductor is the negative electrode of this arrangement the dis- charge takes place, but not when the cooler metal plate is the negative electrode of the charged condenser. The negative charge of the condenser can be carried across the vacuous space from the hot carbon to the colder metal plate, but not in the re- verse direction. This experimental result led me to examine the condition of the vacuous space between the middle metal plate and the nega- tive leg of the carbon loop in the case of the lamp employed in our first experiment. Let us return for a moment to that lamp. I join the galvanometer between the middle plate and the negative terminal of the lamp, and find, as before, no indication of a current. The metal plate and the negative terminal of the lamp are at the same electrical potential. In the circuit of the galvanometer we will insert a single galvanic cell having an electromotive force of rather over one volt. In the first place let that cell be so inserted that its negative pole is in connection with the middle plate, and its positive pole in connec- tion through the galvanometer with the negative terminal of the lamp (see Fig. 11). Regarding the circuit of that cell alone, we find that it consists of the cell itself, the galvanometer wire, and that half-inch of highly vacuous space between the hot carbon conductor and the middle plate. In that circuit the cell cannot send any sensible current at all, as it is at the present moment connected up. But if we reverse the direction of the cell so that its positive pole is in connection with the middle plate, the galvanometer at once gives indications of a very sensible current. This highly vacuous space, lying between the middle metal plate on the one hand, and the incandescent carbon on the other, possesses a kind of unilateral con- ductivity, in that it will allow the current from a single galvanic cell to pass one way but not the other. It is a very old and familiar fact that in order to send a current from a battery through a highly rarefied gas by means of metal electrodes, the electromotive force of u Professor J. A. Fleming [Feb. 14, the battery must exceed a certain value. Here, however, we have indication that if the negative electrode by which that current seeks to enter the vacuous space is made incandescent the current will pass at a very much lower electromotive force than if the electrode is not "^o heated. Fig. 11. Current from Clark cell Ck being sent across vacuous space between negative leg of carbon and middle plate M. Posi- tive pole of cell in connection with plate M thjough galvanometer G. Fig. 12. Experiment showing that when the " middle plate " is a carbon loop rendered incandescent by insulated battery B, a current of negative elec- tricity flows from M to the positive leg of main carbon C across the vacuum. A little consideration of the foregoing experiments led to the conclusion that in the original experiment, as devised by Mr. Edison, if we could by any means render the middle plate very hot, we should get a current flowing through a galvanometer when it is connected between the middle i)late and the negative electrode of the carbon. This experiment can be tried in the manner now to be shown. Here is a bulb (Fig. 12) having in it two carbon loops ; one of these is of ordinary size, and will be rendered incandescent by the current from the mains. The other loop is very small, and will be heated by a well-insulated secondary battery. This smaller incandescent loop shall be employed just as if it were a middle metal plate. It is, in fact, simply an incandescent middle conductor. On repeating the typical experiment with this arrangement, we find that the galvano- meter indicates a current when connected between the middle loop and either the positive or the negative terminal of the main carbon. I have little doubt but that if we could render the platinum plate in our first-used lamp incandescent by concentrating on it from outside a powerful beam of radiant heat we should get the same result. 1890.] on Problems in the Physics of an Electric Lamp, 45 A similar set of results can be arrived at by experiments with a bulb constructed like an ordinary vacuum tube, and having small carbon loops at each end instead of the usual platinum or aluminium wires. Such a tube is now before you (see Fig. 13), and will not Fig. 13. M^^ ^A Vacuum tube having carbon loop electrodes, cc, at each end rendered incandescent by insulated batteries B^ B^, showing current from Clark cell, Ck, passing through the high vacuum when the electrodes are incandescent. allow the current from a few cells of a secondary battery to pass through it when the carbon loops are cold. If, however, by means of well insulated secondary batteries we render both of the carbon loop electrodes highly incandescent, a single cell of a battery is sufficient to pass a very considerable current across that vacuous space provided the resistance of the rest of the circuit is not large. We may embrace the foregoing facts by saying that if the electrodes, but especially the negative electrode, which form the means of ingress and egress of a current into a vacuous space are capable of being rendered highly incandescent, and if at that high temperature they are made to differ in electrical potential by the application of a very small electromotive force, we may get under these circum- stances a very sensible current through the rarefied gas. If the electrodes are cold a very much higher electromotive force will be necessary to begin the discharge or current through the space. These facts have been made the subject of elaborate investigation by Hittorf and Goldstein, and more recently by Elster and Geitel. It is to Hittorf that I believe we are indebted for the discovery of the fact that by heating the negative electrode we greatly reduce the apparent resistance of a vacuum. Permit me now to pave the way by some other experiments for a little more detailed outline of the manner in which I shall venture to suggest these negative molecular charges are bestowed. This is really the important matter to examine. In seeking for some probable explanation of the manner in which these wandering molecules of carbon in the glow-lamp bulb obtain their negative charges, I fall back for assistance upon some facts discovered by the late Prof. Guthrie. He showed some years ago new experiments on the relative powers of incandescent bodies for retaining positive and negative 46 Professor J. A. Fleming [Feb. 14, Fig. 14. charges. One of tlie facts he brought forward * was that a bright red-hot iron ball, well insulated, could be charged negatively, but could not retain for an instant a positive charge. He showed this fact in a way which it is very easy to repeat as a lecture experiment. Here is a gold-leaf electroscope, to which we will impart a positive charge of electricity, and project the image of its divergent leaves on the screen. A looker, the tip of which has been made brightly red- hot, is placed so that its incandescent end is about an inch from the knob of the electroscope. No discharge takes place. Discharging the electroscope with my finger, I give it a small charge of negative electricity, and replace the poker in the same position. The gold leaves instantly collapse. Bear in mind that the extremity of the poker, when brought in contiguity to the knob of the charged electro- scope, becomes charged by induction with a charge of the opposite sign to that of the charge of the electroscope, and you will at once see that this experiment confirms Prof. Guthrie's statement, for the negatively-charged electroscope induces a positive charge on the incandescent iron, and this charge cannot be retained. If the induced charge on the poker is a negative charge, it is retained, and hence the positively-charged electroscope is not discharged, but the nega- tively-charged electroscope at once loses its charge. Pass in imagination from iron balls to carbon molecules. We may ask whether it is a legitimate assumption to suppose the same fact to hold good for them, and that a hot carbon molecule or small carbon mass just detached from an incandescent surface behaves in the same way and has a greater grip for negative than for positive charge ? If this can possibly be assumed, we can complete our hypothesis as follows : — Consider a carbon molecule or small congerie of molecules just set free by the high temperature from the negative leg of the incan- descent carbon horseshoe. This small carbon mass finds itself in the electrostatic field between the branches of the incandescent carbon con- ductor (see Fig. 14). It is acted ujjon induc- tively, and if it behaves like the hot iron ball in Prof. Guthrie's experiment it loses its positive charge. The molecule then being charged nega- tively is repelled along the lines of electric force against the positive leg. The forces moving it are electric forces, and the repetition of this action would cause a torrent of negatively-charged molecules to pour across from the negative to the positive side of the carbon horseshoe. If we place a metal plate in their path, which is in conducting con- I- Eough diagram illus- tratiDg a theory of the manner in which projected carbon molecules may ac- quire a negative charge. * " On a New Relation between Electricity and Heat," Phil. Mag. vol. xlv. p. 308. 1873. 1890.] on Problems in the Physics of an Electric Lamp. 47 Fig. 15. nection with the positive electrode of the lamp carbon, the negatively- charged molecules will discharge themselves against it. A plate so placed may catch more or less of this stream of charged molecules which pour across between the heels of the carbon loop. There are many extraordinary facts, which as yet I have been able only imper- fectly to explore, which relate to the sudden changes in the direction of the principal stream of these charged molecules, and to their guidance under the influence of magnetic forces. The above rough sketch of a theory must be taken for no more than it is worth, viz. as a working hypothesis to Suggest further experiments. These experiments with incandescence lamps have prepared the way for me to exhibit to you some curious facts with respect to the electric arc, and which are analogous to those which we have passed in review. If a good electric arc is formed in the usual way, and if a third insulated carbon held at right angles to the other two is placed so that its tip just dips into the arc {see Fig. 15), we can show a similar series of experiments. It is rather more under control if we cause the arc to be projected against the third carbon by means of a magnet. I have now formed on the screen an image of the carbon poles and the arc between them, in the usual way. Placing a magnet at the back of the arc, I cause the flame of the arc to be deflected laterally and to blow against a third insulated carbon held in it. There are three in- sulated wires attached respec- tively to the positive and to the negative carbons of the arc, and to the third or insulated carbon, the end of which dips into the flame of the arc projected by the magnet. On starting the arc this third carbon is instantly brought down to the same elec- trical potential as the negative carbon of the arc, and if I connect this galvanometer in between the negative carbon and the third or insulated carbon I get, as you see, no indication of a current. Let me, however, change the connections and insert the circuit of my galvanometer in between the positive carbon of the arc and the middle carbon, and we find evidence, by the violent impulse given to the galvanometer, that there is a strong current flowing through it. The direction of this current is equivalent to a flow of negative electricity from the middle carbon through the galvanometer to the positive carbon of the arc. We have here then the " Edison efi*ect " repeated Electric arc projected by magnet against a third carbon, and showing a strong electric current flowing through a galvanometer, G, connected between the positive and this third carbon. 48 Prof. J. A. Fleming [Feb. 14, Fig. 16. with the electric arc. So strong is the current flowing in a circuit connecting the middle carbon with the positive carbon that I can, as you see, ring an electric bell and light a small incandescent lamp when these electric- current detectors are placed in connection with the positive and middle carbons. We also find that the flame-like projection of the arc between the negative carbon possesses a unilateral conductivity. I join this small secondary battery of fifteen cells in series with the galvanometer, and connect the two between the middle carbon and the negative carbon of the arc. Just as in the analogous experiment with the incandescent lamp, we find we can send negative electricity along the flame of the arc one way but not the other. The secondary battery causes the galvanometer to indicate a current flowing through it when its negative pole is in connection with the negative carbon of the arc {see Fig. 16), but not when its positive pole is in connection with the negative carbon. On ex- amining the third or middle carbon after it has been em- ployed in this way for some time, we find that its extremity is cratered out and converted into grajjhite, just as if it had been employed as the positive carbon in forming an electric arc. Time forbids me to indulge in any but the briefest remarks on these experiments; but one suggestion may be made, and that is that they seem to indicate that the chief movement of car- bon molecules in the electric arc is from the negative to the posi- tive carbon. The idea suggests itself that, after all, the crater- Galvanometer^ and battery B inserted - ^^^ ^^ ^^^ positive carbon of in series between negative carbon ot , ® it, t electric arc and a third carbon to .how ^^^ arc may be due to a sand- unihiteral conductivity of the arc be- blast-like action of this torrent tween the negative and third carbons, of negatively-charged molecules which are projected from the negative carbon. If we employ a soft iron rod as our lateral pole, we find that, after enduring for some time the projection of the arc against it, it is converted at the extremity into steel. Into the fuller discussion as to the molecular actions going on in the arc, the source and nature of that which has been called the counter-electromotive force of the arc, and the causes contributing to produce unsteadiness and hissing in the arc, I fear that I shall not be able to enter, but will content myself with the exhibition of one last experiment, which will show you that a high vacuum, or, indeed, FiQ. 17. 1890.] on Problems in the Physics of an Electric Lamp. 49 any vacuum, is not necessary for the production of the " Edison effect." Here is a carbon horseshoe-shaped conductor, not enclosed in any receiver (see Fig. 17). Close to the negative leg or branch, yet not touching it, we have adjusted a little metal plate. The sensitive galvanometer is connected between this metal plate and the base of the other or positive leg of this carbon arch. On sending a current through the carbon sufficient to bring it to bright incandescence, the galvano- meter gives indications of a current flowing through it, and as long as the carbon endures, which is not, how- ever, for many seconds, there is a current of electricity through it equivalent to a flow of negative electricity from the plate through the galvanometer to the positive electrode of the carbon. The interposition of a thin sheet of mica between the metal plate and the negative leg of the carbon loop entirely destroys the galvanometer current.* These experiments and brief expositions cover a very small portion of the ground which is properly included within the limits of my subject. Such fragments of it as we have been able to explore to-night will have made it clear that it is a region abounding in interesting facts and problems in molecular physics. The glow- lamp and the electric arc have revolutionised our methods of artificial lighting, but they present themselves also as subjects of scientific study, by no means yet exhausted of all that they have to teach. [J. A. F.] Edison effect " experiment shown with carbon in open air. ♦ This last experiment is due to my assistant, Mr. A. H. Bate. Vol. XIII. (No. 84.) E 50 Mr. Shelford Bidicell [Feb. 21, WEEKLY EVENING MEETING, Friday, February 21, 1890. John Eae, M.D. LL.D. F.E.S. Vice-President, in the Chair. Shelford Bidwell, Esq. M.A. LL.B. F.R.S. M.B.L Magnetic Phenomena. The space around a magnet in which magnetic action is observed is called a field of magnetic force, or, more shortly, a magnetic field. Following Faraday's conception, we may specify a magnetic field by supposing it to be filled with a number of so-called " lines of force," the direction of the force (that along which a north pole is urged) beinfy indicated by the direction of the lines, and its intensity by their concentration. In a uniform field of unit intensity, the lines of force are straight and parallel, and each line is exactly one centimetre distant from its nearest neighbour ; so that, if a flat surface were held transversely to the direction of the lines, one line would pass through each square centimetre of the surface. In a weaker field the lines would be farther apart ; in a stronger one they would be packed more closely together. The direction of the earth's magnetic force at any point in or near London is, roughly speaking, from south to north, at an inclination of 67° to the horizon; its intensity is approximately such that one line of force traverses every two square centimetres of a transverse plane surface, i. e. half a line, for each unit of area. The intensity of a unit field of magnetic force is therefore equal to about twice the total intensity of the magnetic field due to the earth. It is a remarkable fact that iron, and in a less degree the two rarer metals nickel and cobalt, when placed in a magnetic field, possess the property of multiplying the number of lines that would naturally fill the space occupied by them. Thus, a long and thin iron rod placed lengthwise in the earth's magnetic field will not merely be traversed by half a line for each square centimetre of its section, as a glass or copper rod would be ; the half line will (at least in the middle portion of the rod) be multiplied something like 600 times, raising the actual number of lines through the iron to about 300 per centimetre of section. By means of electric currents it is easy to produce magnetic fields having a far higher intensity than that of the earth. Suppose, for example, we take a long brass tube, and wind around it a quantity of insulated copper wire, forming 16 convolutions in each centimetre of length ; a current of 10 amperes circulating through such a coil would generate in the interior a magnetic field having an intensity of about 200 units. An iron rod placed inside this tube would be 1890.] on Magnetic Phenomena. 51 traversed by perhaps as many as 18,000 lines per centimetre. Although this is a very large number, it will be noticed that it is smaller, in proportion, than was obtained when the magnetic field of the earth alone was employed. In that case a field of half a line to the centi- metre was found to induce 300 lines in the iron, the multiplying power being 600. But with an external field of 200 the multiplying power is only about 90, a very considerable falling ofi". It is usual to denote the number of lines per square centimetre in the magnetic field by the letter H,and those induced in the iron by B, while the multi- plier is indicated by the Greek letter /x. We may therefore write : — B - /xH. B is commonly spoken of as the " magnetic induction," and fx as the " permeability." It used to be assumed that, except in strong fields, the permeability fjL was practically a constant for the same specimen of metal. We have already seen that this is by no means the case, and how very far it is from being so is clearly shown by the following table, in the first and third columns of which are given corresponding values of H and fjL for an average specimen of wrought iron. Table I. — Iron. H B(=;uX H) H- Field, Induction. Permeability. 0-2 80 400 0-5 300 600 1 1,400 1,400 2 4,800 2,400 4 8,800 2,200 7 11,200 1,600 11 13.200 1,200 16 14,400 900 65 (Eowland) 16,500 255 200 (Bidwell) 18,000 90 585 20,000 34 24,500 (Ewing) 45,300 1-9 It will be remarked that, as the strength of the field increases from the smallest values, the permeability at first rises w^ith enormous rapidity, attaining in a field of 2 or 3 units a maximum value of more than 2000 ; then it falls again, rapidly at first, and afterwards more slowly, until with a field of 65 lines to the centimetre the permeability is no more than 255. So far, the figures in the table (which are given in round numbers) are \jasedupon experiments made by Prof. Eowland sixteen years ago. Plotting corresponding values of /x and B, Rowland constructed a curve, the form of which led him to the remarkable conclusion tha£ the value of the magnetic induction B could not E 2 62 Mr. Shelford Bidwell [Feb. 21, possibly exceed a certain definite limit, and that, in fact, no magnetic force, however great, could induce in iron more than about 18,000 lines per centimetre. This conclusion, which seemed to be in agreement with Weber's theory of magnetism, was generally accepted as correct. Unfortunately, however, Rowland's experiment did not go quite far enough. If he had been able to carry his magnetising force a little beyond 65 units, he would have seen that there was no such limit as he supposed. More recently, an induction of 18,000 has been actually obtained with a field of only 200, the permeability being 90. With the stronger field of 585, the induction was found to be 20,000 ; and quite lately, Professor Ewing, employing a field of 24,500, has obtained an induction of 45,300, the permeability being 1-9. Ewing concludes that there is no limit whatever to the degree to which magnetic induction may be raised ; and there can be no doubt that he is right. But while Ewing's experiments tend to show that the number of magnetic lines which can conceivably be made to run through a piece of iron is indefinitely great, they at the same time clearly indicate that the number of additional lines in excess of those contained in the field before the iron was placed there, has a very definite limit. This limit, for the piece of wrought iron which he used, appears to have been about 21,000, and it w^as practically reached with an external field of about 2000. For this sample of iron we may, therefore, say that in fields of 2000 and upwards, B = H + 21,000. Closely connected with the questions which have just been discussed, are the further questions : — What are the conditions affecting the lifting-power of an electro-magnet ? and. What is the greatest lifting-power attainable ? One point of fundamental importance was settled experimentally by Joule many years ago. He found that the power of a uniform electro-magnet varies directly as the sectional area of the iron core, so that, for example, a magnet with a section of two square inches would, other things being equal, carry twice the weight that could be supported by one with a section of only one square inch. Joule also studied the effect of varying the strength of the current passing through the surrounding coil, and ascertained that while up to a certain point increase of current was accompanied by marked increase of lifting-power, yet when the current exceeded a more or less definite limit, further increase of it produced comparatively little effect. Reasoning upon his experiments, he formed the opinion — in which long afterwards Rowland concurred — that no current, however great, "could give an attractive power equal to 200 lbs. per square inch." It has, however, since been shown that this statement is not quite true. In the course of some experiments made in 1886, with a semi- 1890.] on Magnetic Phenomena. 53 circular electro-magnet and a semicircular armature of soft iron, a weight of more than 200 lbs. per square inch was easily carried, though the current was very far indeed from being infinite ; it was, in fact, about 5 amperes. If, as we have seen to be the case, there is no limit to the number of magnetic lines which can be induced in an iron bar, then, theoreti- cally, there can be no limit to the lifting-power which an electro- magnet can be made to exhibit. Practically, however, a limit is imposed by the fact that we cannot command an unlimited current of electricity, nor would wires of any known material convey it even if we could. With sufficient current a little 3-inch electro-magnet might no doubt be made to lift a weight of a ton, but any attemj)t to pass such a current would result in the immediate fusion, or even vaporisation, of the wire-coils by the intense heat that would be generated. The lifting power of an electro-magnet with an iron armature is proportional to the square of the total number of magnetic lines which run through the iron, inclusive of those due simply to the current in the coil. Ewing's experiments enable us to determine the greatest weight that a magnetised iron bar could support by itself, without any assistance from the surrounding coil. In the case of his specimen of iron it would be about 260 lbs. per square inch of section. The permeability of an iron rod depends not only upon the inten- sity of the field in which the rod is placed, but also to some extent upon the physical condition of the iron, and is affected by such causes as mechanical stress or changes of temperature. If, for instance, we hang an iron wire vertically in a not very strong field, and stretch it a little by attaching a weight to its lower end, we shall find that the stretching causes a temporary increase in the longitudinal permea- bility of the wire. But if the experiment be repeated in a strong field, the effect will be reversed ; the same load which before increased the permeability of the wire will be found to diminish it. In a field of a certain medium strength which can be determined by trial, the stretching will have no effect at all upon the permeability. This value of the field is called, after the first discoverer of the phenomenon, the " Villari Critical Point" for a certain load. The permeability of a nickel wire appears to be always diminished by stretching, whatever the strength of the field or the magnitude of the load. As the magnetic qualities of a rod of iron or other magnetisable metal are affected by a temporary strain or slight alteration of its form, so it has been found that the form of such a rod may be slightly altered by magnetising it. By the aid of very delicate apparatus it is possible to show that in a continually increasing field the length of an iron bar is at first increased, and afterwards diminished ; that of a cobalt bar is at first diminished, and afterwards increased ; while that of a nickel bar is always diminished. The following table shows the 54 Mr, Shelford Bidicell [Feb. 2r nature of the changes of length undergone by certain rods of iron, cobalt, and nickel, when magnetised. Magnetising Force. Elongations in ten-million ths of Original Length. Iron. Cobalt. Nickel. 65 13 - 104 125 19* -10 - 167 237 7 -31 - 218 293 0 - 37 -233 343 - 6 -44t -240 500 - 35 -30 , , 745 - 50 0 , , 1120 - 65 45 , , 1400 - m 75 -245 * Maximum increment. t Maximum decrement. It was shown by Professor J. J. Thomson, a year or two ago, that the elongations and contractions of iron under magnetisation are intimately connected with the phenomenon which has been referred to as the Villari reversal. With a knowledge of the Villari elfect, the elongation and subsequent contraction of an iron rod under magnetisation miyht have been predicted, and vice versa. Now, since the elongations and contractions of cobalt are of the opposite cha- racter to those of iron. Professor Thomson's reasoning would lead us to expect a Yillari etfect in cobalt, which would also be of the opposite character. Quite recently, Mr. Ohree, at Professor Thomson's suggestion, made some experiments to test the accuracy of this pre- sumptiou, and found the Villari reversal which was anticipated. Again, the circumstance that nickel is always shortened by mag- netisation, and never lengthened, indicates that there is no Villari reversal in that mi tal ; and, in fact, though one has been looked for by Professor Ewing and others, it has never been found. A few words in conclusion with regard to the effect of heat. Iron, when gradually made very hot, loses its magnetic susceptibility quite suddenly at a low red heat, and practically becomes a non-magneti sable metal. Pure nickel loses the greater part of its magnetic quality at a much lower temperature, perhaps about 300^ C. Both metals again become magnetisable when cold. Dr. Hopkinson has lately dis- covered a very remarkable effect of heat upon the magnetic pro- perties of an alloy of iron and nickel. If a bar or wire of this alloy be made red hot, and then allowed to cool, it is rendered permanently non-magnutic, although the metals of which it is composed are by themselves both strongly magnetic. But if this non-magnetic material be cooled to a temperature a little below the freezing point, and then again allowed to resume the ordinary temperature of the air, it will be found to have become almost as strongly magnetic as a 1890.] on Magnetic Phenomena. 55 piece of steel, and it will continue to be magnetic until it is once more made red hot. This is one of the most remarkable discoveries in magnetism that has been made for many years. It revives the question first suggested by Faraday — whether any metal whatever may not possibly be rendered magnetisable by exposure to a sufficiently low temperature.* [S. B.] t * The discourse was illustrated by about twenty experiments. -^ 56 Professor C. Hubert H. Parry [Feb. 28, WEEKLY EVENING MEETING, Friday, February 28, 1890. Colonel James A. Grant, C.B. C.S.I. F.R.S. Vice-President, in the Chair. Professor C. Hubert H. Parry, Mus. Doc. M.A. Evolution in Music. As far as I can discover, not much has been said on the subject before us as yet; and as there is a great deal to be said, my only pre- liminary will be to remind you of one of Mr. Herbert Spencer's definitions of evolution, which happens to be most apt to our subject. The formula in question is as follows: — Evolution is a "change from indefinite incoherent homogeneity to a definite coherent hetero- geneity," accompanying the dissipation of motion and integration of matter ; * which, for present purposes, I may expand into — a change from vague indefinite chaos to an aggregate of clearly-defined separate entities or organisms, each with functions well determined. I shall endeavour to keep these formulas steadily in view, and to show how the various departments and phases of music, as we know it, have developed in consonance with them. My argument must necessarily take the form of a mere summary, as the strength of the case rests to a great extent on the uniformity of the principles of development ; and I do not think that it will be of any real use to take an isolated department and discuss it in detail before the general aspect of the matter is clearly understood. I will begin then at once with the subject of scale-making. I presume that music began before the existence of scales, and that they were developed in the early attempts made by our savage ancestors to express their feelings in sounds. In fact, though the making of scales and the discussion of scales is now such a dreary and thankless matter, originally they were the product of emotion and imitation. In order to follow the process of development we must take the original material of music before scale-making began to be figuratively a chaos of possibilities, in which no points or relations were established. The process began when some savage expressed his feelings in some group of sounds, and insisted upon them clearly enough, and often enough, to make his fellow savages imitate him. The variety of relations of notes chosen by savages is sufficiently shown by records of varieties of existent savage music ; ranging from the horrible grinding glide of the voice which certain cannibals use to express their feelings when ♦ ' First Principle^,' xvi. § 138. 1890.] on Evolution in Music. 67 contemplating their yet living dinners, which resemble quarter tones, to the strange intervals, exceeding a tone, which occur in many highly-developed scales. The probability is that when we meet with a scale containing an eccentric interval, this eccentric inter- val is the original nucleus of the scale, to which other notes were added as the instinct and general intelligence of the savages improved. The sum of the process of scale-making amounts to this :— That first a simple nucleus of two notes was formed, and by very slow degrees other notes were added, till the whole range of sounds possible to the human voice was mapped out. This, obviously, is the first example of progress from the confused chaos of indefinite and unsystematised sounds to the heterogeneity of perfectly established scales. When the difficulties presented by the problem of contriving scales are realised (as they may be by any one who studies the question a little), it will be seen that the process must have been an enormously long one, taxing the musical instinct of man for probably thousands of years. As a matter of fact, scale-making, even in primary stages, was going on vigorously till not much over a century ago, and in some phases cannot be said to be by any means finished yet. Scales are always liable to alteration, whenever the instinct of composers leads them to divine an opportunity for expanding the material at their command for artistic purposes; and whenever the instinct of a number of musical beings ratifies the change as logical and artisti- cally practical, it takes its place as an established fact. The next step to merely dividing off the possible range of sounds into fixed relative positions, is to classify them into groups in which special notes have special functions. The music of the ancient world being all melodic, men's instincts impelled them to develop a scale system which gave them best opportunities for melodic variety. This naturally resulted in their having as many modes as possible ; or, in other words, having as many varieties of relationship as they could devise between the key-note or final and the other notes of the scale. And they looked upon these various modes as having particular qualities of feeling — one mode being sad, another gay, another solemn, and so forth. The Greek system was, no doubt, a highly-developed one for melodic purposes ; but whatever its traditions were, they did not have much influence on our modern music, except through the actual dis- tribution of the notes into modes. The Romans seem to have had no instinct for music. Their energies were occupied in organising the world as then known into a workable empire, and their leisure was occupied with kinds of amusements which have a tendency to destroy the taste for refined music. No two things seem more poisonous to musical art than spectacles of brutal violence which give people a taste for excessive excitement, and a luxurious life of frivolity into which enters a strong element of vulgar display. The decrepit condition of music in the early centuries of our era was as much owing to the neglect of the art by the Romans as to the 58 Professor C. Hubert R. Parry [Feb. 28, falling to pieces of their empire. I should like to think that -their neglect of the higher art of music was a concomitant of the corrupt condition of society which led to their downfall. At any rate, the state of music when we take it up in the Christian era, is but a ragged reminiscence of Greek traditions. Their scale system had been maintained to a certain extent in the use of the Christian Church, in some of those curiously vague and jDicturesque pieces of melody which go by the name of plain song, or cantus planus. One of the characteristics of these tunes is their strange indefiniteness, which is the chief cause of their picturesqueness ; as our minds instinctively divine them to belong to an ancient and undeveloped age, and recall the poetical side of a primitive religion. This vagueness and homogene- ousness only by degrees passed away, under a phase of musical de- velopment which belongs exclusively to modern times. Under the influence of the development of harmony the scale was classified into new groups, in which the relation of every note to every other in every scale, and the function of every one of them, became by degrees established. The development of harmony pro- ceeded in exactly the same manner. The first experiment was the essentially homogeneous one of singing the same melody in two or three parts at difierent pitches simultaneously. The interval chosen always astonishes the modern mind, because it is so alien to our habits. But it is very easily accounted for. The musicians of the tenth and eleventh centuries chose the intervals of fourth and fifth, partly because it suited the relative distances of the voices from one another, such as tenor to bass and soprano to con- tralto ; and also because the fifth and the fourth are the only intervals at which melodies can be sung without any marked contradiction occurring between the notes of the respective scaler,. If a third was taken, a leading note below the third would conflict with the second of the lower scale, and the second of its scale would conflict with the fourth of the lower, and so on ; whereas the scales of the fourth and fifth only rarely conflict with the lower scale. Combined with this is the fact that these mediasvals' sense of harmony was slow in developing. At first they only regarded the fifths and fourths as consonant, and were very slow indeed in developing the appreciation of such intervals as thirds and sixths. The human mind had to be trained and educated up to it, much in the same way as moderns are educated up to Brahms and Wagner. From harmony in pure fifths, musicians passed slowly on by intro- ducing ornamental notes, which was often done extemporaneously by singers, giving rise to what was called the " contrapnnctus a mente" of later times. 13ut the homogeneous condition of fifths and fourths was slow in passing to a greater variety, and composers were several centuries overcoming the elementary difficulties of part singing, to a large extent owing to the fact that their scale, which had been contrived for melodic clfcct, was not suited for the purposes of harmony. 1890.] on Evolution in Music. 59 The development of harmony for six hundred years, from A.D. 1000 to A.D. 1600, had underlying it a constant but very slow change in the structure of the scales ; and the progress was made all the slower by the notion prevalent in men's minds that these scales were divinely-appointed institutions, and that tampering with them was like mending the ordinances of the Deity. Much of the neces- sary mending was done by profane secularists, who wrote dance tunes and secular songs ; and the changes crept into serious music in defiance of papal restrictions and ecclesiastical reluctance, in obedience to the instinct which was as powerful in its slow steady action as any law of the pliysical world. The thin end of the wedge for altering the scale was inserted in the shape of certain arbitrary accidentals which were introduced to modify obvious crudities of harmony ; and when people got accustomed to them they by degrees established themselves as part of the scales, and supplied the means of a new system of classifying and defining the relative importance and func- tions of notes in a scale. The methods adopted by the mediaeval composers for regulating a piece of music were distinctly homogeneous. The commonest was to take a familiar tune and give it to the tenors to sing, and to add other parts to it in such a way as to produce a harmonious and expressive whole. Another common device was to take two familiar tunes and to twist and alter them about till it was endurable to sing them to- gether ; sometimes adding another part, which sang nonsense syl- lables, such as Balaam, Portare, or what not, to such notes as were available. 1 cannot say that the result is commonly pleasing, but they improved in the course of centuries, and the art in general got the more heterogeneous as they found out fresh methods of artistic procedure. In all of these, till the end of the sixteenth century, the same prin- ciples are discernible. The harmony is always arrived at by com- bining independent voice parts together, never by writing definite lump chords. It was not till after the great development of pure choral art had passed to its highest culmination, in the time of Palestrina and Marenzio, that men began to think of writing chords as chords. While this lengthy development was going on, they were unconsciously absorbing the impressions which the sounds of chords produced upon them ; and no one ever produced more divinely pure sounds in the shape of choral chords than Palestrina and Marenzio ; but they managed to contrive them by the marvellous skill with which they distributed their combined independent voice parts, and not by writing them deliberately as chords ; and the reluctance of the human mind to come to close quarters with chords as such hindered them from discovering the relationship of chords to one another; and hence kept their art in a singularly indefinite state. All the choral music of the greatest period, as well as of earliest days, is singularly indefinite in design, owing to this lack of a sense of chord relation- ship, and to uncertainty and variableness in the aspects of the cadences. 60 Professor C. Hubert H. Parry [Feb. 28, It is true the free lances of art and the secularists had done some- thing towards defining the plan of movements by cadences like ours, but matters did not come to a crisis till men began to alter their point of view. The change of point of view was ultimately brought about by one of the most deliberate and conscious revolutions ever attempted in art. The beginning of our modern development of opera and oratorio, and all the modern instrumental forms of art, was the fruit of some speculations of a group of Italian enthusiasts at the end of the sixteenth century, who hoped to be able to revive the ancient manner of performing Greek dramas. They imagined that it could be achieved by making a musical imitation of the cadences of the voice in declamation, and adding the support of some simple instrumental accompaniment. The result was one of the most chaotic and formless specimens of art ever devised by the mind of man. Their instinct for systematic progressions of chords was totally unde- veloped, as was their sense of key in our modern sense ; and they therefore had no principle by which to arrive at any effect of design. Moreover, their radical idea almost precluded the pos- sibility of musical design, as they thought nothing was needed but recitation of the poetry, and that the dramatic situation and the language would carry the attention along and sufficiently occupy the mind without need of musical form. Their experiments were all the more crude because the composers were practically amateurs, with no knowledge of the technique of their art ; and though they had great zeal, it was by no means zeal according to knowledge, but often outran discretion. But it may be said, on the other hand, that absence of knowledge of the traditions of their art left them all the freer to experiment in the new country they had found, and the obviousness of their mistakes led the sooner to their being reformed. The situation is precisely analogous to that of the earliest stages of scale-making, only in a different plane. The texture of the early oratorios, operas, and cantatas was almost homogeneous. The recita- tive winds helplessly along, page after page, in monotonous inconse- quence, only occasionally varied by a fragment rather more expressive than the rest, and by short fragments of very empty instrumental music called " ritornellos," and equally pointless fragments of chorus. The way in which nuclei began to form was through composers per- ceiving what excellent opportunities for musical expression were offered by salient points of special dramatic or pathetic interest in the plays, and they soon saw that a point which was brought out strongly in this manner, laid special hold of the audience. When this was once discovered, it did not take them long to realise the effect which was produced by repeating such a passage ; and though it took them half a century to find the most suitable manner to dis- pose of such a balance of phrases, it was within twelve years of the first operatic venture that Montcverde made a great effect by the 1890.] on Evolution in Music. 61 simple process of giving a very expressive phrase to a singer in a specially interesting situation, following it by a phrase which is more or less contrasted with it, and then going back to the first phrase again; a process which contains in miniature the design of that aria form which afterwards became so universal that it pervaded all operatic literature, and became a perfect plague from its constant recurrence. The opening of public opera houses in Venice in 1637, and the great success which attended the venture, and its rapid extension, gave composers great opportunities, and enabled them to make rapid progress in defining the contents of their works. The in- troductory instrumental summons to attention, which in Monte- verde's hands was a noisy clatter of braying instruments, all on one chord, developed into the neat little overture of Alessandro Scarlatti, which was of momentous importance as the immediate origin of our modern symphony ; and the texture of the opera itself progressed to a stage in which the arias obtained a distinct and per- manent (though too prominent) form, and alternated throughout with recitatives and ritornellos, and an occasional chorus. Unfortunately, progress was stayed here for a long time, through the indolent care- lessness of operatic audiences, who used the performances even then as fashionable opportunities for gathering and talking, and only cared to listen to the prominent singers ; and even composers as great as Handel fell in with the apparently inevitable too complacently ; and though great skill was evolved in giving variety to the respective arias, and in giving them a definite and contrasting dramatic cha- racter, the scheme was so monotonous that it has condemned the operatic works of all composers till the end of Handel's time to irre- mediable oblivion. This tame acquiescence in the bad taste of the public has been their curse, and ours too ; for though even Alessandro Scarlatti's operas contain fine music, and Handel's hundreds of things which are really splendid, the desperate monotony of the design makes them utterly unendurable as wholes to an average audience ; and even as historical studies, it would take the strongest and most obstinate patience to sit out one of them with attention. The development of oratorio, up to a little before Handel's time, had followed much the same lines as opera. The admirable skill and judg- ment of Carissimi had at first used the opportunities which the oratorio form affords with a success which was full of hopeful auguries ; and his work was followed up with great power by Stradella. They both gave the form a high degree of variety, by introducing large and broad choruses among their solos, and by devising great variety of plan even in their solo music. But the blight of the star system fell upon oratorio likewise in Italy, and for a time it degenerated into the same monotonous scheme of alternate arias and recitatives as the opera; and it was not till this form of art became the cherished favourite of much more earnest and patient nations, that the oratorio developed into the noble plan and the large and well-defined proportions which we find in the few great masterpieces of oratorio art from Handel and 62 Professor C. Hubert E. Parry [Feb. 28, Bach's time onwards. The later development of oratorio and opera depended to a great extent upon the progress of instrumental forms of art, which were slower in making a beginning, but developed more steadily, and under the influence of a greater spirit of earnestness ; as in instrumental music the temptations to mere meretricious display- are not so great and inevitable. Composers were very slow in finding out what to do in instru- mental music. They imitated the old choral forms, such as madrigals and canzonas, being led to the procedure by the similarity of the group of independent instruments to the group of independent voices, but they did not arrive at anything very enjoyable, except in one line, which was our modern type of fugue. This, in its highest form, is probably as much an instrumental product as a vocal one, though originally based on choral forms of art. The immediate origin of its peculiar traditions for enunciating the subject or musical idea, is based upon the obvious device of making the diiferent voices sing the same phrase to the same words ; which was systematised in early days, up to a certain point, by making the voices take the phrases in the parts of the scale which best suited their register. This resulted in a very effective balance of question and answer (or Dux and Comes) even in early times ; but in the old polyphonic days, after the first statement of the initial phrase by each member of the group of voices, the movement tailed off into indefiniteness, and the initial phrases did not appear again. In course of time composers found out the effect of coherence which a frequent repetition of so salient a feature as the initial phrase gave to a whole movement, and began to repeat their subject over and over again. The progress from such modified homogeneity to definite hetero- geneity was arrived at under the influence of modern harmonic conditions and modes of thought, in which these alternations of the subject and the episodes were accompanied by contrasting changes of key — passing out of the original key into others, and drawing the recurrence of the subjects closer and closer as the original key was returned to, and firmly re-established at the conclusion. This form was one of the first to arrive at maturity, partly through the genius of the great organist Frescobaldi, and later, obviously, through Handel and Bach ; and it has not been materially improved upon by after ages, though its wonderful elasticity always admits of its being presented in artistic aspects, and with fresh artistic objects. And though pedantry has run riot in it, it has not ceased to be inviting to some types of really poetical and musical composers. The other kind of instrumental music, which was the ultimate basis and root of at least half of all modern instrumental music, was the aboriginal dance form. At the time when this type began to attract the attention of artistic composers, it had reached the not very advanced stage of a tune divided by a strong close into two halves, the first of which tended out from the principal key centre to a melodic or harmonic centre which was in apposition to it, and the 1890.] on Evolution in Music. 63 second of wliicli journeyed home again. In these the musical material was more or less homogeneous throughout. But the necessity for clear periods and clear grouping of rhythm had impelled composers to discover harmonic closes very early in dance tunes ; and musical instinct, while frequently observing them, was impelled to discover the most suitable ways for distributing them. And this same musical instinct, working on little more than common-sense lines, evolved from this little dance type the remarkable design which serves for all the finest movements of our modern symphonies and sonatas. As this is one of the most remarkable examples of the manner in which things progressed from homogeneity to heterogeneity, I think it worth while to enter into it in detail. The process of the development of the design was as follows : — At first the style of the music through the whole of the movement was homogeneous ; and the only strong points which stood out and defined form were the beginnings and closes of each half of the move- ment. The beginning of the second half matched the beginning of the first half, but began in the antithetical key. The end of the whole matched the end of the first half in musical material ; but the end of the first half was in the key of apposition, and the end of the whole was of course in the principal key. When this is merely described in this manner it sounds like a perfectly symmetrical design. In fact, it was too obviously symmetrical, and covered too little ground. The contrasts were insufficient, and the quality of the music was too uniform ; and in course of time composers and auditors alike found this out. The first step in advance was to give more weight to the closes of each half, by which process a strong contrast began to present itself between the beginning and end of each half, as well as between the halves ; as the cadence portion by degrees developed into such distinctness that it took upon it the appearance of a new subject. Simultaneously with this, the character of the music underwent a change, and instead of a uniform contrapuntal flow, became a well- knit succession of independent and often strongly-contrasted ideas. By this means it came to pass that the movement began with a subject in a principal key, and then moved out to a contrasted key to present a contrasting subject ; and this group formed the first half of the movement. The second half began with a restatement of the principal subject in the key of apposition, and then wandered about through strange keys to give a sense of contrast, till it reached the key the movement started from ; in which key the second subject was given, and the movement then ended. In course of time the defects of this type became apparent. The beginning of the second half did not pre- sent sufficient contrast to the design of the first half. More freedom was obviously required, and more weight on the principal key at the conclusion. To attain this, the principal subject was repeated again when the return to the original key was made near the end. Then it was found that the principal subject came in its concrete form too often ; so its reappearance at the beginning of the second half was 64 Professor C. Hubert H, Parry [Feb. 28, dispensed with, leaving the design exactly as it appears in the finest movements of Mozart, Haydn, Beethoven, and Brahms. The functions of these various divisions may be summarised as follows: — The first half establishes the principal key of the movement and its contrast- ing centre ; everything being contrived with the purpose of marking their apposition, and therefore tending to regularity. The second half begins with such treatment as gives the strongest relief to the regularity of the first by breaking up the subjects into small portions and interlacing them irregularly, and by keeping up a constant shimmer of modulation ; and finally the principal key of the move- ment is re-established firmly by presenting both subjects successively in that key. Into subordinate modifications of this structure, and the details of it, it is not possible to enter here. It must be sufficient to say that in the greatest works of Beethoven there is hardly a bar or a step of one note to another in all the complex structure which has not its intelligible place and function in the general scheme of the movement, and it is difficult to see how the differentiation of parts and the distribution of functions could be carried out more perfectly. The complete design of symphonies and sonatas comprised other movements of less complex and less interesting structure than this, which were combined with it for the sake of contrast and balance. The first type of such grouping of movements was the attempt of early composers to piroduce an artistic effect by playing two or more dance tunes together, so that their contrasts might show off one another. They began with such simple contrasts as Pavans and Galiards, and progressed up to the relative complexity of the suites of Couperin, Bach, and Handel. But this stage of advance was only an arrival at a very modified degree of heterogeneity; for the movements were always in the same key, and almost always in the same form ; that of the dance tune in two balanced halves. The symphonic or sonata group obtained a much higher degree of contrast, by putting the central movements into contrasted keys, and by strongly contrasting the forms of the movements themselves. A common type is that of four movements, of which the first is the highly developed form, comprising strong contrasts above described ; the second an imita- tion of the operatic aria ; the third a dance tune pure and simple ; and the fourth a rondo, which is commonly a simple series of alternate contrasting dance measures. We must now take a rapid survey of the evolution of modern orchestration. The greater part of the evolution has been carried on in the department of instrumental music, especially in the symphonies of the greatest composers. These are derived from the overtures which preceded the early operas, which were divided as early as Alessandro Scarlatti's time into three movements; the first solid and quick, the second slow, and the third quick and light. The practice of playing them apart from the operas began very early, as they were found very useful at the feasts and dinner- 1890.] on Evolution in Music. 66 parties of magnates, who kept private orchestras to encourage con- versation and temper the asperity of any glaring absence of it. These symphonies came very greatly into request in the next genera- tion after Bach and Handel, and were supplied in cartloads apart from their usual connection with operas, but were still called overtures or sinfonias, both of which names had commonly been applied to them while they were attached to operas. These works were of very limited interest, and were evidently very roughly played. The instruments were lumped together crudely to make a noise, and very little variety was aimed at ; while the functions of the instruments were not ascertained or their idiosyncrasies observed. When, under more favouring circumstances, development definitely began, the evolution took the same aspect as in other departments of art. A violin player named Stamitz, who was conductor at Mannheim, gave the development a push by endeavouring to obtain variety in nuances, and by using the difierent qualities of the instruments for purposes of frequent contrast. Mozart visited Mannheim when a young man, just before his second visit to Paris, and was evidently struck by the possibilities Stamifcz's procedure seemed to promise; and he gave his higher abilities to the work of diversifying the effects of orchestral colour. Before this time the violas commonly played a great deal with the basses, the wind instruments with the strings of the same average pitch ; while the horns, which were not tractable enough to follow so slavishly, were the earliest to attain some independence, but did not as yet do much more than fill up the harmonies and increase the mass of sound. The colours had in fact been mixed up in aimless confusion ; and the various instruments, except when playing long solos, did not have much definite independence one from another. After this time the violas drew away from the basses, and found their own separate place in the group, as representing a special colour and a special in- dividuality. In like manner the special individuality of the hautboys found its true place as a factor in the complicated nexus of tone- quality and instrumental idiosyncrasy. Other instruments were added, which supplied other qualities of tone, and the particular functions which each instrument was most fitted to perform were by degrees ascertained by innumerable experiments and by development of instinct; the natural tendency being, as time went on, for each several instrument to attain more and more independence, and for more and more respect to be paid to the various idiosyncrasies of each member of the j^imily. The hautboy and the clarinet no longer struggled to play fiddle passages, nor the bassoon only to reinforce the bass and play passages which were better fi.tted for stringed instruments ; even that distinguished survival from the primitive music of savages, the drum, was no longer condemned merely to add to the noise of forte passages, but was used with dramatic significance, and even at times used to express characteristic musical figures, or to play mysterious and hazy-sounding chords. By such processes, and by establishing a clear distinction between Vol. XIII. (No. 84.) f 66 Professor G. Hiihert H. Parry [Feb. 28, the three groups of stringed, wood wind, and brass instruments, orchestral music progressed from the homogeneity in which all the functions of the different instruments were jumbled up together, to that elaborate heterogeneity of Wagner ; in which every instrument, from piccolo to double bassoon, has its own place in the scheme, and its own function to perform. And, indeed, one of the things which is looked upon as a test point in good writing for an orchestra is that no player shall waste his breath or his muscular efforts in vain ; and a composer who now writes a part for an instrument which does not " tell " is not a full master of his craft. This high development of orchestration is indeed the furthest point of subtlety to which modern musical development has progressed ; and it has grown with a surpris- ing degree of development in the public for appreciating rapid varieties of tone effect, and a certain dangerous susceptibility to the exciting effects of colour, which always has a tendency to deaden the faculty for appreciating beauty of artistic design. And in this direction we already see possibilities of decadence ; as many works which take great hold of musical natures show a decided falling-off from the perfect design of the great masters, towards that hazy indefiniteness and intangible vagueness of progression and structure which clearly portends relapse into homogeneity in one respect. But it must be said, by way of caution against too hastily taking a pessimistic view of the situation, that in artistic works of real value there is always an element which defies pure intellectual analysis: and it may be that the principles of form we so admire in the works of our greatest musicians are undergoing some subtle change to which we are not at present capable of giving a definition. The later evolution of the great forms of opera and oratorio does not demand very lengthy consideration. No branch of art affords so many examples of the non-survival of the imperfect as the opera. The stage offers so many opportunities of obtaining strong im- pressions by vapid means that the vast majority of people who write for it seem to get bewildered, and either deliberately aj^peal to the public by cheap claptrap, or lose their capacity of judging what is worthy of art and what is not ; and the peculiar attitude of the operatic public has always been against thoroughness in any respect ; and the result is that the composer who writes for popular success does nothing for art, and the composer who feels his art deeply gets no thanks or encouragement from the public. The opera of the type written by Handel, Hasse, John Christian Bach, Galuppi, and hundreds more, was once the joy of the world ; but no branch of art is more utterly dead, or more incapable of revival on any terms what- ever. Gluck's reforms came practically too soon, and beautiful as much of his work is, it is almost incapable of revival except in frag- ments. But he did give an impulse to the evolution of operatic art, and set men's instincts to work again to clear out dead matter and help the sluggish evolution to go on again. The stiffs grouping of arias and recitatives was diversified by trios, quartettes, and such 1890.J on Evolution in Music. 67 ensemble pieces ; and by finales elaborately contrived of groups of various forms all well defined. The homogeneous character of the musical material grew into an infinite diversity of characteristic passages, each apposite to the character and situations in the play; and the art of orchestration growing jiarallel to its growth in instru- mental music, afforded absolutely bewihleriug opportunities of efi'ect in the hands of a competent composer. In Weber a very high standard of artistic perfection in all departments was arrived at ; in Wagner, the utmost heterogeneity of which the art seems capable, both in respect of his orchestration, the definition of the several characters, the well-defined independent " leit motive," and the infinite variety of sentiment and expression ; while the several functions of stage effect, dramatic interest, and musical expression are so well and clearly balanced in his best work that it is difficult to say at any given moment that any one is made subservient to the other. The development of oratorio, not so cursed with over many faci- lities, has been on parallel lines to opera, and though it has not arrived at such a comj)lexity of deBnite ingredients, cannot now be said to be in a chaotic or ill-developed c(mdition. It remains now only to point out tlie manner in which the art in general has progressed, like its constituents, from limited sameness to infinite well-defined variety. At the end of the sixteenth century there was nothing but choral music, and a little crude instrumental music, which was chiefly imitated from choral music. At the beginning of the seventeenth century opera and oratorio began to emerge from the nebulous state of the art, and went revolving off. on their respective orbits. Instrumental music began to get independent status in the Suites and Toccatas, and so forth, and rapidly divided itself off into various well-defined groups. The orchestral symphony gained an independent definiteness on its part ; the pianoforte sonata, like in form, but quite distinct in treatment, was defined by the growing skill by which the resources of the instrument were developed by composers and players. Chamber music for solo instruments grew up, with all its special artistic characteristics; then followed the new class of small lyrical compositions for the pianoforte, of which Chopin and Schumann are the happiest exponents, and their variety and well-defined independence in hundreds of examples is too familiar to need insisting upon. And so the art goes on, branching out and subdividing into infinity of part songs, solo songs of many calibres — noble, good, indifferent, and detestable — cantatas, symphonic poems, rhapsodies, concert overtures, comic operas, artistic studies, odes, and hundreds of other forms, each with their particular artistic idiosyn- crasies and special adaptations, and all becoming by degrees more short lived, more journalistic, and more calculated for quick returns and rapid extinctions, to make way for fresh products, which will also serve their time and shortly make way for similarly short-lived journalistic productions, apt for their day in expressing the superficial tastes and moods of the people of their day, and no more. F 2 68 Professor C. Hubert H. Parry on Evolution in Music. [Feb. 28, The planets were evolved first, and are destined for a life of ages ; the smaller things which are evolved after they have settled into their courses, are in great part short-lived and constantly changing their aspects. The greatest achievements of art come early in an art history, when there is room for composers or artists to move in unex- hausted fields, and to create things which are great and broad and simple. When there are no new lands left to conquer or explore, men must make the best of their home gardens, and find something worth doing on a smaller and less permanent scale ; and the best can be no more than that which expresses well and truly the best and truest thinors which lie in the emotions and mind of man. There still are martyrs who sacrifice their lives to ideals, and look for neither popularity nor pay ; and it is still possible in music to write what the present generation on the whole will take no notice of, but the next will cherish. And if the average of what is heard is mere jour- nalism, and the majority of what is produced is condemned by inexorable law to be ephemeral, the world still possesses the permanent great works of art ; and those who have any instinct for what is noble and great in art can always learn to appreciate these products of great eras whose value is not impaired by the flight of time. And the store is so rich and abundant, that there is no fear of our musical hungers finding nothing to feed upon. If we set our minds to it early and late, and determine to appreciate and love the best, the fact that the laws of evolution make it apparently impossible for us to meet any more Homers, or iEschyluses, or Shakespoares, or any more Palestrinas, and Bachs, and Beethovens in the flesh, it is not so much to be regretted as long as we are in possession of their works. [C. H. H. P.] 1890.] General Monthly Meeting. 69 GENERAL MONTHLY MEETING, Monday, March 3, 1890. Sib James Crichton Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Lesley Alexander, Esq. Mrs. Shelford Bidwell, Miss Florence Bramwell, Sir John Coode, K.C.M.G. Sir George Errington, Bart. Ealph Heap, Esq. M.A. (Oxon.). Miss Mary Lawrence, William Eamsay, Esq. Ph.D. F.R.S. Herbert C. Saunders, Esq. Q.C. A. Percy Sinnett, Esq. W. S. Squire, Esq. John Strain, Esq. Sir John Richard Somers Vine, James Walker, Esq. Mrs. James Watney, were elected Members of the Royal Institution The Special Thanks of the Members were returned to Warren DB LA Rue, Esq. M.B.L for his valuable present of a Miniature Portrait of his father, the late Dr. Warren de la Rue, F.R.S. M.B.L The following letter from Lady Gull to the Honorary Secretary was read : — " Dear Sir, •' Torquay, February 1th, 1890. " I beg to thank you for your kind letter of the 5th instant, enclosing the copy of a Eesolution passed by the Managers of the Royal Institution expressive of their deep regret at the loss of my Husband, and of theii- intention to place on record on the Minutes of the Institution their sense of the same. "May I ask you at the next Meeting to convey to the Managers my deep appreciation of their great kindness in this, matter, as also of the expression of their sincere sympathy in my bereavement. " I am, dear Sir, " Yours faithfully, "S. A. Gull." The following Arrangements for the Lectures after Easter were announced : — The Hon. George C. Brodrick, D.C.L. "Warden of Merton College, Oxford — Three Lectures on The Place of Oxford University in English History ; on Tuesdays, April 15, 22, 29. Louis Fagan, Esq. Assistant Keeper of Prints and Drawings, British Museum — Three Lectures on The Art of Engraving: 1. Line Engraving; 2. Wood Engraving ; 3. Mezzotint Engraving ; on Tuesdays, May 6, 13, 20. 70 General Monthly Meeting. [March 3, Andrew Lang, Esq. — Three Lectures on The Natural History of Society ; on Tuesdays, May 27, June 3, 10. C. V. Boys, Esq. A.R.S.M. F R.S. M.E.I. Assistant Professor of Physics, Normal School of Science, South Kensington— Three Lectures on The Heat of THE Moon and Stars (the Tyndall Lectures) ; on Thursdays, April 17, 2-4, May 1. ■ Phofessor Dewar, M.A.F.R.S. M.B.I. Fullerian Professor of Chemistry, R.I. Jacksonian Professor of Xatural Experimental Philosophy, Cambridge — Six Lec- tures on Flame and Explosives; on Thursdays, Mav 8, 15, 22, 29, June 5, 12, Captain W. de W. Abney, R.E. C.B. F.R.S. il/.i?./.— Tliree Lectures on Colour and its Chemical Action ; on Saturdays, April 19, 26, May 3. Charles Waldstein, Esq. Litt.D. Ph.D. — Three Lectures on Excavating IN Greece ; on Saturdays, May 10, 17, 24. The Rev. S. Barix'g-Gould, M. A.— Three Lectures on The Ballad Music op the West of England (with Mu&ical Illustrations); on Saturdays, May 31, June 7, 14. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — for Academy of Natural Sciences, Philadelphia— Proceedings, 1888, Part 2. Svo. 1889. Accademia dei Lincei, Reale, Roma — Atti, Serie Quarta : Rendiconti. 2" Semes- tre. Vol. V. Fuse. 11, 12. 8vo. 1890. American Academy of Arts and Sciences— Troceedings, Vol. XV. Part 2. Svo. 1889. Adronomical Society, i?o//aZ— Monthly Notices. Vol. L. No. 3. 8vo. 1890. Bankers, Institute o/— Journal, Vol. XL Part 2. Svo. 1890. British Architects, Eoyal Institute o/— Proceedings, 1889-90, Nos. 8, 9. 4to. British Museum (Natural History)— Cei\a]og\ie of Fossil Reptilia and Amphibia, Part HI. and Guide to the Mineral Galleries. Svo. lsS9. BucMon, George B. Esq. F.R.S. M.R.I, {the J wf/ior)— Monograph of the British Cicada or Tettigiidae, Part 1. Svo. 1889. Cambridge Observatory — Astronomical Observations, Vol. XXII. 1866-9. 4to. 1890. Cassedij, W. S. Esq. (the Author)— Is the Copernican System of Astronomy True? Svo. 1S88. Chemical Society — Journal for February, 1890. Svo. Cracovie, l Academic des Sciences — Bulletin, 1890, No. 1. Svo. Crisj), Frank, Esq. LL.B. F.L.S. &c. M.R.I. — Journal of the Royal Microscopical Society, Part 6a; 1890, Part 1. Svo. Editors — American Journal of Science for February, 1890. Svo. Analyst for February, 1890. Svo. Athenteum for February, 1890. 4to. Clieniical News for February, 1890. 4to. Chemist and Druggist for February, 1S90. Svo. Electrical Engineer for February, iS90. fol. Engineer for February, 1890. fol. Engineering for February, 1890. fol. Horological Journal for February, 1890. Svo. Industries for February, 1890. fol. Iron for February, 1890. 4to. Ironmongery for February, 1890. IMurray's M'lgazine for February, 1890. Svo. Nature for February, 1S90. 4to. Photogragliic News for February, 1890. Svo. Rrvue Scientilique for February, 1890. 4to. Telegrapliic .Journal for February, 1890. fol. Zoophiliat for February, 1890. 4to. 1890.] General Monthly Meeting. 71 Florence Biblioteca Nazionale Centrale — Bolletino, No. 100. 8vo. 1890. Geological Institute, Imperial, Vienna — Verhandlungen, 1889, No. 18 ; 1890, Nos. 1, 2. 8vo. Geological Society — Quarterly Journal, No. 181. 8vo. 1889. Georgofili, Eeale Accademie — Atti, Quarta Seria, Vol. XII. No. 4. 8vo. 1889. Harlem, Societe Hollandaii-aac Bell and the Lumberman, 'was traced, long after the event, to the colour-blindness of a pilot, who had been unjustly accused of being drunk at the time of the occurrence. In how many instances colour-blindness has been the unsuspected cause of wrecks and other calamities at sea, it is impossible to do more than con- jecture. It is necessary, then, alike in the public interest and in the interest of the colour-blind, who have doubtless often suffered in the misfortunes which their defects have produced, to detect them in time to prevent them from entering into the marine and railway services ; and the next question is, how this detection should be accomplished. We have to distinguish the colour-blind from the colour-sighted ; but we must be careful not to confound colour-blindness with the much more common condition of colour-ignorance. It would surprise many people, more especially many ladies, to discover the extent to which sheer ignorance of colour prevails among 1890.] on Colour-Vision and Colour- Blindness, 129 boys and men of the labouring classes. Many, wbo can see colours perfectly, and who would never be in the least danger of mistaking a railway signal, are quite unable to name colours or to describe, them ; and they are sometimes unable to perceive, for want of education of a faculty which they notwithstanding possess, anything like fine shades of difference. Mr. Gladstone once published a paper on the scanty and uncertain colour-nomenclature of the Homeric poems ; and he might have found very similar examples among his own contemporaries and in his own country. I Lave lately heard a description of a pattern card of coloured silks, issued by a Lyons manufacturer, which contains samples of two thousand different colours, each with its more or less appropriate name. There is here a larger colour-vocabulary than the entire vocabulary, for the expression of all his knowledge and of all his ideas, w^hich is possessed by an average engine-driver or fireman; and, just as most of us would be ignorant of the names of the immense majority of the colours displayed on that card, so hundreds of men and boys among the labouring classes, especially in large towns, where the opportunities of education by the colours of flowers and insects are very limited, are ignorant of the names of colours which persons of ordinary cultivation mention constantly in their daily talk, and expect their children to pick uj) and to understand unconsciously. It is among people thus ignorant that the officials of the Board of Trade, and of railways, have been most successful in finding their supposed colour-blind persons ; and these persons, who would never have been pronounced colour-blind by an expert, have been able, as soon as they have paid a little attention to the observation and naming of colour, to pass an official examination triumphantly. The sense of colour presents many analogies to that of hearing. Some people can hear a higher or a lower note than others, the difference depending upon structure, and being incapable of alteration. No one who can- not hear a note of a certain pitch can ever be trained to do so ; but, within the original auditory limits of each individual, the sense of hearing may be greatly improved by cultivation. In like manner, a person who is blind to red or green must remain so ; but one whose colour-sense is merely undeveloped by want of cultivation may have its acuteness for fine differences very considerably increased. In order to test colour- vision for railway and marine purposes, the first suggestion which would occur to many people would be to employ as objects the flags and signal lanterns which are used in actual working. I have heard apparently sensible people use, with reference to such a procedure, the phrase upon which Faraday was wont to pour ridicule, and to say that the fitness of the suggested method " stands to reason." To be effectual, such a test must be applied in different states of atmosphere, with coloured glasses of various tints, with various degrees of illumination, and with the objects at various distances ; so that much time would be required in order to exhaust all the conditions under which railway signals may present themselves. This being done, the examinee must be either Vol XIII. (No. 84.) k 130 Mr, B. Brudenell Carter [May 9, right or wrong each time. He has always an even chance of being right ; and it would be an insoluble problem to discover how many correct answers might be due to accident, or how many incorrect ones might be attributed to nervousness or to confusion of names. We must remember that what is required is to detect a colour- blind person against his will ; and to ascertain, not whether he describes a given signal rightly or wrongly on a particular occasion, but whether he can safely be trusted to distinguish correctly between signals on all occasions. We want, in short, to ascertain the state of his colour-vision generally; and hence to infer his fitness or unfitness to discharge the duties of a particular occupation. For the accomplishment of this object, we do not in the least want to know what the examinee calls colours, but only how he sees them, wdiat colours appear to him to be alike and what appear to be unlike ; and the only way of attaining this knowledge with certainty is to cause him to make matches between coloured objects, to put those together which appear to him to be essentially the same, and to separate those which appear to him to be essentially different. This principle of testing was first laid down by Seebeck, who required from examinees a complete arrangement of a large number of coloured objects; but it has been greatly simplified and improved by Prof. Holmstren, who pointed out that such a complete arrangement was superfluous, and that the only thing necessary was to cause the examinee to make matches to certain test colours, and, for this pur- pose, to select from materials which contained not only such matches, but also the colours which the colour-blind were liable to confuse with them. After many trials, Holmojren finally selected skeins of Berlin wool as the material best suited for this purpose ; and his set of wools com- prises about 150 skeins [showiij. The advantages of his method over every other are that the wool is very cheap, very portable, and always to be obtained in every conceivable colour and shade. The skeins are not lustrous, so that light reflected from the surfaces does not interfere with the accuracy of the observation ; and they are very easily picked up and manipulated, much more easily than coloured paper or coloured glass. The person to be tested is placed before a table in good daylight, the table is covered by a white cloth, and the skeins are thrown upon it in a loosely arranged heap. The examiner then selects a skein of pale green much diluted with white, and throws it down by itself to the left of the heap [shown]. The examinee is directed to look at this pattern skein and at the heap, and to pick out from the latter, and to place beside the pattern, as many skeins as he can find which are of the same colour. He is not to be par- ticular about lighter or darker shades, and is not to compare narrowly, or to rummage much amongst tlie heap, but to select by his eyes, and to use his hands chiefly to change the position of the selected material. In such circumstances, a person with normal colour-sight will 1890.] on Colour-Vision and Colour-Blindness. 131 select the greens rapidly and without hesitation, will select nothing else, and will select with a certain readiness and confidence easily recognised by an experienced examiner, and wdiich may even be carried to the extent of neglecting the minute accuracy which a person who distrusts his own colour-sight will frequently endeavour to display. Some normal-sighted peoj^le will complete their selection by taking greens which incline to yellow, and greens which incline to blue, while others will reject both ; but this is a difference depending sometimes upon imperfect colour educati(m, sometimes upon the in- terpretation placed upon the directions of the examiner; for the person who so selects sees the green clement in both the yellow- greens and the blue-greens, and is not colour-blind. The completely colour-blind, whether to red or to green, will proceed with almost as much speed and confidence as the colour-sighted; and will rapidly pick out a number of drabs, fawns, stone-colours, pinks, or yellows. Between the foregoing classes we meet with a few people who declare the imperfection of their colour-sense by the extreme care with which they select, by their slowness, by their hesitation, and by their desire to compare this or that skein with the pattern more narrowly than the conditions of the trial should permit. They may or may not ulti- mately add one or more of the confusion colours to the green, but they have a manifest tendency to do so, and a general uncertainty in their choice. One of the great advantages of Holmgren's method over every other is the way in which the examiner is able to judge, not only by the final choice of matches, but also by the manner in which the choice is made, by the action of the hands, and by the gestures and general deportment of the examinee.- When confusion colours have been selected, or when an unnatural slowness and hesitation have been shown in selecting, the examinee must be regarded as either completely or incompletely colour-blind. In order to determine which, and also to which colour he is defective, he is subjected to the second test. For this, the wool is mixed again, and the pattern this time is a skein of light purple — that is, of a mixture of red and violet much diluted with white \sliown\. To match this, the colour-blind always selects deeper colours. If he puts only deeper purples, he is incompletely colour-blind. If he takes blue or violet, either with or without purple, he is completely red-blind. If he takes green or grey, or one alone, with or without purple, he is completely green-blind. If he takes red or orange, with or without purple, he is violet-blind. If there be any doubt, the examinee may be subjected to a third test, which is not necessary for the satisfaction of an expert, but which sometimes strengthens the proof in the eyes of a bystander. The pattern for this third test is a skein of bright red, to be used in the same way as the green and the purple \sliown\. The red-blind selects for this dark greens and browns which are much darker than the pattern ; while the green-blind selects greens and browns which are lighter than the pattern. The method of examination thus described is, I believe, absolutely K 2 132 Mr. R. Briidenell Carter [May 9, trustworthy. It requires no apparatus beyond tlie bundle of skeins of wool, no arrangements beyond a room witb a good window and a table with a white cloth. In examining large numbers of men, they may be admitted into the room fifty or so at a time, may all receive their instructions together, and may then make their selectious one by one, all not yet examined watcLing the actions of those who come up in their turn, and thus learning how to proceed. The time re- quired for large numbers averages about a miuute a person. I have heard and read of instances of colour-blind people who had passed the wool test satisfactory, and had afterwards been detected by other methods ; but I confess that I do not believe in them. I do not believe that in such cases the wool test was applied properly, or in accordance with Holmgren's very precise instructions ; and I know that it is often applied in a way which can lead to nothing but erroneous results. Railway foremen, for example, receive out of store a small collection of coloured wools selected on no principle, and they use it by pulling out a single thread, and by asking the examinee, " What colour do you call that ? " Men of greater scientific pretensions than railway foremen have not always selected their imttern colours accurately, and have allowed those whom they ex- amined, and passed, to make narrow comparisons between the skeins in all sorts of lights, in a way which should of itself have afforded sufficient evidence of defect. Although, however, the expert may be fully satisfied by the wool test that the examinee is not capable of distinguishing with certainty between red and green flags or lights in all the circumstances in which they can be displayed, it may still remain for him to satisfy the employer who is not an expert, the railway manager, or the ship- owner, and to convince him that the colour-blind person is unfit for certain kinds of employment. It may be equally necessary to con- vince other workmen that the examinee has been fairly and rightly dealt with. Both these objects may be easily attained, by the use of slight modifications of the lights which are employed. Lanterns for this special purpose were contrived, some years ago, by Holmgren himself, and by the late Prof. Bonders, of Utrecht, and what are substantially their contrivances have been brought forward within the last few months as novelties, by gentlemen in this country who have re-invented them. The principle of all is the same — namely, that light of varying intensity may be disi)layed through apertures of varying magnitude, and through coloured glasses of varying tint, so as to imitate the appearances of signal lam])S at different distances, and under different conditions of illuminatirn, of weather, and of atmosphere. To the colour-blind, the difierence between a red light and a green one is not a difference of colour, but of luminosity ; the colour to which he is blind appearing the less luminous of the two. He may therefore be correct in his guess as to which of the two is exhibited on any given occasion, and he is by no means certain to mistake one for the other when they are exhibited in immediate 1890.] on Colour-Vision and Colour-Blindness. 133 succession. His liability to error is chiefly conspicuous when he sees one light only, and when the conditions which govern its lumi- nosity depart in any degree from those to which he is most accustomed. With the lanterns of which I have spoken, it is always possible to deceive a colour-blind person by altering the luminosity of a light without altering its colour. This may be done by diminishing the light behind the glass, by increasing the thickness of the red or green glass, or by placing a piece of neutral tint, more or less dark, in front of either [shoion^. The most incredulous employer may be convinced, by expedients' of this kind, that the colour-blind are not to be relied upon for the safe control of ships or of locomotives. With regard to the whole question, there are many points of great interest, both physical and physiological, which are still more or less uncertain ; but the practical elements have, I think, been well-nigh exhausted, and the means of securing safety are fully in the hands of those who choose to master and to employ them. The lanterns, in their various forms, are useful for the purpose of thoroughly ex- posing the colour-blind, and for bringing home the character of their incapacity to unskilled spectators ; but they are both cumbrous and superfluous for the detection of the defect, which may be accomplished with far greater ease, and with equal certainty, by the wool test alone. I have already mentioned that the examinations which have been conducted in the United States, thanks to the indefatigable labours of Dr. Joy Jeffries, have led to the discovery of an enormous and previously quite unsuspected amount of colour-ignorance, a condition which is frequently mistaken for colour-blindness by the methods of examination which are in favour with railway companies and with the Board of Trade ; and this colour-ignorance has been justly regarded as a blot on the American system of national education. It has therefore, in some of the States, led to the adoption of systematic colour-teaching in the schools ; and, for this purpose. Dr. Joy Jeffries has introduced this wall-chart and coloured cards [s/iOi(7?i]. The children are taught, in the first instance, to match the colours in the chart with those of the cards distributed to them ; and, when they are tolerably expert at matching, they are further taught the names of the colours. It must, nevertheless, always be remembered that a knowledge of names does not necessarily imply a knowledge of the things designated ; and that colour- vision stands in no definite relation to colour-nomenclature. Even this system of teaching may leave a colour-blind pupil undetected. [E. B. C] 134: Professor Raphael Meldola [-May 16, WEEKLY EVENING MEETING, Friday, May 16, 1890. Edwakd Fbankland, Esq. D.C.L. LL.D. F.E.S. Vice-President, in the Chair. Professor Eaphael Meldola, F.E.S. M.B.I. The Photographic Image. The history of a discovery which has been developed to such a remarkable degree of perfection as jDhotography has naturally been a fruitful source of discussion among those who interest themselves in tracing the progress of science. It is only my presence in this lecture theatre, in which the first public discourse on photography was given by Thomas Wedgwood at the beginning of the century, that justifies my treading once again a path which has already been so thoroughly well beaten. If any further justification for trespas- sing upon the ground of the historian is needed, it will be found in the circumstance that in the autumn of last year there was held a celebration of what was generally regarded as the jubilee of the dis- covery. This celebration was considered by many to have reference to the public disclosure of the Daguerreotype process, made through the mouth of Arago to the French Academy of Sciences on August 10, 1839. There is no doubt that the introduction of this process marked a distinct epoch in the history of the art, and gave a great impetus to its subsequent development. But, while giving full recognition to the value of the discovery of Daguerre, we must not allow the work of his predecessors and contemporaries in the same field to sink into oblivion. After the lapse of half a century we are in a better position to consider fairly the influence of the work of different investigators upon modern photographic processes. I have not the least desire on the present occasion to raise the ghosts of dead controversies. In fact, the history of the discovery of photography is one of those subjects which can be dealt with in various ways, according to the meaning assigned to the term. There is ample scope for the display of what Mr. Herbert Spencer calls the *' bias of patriotism.'" If the word "photography" be interpreted literally as writing or inscribing by light, without any reference to the subsequent permanence of the inscription, then the person who first intentionally caused a design to bo imprinted by light upon a photo-sensitive compound must be regarded as the first photographer. According to Dr. Eder, of Vienna, we must place this experimeiit to the credit of Johann Heinrich Schulzc, the son of a German tailor, who WHS born in the Duchy of Madgeburg, in Prussia, in 1687, and who died in 174:4:, after a life of extraordinary activity as a linguist, theologian, physician, and philoso^^hcr. In the year 1727, when 1890.1 on the Photographic Image. 135 experimenting on the subject of phosphorescence, Schulze observed that by pouring nitric acid, in which some silver had previously been dissolved, on to chalk, the undissolved earthy residue had acquired the property of darkening on exposure to light. This effect was shown to be due to light, and not to heat. By pasting words cut out in paper on the side of the bottle containing his precipitate, bchulze obtained copies of the letters on the silvered chalk. The German philosopher certainly produced what might be called a temporary photocrram. Whatever value is attached to this observation m the develo'^pment of modern photography, it must be conceded that a considerable advance was made by spreading the sensitive compound over a surface instead of using it in mass. It is hardly necessary to remind you here that such an advance was made by Wedgwood and Davy in 1802.* The impressions produced by these last experi- menters were, unfortunately, of no more permanence than those obtained by Schulze three-quarters of a century before them. ^ It will, perhaps, be safer for the historian of this art to restrict the term photograph to such impressions as are possessed of permanence : I do not, of course, mean absolute permanence, but ordinary durability in the common-sense acceptation of the term. From this point of view the first real photographs, i. e. permanent impressions of the camera picture, were obtained on bitumen films by Joseph Nicephore Niepce, of Chalons-sur-Saone, who, after about twenty years' work at the subject, had perfected his discovery by 1826. Then came the days of silver salts again, when Daguerre, who commenced work m 1824, entered into a partnership with Niepce in 1829, which was brought to a termination by the death of the latter in 1833. The partnership was renewed between Daguerre and Niepce de St. Victor, nephew of the elder Niepce. The method of fixing the camera picture on a film of silver iodide on a silvered copper plate— the process justly asso- ciated with the name of Daguerre, was ripe for disclosure by 1838, and was actually made known in 1839. ^ • • n The impartial historian of photography who examines critically into the evidence will find that, quite independently of the French pioneers, experiments on the use of silver salts had been going on m this country, and photographs, in the true sense, had been produced almost simultaneously with the announcement of the Daguerreotype process, by two Englishmen whose names are as household words m the ranks of science— I refer to William Henry Fox Talbot and Sir John Herschel. Fox Talbot commenced experimenting with silver salts on paper in 1834, and the following year he succeeded m imprinting the camera picture on paper coated with the chloride. In January 1839 some of his "photogenic drawings "—the first "silver prints " ever obtained— were exhibited in this Institution by Michael * " All Account of a Method of Copying Paintings upoB Glass, and of making Profiles by the Agency of Light npon Nitrate of Silver Invented by T Wedgwood, Esq. With Observations by H. Davy." ' Journ. R. I. 180J, p. i/U. 13G Professor Baphael Meldola [^lay 16, Faraday. In the same month he communicated his first paper on a photographic process to the Koyal Society, and in the following month he read a second paper before the same society, giving tlie method of preparing the sensitive paper and of fixing the prints. The outcome of this work was the " Calotype " or Talbotype process, which was sufficiently perfected for portraiture by 1840, and which was fully described in a paper communicated to the Eoyal Society in 1841. The following year Fox Talbot received the Eumford Medal for his " discoveries and improvements in photography." * Herschel's process consisted in coating a glass plate with silver chloride by subsidence. The details of the method, from Herschel's own notes, have been published by his son. Prof. Alexander Herschel.f By this means the old 40-foot telescope at Slough was photographed in 1839. By the kindness of Prof. Herschel, and with the sanction of the Science and Art Department, Herschel's original photographs have been sent here for your inspection. The process of coating a plate by allowing a precipitate to settle on it in a uniform film is, however, impracticable, and was not further developed by its illus- trious discoverer. We must credit him, however, as being the first to use glass as a substratum. Herschel further discovered the im- portant fact that while the chloride was very insensitive alone, its sensitiveness was greatly increased by washing it with a solution of silver nitrate. It is to Herschel, also, that we are indebted for the use of sodium thiosulphate as a fixing agent, as well as for many other discoveries in connection with photography, which are common matters of history. Admitting the impracticability of the method of subsidence for producing a sensitive film, it is interesting to trace the subsequent development of the processes inaugurated about the year 1839. The first of photographic methods — the bitumen process of Niepce — survives at the present time, and is the basis of some of the most important of modern j)hoto-mechanical j)riuting processes. [Specimens illustrating photo-etching from Messrs. Waterlowand Sons exhibited.] The Daguerreotype process is now obsolete. As it left the hands of its inventor it was unsuited for portraiture, on account of the long exposure required. It is evident, moreover, that a picture on an opaque metallic plate is incapable of reproduction by printing through, so that in this respect the Talbotype possessed distinct advantages. This is one of the most important points in Fox Talbot's contributions to photography. He was the first to produce a transparent paper negative from which any number of positives could be obtained by printing through. The silver print of modern times is the lineal descendant of the Talbotype print. After forty * For these anrl other details relating to Fox Talbot's work, necessarily excluded for want of time, I am indebted to liis son, Mr. C. H. Talbot, of Lacock Abbey. t * rhotog. Journ, and Trans. Fhotog. Soc.,' June 15, 1S72. 1890.] on the Photographic Image. 137 years' use of glass as a substratum, we are going back to Fox Talbot's plan, and using tbin flexible films— not exactly of paper, but of an allied substance, celluloid. [Specimens of Talbotypes, lent by Mr. Crookes, exbibited, witb celluloid negatives by tbe Eastman Company.] If I interpret tbis fragment of bistory correctly, tbe founders of modern pbotograpby are tbe tbree men wbose labours bave been briefly sketcbed. Tbe jubilee of last autumn marked a culminating point in the work of Niepce and Daguerre, and of Fox Talbot. Tbe names of tbese tbree pioneers must go down to posterity as co-equal in tbe annals of scientific" discovery. [Portraits by Mr. H. M. Elder shown.] The lecture theatre of the Eoyal Institution offers such tempting opportunities to the chronicler of the history of this wonderful art that I must close this treatment of the subject by reminding myself that in selecting the present topic I had in view a statement of the case of modern photography from its scientific side only. There is hardly any invention associated with the present century which has rendered more splendid services in every de- partment of science. The physicist and chemist, the astronomer and geographer, the physiologist, pathologist, and anthropologist will all bear witness to the value of photography. The very first scientific application of Wedgwood's process was made here by the illustrious Thomas Young, when he impressed Newton's rings ^ on paper moistened with silver nitrate, as described in his Bakerian Lecture to the Eoyal Society on November 24, 1803. Prof. Dewar has iust placed in my hands the identical slide, with the Newton rings still visible, which he believes Young to have used in this classic experiment. [Shown.] Our modern photographic processes depend upon chemical changes wrought by light on films of certain sensitive compounds. Bitumen, under this influence, becomes insoluble in hydrocarbon oils, as in the heliographic process of the elder Niepce. Gelatine mixed with potassium dichromate becomes insoluble in water on exposure to light, a property utilised in the photo-etching process introduced in 1852 by Fox Talbot, some of whose original etchings have been placed at my disposal by Mr. Crookes. [Shown.] Chro- matized gelatine now plays a most important part in the autotype and many photo-mechanical processes. The salts of iron in the ferric condition undergo reduction to the ferrous state under the influence of light in contact with oxidizable organic compounds. The use of these iron salts is another of 8ir John Herschel's contributions to photography (1842), the modern " blue print " and the beautiful platinotype being dependent on the photo-reducibility of these compounds. [Cyanotype print developed with ferricyanide.] ^ Of all the substances known to chemistry at the present time, the salts of silver are by far the most important in photography, on account of the extraordinary degree of sensitiveness to which they can be raised. The photographic image, with which it is my privi- lege to deal on this occasion, is that invisible impression produced by 138 Professor Baphael Meldola [May 16, the action of light on a film of a silver haloid. Many methods of producing such films have been in practical use since the foundation of the art in 1839. All these depend on the double decomposition between a soluble chloride, bromide, or iodide, and silver nitrate, resulting in the formation of the silver haloid in a vehicle of some kind, such as albumen (Nicpce de St. Victor, 1848). or collodion on glass, as made practicable by Scott Archer in 1851. For twenty years this collodion process was in universal use ; its history and details of manipulation, its development into a dry plate process by Colonel Russell in 1861, and into an emulsion process by Bolton and Sajce in 1864, are facts familiar to every one. The photographic film of the present time is a gelatino-haloid (generally bromide) emulsion. If a solution of silver nitrate is added to a solution of potassium bromide and the mixture well shaken, the silver bromide coagulates, and rapidly subsides to the bottom of the liquid as a dense curdy precipitate. [Shown.] If instead of water we use a viscid medium, such as gelatine solution, the bromide does not settle down, but forms an emulsion, which becomes quite homogeneous on agitation. [Shown.] This operation, omitting all details of ripening, washing, &c., as well known to practical photo- graphers, is the basis of all the recent photographic methods of obtaining negatives in the camera. The use of this invaluable vehicle, gelatine, was practically introduced by R. L. Maddox in 1871, previous experiments in the same direction having been made by Gaudin (1853-61). Such a gelatino-bromide emulsion can be spread uniformly over any substratum — glass, paper, gelatine, or celluloid — and when dry, gives a highly sensitive film. The fundamental problem which fifty years' experience with silver haloid films has left in the hands of chemists is that of the nature of the chemical change which occurs when a ray of light falls on such a silver salt. Long before the days of photography — far back in the sixteenth century — Fabricius, the alchemist, noticed that native horn silver became coloured when brought from the mine and exposed. The fact presented itself to Robert Boyle in the seventeenth century, and to Beccarius, of Turin, in the eighteenth century. The change of colour undergone by the chloride was first shown to be associated with chemical decomposition in 1777, by Scheele, who proved that chlorine was given off when this salt darkened under water. I can show you this in a form which admits cf its being seen by all. [Potassium iodide and starch paper were placed in a glass cell with silver chloride, and the arrangement exposed to the electric light till the paper had become blue.] The gas which is given off under these circumstances is either the free halogen or an oxide or acid of the halogen, according to the quantity of moisture present and the intensity of the light. I have found that the bromide aftects the iodide and starch paper in the same way, but silver iodide does not give off any gas which colours the test paper. All the silver haloids become coloured on exposure to light, the change being most marked 1890.] on the Photographic Image. 139 in the cliloride, less in tlie bromide, and least of all in the iodide. The latter must be associated with some halogen absorbent to render the change visible. [Strips of paper coated with the pure haloids, the lower halves brushed over with silver nitrate solution, were exposed.] The different degrees of coloration in the three cases must not be considered as a measure of the relative sensitiveness : it simply means that tlie products of photo-chemical change in the three haloids are inherently possessed of different depths of colour. From the fact that halogen in some form is given off, it follows that we are concerned with photo-chemical decomposition, and not with a physical change only. All the evidence is in favour of this view. Halogen absorbents, such as silver nitrate on the lower halves of the papers in the last experiment, organic matter, such as the gelatine in an emulsion, and reducing agents generally, all accelerate the change of colour. Oxidizing and halogenizing agents, such as mercuric chloride, potassium dichromate, &c., all retard the colour change. [Silver chloride paper, painted with stripes of solutions of sodium sulphite, mercuric chloride, and potassium dichromate, was exposed.] It is impossible to account for the action of these chemical agents except on the view of chemical decomposition. The ray of light falling upon a silver haloid must be regarded as doiug chemical work ; the vibratory energy is partly sj)ent in doing the work of chemical separation, and the light passes through a film of such haloid partly robbed of its power of doing similar work upon a second tilm. It is difficult to demonstrate this satisfactorily in the lecture-room, on account of the opacity of the silver haloids, but the work of Sir John Herschel, J. W. Draper, and others, has put it beyond doubt that there is a relationship of this kind between absorption and decomposition. It is well known, also, that the more refrangible rays are the most active in promoting the decomposition in the case of the silver haloids. This was first proved for the chloride by Scheele, and is now known to be true for the other haloids. It would be presumption on my part, in the presence of Captain Abney, to enlarge upon the effects of the different spectral colours on these haloids, as this is a subject uj)on which he can speak with the authority of an investigator. It only remains to add that the old idea of a special " actinic " force at the more refrangible end of the spectrum has long been abandoned. It is only because the silver haloids absorb these particular rays that the blue end of the spectrum is most active in promoting their decomposition. Mauy other instances of photo-chemical decomposition are known in which the less refrangible rays are the most active, and it is possible to modify the silver haloids themselves so as to make them sensitive for the red end of the spectrum. The chemical nature of the coloured products of photo-chemical decomposition is still enshrouded in mystery. Beyond the fact that they contain less halogen than the normal salt, we are not much in advance of the knowledge bequeathed to us by Scheele in the last 140 Professor Baphael 3Ieldola [May 16, century. The problem has been attacked by chemists again and again, but its solution presents extraordinary difficulties. These products are never formed — even under the most favourable con- ditions of division and with prolonged periods of exposure — in quan- tities beyond what the chemists would call " a mere trace." Their existence appears to be determined by the great excess of unaltered haloid with which they are combined. Were I to give free rein to the imagination, I might set up the hypothesis that the element silver is really a compound body invariably containing a minute percentage of some other element, which resembles the comj)ouud which we now call silver in all its chemical reactions, but alone is sensitive to light. I offer this suggestion for the consideration of the speculative chemist.* For the coloured product as a whole, i. e. the product of photo-decomposition with its combined unchanged haloid, Carey Lea has proposed the convenient term '• photosalt." It will avoid circum- locution if we adopt this name. The photosalts have been thought at various times to contain metallic silver, allotropic silver, a sub- haloid, such as argentous chloride, &c., or an oxyhaloid. The free metal theory is disposed of by the fact that silver chloride darkens under nitric acid of sufficient strength to dissolve the metal freely. The acid certainly retards the formation of the photosalt, but does not prevent it altogether. When once formed the photo-chloride is but slowly attacked by boiling dilute nitric acid, and from the dry photosalt mercury extracts no silver. The assumption of the existence of an allotropic form of silver insoluble in nitric acid cannot be seriously maintained. The sub-haloid theory of the product may be true, but it has not yet been established with that precision which the chemist has a right to demand. We must have analyses giving not only the percentage of halogen, but also the percentage of silver, in order that it may be ascertained whether the photosalt contains anything besides metal and halogen. The same may be said of the oxyhaloid theory : it may be true, but it has not been demonstrated. The oxyhaloid theory was first suggested by Eobert Hunt f for the chloride ; it was taken up by Sahler, and has recently been revived by Dr. W. E. Hodgkinson. It has been thought that this theory is disposed of by the fact that the chloride darkens under liquids, such as hydrocarbons, which are free from oxygen. I have been rej)eating some of these experiments with various liquids, using every possible precaution to exclude oxygen and moisture ; dry silver chloride heated to incipient fusion has been sealed up in tubes in dry benzene, * I have gone so far as to test this idea experimentally in a preliminary way, the result being, as might have been anticipated, negative. Silver chloride, well darkened by loug exposure, was extracted with a hot saturated solution of potas- sium chloride, and the dissolved portion, after precipitation by water, compared with the ordinary chloride by exposure to light. Not the slightest ditierence was observable either in the rate of coloration or in the colours of the products. Perhaps it may be thought worth while to repeat the experiment, using a method analogous to the " method of fractionation " of Crookes. t *Etsearches on Light,' 2nd ed. 1854, ji. SO. 1890.] on the PhotograpJnc Image. 141 petroleum, and carbon tetrachloride and exposed since March. [Tubes shown.] In all cases the chloride has darkened. The salt darkens, moreover, in a Crookesian vacuum.* By these experiments the oxy- chloride theory may be scotched, but it is not yet killed ; the question now presents itself, whether the composition of the photosalt may not vary according to the medium in which it is generated. Analogy sanctions the supposition that when the haloid darkeus under water or other oxygen-containing liquid, or even in contact with moist or dry air, that an oxychloride may be formed, and enter into the com- position of the photosalt.- The analogy is supplied by the corre- sponding salt of copper, viz. cuprous chloride, which darkens rapidly on exposure. [Design printed on flat cell filled with cuprous cliloride by exposure to electric light.] Wohler conjectured that the darkened product was an oxychloride, and this view receives a certain amount of indirect support from these tubes [shown], in which dry cuprous chloride has been sealed up in benzene and carbon tetrachloride since March ; and although exposed in a southern window during the whole of that time, the salt is as white as when first prepared. Some cuprous chloride sealed up in water, and exposed for the same time, is now almost black. [Shown.] When silver is precipitated by reduction in a finely divided state in the presence of the haloid, and the product treated with acids, the excess of silver is removed and coloured products are left which are somewhat analogous to the photosalts proper. These coloured haloids are also termed by Carey Lea photosalts because they present many analogies with the coloured products of photo-chemical change. Whether they are identical in composition it is not yet possible to decide, as we have no complete analyses. The first observations in this direction were published more than thirty years ago in a report by a British Association Committee, | in which the red and chocolate- coloured chlorides are distinctly described. Carey Lea has since contributed largely to our knowledge of these coloured haloids, and has at least made it appear highly probable that they are related to * Some dry silver chloride which Mr. Crookes has been good enough to seal up for me in a high vacuum, darkens on exposure quite as rapidly as the dry salt in air. It soon regains its original colour when kept in the dark. It behaves, in fact, just as the chloride is known to" behave when sealed up in chlorine, although its colour is of course much more intense after exposure than is the case v;ith tlie chloride in chlorine. The tube in which the chloride had been sealed up in benzene, gave ofi" a considerable quantity of hydrogen chloride on breaking the point in June. t These results were arrived at in three ways. In one case hydrogen was passed through silver citrate suspended in hot water, and the product extracted with citric acid. " The result of treating the residue with chlorhydric acid, and then dissolving the silver by dilute nitric acid, was a rose-tinted cliloride of silver." In another experiment the dry citrate was heated in a stream of hydrogen at 212^ P., and tlie product, which was partly soluble in water, gave a brown residue, which furnished "a very pale red body on being transformed by chlorl)ydric and nitric acids." In another experiment silver arsenite was formed, this being treated with caustic soda, and the black precipitate then treated successively with 142 Professor Raphael Meldola [May 16, the products formed by the action of light. [Red photo-chloride and purple photobromide and iodide shown.] The photographic image is impressed on a modern film in an inappreciable fraction of a second, whereas the photosalt requires an appreciable time for its production. The image is invisible simply because of the extremely minute quantity of haloid decomposed. In the present state of knowledge it cannot be asserted that the material composing this image is identical in composition with the photosalt, for we know the composition of neither the one nor the other. But they are analogous in so far as they are both the result of photo- chemical decomposition, and there is great probability that they are closely related, if not identical, chemically. It may turn out that there are various kinds of invisible images, according to the vehicle or halogen absorbent — in other words, according to the sensitiser with which the silver haloid is associated. The invisible image is revealed by the action of the developer, into the function of which I do not propose to enter. It will suffice to say that the final result of the developing solution is to magnify the deposit of j^hotosalt by accumulating metallic silver thereon by accretion or reduction. Owing to the circumstance that the image is impressed with such remarkable rapidity, and that it is invisible when formed, it has been maintained, and is still held by many, that the first action of light on the film is molecular or physical, and not chemical. The arguments in favour of the chemical theory appear to me to be tolerably conclusive, and I will venture to submit a few of them. The action of reagents upon the j^hotographic fihii is quite similar to the action of the same reagents upon the silver haloids when exposed to the point of visible coloration. Reducing agents and halogen absorbents increase the sensitiveness of the film : oxidising and halogenising agents destroy its sensitiveness. It is difficult to see on the physical theory why it should not be j)ossible to impress an image on a film, say of pure silver bromide, as readily as on a film of the same haloid embedded in gelatine. Every one knows that this cannot be done. I liave myself been sur^Drised at the extreme insensitiveness of films of pure bromide prepared by exposing films of silver deposited on glass to the action of bromine vapour. On the chemical theory we know that gelatine is a splendid sensitiser — i. e. bromine absorbent. There is another proof which has been in our hands for nearly thirty years, but I do not think it has been viewed in this light before. It has been shown by Carey Lea, Eder, and especially by Abney — who has investigated the matter most clilorliydric and nitric acids : " Silver is dissolved, and there is left a substance .... [of] a rich chocolate or maroon, &c. " This on analysis was found to con- tain 24 per cent, of chlorine, the normal chloride requirin^^ 24*74 and the sub- chloride 14 'OS per cent. The committee which conducted these experiments consisted of Messrs. IMaskelyne, Hadow, Hardwich, and Llewelyn. ' B. A. Rep.,' 185!), p. 108. 1890.] on the FliotograjpMc Image. 143 thoroughly — that a shearing stress applied mechanically to a sensitive film leaves an impression which can be developed in just the same way as though it had been produced by the action of light. [Pres- sure marks on Eastman bromide paper developed by ferrous oxalate.] Now that result cannot be produced on a surface of the pure haloid ; some halogen absorbent, such as gelatine, must be associated with the haloid. We are concerned here with a chemical change of that class so ably investigated by Prof. Spring, of Liege, who has shown that by mere mechanical pressure it is possible to bring about chemical reaction between mixtures of finely divided solids.* Then again, mild reducing agents, too feeble to reduce the silver haloids directly to the metallic state, such as alkaline hypophosphites, glucose or lactose, and alkali, &c., form invisible images which can be developed in precisely the same way as the photographic image. All this looks like chemical change, and not physical modification pure and simple. I have in this discourse stoically resisted the tempting opportunities for pictorial display which the subject aifords. My aim has been to summarise the position in which we find ourselves with respect to the invisible image after fifty years' practice of the art. This image is, I venture to think, the property of the chemist, and by him must the scientific foundation of photography be laid. We may not be able to give the formula of the photosalt, but if the solution of the problem has hitherto eluded our grasp it is because of the intrinsic difficulties of the investigation. The photographic image brings us face to face — not with an ordinary, but with an extraordinary class of chemical changes due entirely to the peculiar character of the silver salts. The material composing the image is not of that definite nature with which modern chemical methods are in the habit of dealing. The stability of the photosalt is deter- mined by some kind of combination between the sub-haloid or oxy- haloid, or whatever it may be, and the excess of unaltered haloid which enters into its composition. The formation of the coloured product presents certain analogies with the formation of a saturated solution ; the product of photo- chemical decomposition is formed under the influence of light up to a certain percentage of the whole photosalt, beyond which it cannot be increased — in other words the silver haloid is saturated by a very minute percentage of its own product of photo-decomposition. The photosalt belongs to a domain of chemistry — a no-man's land — peopled by so-called "molecular compounds," into which the pure chemist ventures but timidly. But these compounds are more and more urging their claims for considera- tion, and sooner or later they will have to be reckoned with, even if * Tlie comiection between the two phenomena was suggested during a course of lectures delivered by me two years ago (' Chemistry of Photography!^' p. 191), I have since learnt that the same conclusion had been arrived at independently, by Mr. C. H. Botharaley, of the Yorksliire College, Leeds. 144 Professor BapTiael Meldola on the Photographic Image. [May 16, they lack that definiteness which the modern chemist regards as the essential criterion of chemical individuality. The investigation may lead to the recognition of a new order of chemical attraction, or of the old chemical attraction in a different degree. The chemist who discourses here ujDon this subject at the end of the half-century of photograj^hy into which we have now entered, will no doubt know more about this aspect of chemical affinity ; and if I may invoke the spirit of prophecy in concluding, I should say that a study of the photographic tilm with its invisible image will have contributed materially to its advancement. [K. M.] 1890.] Prof, Haddon on Manners, &c. of Torres Straits Islanders. 145 WEEKLY EVENING MEETING, Friday, May 23, 1890. The Right Hon. Earl Percy, F.S.A. Vice-President, in the Chair. Alfred 0. Haddon, Esq. M.A. M.E.I.A. PROFESSOR OF ZOOLOGT' IN THE ROYAL COLLEGE OF SCIENCE, DUBLIN. Manners and Customs of the Torres Straits Islanders. It is not my intention this evening to attempt a special study of any particular institution or series of customs, nor even to discuss the ethnological affinities of the natives inhabiting the islands of Torres Straits. The comparative study of institutions and customs has led to brilliant suggestions, and has especially thrown light upon obscure facts in our own culture, and given a new significance to observances which, because they are of every-day occurrence, are passed by without comment. This field of inquiry is one which has only recently been systematically tilled, but it promises a rich harvest of unexpected results. The detailed study of a single tribe or natural assemblage of people has great interest, as it puts one in touch with such varied subjects as the physical, mental, and moral characters of the people ; and the tracing out of their affinities requires wide study and careful comparisons. A patient research of this kind always opens up questions of wider import than the initial inquiry. Neither of these methods will occupy us to-night, as I wish to present before you as vivid a conception as I can of some of the manners and customs of a people small in number but rich in interest. We will consider, therefore, neither a composite image of savages in general, nor of rude customs, but the particular habits of a disappear- ing people, who, thirty years ago, were naked, unknown savages, who to-day are British subjects, and who in a very few years will have lost the last remnants of their individuality, and possibly ere long will practically cease to exist — at all events as a distinct people. The dissolving views which I shall exhibit this evening are a fit emblem of the facts which they illustrate. My anthropological inquiries in Torres Straits may not inaptly be compared with the methods of the palaeontologist, especially in his study of the more recent fossils. Amongst such fossils we find some representatives of existing forms, others slightly different from those we are accustomed to, others again which are quite dissimilar, and often of these only disconnected fragments may remain, and it takes great patience and careful piecing together to restore the Vol. XIII. (No. 84.) L ]46 Professor A. a Hacldon [May 23, latter into any semblance of their former selves ; nor should surprise be felt if mistakes are occasionally made in the attempt. A similar experience occurs to those who study an isolated people which is rapidly becoming modified and is dying out at the same time. Some facts collected from legend and myth precisely resemble tbe present habits of the natives ; others have only lately fallen into desuetude. Lastly, some customs are so dissimilar from anything in our own country, that it is difficult to thoroughly understand them under favourable circumstances ; but when these customs are no longer practised, and but imperfectly remembered, when they have to be described through the unsatisfactory medium of Jargon English, and when one bears in mind the great difference in the mental concep- tions of narrator and listener, what wonder is there that disconnected narratives are recorded, or that errors creep in ? Happy is that traveller who has the opiDortunity of studying exist- ing habits. It was my lot to recover recently lost or fast dying-out customs ; our archa3ologists graj)ple with the problems of the past ; it is the object of all to assist towards a complete History of Man. Torres Straits, as you are aware, separate New Guinea, the largest island in the world, from Australia, the smallest continent. Although the Straits are eighty miles wide in their narrowest part, yet, owing to the presence of islands and of numerous and often extensive coral reefs, there is only one channel suitable for ocean- going steamers, and that averages a mile in width, and in places is much less. The islands in Torres Straits may be divided into three geological groups by the lines of longitude 142^ 48' E. and 143' 30' E. The islands to the west are composed of old igneous rocks, and are surrounded by fringing reefs. These islands may in fact be regarded as disconnected portions of Northern Queensland. They are fertile, but there is no particularly luxuriant vegetation ; doubt- less irrigation and cultivation would greatly improve their pro- ductiveness. The central group of islands is composed of low coral islets formed by wind and wave action ; the soil is poor, and supports only a scrubby vegetation. Coco-palms grow on some of the islands, and there are occasional mangrove swamps. The eastern islands, Uga, Erub, and the Murray Islands, are of volcanic origin, and are also fringed with coral reefs. In these the soil is rich and vegetation luxuriant, Uga and a great part of Mer being simply large gardens of coco-palms, bananas, and yams. It is interesting to find that the inhabitants of the volcanic islands form one tribe, which I term the Eastern Tribe ; the Western Tribe occupying all the remaining islands. The customs of the two tribes are different and their languages distinct, so much so that there are only a few words in common, and these are mainly trade words. Four subdivisions of the Western Tribe can be distinguished, tbe 1890.] on Manners and Customs of Torres Straits Islanders, 147 members of each of which inhabit certain intermarrying groups of islands. Independently of the above-mentioned subdivisions, the islanders were divided into clans, each clan having some animal for its augiid or " totem." For example, in the Western Tribe there were the dugong, turtle, dog, cassowary, snake, shark-clans, and so forth. There was supposed to be some relation between the clans and their respective auyud, " all same [i.e. similar to] family," as it was expressed to me. A dog-man, for instance, was credited with under- standing the habits and feelings of dogs, or a cassowary-man prided himself on having thin shanks like a cassowary, which would enable him to run quickly through the grass. With the exception of the first two clans, no one was allowed to kill or eat the totem of his own clan ; if he did, his other clansmen would probably kill him for sacrilege. On a dugong ex23edition, no dugong-man might keep the first dugong he captured, but he might partake of the rest ; the same restriction applied also to the turtle and the turtle-clan. If only one dugong or turtle was caught on the first day, the dugong- or turtle- man had to relinquish it ; supposing only one was caught on the succeeding day, the account was, so to speak, "carried forward," and there was no sahi (" tabu ") on it. The dugong and turtle were too important articles of food for the clan members to be entirely deprived from partaking of their augiid. The women, or at all events some of them, used to have a repre- sentation of their augiid cut on the small of the back. I made inquiries on this point on most of the islands in the Straits, but could only find four old women who had them ; these I sketched, and two of them I also photographed. [Various photographs illustrating the appearance of the natives were then thrown on the screen ] I have alluded to the fact that different customs characterise the Eastern and Western Tribes ; as an example of this I may mention that in the latter tribe the girls proposed marriage to the men, while in the Eastern Tribe the more usual course was adopted. It might be some time before a lad had an offer ; but should he be a fine dancer, with goodly calves, and dance with sprightliness and energy at the festive dances, he would, not lack admirers. Should there still be a reticence on the part of his female acquaintances, the young man might win the heart of a girl by robbing a man of his head. Our adventurous youth could join in some foray ; it mattered not to him what was the equity of the quarrel, or whether there was any enmity at all between his people and the attacked. So long as he killed some one — man, woman, or child — and brought the head back, it was not of much consequence to him whose head it was. Possibly a man killed would redound to his greater glory, but any skull was better than none, and its posses- sion was recognised as an order of merit. How much more distinction would a man gain when he could boast of a whole trophy of skulls ! L 2 148 Professor A. C. Haddon [May 23, The girl's heart being won by prowess, dancing skill, or fine appearance, she would plait a string armlet, tiapururu ; this she intrusted to a mutual friend, preferably the chosen one's sister. On the first suitable opportunity, the sister said to her brother, " Brother, I have some good news for yon. A woman likes you." On hearing her name, and after some conversation, if he was willing to go on with the affair, he told his sister to ask the girl to keep some appointment with him in the bush. When the message was delivered, the enamoured damsel informed her parents that she was going into the bush to get some wood or food, or made some such excuse. In due course the couple met, sat down and talked, the proposal being made with perfect decorum. The following conversation is given in the actual words used by my informant, Maino, the chief of Tud. Opening the conversation, the man said, " You like me proper ? " " Yes," she replied, " I like you proper with my heart inside. Eye along my heart see you — you my man." Unwilling to rashly give himself away, he asked, " How you like me?" " I like your fine leg — you got fine body — your skin good — I like you altogether," replied the girl. After matters had proceeded satisfactorily, the girl, anxious to clench the matter, asked when they were to be married. The man said, " To-morrow, if you like." They both went home and told their respective relatives. Then the girl's people fought the man's folk, " For girl more big [i.e. of more consequence] than boy ; " but the fighting was not of a serious character, it being part of the programme of a marriage. " Swapping " sisters was the usual method of getting a wife. If a man had no sisters he might remain unmarried, unless he was rich enough to pay for a wife with a shell armlet {waiwi), or a canoe, or something of equal value. If a youth was " hard up," an uncle might take compassion on him and give one of his own daughters in exchange for a wife for his nephew. This exchange of girls — a sister for a sister, or female cousin for another man's sister — was an economical method of getting a wife, as one was a set off against the other. The usual feasting occurred, but the presents were dispensed with, or at all events the purchase money was saved, and probably there would be no fighting. When a young man of the Eastern Tribe arrived at an under- standing with a girl, he put his gelar (" law " i.e. " tabu ") on her, and made arrangements to fetch her away. She kept awake on the appointed night, listening for the preconcerted signal, and they quietly stole away to his parents' house, and the next morning he sent a messenger to say where the girl was. The girl's friends armed themselves with bows and arrows, shark's teeth fastened on to sticks, and other weapons, and proceeded to the other village, but the fight 1890.] on Manners and Customs of Torres Straits Islanders. 149 was not a serious affair. On the same day the girl would be painted red by her future mother-in-law, and clothed with a large number of leaf petticoats ; and numerous ornaments would be suspended on her back, these making a clanking sound whenever the girl moved. For some months she remained in the house, and under the constant supervision of her future mother-in-law, the young man residing elsewhere. After say three months, negociations would commence between the two families, and the girl's relations would come to taaugwat (or scrape hands), and presents would be exchanged, and some alteration made in the decking of the girl. After a further probation period of a few months, some friend, in the secret, would engage the young man in conversation, and the bride would steal up behind him with some food she had previously cooked, and, while still behind his back, would thrust it by his side. He, looking round, exclaimed, " Why, that's my woman ! " and then hung down his head in shame. Being informed that all was duly performed according to old usage, the couple ate food together, this being the ratification of the contract. It appears that in the Eastern Tribe marriage was regarded as a state of " tabu," the man isolating one woman as his exclusive property, for he had powers of life and death over his wife. For several reasons I suspect that the Eastern Tribe has arrived at a slightly higher stage in the evolution of the family than the Western, as the man has a more independent position, and does not live more or less with his wife's people after marriage, as is the custom among the Western Tribe. In both tribes a wife had to be paid for ; a canoe, dugong-harpoon, shell-armlet, or articles of equal exchange value, being the usual price. Manhood is with us a gradual development of youth ; with nearly all savages it is a state of privilege, the full advantages of which can be gained only by the observance of special ceremonies. The growth of hair on the face warned the father that his boy was growing up, and he consulted with other fathers who had sons of about the same age. " Good thing, " he might have remarked ; " boy no stop along woman now : he got hair, time we make him man now ; " and ar- rangements would be duly made. The following information, respecting the former initiation cere- monies, was gained at Tud (usually known as Warrior Island), the natives of which island were probably the most warlike of all the Western Islanders : — The lads were handed over to their uncles, or to some old man, by their fathers, who then ceased to have any intercourse with them. They were conducted to the Taiiohwod, or open space sacred to the men, where no woman or child ever ventured, and which henceforth had for them many deep-rooted associations. The uncles washed the youths with water and then rubbed charcoal into the skin ; this being daily repeated till the probation period was over. The lads were 150 Professor A. C. Haddon [May 23, covered with mats doubled up like a tent witli closed ends, and there they sat the livelong day in groups, without moving, playing, or even sj^eaking. Four large mats stretched across the TaiioTcwod, the mats belonging respectively to the Sam (cassowary), TJmai (dog), Kodal (crocodile), and Baidam (shark) clans. For each mat there was a fireplace, the fire being tended by the young men of their re- spective clans. The old men sat on their appropriate mats, in the centre were the drums, and the dance-masks were placed along one side. Opposite the centre was a small mat, on which sat the chief of the island ; for, contrary to the general custom of the tribe, this island had a recognised chief, the result, probably, of their belligerent habits. By the side of where the chief used to sit, a large ovoid stone was j^ointed out to me ; it had a dire significance, for long ago four boys, tired of the irksomeness of the discipline, broke bounds, and meeting their mothers in the bush, asked for foori. They were recaptured and were all killed by the old men with that stone, which was then placed in its present position, as a warning to other youths. The boys of the cassowary and dog clans sat at the end beyond the shark- fireplace, and the crocodile and shark boys were placed at the opposite end of the clearing. Their instructors watched the lads, and communicated to them the traditions of the tribe, rules of conduct were laid down, informa- tion in all branches of native lore taught, and thus, generation after generation, the things of the fathers were transmitted to the sons. The following are some of the rules which I was informed were imparted to the youths by the " old men " : — " You no steal." " If you see food belong another man, you no take it, or you dead." " You no take thing belong another man without leave ; if you see a fish -spear and take it, s'pose you break it and you no got s^Dear, how you pay man ? " " S'pose you see a dugong-harpoon in a canoe and take it, and man he no savvy, then you lose it or break it, hov/ you pay him ? You no got dugong-harpoon." " You no i^lay with boy and girl now ; you a man now, and no boy." " You no play with small play-canoe, or with toy-spear ; that all finish now." " You no like girl first ; if you do, girl laugh at you and call you a woman." [That is, the young man must not propose marriage to a girl, but must wait for her to ask first.] " You no marry the sister of your mate, or by and by you will be ashamed ; mates all same as brothers." [But " mates " may marry two sisters.] " You no marry your cousin ; she all same as sister." " If any one asks for food, or water, or anything, you give some- thing ; if you have a little, you give a little ; if you have plenty, give half. 1890.] on Manners and Customs of Torres Straits Islanders. 161 " Look after your mother and father ; never mind if you and your wife go without." " Don't speak bad word to mother." " Give half of all your fish to your parents ; don't be mean." " Father and mother all along same as food in belly ; when they die you feel hungry and empty." " Mind your uncles, too, and cousins." " If woman walk along, you no follow ; by and by man look, he call you bad name." " If a canoe is going to another place, you go in canoe ; no stop behind to steal woman." " If your brother is going out to fight, you help him ; don't let him go first, but go together." Who will say, after this, that the Torres Straits Islanders were degraded savages ? At length the month of isolation expired, and for the last time the uncle washed the lad ; he then rubbed him with scented leaves, and polished him up with oil. Then he was decorated with armlets and leglets, breast-ornaments, and possibly a belt, his ears orna- mented, and a shell-skewer passed through his nose ; bright-coloured leaves would be inserted in his armlets, and liis hair rolled into the approved string-like ringlets. So they " make him flash — flash like hell— that boy." The afternoon of the eventful day was occupied in this congenial task, and at nightfall all the lads who were being initiated were mar- shalled by their uncles behind a large mat, which was held vertically. In this wise they marched to the village until they arrived at an open space where a mat was spread on the ground before a semicircle of friends and relatives. When the approaching party reached this mat the lads seated themselves upon it, and then the screening mat was lowered. Suddenly, for the first time for a month, the fathers and female relatives saw the boys, and great were the crying and shouting and exclamations of delight at the brave show. With tears the mothers cried out, " My boy ! my boy ! " and they and other elderly female relatives rushed up to them and fondled and caressed them, and the mothers surreptitiously put dainty morsels by their boys. Sitting with legs crossed under them and down-turned faces, the boys neither moved nor exhibited the least emotion, for now they were men. Less precise is my information respecting the corresponding rites of the Eastern Tribe. So far as I could gather, there were in Mer, the largest of the Murray Islands, two important ceremonies, which we may term the initiation and the recognition ceremonies. For the first the lads were assembled near a sacred round house, or pelah, in which the awe-inspiring masks were kept. The ceremony was con- ducted by three zogole, or sacred men, and their tamileh, or attendants. The latter arranged themselves in a double row, from the peJah to the 152 Professor A. C. Eaddon [May 23, place where the boys were assembled, and, holding long sticks, per- formed certain movements. Slowly the dread apparition advanced ; the chief zogole came first, wearing a huge mask with human features and a beard of jaw-bones ; the second zogole steadied this mask with a rope ; the third zogole wore a long mask, shaped like a shark. Then for the first time the names of these masks were revealed to the lads — BoMAi and Malu. These were the sacred names which it was not lawful to communicate to the outsider, death to both being the penalty. Their collective name of Agiid was, however, known to all. I can only allude to the customary food-ofPering presented to the zogole, and the course of instruction instilled into the youths, one item of which was the narration of the legend of Malu, and must pass on to the recognition ceremony. This function took place in the afternoon on the sand beach outside the village of Las. A great concourse of people was assembled — men, women, and children — the newly initiated lads occupying the front row. First four men of the dog-clan played about in pairs. (I may here parenthetically remark that it took me a fortnight's work to glean what little information I have respecting these two ceremonies. On one occasion I iuduced a number of men to rehearse some of the dances for me on the actual spot where they were originally per- formed, in order that I might gain a clear comprehension of them. One of my photographic " studies " I now throw on the screen.) The dog-men were followed by pigeon-men, who danced and beat their chests; later, whirling along the strand, came a body of dancers, circling from left to right as they advanced, an outer ring with sticks, an inner ring brandishing stone clubs, and possibly some drum-jDlayers in the centre. Lastly, the three zogole appeared, com- pletely covered wdth white feathers, and each carrying five wands. Although seen by the women, their identity was supposed to be unknown. This was the final function, and was followed by the ever- recurring feast. Thenceforth the lads took standing as men. Strangely enough, at neither Tud nor Mer could I discover that the bull-roarer was employed at these ceremonies. The wide- spread use and sacred character of this simple instrument has been emphasised by Mr. Lang in one of his charming essays. Knowing its universal distribution in Australia, I was not surprised to find that in Muralug, or Prince of Wales' Island, which lies close to Cape York, its use was associated with the initiation of the lads. It was only by speaking in a low voice to the chief of the island and his son Georgie, whose photograph you have already seen, and by assuming more knowledge than I actually possessed, that I could induce them to admit of its being employed. Cautiously looking round to see that no one \vns near, its name, icanes, was whisj^ered to me. After much persuasion, a model of one was made for me, on the express understanding that I should not show it to any woman on the island ; 1890.] on Manners and Customs of Torres Straits Islanders. 153 and I did not. It is now in the British Museum. All that I could gather was that it was whirled in the bush and then shown to the lads. Death was the penalty to both if a man exhibited it to a woman, or to any one who had not been initiated. Great was my surprise when, shortly afterwards, I saw the Saibai bovs who were staying at the mission station on Mer, inlaying with bull-roarers identical with tne one with which I had been so secretly entrusted. The most sacred emblem in one island was a toy in another. In case some of you may not be acquainted with this most interesting implement, I have brought one of these bull- roarers. From these important initiation ceremonies we may pass to others which had a less sacred significance. All the native cere- monies were associated with processions, or with movements of a less regular character, the performers of which were invariably specially dressed for the occasion — usually there was a special costume for a particular rite, one distinguishing feature of which was the wearing of masks or head-dresses. It is convenient to describe these functions as dances ; and a series can be traced extending from the most sacred initiation and funeral dances on the one hand, through the seasonal dances to the war and ordinary festive dances on the other. Profanation of the initiation or of the funeral ceremonies was punished with immediate death. In some instances, at all events, dance-masks could only be worn at the appropriate festival ; even the casual putting on of one was supposed to cause slow but certain death. It was my good fortune to witness a seasonal dance at Thursday Island. This was anticipatory of the fishing season during the north-west monsoon. The men were clotlied with a petticoat made of the shredded sprouting leaves of the coco-palm, and adorned with various armlets and leglets ; but the striking part of the costume was the mask, of which the lower portion represented a conventional crocodile's head, surmounted by a human face ; above this was a representation of a saw-fish, some five feet in length, and overtopping all was a long red triangular erection decked with feathers. The ceremony was called the Waiitutu Jcajp, or " Saw-fish dance." The actual dance consisted of two men at a time coming out from behind a screen and going through their simple evolutions to the monotonous accompaniment of the drum and a lugubrious chant. More varied was the costume of the secular dance. All their bravery was donned. The effective head-dress of egret's feathers, or the cassowary coronet, framed the face, a shell skewer pierced the nose, breast ornaments, coco-palm leaf petticoats, armlets, leglets, ornaments or implements carried in the hand, all went to make up a picture of savage finery. Here, too, the women were occasionally allowed to participate, though of course both sexes never danced together. When women were allowed to be present at the more important dances, they were merely spectators. 154 Professor A. G. Haddon [May 23, The large canoes of the Torres Straits Islander of former times must have been very imposing objects when painted with red, white, and black, and decorated with w'hite shells, black feathers, and flying streamers ; and not less so when actively paddled by a noisy, gesticulating, naked crew, adorned with cassowary coronets, shell ornaments, and other native finery ; or swiftly sailing, scudding before the wind with mat sails erect. The body of a canoe is a simple dug-out, on to the sides of which gunwale boards are lashed. There is a central platform supported on a double outrigger. The thwart jjoles of the outriggers are usually six feet apart, and extend to some ten feet beyond the stem of the canoe ; a doubly-pointed float is attached to the ends of the thwart poles on each side. Eecejitacles are built into each side of the platform for the storage of bows and arrows, fishing gear, water- bottles, and other belongings. The sails are two in number, and are obloncf erections of mattinor placed in the bows, some twelve feet in height, and each about five feet wide. The mats are skewered on to two long bamboos, which suj^poit the sails along their length ; a bamboo stay also serves to keep the sail upright. The longest canoe I measured was nearly sixty-eight feet in length. A stone lashed on to a rope is kept in the bow for an anchor. When sailing, a man stands in the stern holding the steering board. The canoes are made at the mouth of the Fly River, in New Guinea, and are fitted with but a single outrigger, as theirs is only river navigation. I was informed that it was at Saibai that the canoes were refitted, this time with two outriggers, and an attempt at decoration was made, but the latter having a purely commercial significance was rather scant. The ultimate purchasers ornamented their canoes according to their fancy, as they usually j)rided them- selves on having fine canoes. I was much puzzled when I first went to Torres Straits by occasionally seeing a canoe with a single outrigsfer. I afterwards found it belonged to a native of Ware (one of the New Hebrides) residing at Mabuiag, and that he had re-outrigged a native canoe according to the fashion of his own people. When I was staying at Mabuiag some natives of that island were fitting up a canoe in imitation of this one. Here a foreign custom is being copied ; how far it will spread among the Western Tribe it is impossible to say ; but, strangely enough, the Eastern Tribe has entirely adopted an intro- duced fashion, and I did not see a solitary canoe with a double outrigger. It would be tedious to enter into a comparison between these various canoes. In the Eastern Islands the platform baskets are absent, and Europern sails are in universal use — mainsail, fore- sail, and jib. Among the Western Tribe, European sails have not yet quite supi)lanted the original mat sails. Throughout the Straits 1890.] on Manners and Customs of Torres Straits Islanders. 155 the canoes are not decorated in the old style. It was in Mabuiag alone that I found two canoes which were more or less decorated. Utilitarian ideas are now too widely spread for the aesthetic faculty to be indulged in. I have dwelt at some length on this subject, as it is important to record all transitions. As an example of how rapidly and com- pletely some changes occasionally come about, I may mention that at Mer, one of the Eastern Islands, some, at all events, of the young men did not appear to know that there had been a change in the rig of their canoes. But, after all, the most interesting feature in connection with the canoes is the method by which they are purchased. I have previously mentioned that they were made on the mainland of New Guinea on the banks of the Fly Eiver. Supposing a native of Muralug (Prince of Wales' Island, the island which is nearest to Cape York), wants a canoe. He sends word, say, to a relation of his in Moa, for the inhabitants of these two islands often intermarry. The latter sends a message to the next island of Badu. A Badu man passes on the word to Mabuiag (these two also were intermarrying islands) ; the Mabuiag native informs a friend in Saibai, who in turn delivers the message at Mowat, on the mainland of New Guinea, or Daudai, as the islanders call it, thence the word passes along the coast till it reaches the canoe makers. As soon as the canoe is ready it retraverses the route of the order, being handed on from place to place, and island to island, until it at length reaches its destination. Should, however, there be a new canoe for sale on any of the intermediate stations, this might be sold, and thus obviate the tedious delay of waiting for one to be made to order. Another trade route is through Nagir and Tud to Mowat. The Murray Islanders send to Erub, and the natives of the latter island trade directly with Parem and the mouth of the Fly Eiver. The most remarkable feature in these transactions is that payment is usually extended over three years ; in fact, that canoes are purchased on the three years' hire system. This method of purchase, though but recently adopted by ourselves, has for an unknown period been practised by the naked islanders. The mere fact of its existence demonstrates a high level of commercial morality, for if the debts were often repudiated, the whole system would long ago have collapsed. This commercial morality corroborates to a considerable extent the ethical standard said to be imparted to the youths during initia- tion. Nor would I like to say that they acted less up to their standard than we up to ours ; I doubt whether we would be much the gainers by a comparison. In making this statement it must be distinctly understood that I am only comparing their lives with their own ideals, and not judging them by the ethical standards of other races. It is true they were treacherous, often murdered strangers, and were head-hunters ; that their ideas of sexual morality differed from ours, 156 Professor Haddon on Torres Straits Islanders. [May 23, but these "crimes" were not prohibited by public conscience, and there was therefore no wrong in their committing them. Our higher civilisation has swept over these poor people like a flood, and denuded them of more than their barbarous customs ; the old morality has largely gone too.* [A. C. H.] * Further information as to customs and legends of the Torres Straits Islanders will be found in 'The Journal of the Anthropological Institute,' vol. xix. 1890, and in « Folk-lore,' vol. i. 1890. 1890.] Mr. A. A. Common on Astronomical Telescopes. 157 WEEKLY EVENING MEETING, Friday, May 30, 1890. William Huggins, Esq. D.C.L. LL.D. F.R.S., Vice-President, in the Chair. A. A. Common, Esq. F.R.S. Treas. R.A.S. M.B.I. Astronomical Telescopes. Before speaking of the enormous instruments of the present day, with their various forms and complicated machinery, it will be well to give some little time to a consideration of the principles involved in the construction of the telescope, the manner in which it assists the eye to perceive distant objects, and in a brief and general way to the construction and action of the eye as far it affects the use of the telescope, all as a help to consider in which way we may hope to still further increase our sense of vision. I will ask you to bear with me when I mention some things that are very well known, but which if brought to mind may render the subject much more easy. Within pretty narrow limits the principles involved in the construction of the telescope are the same whatever form it ultimately assumes. I will take as an illustration the telescope before me, which has served for the finder to a large astronomical telescope, and of which it is really a model. On examination we find that it has, in common with all refracting telescopes, a large lens at one end and several smaller ones at the other ; the number of these small lenses varies according to the purpose for which we use the telescope. Taking out this large lens we find that it is made of two pieces of glass ; but as this has been done for a purpose to be presently explained which does not affect the principle, we will disregard this, and consider it only as a simple convex lens, to the more important properties of which I wish first of all particularly to draw your attention, leaving the construction" of telescopes to be dealt with later on. Stated shortly, such a lens has the power of refracting or bending the rays of light that fall upon it : while they are passing through the lens the course they take is altered ; if we allow the light from a star to fall upon the lens, the whole of the parallel rays coming from the star on to the front surface are brought by this bending action to a point at some constant distance behind, and can be seen as a point of light by placing there a flat screen of any kind that will intercept the light. For all distant objects the distance at which the crossing of the rays takes place is the same. It depends entirely on the 158 Mr. A. A. Common [May 30, substance of the lens and the curvature we give to the surfaces, and not at all upon the aj)erture or width of the lens. The brightness only of the picture of the star, depends upon the size of the lens, as that determines the amount of light it gathers together. If, instead of one star we have three or four stars together, we will find that this lens will deal with the light from each star just as it did with the light of the first one, and just in proportion to the angular distance they are apart in the sky, so will the pictures we see of them be apart on our screen. So if we let the light from the moon fall on our lens, all the light from the various parts of the moon's surface will act like the separate stars, and produce a picture of the whole moon (in the photographic camera the lens produces in this manner a picture of objects in front of it, and this picture we see on the ground glass). When we attempt to get pictures of near objects that do not send rays of light that are parallel, we find that as the rays of light from them do not fall on the lens at the same angle to the axis, the picture is formed further away from the lens. The nearer the object whose picture we wish to throw upon the screen is to the lens, the further the screen must be moved. If we try this experiment we shall find, when we have the object at the same distance as the screen, the picture is then of the same size as the object, and the distance of the screen from the lens is twice that which we have found as the focal length ; on bringing the object still nearer the lens, we find we must move the screen further and further away, until when the object is at the focus the picture is formed at an infinite distance away, or, what is more to our purpose, the rays of light from an object at the focus of a convex lens after passing through the lens are parallel, exactly as we have seen such parallel rays falling on the glass come to a focus, so that our diagram answers equally well whatever the direction of the rays ; and this holds good in other cases where we take the efiect of reflection as well as refraction. We can also produce pictures by means of bright concave surfaces acting by reflection on the light falling upon them. Such a mirror or concave reflecting surface as I have here will behave exactly as the lens, excepting, of course, that it will form the picture in front instead of behind. The bending of the rays in the case of the convex lens is convergent, or towards the axis, for all parallel rays; if we use the reverse form of lens — that is, one thicker at the edge than in the middle — we find the reverse efiect on the parallel rays ; they will now be divergent, or bend away from the axis ; and so with reflecting surfaces if we make the concavity of our mirror less and less, till it ceases and we have a plane, we shall get no efiect on the parallel rays of light except a change of direction after reflection. If we go beyond this and make the surface convex we shall then have practically the same efi'ect on the reflected rays as that given to the refracted ray by the concave glass lens. As regards the size of the picture produced by lenses or mirrors of difierent focal length, the picture is larger just as the focal length 1890.] on Astronomical Telescopes. 159 is greater, and the angular dimension is converted into a linear one on the screen in due proportion. Now, as we shall assume that the eye sees all things best at the distance of about nine inches, we may say that the picture taken with a lens of this focal length gives at once the proper and most natural representation we can possibly have of anything at which we can look. Such a picture of a land- scape, if placed before the eye at the distance of nine inches, would exactly cover the real landscape point for point all over. A picture taken with a lens of shorter focal length, say four inches, will give a picture as true in all the details as the larger one, but if this picture is looked at, at nine inches distance, it is not a true representation of what we see ; in order to make it so, we must look at it with a lens or magnifier. With a larger picture one can look at this at the proper distance, which always is the focal distance cf the lens with which it was obtained, when we will see everything in the natural angular position that we have in the first case. But if, instead of looking at this larger picture, which we may consider taken with a lens of say ninety inches focal length, at a dis- tance of ninety inches, we look at it at a distance of nine inches, we have practically destroyed it as a jjicture by reducing the distance at which we are viewing it, and we have converted it into what is for that particular landscape a telescopic picture ; we see it, not from the point at which it was taken, but just as if we were at one-tenth of the distance from the particular part that we examine. A telescope with a magnifying power of ten, would enable us to see the landscape just as we see it in the photograph, when we examine it in the way I have mentioned. Having thus seen how a lens or mirror acts, we will turn our at- tention to the eye. Here we find an optical combination of lenses that act together in the same way as the single convex lens of which we have been speaking. We will call this combination the lens of the eye. It produces a picture of distant objects which in the normal eye falls exactly in focus upon the retina. We are conscious that we do see clearly at all distances beyond about nine inches. At less than this distance objects becomes more and more indistinct as they are brought nearer to the eye. From what we have seen of the action of the lens in producing pictures of near and distant objects, we know that some movement of the screen must be made in order to get such pictures sharply focussed, a state of things necessary to perfect vision. We might therefore suppose that the eye did so operate by increasing when necessary the distance between the lens and retina, but we know that the same effect is produced in another way ; in fact, the only other way. The eye by a marvellous provision of nature, secures the distinctness of the picture on the retina of all objects beyond a distance of about 9 inches, by slightly but sufficiently varying the curvature of one of the lenses ; by an effort of will, we can make the accommodating power of the eye slightly greater, and so see things clearly a little nearer ; but at about the distance of 9 inches, the 160 Mr. A. A. Common [May 30, normal eye is unconscious of any effort in thus accommodating itself to different distances. The picture produced by the lens of the eye, whose focal length we will assume to be six-tenths of an inch, falls on the retina, which we will assume further to be formed of a great number of separate sensible points, which, as it were, pick up the picture where it falls on these points, and through the nervous organi- sation, produce the sense of vision. Possibly when these points are affected by light, there may be some connective action, either produced by some slight spherical aberration of the lens or otherwise ; but I do not wish to go any further in this matter than is necessary to elucidate my subject. What I am concerned with now is the extent to which the sensibility of the retina extends. Experiment tells us that it ex- tends to the perception of two separate points of light whose angular distance apart is one minute of arc, or in other words, at the distance we can see best, two points whose distance apart is about 1/400 of an inch. This marvellous power can be better appreciated when we remem- ber that the actual linear distance apart of two such points on the retina is just a little more than 1/6000 of an inch. In dealing with the shape of small objects the difference between a circle, square, and triangle, can be detected when the linear size of their images on the retina is about 1/2000 of an inch. It may be therefore fairly taken that these separate sensible points of the retina are somewhere about 1/12,000 part of an inch apart from each other. Wonderfully minute as must this structure be, we must remember, as we have already shown, that the actual size of the image it deals with is also extremely small. This minuteness becomes apparent when we consider what occurs when we look at some well-known object, such as the full moou. Taking the angular diameter of the moon as 30 minutes of arc, and the focal length of the eye at six- tenths of an inch, we find the linear diameter of the picture of the full moon on the retina is about 1/2U0 of an inch, and assuming that our number of the points in the retina is correct, it follows that the moon is subject to the scrutiny of 2800 of these points, each capable of dealing with the portion of the picture that falls upon it. That is to say, the picture, as the retina deals with it, is made up to this number of separate parts, and is incapable of further division just as if it were a mosaic. I think this is really the case, and as such a supposition permits us to explain not only what occurs when we assist the eye by means of a telescope, but also what occurs when we use the telescope for photographing celestial objects, we will follow it up. In the case of the eye we suppose the image of the moon to be made up through the agency of these 2800 points, each one capable of noting a variation in the light falling upon it. In order to make this rather important point plainer, I have had a diagrammatic draw- ing made on this plan. Taking a circle to represent the full moon I have divided it into this number of spaces, and into each space 1890.] on Astronomical Telescopes, 161 I have put a black dot, large or small, according to the intensity of the light falling on that part of the image as determined by looking at a photograph of the moon. You will see by the picture of this moon the effect produced. It represents to those who are at a sufficient distance the moon much as it is really seen in the sky. We can now with a lens of the same focal length as the eye obtain a picture of the full moon exactly of the size of the actual picture on the retina, and if we take a proper photographic process we can get particles of silver approximately of the same sizes as the dots we have used in making our diagram of the moon ; the grouping is not exactly the same, but we may take it as precisely so for our purpose. I have not any photographs of the full moon of this size, but I have some here of the moon about five, seven and eight days old, which give a good idea of what I mean by the arrangements of the particles of silver being like our diagram. It is now quite apparent that if we can by any means increase the size of the picture of the moon on the retina or make it larger on the photographic plate, we shall be able to employ more of our points in the retina of the eye or of our particles of silver in the photo- graphic film, and so be able to see more clearly just in proportion as we increase the size of the picture in relation to the size of the separate parts that make it. Now the telescope enables us to do this for the eye, and a lens of longer focal length will give us a larger photographic picture. Let us assume that by means of the telescope we have increased the power of the eye one hundred times. The picture of the moon on the retina would now be one-half inch diameter, and instead of employing 2800 points to determine its shape, and the various mark- ings upon it, we should be employing 28,000,000 of these points ; and similarly with the photograph, by increasing the size of our lens we shall obtain a picture made up of this enormous number of particles of silver. But we can go further in the magnification of the picture on the retina — we can also use a still longer focus photographic lens. A power of magnification of one thousand is quite possible under favourable circumstances ; this means that the picture of one two-hun- dredth of an inch would be now of five inches in diameter, so we must deal with only a portion of it. Let us take a circle of one-tenth of this, equalling one-hundredth of our original picture, which in the eye, unaided by the telescope, would have a diameter of one two- thousandth of an inch, or an area of less than one five-millionth of a square inch. This means that with this magnification, we have in- creased the power so enormously that we are now employing for the photographic picture two thousand eight hundred million particles of silver, and in the eye the same degree of increase in the number of points of the retina employed in scrutinising the picture piece by piece as successive portions are brought into the central part. Photography enables me to show that the result I have given of Vol. XIII. (No. 84.) m 162 Mr. A, A. Common [May 30, the wonderful effect of increasing the optical power is perfectly correct as far as it is concerned. We will deal with a part only of the moon, representing, as I have just said, about one-tenth of its diameter, or one-hundredth of its visible surface. Two such portions of the moon are marked, as you see, on the diagram. I have selected these por- tions as I am able to show you them just as taken on a large scale by photography so that you can make the comparison in the most certain manner ; but let us first analyse our diagrammatic moon — let us magnify it about ten times, and see what it looks like. I now show you a picture of this part of the diagram, inclosing the portions I wish to speak about, magnified ten times, so that you can see that about twenty-eight of our points, and by supposition twenty-eight of our particles of silver on the photographic plate, make up the picture. You will see that these dots vary in size ; the difference is due to the amount of light falling within what we may call the sphere of action of each point, and should represent it exactly. The result can hardly be called a picture, as it conveys no impression of continuity of form to the mind. We have got down to the structure or separate parts, and to the limit of the powers of the eye and the photographic plate, of course on the assumption we have made as to the size of the points in the one case and the particles of silver in the other. I will now show you the same parts of the moon as rej)re- sented by the circles on our diagram exactly as delineated by photo- graphy. You now see a beautiful picture giving mountains, valleys, craters, peaks, and plains, and all that makes up a picture of lunar scenery. We have thus seen how the power of the eye is increased by the enlargement of the picture on the retina by the telescope, and also how, by increasing the size of the photograph, we also get more and more detail in the picture. We know we cannot alter the number of those separate points on the retina which determine the limit of our powers of vision in one direction, but we may be able to increase enormously the number of particles of silver in our photographic picture by processes that will give finer deposits, and so, in conjunction with more perfect and larger photographic lenses, we may reasonably look for a great improvement in our sense of vision — it may be even beyond that given by the telescope alone ; although it always will be something in favour of the telescope that the magnification obtained in the eye is about fifteen times greater than that obtained by photography when the image on the retina is pitted against the photograph of the same size, unless we use a lens to magnify the photograj)h of the same focal length as the eye, in which case it is equal. But we may go much further in our magnification of the ^photographic image. In other ways there is great promise when we consider the difference in the action of the eye and the chemical action in the sensitive film under the action of light. As I pointed out in the discourse I gave about four years ago in this theatre, the eye cannot perceive objects that are not sufficiently illuminated, though this same amount of 1890.] on Astronomical Telescopes. 163 illumination will, by its cumulative effect, make a photographic picture, so that there are ways in which the photographic method of seeing celestial bodies can be possibly made superior to the direct method of looking with a telescope. With some celestial objects this has been already done : stars too faint to be seen have been photographed, and nebulae that cannot be seen have also been photographed; but much more than this is possible : we may be able to obtain photographs of the surface of the moon similar to those I have shown, but on a very much larger scale, and we may obtain pictures of the planets that will far surpass the pictures we would see by the telescope alone. I have mentioned that the distance at which the normal eye can best see things is about nine inches, as that gives the greatest angular size to the object while retaining a sharp picture on the retina ; but, as many of us know, eyes differ in this power : two of the common infirmities of the eyes are long or short-sightedness, due to the pictures being formed behind the retina, in the first case, and in front of it in the other. Towards the end of the thirteenth century it was found that convex lenses would cure the first infirmity, and, soon afterwards, that concave lenses would cure the second, as can be easily seen from what I have said about the action of these lenses ; so that during the fifteenth and sixteenth centuries the materials for the making of a telescope existed ; in fact, in the sixteenth century. Porta invented the camera obscura, which is in one sense a telescope. It seems very strange that the properties of a convex and concave lens when properly arranged were not known much earlier than 1608. Most probably, if we may judge from the references made by some earlier writers, this knowledge existed, but was not properly appre- ciated by them. Undoubtedly, after the first telescopes were made in Holland in 1608, the value of this unique instrument was fully appreciated, and the news spread rapidly, for we find that in the next year " Galileo had been appointed lecturer at Padua for life, on account of a perspective like the one which was sent from Flanders to Cardinal Borghese." As far as can be ascertained, Galileo heard of the telescope as an instrument by which distant objects appeared nearer and larger, and that he, with this knowledge only, reinvented it. The Galilean telescope is practically, though not theoretically, the simplest form. It is made of a convex lens in combination with a concave lens to intercept the cone of rays before they come to a focus, and render them parallel so that they can be utilised by the eye. It presents objects as they appear, and the picture has less colour in this form than in the other where a convex eye-glass is used. It is used as one form of opera-glass at the present time. Made of one piece of glass in the shape of a cone, the base of which is ground convex, and the apex slightly truncated and ground concave, it becomes a single- lens telescope that can be looked upon just as an enlargement of the outer lens of the eye. Galileo was undoubtedly the first to make an astronomical M 2 164 Mr. A. A. Common [May 30, discovery with the telescope: his name is, and always will be, associated with the telescope on this account alone. Very soon after the introduction of the Galilean telescope, the difficulties that arise from the coloured image produced by a single lens turned attention to the possibility of making a telescope by using the reflecting surface of a concave mirror instead of a lens. Newton, who had imperfectly investigated the decomposition of light produced by its refraction through a prism, was of opinion that the reflecting principle gave the greatest possibilities of increase of power. He invented, and was the first to make, a reflecting telescope on the system that is in use to the present day ; thus the two forms of telescope — the refracting and reflecting — came into use within about 60 years of each other. It will be perhaps most convenient in briefly running through the history of the telescope, that I should give what was done in each century. Commencing, then, with the first application of the telescope to the investigation of the heavenly bodies by Galileo in 1609, we find that the largest telescope he could make gave only a magnifying power of about 30. The first improvement made in the telescope, as left by Galileo, was due to a suggestion — by some attributed to Kepler, but certainly used by Gascoigne— to replace the concave eye-lens that Galileo used by a convex one. Simple as this change looks, it makes an important, indeed vital improvement. The telescope could now be used, by placing a system of lines or a scale in the common focus of the two lenses, to measure the size of the image produced by the large lens ; the axis or line of collimation could be found, and so the telescope could be used on graduated instruments to measure the angular distance of various objects ; in fact, we have now in every essential principle the true astronomical telescope. It is useless as an ordinary telescope, as it inverts the objects looked at, while the Galilean retains them in their natural position. The addition, however, of another lens or pair of lenses reinverts the image, and we then have the ordinary telescope. It was soon found that the single lens surrounds all bright objects with a fringe of colour, always of a width of about one-fiftieth of the diameter of the object-glass, as we must now call the large lens ; and as this width of fringe was the same whatever the focal length of the object-glass, the advantage of increasing this focal length and so getting a larger image without increasing the size of the coloured fringe became apparent, and the telescope therefore was made longer and longer, till a length of over one hundred feet was reached ; in fact, they were made so long that they could not be used. A picture of one of these is shown, from which it can be easily imagined the difficulties of using it must have been very great, yet some most important measurements have been made with these long telescopes. Beyond the suggestions of Gregory and Cassegrain for improvements in the reflecting telescope, little was done with this instrument. 1890.] on Astronomical Telescopes. 165 During the eighteenth century immense advances were made in both kinds of telescopes. With the invention of the achromatic telescope by Hall and Dollond, the long-focus telescopes dis- appeared. Newton had turned to the reflecting telescopes believing from his investigations that the dispersion and refraction were constant for all substances ; this was found not to be so, and hence a means was possible to render the coloured fringe that surrounds bright objects when a single lens is used less prominent, by using two kinds of glass for the lens, one giving more refraction with somewhat similar dispersion, so that while the dispersion of one lens is almost corrected or neutralised by the other, there is still a refraction that enables the combination to be used as a lens giving an image almost free from colour. In 1733, Hall had made telescopes having double object-glasses on this plan, but never published the fact. Dollond who had worked independently at the subject, came to the conclusion that the thing could be done, and succeeded in doing it ; the invention of the achromatic telescope is with justice, therefore, connected with his name. Although this invention was a most important one, full advantage could not be taken of it owing to the difficulty of getting disks of glass large enough to make into the compound object-glass, disks of about four inches being the largest diameter it was possible to obtain. With the reflecting telescope, unhampered as it always has been by any except mechanical difficulties, advance was possible, and astronomers turned to it as the only means of getting larger instru- ments. Many most excellent instruments were made on the Newtonian plan. The plan proposed by Gregory was largely used, as in this instrument objects are seen in their natural position, so that the telescope could be em23loyed for ordinary purposes. Many were also made on the plan proposed by Cassegrain. The diagrams on the wall enable you to at once see the essential points of these different forms of reflectors. About 1776 Herschel commenced his astronomical work ; beginning with reflecting telescopes of six or seven inches, he ultimately suc- ceeded in making one of four feet aperture. With these instruments, as everyone knows, most brilliant discoveries were effected, and the first real survey of the heavens made. Herschel's larger telescopes were mounted by swinging them in a surrounding framed scaffolding that could itself be rotated. The smaller ones were mostly mounted on the plan of the one now before us, which the Council of the Eoyal Astronomical Society have kindly allowed me to bring here. The plan nearly always used by Sir William Herschel was the Newtonian, though for the larger instru- ments he used the plan proposed years before by Le Maire, but better known as the Herschelian, when the observer looks directly at the large mirror, which is slightly tilted, so that his body does not 166 Mr. A. A. Common [May 30, hinder the light reaching the telescope. In all cases the substance used for the mirrors was what is called speculum metal. During the present century the aperture of the refracting telescope has increased enormously ; the manufacture of the glass disks has been brought to a high state of perfection, particularly in France, where more attention is given to this manufacture than in any other country. Early in the century the great difficulty was in making the disk of flint glass. M. Guinand, a Swiss, beginning in 1784, succeeded in 1805 in getting disks of glass larger and finer than had been made before, and refractors grew larger and larger as the glass was made. In 1823 we have the Dorpat glass of 9 * 6 inches, the first large equatorial mounted with clock-work ; in 1837 the 12-inch Munich glass; in 1839 the 15-inch at Harvard, and in 1847 another at Pulkowa; in 1863 Cooke finished the 25-inch refractor which Mr. Newall gave, shortly before his death last year, to the Cambridge University. This telescope the University has accepted, and it is about to be removed to the Observatory at Cambridge, where it will be in charge of the Director, Dr. Adams. In accordance with the expressed wish of the late ]VIr. Newall, it will be devoted to a study of stellar and astronomical physics. There is every prospect that this will be properly done, as Mr. Frank Newall, one of the sons of the late Mr. Newall, has ofiered his personal services for five years in carrying on this work. Succeeding this we have the 26-inch telescope at Washington, the 2 6-inch at the University of Virginia, the 30-inch at Pulkowa, and the 3 6 -inch lately erected at Mount Hamilton, California — all these latter by A Ivan Clark and his sons. By Sir Howard Grubb we have many telescopes, including the 28-inch at Vienna. Most of these telescopes have been produced during the last twenty years, as well as quite a host of others of smaller sizes, including nearly a score of telescopes of about 13 inches diameter by various makers, to be employed in the construction of the photo- graphic chart of the heavens, which it has been decided to do by international co-operation. The first of these photographic instruments was made by the Brothers Henry, of the Paris Observatory, who have also made many very fine object glasses and specula, and more important than all, have shown that plane mirrors of perfect flatness can be made of almost any size; the success of M. Loewy's new telescope, the equatorial coude, is entirely due to the marvellous perfection of the plane mirrors made by them. The reflecting telescope has quite kept pace with its elder brother. Lassell in 1820 began the grinding of mirrors, he like Sir William Herschel working through various sizes, finally com- pleting one of 4 feet aperture, which was mounted equatorially Lord Kosse also took up this work in 1840 ; he made two 3-foot specula, and in 1845 finished what yet remains the largest telescope. 1890.] on Astronomical Telescopes, 167 one of 6 feet aperture. All these were of speculum metal, and all on the Newtonian form. In 1870, Grubb completed for the Melbourne Observatory a telescope of 4 feet aperture, on the Cassegrain plan, the only large example. The mirror of this is of speculum metal. In 1856 it was proposed by Steinheil, and in 1857 by Foucault, to use glass as the material for the concave mirror, covering the surface with a fine deposit of metallic silver in the manner that had then just heen perfected. In 1858 Draper in America, completed one on this plan of 15 inches aperture, soon after making another of 28 inches. In France several large ones have been made, including one of 4 feet at the Paris Observatory : in England this form of telescope is largely used, and mirrors up to 5 feet in diameter have been made and mounted equatorially. Optically the astronomical telescope, particularly the refractor, has arrived at a splendid state of excellence ; the purity of the glass disks and the perfection of the surfaces is proved at once by the performances of the various largo telescopes. No limit has yet been set to the increase of size by the impossibility of getting disks of glass or working them, nor is it probable that the limit will be set by either of these considerations. We must rather look for our limiting conditions to the immense cost of mounting large glasses, and the absorption of light by the glass of which the lenses are made, coming injuriously into play to reduce the light-gathering power, though it will be probably a long time before this latter evil will be much felt. With the reflecting telescope the greater attention given to the working and testing of the optical surface has enabled the concave mirror to be made with a certainty that the earlier workers never dreamed of. The examination of the surface can be made optically at the centre of curvature of the mirror in the manner that was used by Hadley in the beginning of the last century, and revived some years ago by Foucault who brought this method of testing specula to a high degree of perfection ; in fact, with the addition of certain methods of measuring the longitudinal aberrations we have now a means of readily testing mirrors with a degree of accuracy that far exceeds the skill of the worker. It enables every change that is made in the surface during the progress of the figuring, as the para- bolisation of the surface is called, to be watched and recorded, and the exact departure of any part from the theoretical form measured and corrected ; mirrors can be made of very much greater ratio of aperture to focal length. I have one here where the focal length is only 2i times the aperture : such a mirror in the days of speculum metal mirrors with the methods then in use would have necessarily had a focal length of about 20 feet. The difference in curvature between the centre and edge of this mirror is so great that it can be easily measured by an ordinary spherometer, amounting as it does with one of 6 inches diameter to 3/10,000 of an inch, an amount Bufficient to make the focus of the outer portion about 1 inch longer 168 3Ir. A, A. Common [May 30, than the inner when it is tested at the centre of curvature. The diagram on the wall, copied roughly from one of the records, I keep of the progress of the work on a mirror during the figuring, shows how this system of measurements enables one to follow closely the whole operation. The use of silver on glass as the reflecting surface is as important an improvement in the astronomical telescope as the invention of the achromatic telescope. It gives a permanency to a good figure once obtained that did not exist with the mirrors of speculum metal. To restore the surface of silver to the glass speculum is only a small matter now. How readily this is done may be seen by the practical illustration of the method I will give. I have here two liquids — one a solution of the oxide of silver, and another a reducing agent, the chief material in solution being sugar. I pour the two together in this vessel, the surface of which has been cleaned and kept wet by distilled water, which I shall partly empty, leaving the rest to mix vrith the two solutions ; you will see in the course of about 5 minutes the silver begin to form, eventually covering the whole surface with a brilliant coating that can be polished on the outer surface as bright as that you will see through the glass. Eeflecting telescopes have advantages over the refracting telescopes in many ways, but in some respects they are not so good. They give images that are absolutely achromatic, while the other form always has some uncorrected colour. They can be made shorter, and as the light-grasping power is not reduced by the absorption of the glass of which the lenses are made, it is in direct proportion to the surface or area of the mirror. They have not had in many cases the same care bestowed upon either their manufacture or upon their mounting as has been given in nearly every case to the refracting telescope. Speaking generally, the mounting of the reflecting telescope has nearly always been of a very imperfect kind — a matter of great con- sequence, for upon the mounting of the astronomical telescope so much depends. To direct the tube to any object is not difficult, but to keep it steadily moving so that the object remains on the field of view requires that the tube should be carried by an equatorial mount- ing of an efficient character. The first essential of such a mounting is an axis parallel to the axis of rotation of the earth. The tube, being supported on this, will follow any celestial object, such as a star, by simply turning the polar axis in a contrary motion to that of the earth, and at the same rate as the earth rotates on its axis. If we make the telescope to swing in a plane parallel to the polar axis, we can then direct the telescope to any part of the sky, and we have the complete equatorial movement. There are several ways in which this is practically done : we can have a long open-work polar axis supported at top and bottom, and swing the telescope in this, or we can have short strong axes. As examples of the first, I will show you pictures of the mountings designed for Cambridge and Greenwich Observatories some forty years ago by Sir G. Airy, 1890.] on Astronomical Telescopes. 169 lately and for so long our eminent Astronomer-Eoyal ; and as examples of the other form, amongst others, the large telescope lately erected at Nice, and also the larger one at Mount Hamilton, California, now under the direction of Prof. Holden. The plan of bringing all the various handles and wheels that control the movement of the telescope and the various accessories down to the eye end, so as to be within reach of the observer, is carried to the highest possible degree of perfection here, as we can see by an inspection of the picture of the eye end of this telescope. The observer with the ■ reflecting telescope is, with moderate-size instruments, never very far from the floor, but in the case of the Lick telescope he might have to ascend some thirty feet for objects low down in the sky. Thanks to the ingenuity of Sir Howard Grubb, to whom the idea is due, the whole of the floor of the Observatory is made to rise and fall by hydraulic machinery at the wdll of the observer — a charming but expensive way of solving the difficulty, as far as safety goes, but not meeting the constant need of a change in position as the telescope swings round in keeping up with the motion of the object to which it is directed. The great length of the tube of large re- fractors is well seen in this picture of the Lick telescope : it suggests flexure as the change is made in the direction in which it points, and the consequent change of stress in the different parts of the tube. The mounting of the reflector has been treated, if not so success- fully, with more variety than in the case of the refractor as we shall see from the pictures I will show you, especially where the Newtonian form is used. The 4-foot reflector at Melbourne is mounted on the German plan, in a similar way to a refractor, and an almost identical plan has been followed by the makers of the 4-foot at the Paris Observatory. Lassell, who was the first to mount a large reflector equatorially, used a mounting that may be called the forked mounting, the polar axis being forked at its upper end, and the tube of the telescope swinging between the forks ; a very excellent plan, dispensing with all counterpoising. Wishing to obtain certain con- ditions that I thought and think now favourable to the performance of the reflector, I devised a mounting where the whole tube was supported at one end on a bent arm ; a 3-foot mirror was mounted on this plan in 1879, and worked admirably. The Newtonian form demands the presence of the observer near the high end of the tele- scope, and the trouble of getting him there and keeping him safely close to the eye-piece is very great. As we see from the various photographs, several means have been employed to do this, none of them quite satisfactory. All the refracting telescopes of note in the world are covered by domes that effectually protect them from the weather ; these domes are in some cases comparable in cost with the instruments they cover. It is not surprising, therefore, that efforts have been made to devise a means of getting rid of this costly dome and the long movable tube. It was suggested many years ago that a combination of plane 170 Mr, A. A. Common [May 30, mirrors could be used to direct light from any object into a fixed telescope. This idea in a modified form has often been used for special work, one plane mirror being used as we see in the picture on the screen to throw a beam of light into a telescope fixed horizon- tally ; for certain kinds of work this does admirably, but the range is restricted as can be easily seen, and the object rotates in the field of view as the earth goes round. The next step would be to place the telescope pointing parallel to the axis of the earth and send the beam of light into it from the mirror, which could now be carried by the tube so that by simply rotating the tube on its own axis the object would be kept in the field of view. Sir Howard Grubb makes a small telescope on this plan, and some years ago proposed a somewhat similar plan. A sketch of this plan I will show you. You will see, however, that here again the range is restricted, and to use the tele- scope, means would be required to constantly vary the inclination of the small mirror at one-half the rate of inclination of the short tube carrying the object-glass. By the use of two plane mirrors, however, the solution of the problem of a rotating telescope tube placed as a polar axis is solved. By having such a telescope with a plane mirror at an angle of 45° to the axis of the telescope in front of the object-glass, we can, by simply rotating the telescope, see every object lying on the equator ; and by adding another similar plane mirror at an angle of 45° to the axis of the telescope, as bent out at right angles by the first plane mirror. and giving the mirror a rotation perpendicular to this axis, we obtain the same power of pointing the telescope as we have in the equatorial. The idea of doing this was published many years ago, but it was left to the skill and perseverance of M. Loewy, of the Paris Observatory, to put it into practical use. He devised, and had made, a telescope on this principle, of 10^ inches aperture, which was completed in 1882. It has proved itself an unqualified success, and many other larger ones are now being made in Paris, including one of 23 inches aperture, now nearly completed, for the Paris Observatory. A lantern copy of a drawing of this latter telescope will be thrown on the screen, in order that you may see what manifest advantages exist in this form of telescope. There is but one objection that can be urged — that is, the possible damage to the definition by the 2)lane mirrors ; but this seems, from what I have seen of the wonderful per- fection of the plane mirrors made by the Brothers Henry, to be an unreasonable one — at any rate not an insurmountable one. In every other respect, except perhaps a slight loss of light, this form of tele- scope is so manifestly superior to the ordinary form that it must supersede it in time, not only for general work, but for such work as photography and spectroscopy. 1890.] on Astronomical Telescopes. 171 Note on a Method op Silvering Glass Mirrors. Solutions. — Make up 10 per cent, solutions of pure recrystallised nitrate of silver, pure caustic potash, and loaf sugar. To the sugar solution add ^ per cent, of pure nitric acid and 10 per cent, of alcohol. The sugar solution is very much improved by keeping, its action being more rapid and the film cleaner when the sugar solution has been made for a long time. Make up also a weak solution, say 1 per cent, of nitrate of silver and a 10 per cent, solution of ammonia. (90 per cent, distilled water, 10 per cent, ammonia, '880 specific gravity). Distilled water must be used for all the solutions. Cleaning the Mirror. — Thoroughly clean the mirror. To do this pour on a strong solution of caustic potash, rub well with cotton wool, rinse with ordinary water, wash again with absolute alcohol, and rinse ; finally pour on strong nitric acid, and rub with a piece of cotton wool, inserted in the open end of a test tube. Rinse again thoroughly with ordinary water, and then place the mirror face downwards in distilled water in a dish sufiiciently large to leave two inches margin round the edge of the mirror, and to keep the face of the mirror one inch from the bottom of the dish. The liquid should stand half an inch above the face of the mirror which should not be completely submerged, and care should be taken to exclude all air-bubbles. For Silvering a 12-incJi Mirror. — Take 400 c.c. of the nitrate of silver solution and add strong ammonia until the brown precipitate first formed is nearly dissolved, then use the diluted ammonia until the solution is just clear. Then add 200 c.c. of the caustic potash solution. A brown precipitate is again formed, which must be dis- solved in ammonia exactly as before, the ammonia being added until the liquid is just clear. Now add the 1 per cent, solution of silver nitrate until the liquid becomes a light brown colour, about equal in density of colour to sherry. This colour is important, and can only be properly obtained by adding the weak solution. Dilute the liquids to 1500 c.c. with distilled water. All being ready add 200 c.c. of the sugar solution to 500 c.c. of water. Then lift the mirror out of the dish, taking care to keep its face downwards during the time it is out of the water, pour the washing water away, add the sugar solution to the silver potash solution, taking care they are thoroughly mixed, and pour them into the dish. Place the mirror face downwards in this solution, taking care to exclude all air-bubbles. The liquid will turn light brown, dark brown, and finally black. In four or five minutes, often sooner, a thin film of silver will com- mence to form on the mirror, and this will thicken until in about twenty minutes the whole liquid has acquired a yellowish brown colour, with a thin film of metallic silver floating on the surface. Lift the mirror out, thoroughly wash with distilled water, and stand the mirror on its edge, or rest it in an inclined position until it is dry ; if time can be allowed, the silvered mirror may be left to soak 172 Mr. A. A. Common on Astronomical Telescopes. [May 30, in distilled water over niglit. Leave it to dry until next day, then the slight yellowish " bloom " can be polished off by rubbing softly with a pad of chamois leather and cotton wool. Carefully polish afterwards with a little dry well-washed rouge on the leather pad. The film should be opaque and brilliant, and with careful handling will be very little changed with long use. Dishes. — Use porcelain, glass, or earthenware dishes whenever possible ; but, if these are not available, a zinc dish, coated inside with paraSSn or best beeswax. For small mirrors (up to 12 inches) the easiest method of supporting them during silvering is to attach them to a wooden rod by pitch, and arrange the dish thus WOODEN ROD WOODEN BLOCK PITCH :'; ' ''''''''';'''1!!lil'!lH!111llillT!!lllllll!!illlllllilllll!llllll!IIITi'i'l^;!^^ "W!l [„P... '■ ;: MV MIRROR J-3^^€=w-=^: ;---€>z-r-ZH: S??^?? ^r^3^§>^i=|£gr|S '^-^:^-:i5:-'^:P:~z-:Sooiei?/— Quarterly Journal, Vol. XLVI. Part 2, No. 182. 8vo. 1890 Geor go fili, Beale Accademia—A.ii\,Yo\. '^111. 'Dis^. 1. 8vo. 1890. Johns Hopkins University — University Circulars, No. 80. 4to. 1890. Laboratory Club — Transactions, Vol. HI. No. 5. 8vo. 1890. Linnean Society— J omn&l, Vol. XXVII. No. 182. 8vo. 1890. Meteorological Office— ^Yeek\y Weather Reports, Nos. 17-21. 4to. 1890. Meteorological Observations at Foreign and Colonial Stations, 1852-1886. 4to. 1890. Meteorological Society, i?o?/riZ— Quarterly Journal, No. 74. 8vo. 1889. Meteorological Record, No. 35. 8vo. 1889. National Life-boat Institution — Annual Report for 1890. 8vo. 1890. North of England Institute of Mining and Mechanical Engineers — Transictions, Vol. XXXVIII. Part 5. 8vo. 1890. Odontological Society of Great Britain — Transactions, Vol. XXII. No. 6. New- Series. 8vo. 1890. Paris Universal Exhibition, 1889 — British Section, Report of the Council. 12mo. 1890. Pharmaceutical Society of Great Britain — Journal, May, 1890. 8vo. Photographic Society— J omnAi, Vol. XIV. Nos. 7, 8. 8vo. 1890. Bathbone, E. P. Esq. (the Editor) — The Witwatersrand Mining and Metallurgical Review, No. 4. 8vo. 1890. Bio de Janeiro Observatory— 'Revista., No. 4. 8vo, 1890. Boyal Irish Academy — Transactions, Vol. XXXIX. Part 13. 4to. 1890. " Cunningham Memoirs," No. 5. 4to. 1890. Boyal Society of Antiquaries of Ireland — Journal, Vol. I. No. 1. 5th Series. Svo. 1890. Boyal Society of London — Proceedings, No. 288. 8vo. 1890. Saxon Society of Sciences, Boyal — Philologisch-historischen Classe : Abhandlungen, Band XI. No. 6. 8vo. 1890. Berichte, 1889, No. 4. 8vo. 1890. Mathematische-Physischen Classe : Abhandlungen. Band XV. Nos. 7-9. 4to. 1889. Berichte, 1889, Nos. 2-4. Svo. 1890. Register-Berichte, 1846-1885; Abhandlungen, Band I.-XII. Svo. 1889. Selborne Society — Nature Notes, Vol. I. No. 5. Svo. 1890. Simpson, James, Esj. (the Author) — The Scottish Press and the Gipsies. Svo. 1890. Smithsonian Institution — Bureau of Ethnology, Fifth and Sixth Reports. 4to. 1887-1888. Various Papers. Svo. 1887-1889. Society of Architects— Proceedings, Vol. II. No. 10. Svo. 1890. Society of ^rfs— Journal for INIay, 1890. Svo. Teyler Museum— Archives, Serie I[. Vol. III. Fas. 4. 4to. 1890. Catalogue de la Bibliotheque, Vol. II. Livraison 1-3. 4to. 1890. United Service Institution, Boycd— Jour ua], No. 152. Svo. 1890. United States Geological Survey — Seventh Annual Report, 1885-86. 4to. 1890. University of London — Calendar, 1890-91. Svo. Vereins zur Beforderiing des Gewerbfieises in Preussen — Verhandlungen, 1890 : Heft 4. 4to. Victoria Institute — Transactions, No. 92. Svo. 1890. Yorkshire Archxological and Topographical Association — Journal, Parts 41, 42. Svo, 1890. 18 90. J Prof. W. Boyd DawMns on Search for Coal, dec. 175 WEEKLY EVENING MEETING, Friday, June 6, 1890. Basil Woodd Smith, Esq. F.R.A.S. F.S.A. Vice-President, in the Chair. Professor W. Boyd Dawkins, M.A. F.R.S. The Search for Coal in the South of England. 1. Introductory — 2. The conditions under which the coal-measures were formed — 3. The break up of the Carboniferous alluvia into isolated coal-basins — 4. Godwin-Austen's conclusions — 5. The conclusions of Prestwich and the Coal Commission — 6. Tlie range of the coal-measures under the Newer Eocks of Somerset — 7. Coal-measures in Oxfordshire — 8. The district of London — 9. The Weald of Sussex — 10. The coal-fields of Northern France, Belgium, and Westphalia — 11. The discovery of a coal-field at Dover— 12. General conclusions. 1. The bare facts of the recent discovery of coal-measures at Shake- speare Cliff, near Dover, have been published in the press, and the full account cannot be written till the completion of the inquiry which is now going on. It is, however, not unfitting that the bearing of the discovery on the general question of the existence of workable coal- fields in Southern England should be discussed within these walls, not merely on account of its general interest, but because it naturally follows the paper read by Mr. Godwin-Austen before the Eoyal Institution, in 1858, " On the Probability of Coal beneath the South- eastern parts of England." In 1855 he had placed before the Geo- logical Society of London the possibility of the existence of coal in South-eastern England at a workable depth. In the two years which had elapsed, " the possibility " had grown in his mind into the " pro- bability," and in the thirty-two years which have passed between the date of the paper before this Institution and the present time, " the probability " has been converted into a certainty by the recent dis- covery at Dover. In this communication, the lines of the inquiry laid down by Godwin-Austen will be strictly followed. We must first examine the conditions under which the coal-measures were accumulated. 2. The seams of coal are proved, by the surface-soil traversed by roots and rootlets, to which in some cases the trunks are still attached, to have been formed in situ by the growth and decay of innumerable generations of Plants (Lepidodendra, Sigillaria, Catamites), Pines, (Trigonocarjpa, Dadoxylon, Sternhergia), allied to Salishurla, and a vast undergrowth of Ferns, all of which contributed to form a peat- like morass. Each seam represents an accumulation on a land- surface, just as the sandstones and shales above it point to a period 176 Professor W. Boyd DawJcins [June 6, of depression during whicli sandbanks and mudbanks were deposited by water. The fact also that the coal-seams in a given sinking are parallel, or nearly parallel, implies that they were formed on horizontal tracts of alluvium, while the marine and fresh-water shells in the associated sandstones and shales prove that they were near the level of the sea, or within reach of a mighty river. This tract of forest- clad marsh-lands, as Godwin-Austen and Prestwich have pointed out, occupied the greater part of the British Isles, from the Highlands of Scotland southwards as far as Brittany, and eastwards far away into the valley of the Rhine, and westwards over the greater part of Ireland. It swept round the hills of South Scotland and the Lake district and the region of Cornwall. It occupied a delta like that of the Mississippi, in which the forest-growths were from time to time depressed beneath the water-line, until the whole thickness of the coal- measures (7200 feet thick in Lancashire, 7600 in South Wales, and 8400 in Somersetshire) was built up. After each depression the forest spread again over the sand and mud of the submerged parts, and another peat-layer of vegetable matter was slowly accumulated above that buried beneath the sand and mud. The great extent of this delta implies the existence of a large river draining a large continent, of which the Highlands of Scotland and the Scandinavian peninsula formed parts, and which I have described before the Eoyal Institution under the name of Archaia. 3. At the close of the Carboniferous age, this vast tract of alluvium was thrown into a series of folds by earth-movements. These have left their mark in the south of England and the adjacent parts of France, in the anticline of the English Channel, the syncline of Devonshire, the anticline of the Mendip Hills and of the lower Severn, and the syncline of the South Wales coal-fields. These great east and west folds have been traced from the south of Ireland on the west, through 35 degrees of latitude, through North France and Belgium, as far as the region of Westphalia. Next, the upper portions of the folds were attacked by the subaerial and marine agents of denudation over the whole of the Carboniferous area, leaving the lower parts to form the existing coal-fields which lie scattered over the surface of the British Isles, and are isolated from each other by exposures of older rocks ; and a broad east and west ridge was carved out of the folded and broken Carboniferous and older rocks, extending from the anticline of the Mendip Hills eastward through Artois into Germany, and constituting the ridge or axis of Artois of Godwin- Austen. The next stage in the history of the folded Carboniferous and older rocks is marked by the deposition of the Permian and Secondary rocks on their eroded and waterworn edges, by which they were partially concealed or wholly buried, and these newer strata thin off as they approach the ridge of Artois. This barrier, also, of folded Carboniferous and older rocks sank gradually beneath the sea in the Triassic, Liassic, Oolitic, and Cretaceous ages, and against it the strata of the first three named ages thin off, while in France and 1890.] on the Search for Coal in the South of England. 177 Belgium the Cretaceous deposits rest immediately upon the waterworn older rocks. From these general considerations it is clear that the coal-measures which formerly extended over nearly the whole of Southern England can now only be met with in isolated basins under the newer rocks, and that these are thinnest along the line of the above-mentioned barrier. 4. The exposed coal-fields in Britain, and on the Continent also, Godwin-Austen pointed out, along this line, are of the same mineral character, and the pre-Cavboniferous rocks are the same. This ridge or barrier also, where it is concealed by the newer rocks, is marked by the arch-like fold (anticlinal) of the chalk of Wiltshire, and by the line of the North Downs in Surrey and Keut. Godwin-Austen finally concluded that there are coal-fields beneath the Oolitic and Cretaceous rocks in the South of England, and that they are near enough to the surface along the line of the ridge to be capable of being worked. He mentioned the Thames valley and the AVeald of Kent and Sussex as possible places where they might be discovered. These strikingly original views gradually made their way, and in the next eleven years became part of the general body of geological theory. They were, however, not accepted by Sir Eoderick Murchison, the then head of the Geological Survey, who maintained to the last that there were no valuable coal-fields in Southern England. 5. The next important step in the direction of their verification was that taken by the Coal Commission of 1866-67, by whom Mr. Godwin- Austen was examined at length, and the results of the inquiry embodied in the Eeport by Mr. JPrestwich. In the Report Mr. Godwin-Austen's views are accepted, and fortified by a vast number of details relating both to the coal-fields of Somersetshire and of France and Belgium. Mr. Prestwich also calls special attention to the physical identity of the coals of these two regions, and to the fact that the Carboniferous and older rocks in both are similarly disturbed. He concludes, further, that the coal-fields which now lie buried beneath the newer rocks are probably equal in value and in extent to those which are exposed in Somerset and South Wales on the west, and in Belgium and France on the east. We will now proceed to test these., theoretical conclusions by the light of recent observations. 6. The coal-fields of Somerset and Gloucester were proved by the labours of Prof. Prestwich and the Coal Commission of 1866-67 to be small fractions of the great coal basin which lies buried beneath the Triassic, Liassic, and Oolitic rocks, from the Mendip Hills northwards past Bristol to Wickwar. On the west also three small isolated coal-basins occur — those of Nailsea and Portishead, which are par- tially, and that of Aust, which is wholly, concealed by the newer rocks. The coal-measures are folded and broken, and traversed by- great " overthrust " faults, which at Kingswood give the same series of coals twice over in the sinkings of one colliery. Their southern Vol. XIII. (No. 84.) n 178 Professor W. Boyd Datokins [June 6, boiiuclary is the line of the Mendip Hills. They also probably occur at a depth which remains to be proved, still further to the south, in the valley of the Axe and the district of Glastonbury, the most southern boundary being the mountain limestone of Cannington, near Bridgwater (see map). The great Somerset and Gloucester held may extend to the east under the newer rocks, between Freshford and Beckington, in the district south of Bath. The value of the evidence of the coal-fields of the West of England on the general question consists in the fact that they may be taken as fair samples of those which lie concealed along the line of the buried ridge through South-eastern England in the direction of France, Belgium, and Germany. 7. One of these concealed coal-fields has been struck in a deep boring at Burford, near Witney, in Oxfordshire, at a depth of 1184 feet, under the following rocks: — Oolites 148 feet. Lias 598 „ Ehoetic 10 „ Triassic rocks 428 „ The sandstones and shales of the coal-measures were penetrated to a depth of 225 feet.* These coal-measure rocks form, as suggested by Hull, one of the same series of coal-basins as those of South Wales and the Forest of Dean, and probably mark the line of the continuation of the South Wales syncline in the direction of Harwich, where Carboniferous shale has been struck at a depth of 1052 feet from the surface. This boring proves not merely the presence of coal-measures at a workable depth in Oxfordshire, but also the important fact that the Triassic rocks, which are of great thickness further north, have dwindled down to an unimportant thickness in their range south- wards and eastwards. Further, that south, in the London area, these rocks are wholly absent ; and farther to the east, at Harwich, the Liassic and Oolitic strata and Lower Greensand are absent, and the Gault rests on the eroded Lower Carboniferous rocks, inclined at a high angle. 8. The water-worn surface of the folded rocks, which are older than the Carboniferous, has been repeatedly struck in deep borings for water in the neighbourhood of London, at depths ranging from 839 feet at Ware to 1239 feet at Richmond. They consist of Silurian strata in the north at Ware, and of Old Red Sandstone or Devonian rocks in the other localities. From their high angle of dip, as in the case of similar rocks underlying the coal-fields of Somerset and Northern France and Belgium, it may be inferred that coal-fields lie in the synclinal folds in the neighbouring areas. From the fact of the Silurian rocks being in the north, while all * De Kance, Mauch. Geol. Soc, 20th March, 1878. 1890.] on the Search for Coal in the South of England, 179 the rest of the borings to the south termiDate in the Devonian or Old Eed rocks, it may be inferred that the chalk of the North Downs probably conceals the coal-measures. It must also be noted that there are no Wealden rocks in the London area, and no Lower Greensands, and that the Lower Oolites at their thickest are only 87 feet. The secondary rocks, which are of great thickness in the midland and northern counties, thin off as they pass southwards towards London, against the ridge of older rocks, as both Austen and Prestwich have pointed out. It is therefore in the area south of London, rather than in that immediately to the north, that the coal-measures are to be looked for at a workable depth beneath the surface, and underneath the chalk of the North Downs. It must, however, be noted that the line of the South Wales syncline through Burford passes to the north of Ware, and that there may be coal-measures in the northern parts of Essex and of Hertfordshire at a workable depth. 9. The Eeport of the Coal Commission was published in 1871, and in the following year the Sub-Wealden Exploration Committee was organised by Mr. Henry Willett, to test the question of tlie existence of the Carboniferous and pre-Carboniferous rocks in the Wealden area by an experimental boring. The site chosen was Netherfield, about three miles south of Battle, in Sussex, where the lowest rocks of the Wealden formation constitute the bottom of the valley. The rocks penetrated were as follows : — Section ov Netheefield. Purbeck strata .. .. 200 feet. Portland strata 57 „ Kimmeridge clay 1073 „ Corallian strata .. 515 „ Oxford clay 60 „ 1905 „ This boring showed that the coal-measures and older rocks are, in that region, more than 1900 feet from the surface of the ground. We may also infer, from the fact of the bottom of the bore-hole being in the Oxford clay, and from the known thickness of the Bath Oolitic strata in the nearest places, that it lies buried beneath considerably more than 2000 feet of newer rocks. With this valuable, though negative result, the Sub-Wealden Exploration came to an end. It was a purely scientific inquiry, paid for by subscription, and largely supported by those who had no pecuniary interest in the result. The experience of the boring at Netherfield showed that the search for the coal-measures and older rocks of God win- Austen's ridge would have to be carried out at some spot further to the noith, in the direction of the North Downs. In the district of Battle the Oolitic rocks were proved to be more than 1700 feet thick, and the great and increasing thickness of the successive rocks of the Wealden formation above them, which form the surfiice of the ground between Nether- N 2 180 Professor W. Boyd Dawhiiis [Juue 6, Held and the North Downs, rendered it undesirable to repeat the experiment vvitliin the Wealden area proper, where the Weaklen rocks presented a total thickness of more than 1000 feet, in addition to that of the Oolites. My attention, therefore, was directed to the lino along the North Downs, where Godwin- Austen believed that the Wealden beds abruptly terminated against the ridge of coal-measures and older rocks, and where, therefore, there would be a greater chance of success. 10. The evidence, also, of the French, Belgian, and Westphalian coal-fields pointed in the direction of the North Downs. The Carboniferous and older rocks, which we have hitherto traced only as far as the area of London from their western outcrops in Somerset, Gloucestershire, and South Wales, reappear at the sur- face in Northern France, Belgium, and WeBt23halia, and contain most valuable coal-fields, which are long, narrow, and deep. These extend from the district of the Euhr on the east, through Aachen, Liege, Namur, Charleroi, Mons, and Valenciennes. The enormous value of the last field led, during the last hundred years, to numerous borings through the newer rocks, which have extended the western range of the coal-measures ujDwards of 95 miles away from its disappear- ance under the Oolites and chalk, as far as Flechinelle, south of Aire, or to within 30 miles of Calais. It occupies throughout this distance a narrow trough or syncline, 11 miles across at Douchy, and about half a mile at its western termination. It is represented still further to the west by the faulted and folded coal-fields of Hardinghen and Marquise, which are within about 12 miles of Calais. The coal- measure shales and sandstones found in a boring at Calais, at a dej^th of 1101 feet from the surface, in 1850,* reveal the existence of another coal-field in the same general line of strike, and making fur Dover and the North Downs. 11. We have seen that the range of the coal-measures has been pushed farther and farther to the west by experimental borings, until they have been proved to exist underneath Calais. The opposite shores of the Straits of Dover, therefore, presented the best locality for a trial still further to the west. In choosing a site, the Channel Tunnel works, close to Shakespeare Clitf, Dover, appeared to me to present great advantages, which I embodied in a report to Sir Edward W. Watkin, in 1886. The site is within view of Calais, and not more than six miles to the south of a spot where about 4 cwt. of bituminous material was found imbedded in the chalk in making a tunnel, which, according to Godwin-Austen, had been probably derived from the coal-measures below. Prestwich also had pointed out, in 1873, in dealing with the question of a tunnel between England and France, that the older * This fact is doubted by Gosselet. I am, however, intbriued by Prestwich that both lie and Elie tie Beaumont identified them as ooal-nicasuies at the time, and I see no reason for doubting the accuracy of those two eminent observers. The cores were, uuibrlunately, lost in the first Paris Exiiibition. 1890.] on the Search for Coal in the South of England, 181 rocks were witbin such easy reach at Dover, that they could be utilised for the making of a submarine tunnel. Sir Edward Watkin acted with his usual energy, and the work was begun in 1886, and has been carried on down to the present time, under my advice, and at the expense of the Channel Tunnel Company. The boring operations have been under the direction of Mr. F. Brady, the Chief Engineer of the South-Easteru Eailway, to whose ability we owe the completion of the work to its present point, under circumstances of Fig. 1. OliaXk. GavXt. L. Greensand ^M Oolite. Coal^reasiirc.'f. A Boring. ^.Channel Tunnel Shaft. Boring at Shakespeare Cliff. great difficulty. A shaft has been sunk (A) [See Fig. 1] on the west side of the Shakespeare Cliff, close to the shaft of the Channel Tunnel (B) to a depth of 44 feet, and from this a bore-hole has been made to a depth of 1180 feet. Section at Shakespea-re Cliff, Dover. Feet. Lower grey chalk, and chalk marl ^ Glaiiconite marl .. I kaq Gault I Neocomian = j Portland iau "j Kimmeridgian I Corallian V fjp q Oxfordian .. f Callovian I Bathonian ) Coal measures, sandstones, and shales and clays, ) -q with one seam of coal f 182 Professor W. Boyd DaicJcins [June 6 Tlie coal-measures were struck at a depth of 1204 feet from the surface, or 1160 feet from the top of the bore-hole, and a seam of good blazing coal was met with 20 feet lower. 12. This discovery proves up to the hilt the truth of Godwin- Austen's views as to the range of the coal-measures along the line of the North Downs, and as to the thinning off of the Oolitic and Wealden strata against the buried ridge. The former are less than one-third of their thickness at Netherfield, and the latter are wholly unrei^resented. It establishes the existence of a coal-field in South- eastern England, at a depth well within the limits of working at a profit. The principal coal-j^its in this country are worked at depths ranging from over 1000 to 2800 feet, and one at Charleroi, in Belgium, is worked to a depth of 3412 feet. The Dover coal-field probably forms part of the same narrow trough as the Calais measures, prolonged westward under the Channel further to the south than Godwin-Austen drew it in 1858. Whether it is a trough similar to that which extends through Northern France for more than 100 miles from east to west, as God win- Austen has drawn it in the diagram on the wall, reaching as far to the west as Reading, or whether it is a small, faulted, insignificant fragment of a field, such as that of Marquise and Fig. 2. Cham Gau Greensand Measures Probable Kange of Coal Measures between Doveb and Calais. Hardinghen, remains to be proved. It is, however, one of a chain of coal-fields, which will, in my opinion, ultimately be proved to extend under the newer rocks between Dover and Somerset, along the line of the North Downs, in long narrow east and west troughs. It is probably a continuation beneath the Straits of Dover of the coal measures struck at Calais. (See Fig. 2.) The further question as to the value of these fields may be answered by the amount of coal in the fields which are now being 1890.J on the Search for Coal in the South of England. 183 worked in Westphalia, Belgium, FraDce, and Somersetshire. The Westphalian coal-field coutains 294 feet of workable coal, distributed in 117 seams; that of Mons, 250 feet, in 110 seams; and that of Somerset, 98 feet, in 55 seams. The North French coal-field in 1887 yielded 7,119,633 tons, and gave employment at the pits to 29,000 men, and is rapidly increasing its output. It may be inferred that the buried coal-fields which await the explorer in the North Downs are in all probability not inferior to these. Godwin- Austen, in his memorable paper before the Geological Society, in 1855, said that if one of these buried fields had once been struck in South-eastern England, their exploration would be an easy matter. It has been struck at Dover, and the necessary base is laid down for further discoveries, which in all probability will restore to South-eastern England the manufactures which have long since fled away to the coal districts of the West and North, and which will put off by many years the evil day when the energy stored up in the shape of coal in these islands shall have been spent. [W. B. D.] WEEKLY EVENING MEETING, Friday, March 7, 1890. Sir James Crichton Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Francis Gotch, Esq. Hon. M.A. Oxon. B.A. B.Sc. Electrical Belations of the Brain and Spinal Cord, (Abstract.) (1) The lecturer first described the anatomical structure of the nerve fibres and nerve cells found in the various parts of the mammalian nervous system. He then drew attention to the only physical indication of the passage of a nervous impulse along a nerve fibre, viz. the development in each successive portion of the nerve of an electrical effect. This electrical indication was then demonstrated to the audience by connecting the surface and cross- section of one portion of an isolated frog's nerve with the terminals of a sensitive reflecting galvanometer, and exciting a series of nerve impulses by applying rapidly recurring stimuli to a more distal portion of the same nerve. 184 Mr. F. Gotchon Electrical Relations of Brain, dc. [March 7, (2) The anatomical plan and minute structure of the spinal cord and brain were then described, and the condition of the brain in diflferent mammals was depicted. Special attention was drawn to the important recent additions which had been made to our knowledge of the course of nerve fibres through these complex organs, by the employment of histological methods which differentiated between degenerated and sound nerve fibres, and between partially and com- pletely developed nerve fibres. Observations made along such lines had, it was pointed out, grouped together certain fibres as having common centres both of nutrition and of growth. (3) The results of the investigations of the last ten years into the j)hysiological relations of the brain and spinal cord were then referred to, and the extent of our knowledge of cerebral localisation determined. The indirect nature of the evidence as to the actual passage of nerve impulses in either direction along the nerve fibres composing the spinal cord was next alluded to — this evidence being the arrival of the nerve impulses at outlying muscles. (4) Details were then given of the application of the method previously used to determine the electrical changes in the nerves in order to ascertain what changes of a similar kind were present in the spinal cord. Exj)eriments made for the first time by Y. Horsley and the lecturer were cited to show that such electrical effects were produced when {a) the so-called motor regions of the brain, (h) the columns in the spinal cord, and (c) the entering sensory spinal nerves were stimulated ; and evidence was adduced to prove that the electrical effects thus obtained were true indications of the passage of nerve impulses along the nerve fibres in the particular region of the cord investigated. (5) The physiological relations of the brain, spinal cord, and spinal nerves as determined by the newly discovered electrical relations of these organs were then touched upon ; and a series of experimental investigations still in progress were referred to which seemed to warrant the belief that a basis had been reached for the construction of a scheme of physiological localisation in the fibres of the cord for both efferent (motor), and afferent (sensory) fibres, such as would be in harmony with the known anatomical relations of the central nervous system. [F. G-l 1890.J Sir Frederick Bramwell on Welding hy Electricity. 18^ WEEKLY EVENING MEETING, Friday, April 18, 1890. Sir Frederick Abel, C.B. D.C.L. F.E.S. Vice-President, in the Chair. Sir Frederick Bramwell, Bart. D.C.L. M. Inst. C.E. F.R.S. Eon. Sec. and V.P.B.L Welding hy Electricity. There are certain technical words which relate to operations of a character so decisive, that the words have been adopted into ordinary language, such words as "grafting," " safety valve," "stereotyping," "welding." I dare say that every one who speaks of "grafting," or of a " safety valve," knows something of the operation or of the function of the apparatus of which he is speaking ; perhaps he is not quite so clear about " stereotyping." But when it comes to " welding," I doubt whether many persons know what the term really means, as we engineers understand it, or could tell how many and what metals are capable of being united by welding ; and I also doubt whether there are many who could distinguish between " fusing and burning together " and true " welding." I do not myself know how to give a definition of " welding " as it is understood by practical men ; but Dr. Percy did know, and if you will pardon me I will read a few lines from his book, which state more clearly than I could hope to do in words of my own, the meaning of welding, as ordinarily practised. He says :* — " Iron has one remarkable and very important property, namely, that of continuing soft and more or less pasty through a considerable range of temperature below its melting-point. It is sufficiently soft at a bright red-heat to admit of being forged with facility, as every one knows ; and, at about a white-heat, it is so pasty that when two pieces at this temperature are pressed together they unite intimately and firmly. This^ is what occurs in the common process of welding. Generally metals seem to pass quickly from the solid to the liquid state, and so far from being pasty and cohesive at the temperature of incipient fusion, they are extremely brittle, and in some cases easily pulverisable. But, admitting that there is a particular temperature at which a metal becomes pasty, its range is so limited in the case of the common metals, that it would scarcely be possible to hit upon it with any certainty in practice ; or, if it were possible, its duration would be too short for the performance of the Percy's 'Metallurgy,' Iron and Steel, 1864, pp. 5 and 6 186 Sir Frederick Bramwell [April 18, necessary manipulations in welding." This, to my mind, is a concise and complete descrijstion of welding as we engineers understand it. In the Arts, I suppose there are practically, only two easily weld- able metals — iron (with its variant, steel, now so commonly substituted for it) and platinmn. I had hoped to have practised before you to- night, welding in an ordinary fire, in order to show you the metals which could be welded, by this means, and those which could, not ; and then to show you that metals which could not be welded by the ordinary fire could be easily welded by electricity. But I must ask you to take my word in respect to these matters because wc have not room, in this extraordinary structure which has been put up to prevent the sparks flying about, for a fire-heating implement of any kind along with the workmen and the anvil ; and therefore the idea had to be given up. I am sorry, for I had hoped there would have been time for all ; but probably you have all seen the art of welding practised in the ordinary manner. Now there are several kinds of welds, and I cannot do better than show you some of them as used in former days to weld the tyres of railway carriage and engine wheels. During the last quarter of a century such tyres have not been welded, but have been made in the circular or hoop form, without welding, still their former mode of manufacture will serve to illustrate the diiferent kinds of welds. The most commonly used kind was that known as a scarf weld. In this the two portions of the tyre before being brought together were made with inclined surfaces. Preparatory to this being done the ends of the bar were thickened by beating them endways — technically known as "upsetting." Then they were "scarfed" or thinned down in a regular incline ; the object of this was twofold : one to in- crease the amount of the surfaces brought into contact, and by thus magnifying these surfaces to increase the strength of the joint — the other to bring the two faces into a good position and shape for being operated upon by the hammer of the workman. Another form of weld is that known as " a double-wedge weld " ; in this case each end of the bar is cut to an obtuse double bevel, so that when the ends are brought together and laid upon the anvil, there are two Y-shaped cavities, — one above the centre of the bar, and the other below it, — two separate wedge-shaped pieces are prepared to fill these cavities and the whole is brought to a welding heat. You can imagine that, if a bar thus prepared and fitted with the wedges is laid down on its edge, and is hammered upon its top edge, that these two separate wedge pieces will be forced into the cavities in the ends of the bar, and a weld will thus be made. But in the later days of the manufacture of tyres by welding, at any rate for passenger carriage wheels, the weld was made by what is called a *' butt " weld. In this case the ends of the bar were cut perfectly square, were put into the fire, having a screwed clamp placed round about the tyre, and, being heated to the welding heat, the pressure of the screw was exerted, and one end of the bar was forced against the 1890.] on Welding hy Electricity. 187 other, with the result that the surfaces were welded and that there was made a projection all round the weld (owing to the plastic con- dition of the metal), which projection was afterwards beaten down on the anvil. That is the kind of weld that you will see practised to-night electrically. I bring the matter forward now to show you that a butt weld is old in itself. Now the heating of these pieces of metal was done in a " smith's fire," and the smith's fire, as made in London with Newcastle coal, was really a work of art. The smith succeeded in building up a perfect " grotto " of small coal, and coal dust, beaten together and moistened. In this grotto the thing to be welded could be put. The object of that w^as as far as possible to obtain the heat, while prevent- ing the introduction of dirt between the surfaces to be united ; for one of the greatest difficulties in welding is that there is a danger of foreign matter being introduced between the surfaces, thus pre- venting a good union being effected. In this way the heating and welding were done in former times, and when proper care and skill were exercised the welds were extremely good. To my mind, there is no more interesting work than that of the smith. It is one of the few things left, in which skill of eye and hand, and the intuitive knowledge born of experience, are all that the man has to trust to, and in which the result of the work is in no wise due to dies and moulds, which have in some other departments of handicraft pretty well superseded the skill of the man. It has always been to me, and is still, a source of pleasure, to see a smith at work. I must qualify this remark about the use of dies a little, because there are those present who know that we do in these days, even in smiths' work, use dies which get rid to some extent of the necessity for his skilled labour. It is obvious that in all welds where the heat is obtained from the ordinary fire the metal must be heated from the outside. Under that condition you are sometimes subjected to the difficulty which at times occurs in the unskilful cooking of a joint of meat, the out- side being burnt, while the inside is raw. But this difficulty is, you will find, entirely obviated in the case of electric welding. Now, the desiderata in heating for welding are — uniformity of heating throughout the sectional area of the metal, regulation of the heat, freedom from the possibility of introduction of dirt, arising either from particles of fuel or from the presence of sulphur in the coal, or any matter of that sort ; and also, facility of inspection during heating. This last point is of great importance, because in the ordinary method of welding by heating in a forge, the work has to be frequently taken out to see how the heat is progressing, and in this taking it out, and in putting it back, the risk is run of doing that which you wish to avoid, i. e. introducing dirt between the surfaces. Probably the majority of the present audience are aware, that the heating eff3ct of an electric current depends upon the quantity of that current and not upon its pressure, or voltage, or, to use the 188 Sir Frederick Bramwell [Aj^ril 18, common term, its electromotive force. It also depends upon the electrical resistance of the material through which the current is passing. This resistance is very different in various substances, and varies even in the same substance under varying conditions, as I shall show you hereafter. You have all seen over and over again the experiment of heating a wire which seemed, before heating, to be the same from end to end, that is to say, all of one diameter and of one appearance ; but on passing an electric current through it you found that it was made up of two different materials ; for while it was white-hot in alternate sections, it was dull in the intermediate portions. Those parts which remained dull did so because they were made of a metal (probably of Silver) which allowed the electric current to pass without much opposition, as compared with the parts which glowed, these being probably of Platinum, this metal offering a greater resistance to the current, and thus generating greater heat. I have placed in the "jaws" or " holders" of the electric welding machine before you, a compound wire made of a length of copper, a length of iron, and a length of German silver, or, as a matter of fact, the German silver is between the other two, all being of equal diameter. On passing the electric current through, I trust you will find that the German silver becomes hotter than the iron, because the resistance of an equal sec- tional area of it is in round numbers double that of iron, and that the copper does not apparently become hot at all, because its resistance is only one-sixth that of the iron, or one-twelfth that of German silver ; in stating these proportions I am referring to ordinary atmo- spheric temperature, for when metals are heated an entirely new set of resistances come into play, these varying considerably with variations in their temperature. That upper arch is the German silver. It is, as you see, very hot ; the left-hand portion is less hot, and the right-hand part is apparently unheated. Those metals are, as I have said, iron, German silver, copper. I told you just now that the electrical resistance of metals and of other bodies alters with their temperature. This alteration is different with different metals ; but in the case of the metal with which I am concerned to-night — iron — the variation is very considerable. Many persons have studied this question of the changes of resistance due to the increase of temperature, and among them Dr. Hopkinson. He has kindly furnished me with the results of his experiments, and I exhibit them to you on this diagram in the form of a curve. From this we find that if the resistance of iron at 32^ Fahr. be taken as unity, at 1832^ Fahr. the resistance has gone up to over eleven times. You see the way in which it rises, and the peculiar kink there is in the curve at about 1400^ or 1500^, when the resist- ance is about ten times what it is at 32^. This fact of the lars^e increase of electrical resistance with the increase of temperature is a matter of the utmost importance in welding by electricity, as I hope to show you later on. 1890.] on Welding by Electricity. 189 I have said that the heating effect of an electric current depends upon the quantity of the current, and upon the drop or reduction in electrical pressure. We have four lamps here upon the table, and I think you will see when I turn on the current they are glowing uni- formly; not giving much light, however, for they are glowing very badly, but all of them uniformly bad, no one better than the other. Now I will ask you to remember that if we are introducing a given quantity of electric current here, at the first lamp, at a pressure of say 100 volts, and it is leaving the fourth lamp at zero, we are introducing the same quantity of electricity here at the second lamj) as at the first, but the pressure is only 75 volts, we have therefore dropped 25 volts between the two. We are also introducing the same quantity of current to the third lamp, but at 50 volts, we therefore drop another 25 volts. We are introducing it to the fourth lamp at 25, and using this pressure up in this lamp, we come down to zero. What we have done is this : wo have destroyed an equal amount of electrical energy in every lamp by these reductions, and have turned it into heat, making the lamps glow, and it is, as you will have seen, a matter of absolute indifier- ence as regards heating effect, whether we have done this by taking 25 out of 100 and leaving 75, or by taking 25 out of 25 leaviuo- zero. If we change the switch and throw one of the lamps out of circuit, we have now the same initial electrical pressure, i. e. 100 volts, but there are only three resistances instead of four, and we are consequently now dropping by 33 volts at each lamp. You observe the increase in brightness, but still the three lamps all glow alike. If we switch another lamp out we have only two lamps' re- sistance to overcome, and are dropping by 50 instead of by 33 volts. We therefore get a further increase of brightness'. We take the third lamp out, and may thus destroy the one remaining, for we now have the whole drop of 100 volts occurring at this one lamp, and you see the intense glow that results, although fortunately it has not oiven way. But the increases in the heating effect have not varied in the mere ratios of 25 to 33^, 25 to 50, or 25 to 100 ; but have varied as the squares of these ratios, and have done so for this very simple reason. Daring our experiment, we have always commenced with the same electrical pressure of 100 volts ; but when we used only three lamps in the circuit, instead of the fOur which I first showed you, the resistance was only that of the three lamps, i.e. three-fourths of the four, but the pressure being the same the current became four-third times that which it originally was when each of the four lamps was used. The drop in voltage was 33J- volts for each lamp, instead of 25, that is to say, this was also four-third times as much as before. The disappearance of electrical energy was therefore four-third times four-thirds = sixteen-ninths, or, in other words, each of the three lamps was heated to ly-th times the heat which was generated in each one of the four lamps. When we had only two lamps in the circuit, the resistance was one-half that which it was when we had 190 Sir Frederick Bramwell [April 18, the four, thus the current was doubled, the drop of pressure per lamp was also doubled, giving, therefore, the double of the double, or four times the heating effect ; while when we had only one lamp in the circuit the current and the drop were each four times as great as when the four lamps were in, so that in this case we had four times four, or sixteen times the heat generated. Here is another way of showing this effect. We have in this machine two hoops, side by side and shaped like small croquet hoops. They are made of similar iron wire, but one is double the length of the other. The electrical pressure being the same at the two ends of each of the two hoops, we shall have quantities of currents coming through which will be in proportion to the lengths of these hoops. That is to say, you will have half the current coming through the long one which comes through the short one. The short one there- fore ought to glow more brightly, because it will be hotter than the long one. Now I turn on the current and the short one begins to glow, but you cannot see any light at present from the long one. Now I can see a feeble light appearing in the long one, but probably those who are not so near as I am cannot do so yet. I am sorry that we have not sufficient horse-jDower in our engine here to enable us to do that which I did at the Institution of Civil Engineers — to go on with an increased current till the short one is fused. Now the long one is glowing fairly, and the short hoop is very bright indeed. There you see an instance where, the electric potential being the same at each end of two bars, but one being double the length of the other, and carrying therefore only half the amount of current, shows hardly any light at all, while the other has a con- siderable amount of luminosity. It is obvious that if we were using a perfect conductor of electricity we could have no electric heating whatever, because a perfect conductor would not destroy any of the electrical energy of the current passing through it, and, therefore, no heat would be produced. It is equally obvious that if we had sub- stances absolutely impermeable to electricity, so that no current could pass through it, we could not heat such a substance. "What we want, therefore, is something between the two. Fortunately for us, both iron and steel hold a very happy position in respect of their electrical conducting power, or to use the converse term which I have hitherto employed — their resistance. At the ordinary temperature of 60° Fahr. a piece of wrought iron, 1 foot long and 1 square inch in section, would need half a volt to drive 10,000 amperes through it, and in doing this 3700 foot-pounds of electrical energy would be destroyed in every second of time, equal, therefore, to the production of 4f units of heat in the conductor. If we had a similar length and area of German silver, as it is so much worse as a conductor, we should in the same time destroy rather more than double the foot- pounds of electrical energy, namely, 7700. Tliis is equivalent to the production of a little over ten units of heat in each second. A 1890.] on WekUncj hi/ Electricity. 191 similar length and area of silver would, however, destroy only some 615 foot-pounds of electrical energy in the same time, giving only two-thirds of a unit of heat. Iron (which is nearly as good a con- ductor as silver) is therefore, as you will see, happily placed between silver and copper on the one hand, and German silver on the other. It is extremely likely that at the temperature at which welding can be performed, the resistance of iron to the passage of an electric current is increased to very much more than eleven-fold that which it had at 32'^ Fahr., because, probably, the welding temperature is about 3000° Fahr., while, as we saw from Dr. Hopkinson's curve, at 1532^ Fahr., we get eleven times the resistance there is at freezing- point. But assume the electrical resistance to be increased only to eleven times that which the iron had when cold. What follows ? Why this: tl:at, a piece of iron 1 foot long, and having a section of 1 square inch, would, under these circumstances, destroy in a second of time 40,700 foot-j)ounds of electrical energy. But, as you see, the bar which is being heated, is much shorter, than a foot. It is only about 2 inches, and thus it only destroys about one-sixth of this, or about 6600 foot-pounds of electrical energy j)er second of time, equal to about nine units of heat, or a little more. But the specific heat of wrought iron being only -11379 — water, as you know, beiug unitv — these ten units would raise one pound weight of iron 90 deo-rees in each second. But the portion heated up is only about two-thirds of a pound, and it would be heated, therefore, 135° Fahr. each second • but, as I have told you, as the temperature increases, the resistance, and therefore the heating effect, increases In a lengthened trial with a machine dealing with pieces of good bar iron having a sectional area of about 1 square inch, the maximum heat developed per second of time was 18 units, and the welding heat was reached in 22 seconds. Now I shall have to refer, as an illustration of electrical phe- nomena, to a very old friend for this purpose, viz. water. Suppose it is a question of working a hydraulic lift, or anything of that kind. If you have 100 gallons of water, multiplied by 50 lbs. of pressure, you get 5000 gallon-pounds. If you multiply 50 gallons by 100 lbs. of pressure, you equally get 5000 gallon-pounds. Similarly, if you multiply 100 amperes of electrical current by 50 volts of j^ressure of electrical current, you get 5000 watts, which is the equivalent in this illustration of the gallon-pounds of the water ; and if you multiply 50 amperes by 100 volts, you equally get 5000 watts. From what I have told you as to the resistance of metals, it is clear that for welding purjjoses we want the electrical energy in the form of large quantity and of low pressure. So that if I have at my disposal a total energy of 5,000,000 watts, it may for some purposes suit me to have it in the form of 1000 amperes of quantity by 5000 volts of pressure, but for welding I should undoubtedly jDrefer to have it in the form of larger quantity and low 2^i't3ssure, say, 192 Sir Frederick Bramwell [April 18, 5,000,000 amperes of quantity by 1 volt of pressure ; but whatever the form may be, there are still 5,000,000 watts. Now let us take another illustration, a monetary one. Suppose I wish to send live pounds of money by post ; it would obviously be best that I should send it in the form of a 5/. note. It weighs less than five sovereigns, and takes up less room. Take this as an illus- tration of the greatest " pressure " and the least " quautity." Suppose, however, I want to give 100 Sunday school children each a shilling, I do not want either a 51. note, or even five sovereigns ; I want 100 shillings. I should have then a comparatively great weight, which it would not be so convenient to send by post, but which is, however, in a suitable form for my purpose of distribution to the children. This is my five pounds sterling in the form illustrating large quantity and low pressure. Similarly in the case of electricity. Depending upon the con- struction of the dynamo, and upon its velocity of revolution, you can produce your electricity either in the form of high voltage and of small quantity, or, if the construction is varied, of low voltage and of large quantity — either the 5/. note or the shillings. But if you produce it in the condition of large quantity and of low pressure, and you desire to transmit it to the smith for him to use it in welding machines, you will find that form of current to be very inconvenient, because it clearly involves the employment of conductors so amjDle in sectional area as to admit of all this large quantity being brought through them to the iron, to heat it up to the welding point, without the waste of electrical energy due to useless heating up of the con- ductors themselves. The conductors must therefore be very large, and of yevj excellent conducting material. Therefore it is desirable to produce the electricity in the 61. note form in the first instance, and convert it into the shilling form, or it may be even into the form of farthings, after it has been transported to the very machine in which it is to be used. Now how is this change to be made '? Who is to be our money changer? Who is to change the electricity of small quantity and of high pressure into that of large quantity and low pressure ? Some half century ago Euhmkortf invented the coil by which, as you have all seen, the low potential or j)ressure of a few cells of a battery, incapable of making an appreciable sjjark, is translated into small quantity and large voltage, capable of leapiug through considerable distances. We have before us here, at my right hand, a Ivuhmkorlf coil, which contains 70 yards of primary wire, weighing 6 lbs. The secondary coil is 8 miles in length, and weighs 1'2 lbs. The sec- tional areas of these two wires are as 100 to 1. We have a battery here of five cells. We will put it to work, in conjunction with the <;oil, in the first instance sin)ply to give us a spark. You will see now it has converted the low potential of the five cells into that which is capable of leaping across a space of 1| iuclies, and you can, with suitable arrangements, get results a great deal higher than 1890.] on Welding by Electricity. 193 that. You will see that there we have transformed our 100 shillings into a 5Z. note. We are now about to transport the 5Z. note across these wires [they might have been even finer], and we are putting this current into the secondary coil of another Ruhmkorff coil. We shall by this arrangement change the 6/. note into the 100 shillings again, and deliver them through that little incandescent lamp, which will glow, because we have lowered the pressure, and thereby increased the quantity sufficiently to enable us to get a current suitable for that purpose. This lamp, which is glowing, is, as you can see, on the 100 shilling circuit ; the other lamp, to which I should have previously called your attention, is on the bl, note circuit, and although the same number of watts are passing through, it is dull, and does not glow. Similarly, if we had put a fine wire from the secondary coil of the first Ruhmkorff to the secondary coil of the second Ruhmkorfi^, that fine wire would have remained absolutely cold. We have taken a piece of the same wire, and put it in position there ; as you will see when I turn on the current, I can melt it. That shows the different effect for heating purposes of a large or of a small quantity of current, and shows, too, that you can vary your electricity, so as to have it in whichever form you please. And now, I think, the time has come to describe and to show you the electrical welding machine itself in work. Unhapj)ily, we have not sufficient power at our command in this building to work the large machine. We can only work the second sized one. The drawings that I have here are drawings of the large machine; but if you will allow me, I will describe the machine from the machine itself. This is the machine, and in these two pairs of jaws are fixed the pieces to be welded together : in this case pieces of wire rope. The pieces of rope are grasped by the two jaws, which are made of gun- metal. They are in electrical communication with two conductors, and these two conductors are the terminals of a hollow copper core that passes through coils at the back of the machine, these coils being similar to those of a Ruhmkorff coil. Inside these we have a cylinder built up of a number of sheet-iron discs insulated one from another, and round about these there go 70 convolutions of wire, and therefore of the current from the dynamo. That is, the 5Z. note form of electricity passes from the dynamo through these 70 con- volutions of wire. But by the time the^ current has passed through, the , pressure has exhausted itself in producing the shilling state in the copper core and in the conductors connected with it. One of the jaws is movable, and can be forced forward by this screw arrange- ment; the other jaw is fixed, and forms the abutment. This other apparatus is one by which the strength of the current can be regu- lated as desired by the operator ; it consists of a number of lengths of wire, the regulation of the current being performed by the operator switching into or out of the circuit of wire (through which the 5/. note current flows to the machine), a greater or less number of these lengths, thus delivering to the welding machine a Vol. XIII. (No. 84.) o 194 Sir Frederick Bramwell [April 18, varying amount of electrical energy for it to convert into the welding current. I have already, when dealing with the weld itself, called your attention to the important part played by the increase in electrical resistance due to increase in temperature, but I now wish you to see how valuable this increase of resistance is when considered in relation to the question of obtaining uniformity of temperature over the whole of the surfaces to be united. These surfaces, when first brought into contact, are rough, and thus only a very small portion of them — that is to say, the extreme prominences — come together, and, as a consequence, the current which is i^assing is confined to these points. As these become heated, however, by the passage of the current, they soften ; the continued pressure applied by means of the screw flattens them, and thus enlarges tlie area of contact. But, as I have shown you, the hottest parts are the worst conductors, and thus the greater quantity of electricity passes through the less hot parts of the enlarged area of contact, raises their temperature, and the flattening of these by the continued pressure causes further surfaces to come together, till all are in contact ; while the current, still seeking out the coolest parts as offering less resistance to its passage, raises their temperature until a uniform heat and a uniform resistance are established, and then this heating goes on still increasing as the current is continued, in consequence of the increased electrical resistance due to the increased temperature. I think you will agree with me that this increase of electrical resistance, which follows from the rise of temperature, is most valuable in enabling the necessary welding heat to be produced by the passage of an electric current. You will observe presently, when we work the machine, that the careful operator, in order to avoid burning the small surface of the prominences which first come into contact, takes great care to apply the current very gently. I will now ask to have a piece of cast steel welded to another piece of cast steel. I should explain that the machine has been put on to a turn-table, with the object of moving it round to face different parts of the room, so as to afford a better view to the audience. I do not know how many of you are aware of the difficulty of welding cast steel as compared with the welding of iron. This difficulty depends largely on the amount of carbon in the steel. An extremely mild steel, such as is used for gun making, is easily weldable, contain- ing as it does only a very low percentage of carbon ; while tool steel, containing over one per cent, of carbon, presents great welding difficulties. We have here two pieces of tool steel, which it would be almost impossible to weld in the ordinary manner. The humming noise which you hear when the current is turned on to the machine is produced by our coil (our money changer) at work. I may tell you that I shall have to talk about a number of welds 1890.] on Welding hy Electricity. 195 made at Fanshawe Street by two electricians, who, not being smiths, of course worked at a disadvantage ; but the competent smith who is now before you was then taken to the machine, and at the fourth attempt he made a satisfactory weld, and has been working the machine ever since. You see that the two pieces of steel have been welded together, and then bent at an acute angle, thus showing roughly the satisfactory nature of the weld. As time is running short, I will ask the smith next to show you the welding of a tube. These are two pieces of ordinary steel tube which will now be welded in the machine. I do not know whether I can manage to direct this machine so as to be seen by every individual in the room ; but I hope that I shall succeed in enabling most of you to see completely through the tube when it has been welded, and thus to show you that the internal circularity of the tube has in no way suffered by the welding. Though I believe that the function of this machine will not be the performance of ordinary work, but that it will be applied to welding difficult sections or difficult metals, I thought it well to have it tested, by making 80 welds in l^th inch round iron bars. These were made, as I have said, by two electricians, not smiths, and they took an average of 2j minutes to make each weld, equal to 135 seconds, and the time was roughly divided thus : — Fixing the iron and heating up to full heat at one operation, 26 seconds ; full heat to taking out of jaws, 11 seconds ; work on anvil, 15 seconds ; re-putting in to full hot, 21 seconds ; full hot to taking out again, 10 seconds ; retaking out to completion, 32 seconds ; completion and putting in next piece, 20 seconds ; making a total, as I have said, of 135 seconds. Then two smiths were put to make welds in the ordinary manner, that is to say, scarf welds in an ordinary smith's fire. They made 44 welds in three hours and a little over, or practically the same time as was taken in making the 80 welds (nearly twice the number) in the machine. Then all the welds were sent to a well-known tester of metals, Mr. Kirkaldy, and he tested about one-half of them, with the following results, which I think it important you should hear : — Kestjlts of Mr. Kiekaldy's Tests. Per Square Inch of Original Sectional Area. Average strength of the bars before wekling . . . . 52 , 642 lbs. Average strength of those which broke at the weld when welded electrically 48,215 „ Average strength of those which broke at the weld when the welds were made by hand .. .. .. 46,899 „ From these tests we thus have a right to say that this electrical butt welding gives at least an equal tensile strength with the scarf welding done by hand. It is probable, as I have said, that the great value of this inven- tion will not be for common work, but for difficult sections and for refractory metals. I have shown you the butt welding of wire rope o 2 196 Sir Frederick Bramivell on Welding hy Electricity, [April 18, and could show you work done on T-iron and on various other forms of metal. But there is not time to do so, and I, of all men, should not offend by exceeding the allotted hour, for if I did I could not as Secretary, call others to account. The most difficult metals can be dealt with in this machine. You will remember Dr. Percy tells us that the great difficulty in welding most metals is to find out the critical point of temperature and to maintain it. I wish now to prove to you that the current is under absolute control in the machine, and the object to be welded being under continuous observation during the operation, one is enabled to deal with any one of the refractory metals in the required way, and so to get a union, by bringing the surfaces into the necessary pasty condition of temperature and at the right moment to operate upon them. We have here a much smaller welder, which is automatic in its action. It is intended for welding together pieces of wire, &c. By the time the two portions are sufficiently heated and are pressed together, the machine is automatically thrown out of gear, and the operation is completed. Two pieces of copper wire are in now, and, it you observe the machine you will see that when the work is done, it of itself, stops the current. There is the welded wire, and I think you will admit that the work is good ; for you see I cannot by bending it backwards and forwards break it at the weld. Now we will try a piece of aluminium. That is commonly supposed to be a very difficult metal to unite, but this machine will do it easily. Here it is, welded, and you see that it is perfectly competent to be bent without breaking at the weld. And now a piece of German silver, this being the metal which, you will remember, gave such a high resistance when we used it before. I regret that time does not admit of my showing you other different kinds of work done in the machines, and that I must bring my remarks to a conclusion by saying: — I think it is obvious that a machine which gives us this power of heating any metal, with absolute control over the heat, and that affords such thorough facility for inspecting the work during the heating, must have many uses in the Arts. Indeed, there can be no doubt that the existence of such a machine will of itself give rise to a large number of new uses. [F. B.] 1890.] General Monthly Meeting. 197 GENERAL MONTHLY MEETING. Monday, July 7, 1890. Sir James Crichton Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Tliomas To wu send Bnckuill, Esc]^. Q.C. Edward A. Harvey, Esq. Malcolm Morris, Esq. F.R.C.S. William Thomas Eabbits, Esq. F.L.S. were elected Members of the Royal Institution. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz : — FROM The Governor-General of India — Geological Survey of India : Kecords, Vol. XXIII. Part 2. 4to. 1890. Accademia dei Lincei, Reale, Roma — Atti, Serie Quarta : Rendiconti. 1° Semes- tre, Vol. VI. Fasc. 7. 8vo. 1890. Academy of Natural Sciences. Philadelphia — Proceedina^s, 1890, Part 3. 8vo. American Philosophical Society — Transactions, Vol. XVI. Part 3. 4to. 1890. Astronomical Society, Royal — Monthly Notices, Vol. L. No. 7. 8vo. 1890. Bankers, Institute of — Journal, Vol. XI. Part 6. 8vo. 1890. Bischofsheim, M. R. L. — Annales de I'Observatoire de Nice. Tome III. Text and Atlas. 4to and fol. 1890. British Architects, Royal Institute of — Proceedings, 1889-90, Nos. 16, 17. 4to. Chemical Society — Journal for June, 1890. 8vo. Civil Engineers' Institution — Proceedings, Vol. C. 8vo. 1890. Cornwall Polytechnic Society, Royal — Annual Koport for 1889. 8vo. 1890. Cracovie, V Academic des Sciences — Bulletin, 1890, No. 5. 8vo. Crisp, Frank, Esq. LL.B. F.L.S. &c. M.R.I. — Journal of the Royal Microscopical Society, 189U, Part 3. 8vo. East India Association — Journal, Vol. XXII. No. 2. 8vo. 1889. Editors — American Journal of Science for June, 1890. 8vo. Analyst for June, 1890. 8vo. Athenaeum for June, 1890. 4to. Brewers' Journal for June, 1890. 4to. Chemical News for June, 1890. 4to. Chemist and Druggist for June, 1890. 8vo. Electrical Engineer for June, 1890. fol. Engineer for June, 1890. fol. Engineering for June, 1890. fol. Horological Journal for June, 1890. 8vo. Industries for June, 1890. fol. Iron for June, 1890. 4to. Ironmongery for June, 1890. 4to. Murray's Magazine for June, 1890. 8vo. Nature for June, 1890. 4to. Photographic News for June, 1890. 8vo. Kevue Scientilique for June, 1890. 4to. Telegraphic Journal for June, 1890. fol. Zoophilist for June, 1890. 4to. 198 General Monthly Meeting. [July 7, Electrical Engineers, Institution of — Journal, No. 87. 8vo. 1890. Florence Bihlioteca Nazionale Ceutrale — BoUetino, Nos. 107, 108. 8vo. 1890. Franklin Institute — Journal, No. 774. 8vo. 1890. Geographical Society^ Eoijal — Proceedings, New Series, Vol. XII. Nos. 6, 7. 8vo. 1890. Geological Institute, Imperial, Vienna — Abhandlungen, Band XV. Heft 2. fol. 1890. Johns Hopkins University — University Circulars, No. 81. 4to. 1890. American Chemical Journal, Vol. XI, No. 7. 8vo. 1889. American Journal of Philology, Vol. X. Nos. 2, 3. 8vo. 1889. Studies in Historical and Political Science, 7th Series, Nos. 21, 22. 8vo. 1889. Annual Report. 8vo. 1889. Laboratory CZw&— Transactions, Vol. III. No. 6. 8vo. 1890. Linnean Society — Proceedings, May, 1890. 8vo. Manchester Geological Society — Transactions, Vol. XX. Parts 18, 19. 8vo. 1890. Mechanical Engineers' Institution — Proceedings, 1890, No. 1. 8vo. Meteorological Office— Weekly Weather Reports, Nos. 22-26. 4to. 1890. Ministry of Public Works, i?o»ie— Giornale del Genio Civile, Seria Q.uinta, Vol. IV. Nos. 2, 3. And Disegni. fol. 1890. New York Academy of Sciences — Transactions, Vol. IX. Parts, 1, 2. 8vo. 1890. Annals, Vol. XV. Nos. 1, 2, 3. 8vo. 1889. Noricegian North Atlantic Expedition, Editorial Committee — Danielssen, D.C. Actinida, Part 19. fol. 1890. Odontological Society of Great Britain — Transactions, Vol. XXII. No. 7. New Series. 8vo. 1890. Pennsylvania Geological Survey — Atlases, A.A. Parts 2-4. 8vo. 1889. Pharmaceutical Society of Great Britain — Journal, June, 1890. 8vo. Popof, Constantine, Esq. (the Translator) — Boyhood, Adolescence, and Youth. By L. Tolstoi. 8vo. 1890. Rathbone, E. P. Esq. (the Editor) — The Witwatersrand Mining and Metallurgical Review, No. 5. 8vo. 1890. Bichardson, B. W. (the Author)— The Asclepiad, No. 26. 8vo. 1890. Bio de Janeiro Observatory — Revista, No. 5. 8vo. 1890. Boyal Society of London — Proceedings, Nos. 289, 290. Svo. 1890, Selborne Society— Mature Notes, A^ol. I. No. 6. 8vo. 1890, Smithsonian Institution — Contributions to Knowledge, Vol. XXVI. fol. 1890. Society of Architects — Proceedings, Vol. II. No. 11. 8vo. 1890. Society of Arts — Journal for June, 1890. 8vo. St. Petersbourg Acade'mie Imp^riales des Sciences — Me'moires, Tome XXXVII. Nos. 6, 7. 4to. 1890. Vereins zur Beforderung des Gewerbfleises in Preussen — Verhandluugen, 1890 : Heft 6. 4to. Victoria Institute — Transactions, No. 93. 8vo. 1890. Wisconsin Academy of Sciences, dc. — Transactions, Vol. VII. 1883-7. 8vo. 1889. Zoological Society of London — Proceedings, 1890, Part I. 8vo. 1890.] General MontJily Meeting. 199 GENERAL MONTHLY MEETING, Monday, November 3, 1890. Sir Jambs Crichton Browne, M.D. LL.D. F.B.S. Treasurer and Vice-President in the Cliair. J. Viriamu Jones, Esq. M.A. C. N. Nicholson, Esq. M.A. John Hartley Perks, Esq. J.P. The Hon. Sir James Stirling (Justice of the Supreme Court), were elected Members of the Royal Institution. The Special Thanks of the Members were returned to Dr. J. A Fleming, M.B.I, for the presentation on behalf of Professor Elihu Thomson of the apparatus employed by Professor Thomson in his experiments on Electro-magnetic Repulsion ; and to Hervey Pechell, Esq. M.B.I. for his present of an old engraving (1809) of the Library of the Royal Institution. The Managers reported, That at their Meeting held this day they had elected Victor Horsley, Esq. F.R.S. M.B.I. FuUerian Professor of Physiology for three years (the appointment dating from January 12, 1891). The Managers further reported, That the Royal Institution was now connected with the National Telephone Company's Exchange System, No. 3669. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FROM The Governor-General of India — Geological Survey of India; Records, Vol. XXIII. Part 3. 4to. 1890. Memoirs, Vol. XXIV. Part 2. 4to. 1890. Madras GovernmentSouth Indian Inscriptions. By E. Hultzsch. Vol. I. fol. 1890. Academy of Natural Sciences, Philadelphia — Proceedings, 1890, Part 1. 8vo. Accademia dei Lincei, Reale, Roma — Atti, Serie Quarta : Eendicouti. 1" Semes- tre, Vol. VI. Fasc. 8-11, 8yo. 1890. Atti, Anno 42, Sess. 4-7. 4to. 1889. Memorie, Vol. V. 4to. 1888. Agricultural Society of England, Royal — Journal, 3rd Series, Vol. I. Parts 2, 3. 8vo. 1890. General Index, Vol. I.-XXV. 8vo. 1890. American Academy of Arts and Sciences — Proceedings, Vol. XXIV. 8vo. 1889. American Association for the Advancement of Science — Proceedings, 38th Meeting held at Toronto, 1889. 8vo. 1890. American Philosophical Society — Proceedings, Nos. 131-133. 8vo. 1890. Antiquaries, Society of — Proceedings, Vol. XIII. No, 1. 8vo. 1890. Index to Archaeologia, Vols. I.-L. fol. 1889. 200 General 3Tont1ily Meeting. [Nov. 3, Aristotelian Society — Proceedings, Vol. I. No. 3, Part 2. 8vo. 1890, Asiatic Society of Bengal — Journal, Vol. LVII. Part 2, No. 5 ; Vol. LVIII. Part 1, Supplement; Vol. LIX. Part 1, Nos. 1, 2; Part 2, Nos. 1, 2. Svo. 1890. Proceedings, 1890, Parts 1-3. 8vo. Astronomical Societi/, Royal — Monthly Notices, Vol. L. No. 8. 8vo. 1890. Memoirs, Vol. XLIX. Part 2. 4to. 1890. Bankers, Institute of — Journal, Vol. XI. Parts 7, 8. Svo. 1890. Barnard, Frank, Esq. {the Author') — Picturesque Life in Shetland, fol. 1890. Bavarian Academy of Sciences — Abhandlungen, Band XVII. Abth. 1. 4to. 1890. SitzuniTsberichte, 1890, Heft 1-3. Svo. Bell and Sons, Messrs. G. (the Publishers) — School Calendar, 1890. 12mo. Bischoffsheim, M. B. L. — Annales de I'Observatoire de Nice. Tome II. 4to. 1887. British Architects, Royal Institute of — Proceedings, 1889-90, Nos. 18-20; 1890-1, No. 1. 4to. British Museum— Catalogue of Oriental Coins, Vol. IX. (1876-88). Svo. 1889. Catalogue of the Cuneiform Tablets. By C. Bezold. Vol. I. Svo. 1889. British Museum (Natural History) — Catalogue of Birds, Vols. XIII. XV. XVIII. Svo. 1890. Catalogue of Fossil Reptilia and Amphibia, Part 4. Svo. 1890. Guide to Galleries of Geology and Palaeontology, Parts 1 and 2. Svo. 1890. Buclcton, G. B. F.R.S. M.R.I, (the Author) — Monograph of the British Cicadas or Tettigid?e, Parts 3, 4. Svo. 1890. California, University of — Publications, 1888-90. Svo. Cambridge University Press, Syndics of — Scientific Papers of James Clerk Maxwell. Edited by W. D. Niven. 2 vols. fol. 1890. Canadian Institute— Fvoceedinga, 3rd Series, Vol. VII. Fas. 2. Svo. 1890. Chemical Industry, Society of — Journal, Vol. IX. Nos. 6-9. Svo. 1890. Chemical Society — Journal for July to October, 1890. Svo. Chief Signal Officer, U.S. Army — Annual Report for 1889. Svo. 1890. Civil Engineers' Institution — Proceedings, Vol. CI. CII. Svo. 1890. City of London College— CaleTidar, 1890-91. Svo. 1890. Clinical Society — Transactions, Vol. XXIII. Svo. 1890. Colonial Institute, Royal — Proceedings, Vol. XXI. Svo. 1890. Cracovie, V Academic des Sciences — Bulletin, 1890, Nos. 6, 7. 8vo. Crisp, Frank, Esq. I.L.B. F.L.S. &c. 31. R.I. — Journal of the Royal Microscopcial Society, 1890, Parts 4, 5. Svo. Devonshire Association for Advancement of Science, Literature, and Art — Report and Transactions, Vol. XXII. Svo. 1890. Devonshire Domesday, Part VII. Svo. 1890. East India- Association — Journal, Vol. XXII. Nos. 3, 4, 5. Svo. 1889. Editors — American Journal of Science for July-October, 1890. Svo, Analyst for July-October, 1890. Svo. Athenaeum for July-October, 1890. 4to. Brewers' Journal for July-October, 1890. 4to. Chemical News for July-October, 1890. 4to. Chemist and Druggist for July-October, 1890. Svo. Electrical Engiiu er for July-October, 1890. fol. Engineer for July-October, 1890. fol. Engineering for July-October, 1890. f<>l. Horological Journal for July-October, 1890. Svo. Industries for July-October, 1890. fol. Iron for July-October, 1890. 4to. Ironmongery for July-October, 1890. 4to. Murray's Magazine for July-October, 1890. Svo. Nature for July-October, 1890. 4to. Open Court for July-October, 1890. 4to. Photographic News for July-October, 1890. Svo. Public Health for July-October, 1890. Svo. Revue Scientilique for July-October, 1890. 4t(>. 1890.] General Monthly Meeting. 201 Editors — cont. — Telegraphic Journal for July-October, 1890. fol. Zoophilist for July-October, 1890. 4to. Edmunds, Lewis, Esq. D.Sc. F.C.S. M.R.I. (the Author) — Law and Practice of Letters Patent tor Inventions. 8vo. 1890. Electrical Engineers, Institution of — Journal, No. 89. 8vo. 1890. Engineering, The Editor of — Metalluriry of Silver, Gold, &c. in United States. By T. Egleston. Vol. II. 4to. 1890. Fleming, J. A. Esq. M.I.E.E. M.R.I, {the Author) —Electrical Papers. 8 vo. 1874-89. Alternate Current Transformer, Vol. I. 8vo. 1889. Florence Bihlioteca Nazionale Centrale — Bnlletino, Nos. 109-116. 8vo. 1890. FranMin Institute — Journal, Nos. 775-778. 8vo. 1890. Geographical Society, Royal — Proceedings, New Series, Vol. XII. Nos. 8-10. 8vo. 1890. Supplementary Papers, Vol. III. Part 1. 8vo. 1890. Geological Institute, Imperial, Vienna — Verhandlungen, 1890, Nos. 6-9. 8vo. Geological Society — Quarterly Journal, No. 183. 8vo. 1890. Goppelsroeder, Dr. F. {the Author) — Ueber Feuerbestattung. 8vo. 1890. Harlem, Socie'te Hollandaise des Sciences — Archives Neerlandaises, Tome XXIV. Liv. 2, 3. 8vo. 1890. Horticultural Society, Royal — Journal, Vol. XII. No. 2. 8vo. 1890. lotva Laboratories of Natural History — Bulletin, Vol. I. Nos. 3 and 4. 8vo. 1890. Iron and Steel Institute — Journal for 1890, Vol. I. 8vo. Johns Hopkins University — University Circulars, No. 82. 4to. 1890. American Chemical Journal, Vol. XI. No. 8; Vol. XII. Nos. 1-5; General Index, Vols. I.-X. 8vo. 1889-90. American Journal of Philology, Vol. X. No. 4 ; Vol. XI. No. 1. 8vo. 1889-90. Studies in Historical and Political Science, 8th Series, Nos. 1-4. 8vo. 1890. Kerslake, Thomas, Esq. {the Author) — Richard, the King of Englishmen. 8vo. 1890. Laboratory Club — Transactions, Vol. III. No. 7. 8vo. 1890. Langley, S. P. and F. W. Very — On tlie Cheapest Form of Light. 8vo. 1890. Linnean Society— J omnal, Nos. 124, 125, 145, 146, 175, 183, 184. 8vo. 1890. Lisbon Academy of Sciences — Historia do Infante D. Duarte. Por J. Eamos Coelho. TomoII. 8vo. 1890. Madras Government Central Museum — Report, 1889-90. . fol. 1890. Maiden, J. H. Esq. F.L.S. F.C.S. {the ^wf/ior)— Wattles and Wattle Barks. 8vo. isyo. Manchester Literary and Philosophical Society — Memoirs and Proceedings, Vol. III. N.S. 8vo. 1890. Manchester Steam Users' Association — Report on Red-hot Furnace Crown Ex- periments. 8vo. 1889. Manila Universidad de Sto. Tomds — Discurso, Por F. J. M. Ruiz. 4to. 1890. Mechanical Engineers' Institution — Proceedings, 1890, No. 2. 8vo. Mensbrugghe, M. G. Van der (the Author) — La Surface Commune a deux Liqiiides, 1^ and 2° Partie. 8vo. 1890. Meteorological Office — Weekly Weather Reports, Nos. 27-43. 4to. 1890. Quarterly Weather Report, No. 50. fol. 1890. Variability of Temperature of Britisli Isles, 1869-1883. By R. H. Scott. (Proceed. R.S.) 8vo. 1890. Meteorological Society, Royal — Quarterly Journal, No. 75. 8vo. 1890. Meteorological Record, Nos. 36, 37. 8vo. 1890. Minister of Finance, Halifax — Dictionary of Laniruages of Micmac Indians. By Rev. S. Rand. 4to. 1888. Ministry of Public Works, Rome — Giornale del Genio Civile, Seria Quinta, VoL IV. Nos. 4, 5, 6. And Designi. fol. 1890. Mitchell, C. Pitfield, Esq. M.R.I, {the Author)— The Philosophy of Tumour Disease. 8vo. 1890. Musical Association — Proceedings, 16th Session, 1889-90. 8vo. 1890. Odontological Society of Great Britain— Tvaiis-Aciions, Vol. XXII. No. 8. New Series. 8vo. 1890. 202 General Monthly fleeting. [Nov. 3, New South Wales Agent-General — History of Progress of New South Wales. By T. Coghlan. 8vo. 1889. North of England Institute of 3Tining and Mechanical Engineers — Report of Use of Explosives in Mines, Part 1. 8vo. 1890. Norwegischen Commission der Europdischen Gradmessung — Geodatische Arbeiten, Heft 6 and 7. 4to. 1888-90. Pharmaceutical Society of Great Britain — Journal, July-October, 1890. 8vo. Photographic Society— J omnal. Vol. XIV. No. 9; Vol.'XV. No. 1. 8vo. 1890. Preussische Akademie der Wissenschaften — Sitzungsberiehte, Nos. I.-XIX. 8vo. 1890. Bathhone, E. P. Esq. (the Editor) — The Witwatersrand Mining and Metallurgical Review, Nos. 6-9. 8vo. 1890. Eichardson, B. W. {the Author)— T\\e Asclepiad, No. 27. 8vo. 1890. Rio de Janeiro, Ohservatoire Imperial de — Annales, Tome IV. Parts 1, 2. fol. 1889. Anuuario, Tomes V. and VI. 12mo. 1889-90. Revista, Nos. 6, 7, 8. 8vo. 1890. Royal College of Surgeons in England — Calendar, 1890. 8vo. Royal Dublin /S'octef^— Proceedings, Vol. VII. Parts 7-9. 8vo. 1890. Royal Institution of Cormcall — Journal, Vol. X. No. 1. 8vo. 1890. Royal Societi/ of Antiquaries of Ireland — Journal, Vol. I. (5th Series), No. 2. 8vo. 1890. Royal Society of Canada — Proceedings and Transactions, Vol. VII. 4to. 1889-90. Royal Society of Edinburgh — Transactions, Vol. XXIII. Part 3; Vol. XXV. 4to. 1888-90. Roijal Society of London — Proceedings, Nos. 291-294. 8vo. 1890. Saxon Society of Sciences, Eoijal — Mathematisch-physische Classe : Abhandlung. Band XVL Nos. 1, 2. 8vo. 1890. Berichte, 1890, No. 1. 8vo. 1890. Philologisch-bistorischen Classe : Abhandlung. Band XI. No. 7. 8vo. 1890. Seismological Society of Japan — Transactions, Vol. XIII. Part 2. 8vo. 1890. Selborne Society— ^atme Notes, Vol. I. Nos. 7-10. 8vo. 1890. Smithsonian Institution — Annual Report, 1886, Part 2 ; 1887, Parts 1, 2. 8vo. 1889. Society of Arts — Journal for July-October, 1890. 8vo. Statistical Society— J onvnal. Vol. LIII. Parts 2, 3. 8vo. 1890. St. Petersbourg Academic Imp&iales des Sciences — Me'moii-es, Tome XXXVII. Nos. 8-10. 4to. 1890. Tasmania Royal Society — Proceedings for 1889. 8vo. 1890. United Service Institution, Royal — Journal, No. 153. 8vo. 1890. United States Geological Survey — Eighth Annual Report, 1886-7. 4to. 1890. Monographs, Vol. XV. XVI. 4to. 1889. Bulletins, Nos. 54-57. 8vo. 1889-90. United States Navy — General Information Series, No. 9. 8vo. 1890. Upscd Royal Society of Sciences — Nova Acta, Series 3, Vol. XIV. Fas. 1. 4to. 1890. Catalogue Methodique, 1744-1889. 4to. 1890. Upsal University — Bulletin de L'Observatoire Mete'orologique, Vol. XXI. 4to. 1889-90. Uruguay Consulate General — Catalogues, Reports, &c. of International Exhibition of Mining and Metallurgy, 1890, Parts 1 and 2. 8vo. Verei7is zur Beforderung des Geicerbfleises in Preussen — Verhandlungen, 1890 : Heft 7, 8. 4to. Victoria Institute — Transactions, No. 94. 8vo. 1890. Wagner Free Institute of Sciences — Transactions, Vol. III. 4to. 1890. Wild, Dr. H. — Aunalen der Piiysikalischen Central — Observatoriums, 1889, Theil I. 4to. 1890. Zoological Society of London — Proceedings, 1890, Parts 2, 3. Svo. 1890.] General Monthhj Meeting. 203 GENEEAL MONTHLY MEETING, Monday, December 1, 1890. Sir James Crtciiton Browne, M.D. LL.D. F.E.S. Treasurer and Vice-President, in the Chair. Charles Arthur Aikin, Esq. F.R.C.S. Louis Brennan, Esq. A. M. Dunlop, Esq. Henry Gourlay, Esq. John Eose Innes, Esq. B.Sc. B.A. Maurice Marcus, Esq. Charles Gibson Millar, Esq. George Danford P. Thomas, M.D. M.E.C.S. were elected Members of the Eoyal Institution. The following Lecture Arrangements were announced : — Pkofessor Victor Hoesley, F.R.S. B.S. F.K.C.S. M.E.L Fullerian Professor of Physiology, K.I. Nine Lectures on The Structure and Functions of the Nervous System: Part I. The Spinal Cord, and GangUa. On Tuesdays, Jan. 20, 27, Feb. 3, 10, 17, 24, March 3, 10, 17. Hall Caine, Esq. Three Lectures on The Little Manx Nation. On Thursdays, Jan. 22, 29, Feb. 5. Professor C. Hubert H. Parry, Mus. Doc. M.A. Professor of Musical History and Composition at the Royal College of Music, Three Lectures on The Position of Lulli, Purcell, and Scarlatti in the History op the Opera (with Musical Illustrations). On Thursdays, Feb. 12, 19, 26. Professor C. Meymott Tidy, M.B. F.C.S. M.B.I. Professor of Chemistry and of Forensic Medicine at the London Hospital, Three Lectures on Modern Chemistry in relation to Sanitation. On Thursdays, March 5, 12, 19. W. Martin Conway, Esq. M.A. F.S.A, Three Lectures on Pre-Greek Schools of Art. On Saturdays, Jan. 24, 31, Feb. 7. The Right Hon. Lord Rayleigh^ M.A. D.C.L. LL.D. F.R.S. M.B.I. Professor of Natural Philosophy, R. I. Six Lectures on the Forces of Cohesion. On Saturdays, Feb. 14, 21, 28, March 7, 14, 21. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FROM Accademia dei Lincei, Beale. Boma — Atti, Serie Quarta : Rendiconti. 2° Semes- tre, Vol. VI. Fasc. 5. 8vo. 1890. Astronomical Society, Boyal — Monthly Notices, Vol. L. No. 9 and Appendix. Svo. 1890. Bankers, Institute o/— Journal, Vol. XI. Part 9. Svo. 1890. 204 General Monthly Meeting. [Dec. 1, Birmingham Philosophical Society — Proceedings, Vol. VII. Part 1. 8vo. 1889-90. British Architects, Royal Institute of — Proceedings, 1890-1, Nos. 2, 3. 4to. Calendar, 1890-1. 8vo. Cambridge Philosophical Society — Proceedings. Vol. VII. Part 2. Svo. 1890. Chemical Industry, Society of — Journal, Vol. IX. No. 10. 8vo. 1890. Chemical Society — Journal for November, 1890. 8vo. Cracovie V Academic des Sciences — Bulletin, 1890, No. 8. Svo. Dax : Societe de Borda — Bulletin, quinzieme annee. l"" Treniestrc. Svo, 1890. Editors — American Journal of Science for November, 1890. Svo. Analyst for November, 1890. Svo, Atlienseum for November, 1890. 4to. Brewers' Journal for November, 1890. 4 to. Chemical News for November, 1890. 4to. Chemist and Druggist for November, 1890. Svo. Electrical Engineer for November, 1890. fol. Engineer for November, 1890. fol. Engineering for November, 1890. fol. Horological Journal for November, 1890. Svo. Industries for November, 1890. fol. Iron for November, 1890. 4to, Ironmongery for November, 1890. 4to. Murray's Magazine for November, 1S90. Svo. Nature for November, 18^0. 4to. Open Court for November, 1890. 4to. Photographic News for November, 1890. Svo. Public Health for November, 1890. Svo. Eevue Scientifique for November, 1890. 4to. Telegraphic Journal for November, 1890. fol. Zoophilist for November, 1890. 4to. Fleming, J. A. Esq. 3lA. D.Sc. M.I.E.E. M.E.L (the Author)— On Piof. E. Thomson's Electro-Magnetic Induction Experiments. Svo. 1890. Franhlin Institute — Journal, No. 779. Svo. 1890, Geographical Society, Royal — Proceedings, New Series, Vol. XII. No. 11. Svo. 1890. Geological Society — Quarterly Jom-nal, No. 184. Svo. 1890. Georgofili, Reale Accademia — Atti, Vol. XIII. Disp. 2*. Svo. 1890. Glasgow Philosophical Society — Proceedings, Vol. XXI. Svo. 1889-90. Houghton, George W. W., Esq., {the Author) — The Coaches of Colonial New York. 1890. Johns Eophins University — University Circulars, No. 83. 4to. 1890. Lewins, R. M.D. — Induction and Deduction, by C. C. W. Naden. Svo. 1890. Linnean Society— J ourn^h Nos. 185, 186, 189, 191. Svo. 1890. Maryland Medical and Chirurgical Faculty — Transactions, 92nd Session. Svo. 1890. Meteorological Office — Weekly Weather Keports, Nos. 44, 45. 4to. 1890. Meteorological Society, Royal — Quarterly Journal, No. 76. Svo. 1890. Ministry of Public WorJis, Rome — Giornale del Genio Civile, Seria Quinta, Vol. IV, Nos. 7, 8. And Designi. fol. 1890. New South Wales, Agent General — Official Eecord of the Australian Federation Conference, 1890. Svo. 1890. Wealth and Progress of New South Wales. 1888-9. ByJ. Coghlan. Svo. 1889. North of England Institute of Mining and Mechanical Engineers — Report on Use of 'Explosives in Mines, Part 2. Svo. 1890. Odontological Society of Great Britain — Transactions, Vol. XXIII. No. 1. New Series. Svo. iS90. Pharmaceutical Society of Great Britain — Journal, November, 1890. Svo. Physical Society of London — Proceedings, Vol. X. Part 4. Svo. 1890. Preussische Akademie der Wissenschaften — Sitzungsberichtc, Nos. XX.-XL. Svo. 1890. 1890.] General Monthly Meeting. 205 Bichardson, B. W. M.D. F.B.S. M.B.L {the Autlior)— The Asclepiad, No. 28. 8vo. 1890. Bio de Janeiro, Ohservatoire Imperial de — Revista, No. 9. 8vo. 1890. Sanitary Institute — Transactions, Vol. X. 8vo. 1890. Selborne Societij—1^ ature Notes, Vol. I. No. 11. 8vo. 1890. Socide' Archeologique du midi de la France — Bulletin. Serie in Svo, No. 4. 1889. Memoires. 2« Serie. Toine XIV. 1886 a 1889. Society of Architects — Proceed in,2:s, Vol. III. No. 1. Svo. 1890. Society of Arts — Journal for November, 1890. 8vo. Stopes, H. Esq. F.G.S. F.E.H.S. &c. — Indication of Retrogression in Pre- historic Civilization. 4to. 1890. United Service Institution, Bo7/al — Journal, No. 154. 8vo. 1890. Veneto, L'Jfewfio— Rivista, Sme XIII. Fasc. 4-6; Serie XIV. Fmsc. 1-6. 4to. 1889-90. 206 Professor Silvanus P. Thompson [June 13, WEEKLY EVENING MEETING, Friday, June 13, 1890. Sir James Crichton Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in tlie Chair. Professor Silvanus P. Thompson, D.Sc. MM.L The Physical Foundation of Music. Something in the constitution of the human mind impels us to search, to examine, to analyse. Even music^ — the art which appeals above all to the emotions — cannot remain exempt. We receive the impression on our senses, and forthwith are impelled to the enquiry : Why does this move us ? How can the mere movement or tremor of the air enter thus into our senses ? The instinct to analyse will not let us alone until we have found some sort of an explanation — a mental resting-place — enabling us to account to ourselves for the things that would otherwise seem an inscrutable mystery. Now, in music, there are three main questions for which in this way an answer has been sought : — (1) Why is it that the ear is pleased by a succession of sounds belonging to a certain particular set called a scale ? (2) Why is it that when two (or more) musical sounds are simultaneously sounded, the ear finds some combinations agreeable and others disagreeable ? (3) Why is it that a note sounded on a musical instrument of one sort is different from, and is distinguishable from, the same note sounded with equal loudness upon an instrument of another sort ? In brief, we desire to know the origin of melody, the cause of harmony, and the nature of timbre. The theories which have been framed to account for each of these three features of music are based on a double foundation — partly physical, partly physiological. With the physiological aspect of this foundation we have to-night nothing to do, being concerned only with the physical aspect. What, then, are the physical founda- tions of melody, of harmony, and of timbre? Demonstrable by experiment they must be, in common with all other physical facts, otherwse they cannot be accepted as proven. What are the facts, and how can they be demonstrated ? To Pythagoras and the Greeks it was known that the notes of the melodic scale corresponded in a curiously- perfect way to certain numerical relations between the lengths of the stretched strings. Modern research has transferred these numerical relations to the frequency of the vibrations executed by the moving body, and pitch is now a matter assignable in definite numbers. In the philosophical 1890.] on the Physical Foundation of Music. 207 pitch the middle c' between the bass and treble staves is defined as consisting of 256 complete vibrations. In concert pitch the usual number given to the same note is 268 or 270. Further, the notes of the major scale are always related to one another in the following definite ratios : — 9 5 4 3 5 15 •8*4'3'2*3' 8 • In the execution of music the performer does not always adhere rigidly to these ratios. For pure melodic purposes, the actual scale is nearer to that called the Pythagorean ; but for the purpose of harmony in any one key the above ratios must be precisely observed. But, obviously, a scale is wanted which will serve both purposes, melodic and harmonic ; hence the same scale is attempted to be used for melody as for harmony. Further, the requirements of modern music, ever since the time of Bach, have necessitated a further modification of the scale to enable the performer to modulate into harmonies, not in one key, but in all ; so that he may enjoy the tonal relations of contrasted keys, modulating from key to key. In order that this may be done, and yet that all the keys may be played from one key-board, musicians have been content to spoil the exact consonances in individual keys by departing from these exact ratios by the device of tempering all the keys, so that twelve successive fifths shall exactly equal seven successive octaves. I am not here, however, to fight over again the battle of the temperaments, nor do I purpose to enter upon a discussion of the origin of melody, which, indeed, I believe to be associative rather than physical. I shall confine myself to two matters only — the cause of harmony and the nature of timbres. Eeturning, then, to the ratios of the vibration-numbers of the major scale, we may note that two of these, namely, the ratios 9 : 8 and 15 : 8, which correspond to the intervals called the major whole tone and the seventh, are dissonant — or, at least, are usually so re- garded. It will also be noticed that these particular fractions are more complex than those that represent the consonant intervals. This naturally raises the question: Why is it that the consonant intervals should he rejpresented hy ratios made up of the numbers 1 to 6, and hy no others ? To this problem the only answer for long was the entirely evasive and metaphysical one that the mind instinctively delights in order and number. The true answer, or rather the first approximation to a true answer, was only given about forty years ago, when von Helm- holtz, as the result of his ever-memorable researches on the sensa- tions of tone, returned the reply : Because only by fulfilling numerical relations which are at once exact and simple, can the " heats " be avoided, which are the cause of dissonance. The phenomenon of beats is so well known that I may assume the term to be familiar. An excellent mode of making beats audible to a large audience is to place upon a 208 Professor Silvanus P. Thompson [June 13, wind chest two organ-pipes tuned to uty = 128, and then flatten one of them slightly by holding a finger in front of its mouth. Von Helmholtz's theory of dissonance may be briefly summarised by say- ing that any two notes are discordant if their vibration numbers are such that they produce beats, maximum discordance occurring when the beats occur at about 33 per second ; beats if either fewer than these, or more numerous, being less disagreeable than beats at this frequency. It is an immediate consequence that the degree of disso- nance of any given interval will depend on its position on the scale. For example, the interval of the major, whole tone, represented by the ratio 9 : 8, produces four beats per second at the bottom of the pianoforte keyboard, 32 beats per second at the middle of the key- board, and 256 beats per second at the top. Such an interval ought to be discordant, therefore, in the middle octaves of the scale only. Von Helmholtz expresses elsewhere the opinion that beats only occur between two tones when the intervals between these tones are within a minor third of one another. To this view of von Helmholtz it was at first objected that if that were the whole truth, all intervals should be equally harmonious provided one got far enough away from being in a bad unison : fifths, augmented fifths, and sixths minor and major ought all to be equally harmonious. This no musician will allow. To account for this von Helmholtz makes the further supposition that the beats occur, not simply between the fundamental or prime tones, but also between the upper partials which usually accompany prime tones. This leads me to say a word about upper partial-tones and harmonics. I believe many musicians use these two terms as synonymous ; but they ought to be carefully distinguished. The term harmonics ought to be rigidly reserved to denote higher tones which stand in definite har- monic relations to the fundamental tone. The great mathematician Fourier first showed that any truly periodic function, however comj)lex, could be analysed out and expressed as the sum of a certain series of periodic functions having frequencies related to that of the funda- mental or first member of the series as the simple numbers 2, 3, 4, 5, &c. Thirty years later G. S. Ohm suggested that the human ear actually performs such an analysis, by virtue of its mechanical structures, upon every complex sound of a periodic character, resolving it into a fundamental tone, the octave of that tone, the twelfth, the double octave, &c. Von Helmholtz, arming himself with a series of tuned resonators, sought to pick up and recognise as members of a Fourier-series, the higher harmonics of the tones of various instruments. In his researches he goes over the ground previously traversed by Eameau, Smith, and Youug, who had all observed the co-existence in the tones of musical instruments, of higher partial tones. These higher tones correspond to higher modes of vibration, in which the vibratile organ — string, reed, or air column, — subdivides into two, three, four, or more parts. Such parts naturally possess greater frequency of vibration, and their higher tones, when tliey co- exist along with the 1890.] on the Physical Foundation of Music. 209 lower or fimdamental tone, are denominated upper partial /owes, thereby signifying that they are higher in the scale, and that they corre- spond to vibrations in parts. It is to be regretted that Professor Tyndall in his Lectures on Sound, rendered von Helmholtz's cAerpartialtone by the term overtones, omitting the most significant half of the word. To avoid all confusion in the use of such a terra I shall rather follow Koenig in speaking of these as sounds of sub- division. And I must protest emphatically against calling these sounds harmonics, for the simple reason that in many cases they are very inharmonious. It is a matter to which I shall recur hereafter. Eeturning to the subject of beats, the question arises : What becomes of the beats when they occur so rapidly that they cease to produce a discontinuous sensation upon the ear ? The view which I have to put before you to-night in the name of Dr. Koenig is that they blend to make a tone of their own. Earlier acousticians have propounded, in accordance with this view, that the grave harmonic of Tartini (a sound which corresponds to a frequency of vibration which is the difference between those of the two tones pro- ducing it) is due to this cause. Von Helmholtz has taken a different view, denying that the beats can blend to form a sound, giving reasons presently to be examined. Von Helmholtz considered that he had discovered a new species of combinational tone, namely one corre- sponding in frequency to the sum of the frequencies of the two tones, whereas that discovered by Tartini (and before him by Sorge) corresponded to their difference. Accordingly he includes under the term of combinational tones the differential tone, of Tartini and the summational tone which he considered himself to have discovered. To the existence of such combinational tones he ascribed a very impor- tant part in determining the character, harmonious or otherwise, of chords; and to them also he attributes the ability of the ear to discriminate between the degrees of harmoniousness possessed by such intervals (fifths, sixths, &c.) as consist of two t(mes too widely apart on the scale to give beats of a discontinuous character. He also considers that such combinational tones are chiefly effective in pro- ducing beats, the summational tones of the primaries beating with their upper partial tones ; and that ,this is the way in which they make an interval more or less harmonious. The whole fabric of the tlie<»ry of harmony as laid down by Von Helmholtz is thus seen to repose upon the presence or absence of beats ; and the beats themselves are in turn made to depend not upon the mere interval between two notes but upon the timbres also of those notes, as to what upper partials they contain, and whether those partials can beat with the summational tone of the primaries. It becomes then of the utmost importance to ascertain the precise facis about the beats and about the supposed combinational tones. What the numbers of beats are in any given case : whether they do or do not correspond to the alleged differential and summational Vol. XIII. (No. 84.) p 210 Professor Silvanus P. Thompson [June 13, tones : tliese are vital to the theory of harmony. Equally vital is it to know what the timbres of sounds are, and whether they can be accurately or adequately represented by the sum of a set of pure harmonics corresponding to the terms of a Fourier-series. And here let me take the opportunity of saying that the views which 1 am about to propound, and which for to-night I must be con- sidered to adoj)t, are those which have been jDut forth as the result of a quarter of a century of patient work by Dr. Eudolph Koenig of Paris. Dr. Koenig, whose recent visit to this country will be remembered by some here present, is, as is well known, the constructor of the finest and most accurate acoustical instruments in the world, and is not only a constructor but an investigator of great distinction, and author of numerous memoirs on acoustics which have from time to time appeared in the Annalen of Poggendorff, and in those of Wiede- mann, and elsewhere. The splendid apparatus around me belongs to him, and forms but a very small part of the collection which adorns his atelier on the Quai d'Anjou. He lives and works in seclusion, surrounded by his instruments, even as our own Faraday lived and worked amongst his electric and magnetic apparatus. His great tonometer, now nearly completed, comprises a set of standard tuning forks, adjusted each one by his own hands, ranging from 20 vibrations per second up to nearly 40,000, with perfect continuity, many of the forks being furnished with sliding adjustments, so as to give by actual marks upon them any desired number of vibrations within their own limits. Besides this colossal masterpiece. Dr. Koenig's collection includes several large wave-sirens, and innumer- able pieces of apparatus in which his ingenious manometric flames are adapted to acoustical investigation. There also stands his tonometric clock ; a timepiece governed, not by a pendulum, but by a standard tuning-fork, the rate of vibration of which it accurately records. Lest I should forget it at a later stage, let me here return my most cordial thanks to Dr. Koenig for the extreme kindness and courtesy with which he has put at my disposal for this discourse all the apparatus wherewith to illustrate the various points in his researches. In investigating beats and combinational tones Dr. Koenig deemed it of the highest importance to work with instruments jiroducing the purest tones ; not with harmonium reeds or with polyphonic sirens, the tones of which are avowedly complex in timbre, but with massive steel tuning-forks, the pendular movements of wliich are of the simplest possible character. Massive tuning-forks properly excited by bowing with a violoncello bow, or, in the case of those of high pitch, by striking them with an ivory mallet, emit tones remarkably free from all sounds of subdivision, and of so truly pendular a character (unless over-excited) that none of the harmonics corre- sponding to the members of a Fourier-scries can be detected. No living soul has had a tithe of the experience of Dr. Koenig in the handling of tuning-forks. Tens of thousands of them have passed 1890.] on the Phijsical Foundation of Music. 211 througli his hands. He is accustomed to tune them himself, making use of the phenomenon of beats to test their accuracy. He has traced out the phenomena of beats through every possible degree of pitch, even beyond the ordinary limits of audibility, with a thoroughness utterly impossible to surpass or to equal. Hence, when he states the results of his experience, it is idle to contest the facts gathered on such an unique basis. The results of Dr. Koenig's observations on beats are easily stated. He has observed primary beats, as well as beats of secondary and higher orders, from the interference of two simple tones simul- taneously sounded. When two simple tones interfere, the j^rimary beats always belong to one or other of two sets, called an inferior and a superior set, corresponding respectively in number to the two remainders, positive and negative, to be found by dividing the frequency of the higher tone by that of the lower. This mode of stating the facts is a little strange to those trained in English modes of expressing arithmetical calculations : but an example or two will make it plain. Let tbere be as the two primary sounds two low tones having the respective frequencies of 40 vibrations and 74 vibrations. What are the two remainders, positive and negative, which result from dividing the higher number, 74 by the lower number 40 ? Our English way of stating it is to say that 40 goes into 74 once, and leaves over a (positive) remainder of 34. But it is equally correct to say that 40 goes into 74 twice, all but 6 : or that there is a negative remainder of 6. Well, Dr. Koenig finds that when these two tuning-forks are tried, the ear can distinguish two sets of beats, one rapid, at 34 per second, and one slow, at 6 per second. Again, if the forks chosen are of frequencies 100 and 512, we may calculate thus : 100 goes into 512 five times, plus 12 ; or 100 goes into 512 six times, minus 88. In this actual case the 12 beats belonging to the inferior set would be well heard: the 88 beats belonging to the superior set would probably be almost indistin- guishable. As a rule the inferior beat is heard best when its number is less than half the frequency of the lower primary, whilst, when its number is greater^ the superior beat is then better heard. Dr. Koenig has never been able toJaear any primary beat which did not fall within the arithmetical rule which I have previously stated. I will now illustrate to you the beats, inferior and superior, as produced by these two massive tuning-forks, each weighing about 50 pounds, and each provided with a large resonating cavity consisting of a metal cylinder with an adjustable piston. One of them is tuned to the note ut^ = 64. The other also sounds ut^ ; but by sliding down its prongs the adjustable weights of gun-metal, and screwing in the piston, I can raise its pitch a w^hole tone to re^ = 72. I excite them with the 'cello bow, first separately, that you may hear their individual tones, then together. At once you hear an intolerable beating — the beats coming 8 per second. This is the inferior beat, p 2 212 Frofessor Silvanus P. Thampson [June 13, corresponding to the positive remainder, the superior beat you cannot hear. I raise the note of the second fork from re^ to mij^ = 80 ; and the beats quicken to 16 per second. Kaising it to fa^^ = 85^, and then to soli = 96, while the first fork is still kept at ut^, the beats increase in rapidity, but are fainter in distinctness. If I now substitute for the second fork a similar one which begins with soli, and raise its pitch to lai= 106| you may be able to hear two beats, the inferior one rapid and faint at 42f per second, and the superior one slower, but also faint, at 21i per second. Still raising the pitch to the true seventh tone = 112, the rapid inferior beat has died out, but now you hear the superior strongly at 16 per second. I raise it once more to si^ = 120 (the seventh of the ordinary scale) and the beats are still stronger and slower at 8 per second. Finally I bring the pitch lip to the octave ut^ = 128, to find that all beats have disappeared ; there is a perfectly smooth consonance. The facts so observed are tabulated for vou as follows : — TABLE I. Primary Beats. Primary Tones. Ratio. Inferior Beats. Superior Beats. 1 w^ ( 64 72 f •• 8 : 9 8 — t 64 mil 1 80 1 ■■ 4 : 5 16 — 1 «^ I 64 8oif " 3 : 4 21i — I 64 96 1 " 2 : 3 32 32 ( 64 /«i| 106|l " 3 : 5 42-1 2H 1 64 112 1 4 : 7 — 16 1 w*i \ 64 120 1 8 : 15 — 8 1 «^ I 64 128 ( " 1 : 2 — 0 Suppose now, keeping the lower fork unaltered, we raise the pitch of the higher note (taking a new fork tliat starts at the octave) from ut.2 to sol, by gradual steps, we shall find that there begins a new set of primary beats— an inferior set, which are at first slow, then get 1890.] on the Physical Foundation of Music. 213 more rapid and become undistinguishable ; but these are succeeded by another set which gradually emerge from the intolerable vacarme, and, though rapid at first and indistinct, grow slower and stronger as the pitch is raised, until, when it reaches 80I2, the frequency of which is exactly three times that of uti, all beats again vanish. This rauge between the octave and the twelfth tone may be called the second " period," to distinguish it from the period from unison to the first octave, which was our first period. Similarly, the range from the twelfth tone to the second octave is the third period, and from thence to the major third above is the fourth period, and so forth. In each period, up to the sixth or seventh of such periods, a set of inferior and a set of superior beats may be observed ; and in every case the frequency of the beats corresponds, as I have said, to one or other of the two remainders of the frequencies of the two tones. Ko beat has ever been observed corresponding to the sum of the frequencies, even when usinec the slowest forks. None has ever been observed corresponding to the diiference of the frequencies, save in the first period ; where, of course, the positive remainder is simply the difference of the two numbers. That you may hear for yourselves the beats belonging to one of the higher periods, I will take a pair of forks which will give us some of the superior beats in the fourth period. One of the forks is the great ut^, 64 as previously used. The other is mi^ = 320 ; their ratio being 1 : 5. Sounded together they give a pure consonance, but if the smaller one is loaded with small pellets of wax to lower its pitch slightly, and I then bow it, at once you hear beats. It was in studying the beats of these higher periods that Dr. Koenig made the observation that whereas the beats of an imperfect unison are heard as alternate silences and sounds, the beats of the imperfect consonances of higher periods — twelfth tone, double octave, &c. — consist mainly in variations in the loudness of the lower of the two primary tones ; an observation which was independently made by Mr. Bosanquet, of Oxford. Passing from the beats themselves, I approach the question, what becomes of the beats when they occur too rapidly to produce on the ear a discontinuous sensation ? On this matter there have been several conflicting opinions : some^ holding with Lagrange and Dr. Thomas Young, that they blend into a separate tone ; others, with von Helmholtz, maintaining that the combinational tones cannot be so explained, and arise from a different cause. Let it be observed that, even if beat-tones exist, it is quite possible for beats and beat- tones to be simultaneously heard. A similar co-existence of a continuous and discontinuous sensation is afforded by the familiar experiment of producing a tone by pressing a card against the periphery of a rapidly rotating toothed wheel. There is a certain speed at which the individual impulses begin to blend into a continuous low tone, while yet there are distinguishable the discon- tinuous impulses ; the degree of distinctness of the two co-existing 214 Professor Sllvanus P. Thompson [June 13, sounds being dependent on the manner in wliicli the card is pressed against the wheel — that is to say, on the nature of the individual impulses themselves. The opponents of the view that beats blend into a tone, state plainly enough that, in their opinion, a mere succession of alternate sounds and silences cannot blend into a tone different from that of the beating tone. Having said that the beats cannot blend, they then add that they do not blend ; for, say they, the combinational tones are a purely subjective phenomenon. Lastly, they say that if even the beats blend they will not so exi)lain the ex- istence of combinational tones, because the combinational tones have frequencies Avhich do not correspond to the number of the beats. In the teeth of all these views and ojunions. Dr. Koenig — without dogmatising as to how or why it is — emphatically affirms that beats do jDroduce heat-tones; and he has pursued the matter down to a point that leaves no room for doubting the general truth of the fact. The alleged discrepancy between the frequency of the observed combinational tones and that of the beats disappears when closely scrutinised. Those who count the beats by merely taking the difference between the frequencies of the two primary tones, instead of calculating the two remainders, will assuredly find that their numbers do not agree in pitch wdth the actual sounds heard. But that is the fault of their miscalculation. Those who use harmo- nium reeds or polyphonic sirens instead of tuning-forks to produce their primary tones must not expect from such impure sources to reproduce the effects to be obtained from pure tones. And those who say that the beats calculated truly from the two remainders will not account for the summational tones, have unfortunately something to unlearn — namely, that, when pure tones are used, under no circum- stances is a tone ever heard, the frequency of which is the sum of the frequencies of the two primary tones. The apparatus before you enables me to demonstrate, in a manner audible, I trust, to the whole assembly in this theatre, the existence of the beat-tones. My first illustrations relate to tones of primary beats, some belonging to the inferior, others to the superior set, in the first period. I take here the fork w^g = 2048, five octaves higher than the great ut^. To excite it, I may either bow it or strike it with this ivory mallet. With it I will take the fork one note higher, rcg = 2304. When we took the same interval with ut^ and re^, the number of beats was 8. The ut and re of the next octave higher would have given us 16 beats, that of the next 32, that of the next 64, of the fourth octave 128, and that of the fifth octave higher 256. But 256 per second is a rapidity far too great for the ear to hear as separate sounds. If there were 256 separate impulses, they would blend to give us the note ut^ = 256. They are not impulses, but heats: nevertheless, they blend. I strike the ut^, then the rCg, both shrill sounds when you hear them separately ; but when I strike them in quick suc- cession one after the other, at the moment when the mallet strikes 1890.] on the Physical Foundation of Music. 215 the second fork you hear this clear ut^ sounding out. I am not going to waste your time in a disputation as to whether the sound you hear is objective or subjective. It is enough that you hear it, pure and unmistakable in pitch. It is the grave harmonic ; and the number 256, which is its frequency, corresponds to the positive remainder when you divide 2304 by 2048. Now let me give you a beat-tone belonging to the superior set : it also will be a grave harmonic, if you so please to call it ; but its frequency will correspond neither to the difference nor to the sum of the frequencies of the two primary tones. I take utg = 2048 as previously, and with it sig = 3840. Let us calculate what the superior beats ought to be. 2048 goes into 3840 twice, less 256. Then, 256 being the negative remainder, we ought to hear from these two forks the beat-tone of 256 vibrations, which is ut^, the same note as in our last experiment. I strike the forks, and you hear the result. The beat-tone, which is neither a differential tone nor a summational tone, corresponds to the calculated number of beats. If I take utQ = 2048 and soIq = 3072, the two remainders both come out at 1024, which is utr,. Let me sound ut^ itself, separately, on an tit^ fork, that you may know what sound to listen for. Its sound has died away ; and now I strike utg and soIq, when at once you hear M^5 ringing out. That sound which you all heard corre- sponds in frequency to the calculated number of beats. That is enough for my present purpose. The next illustration is a little more complex. I select a case in which the beat-tones corresponding to the inferior and the superior beats will both be present. We shall have four tones altogether — two primary tones and two beat-tones. The forks I select are iUq = 2048 as before, and a fork which is tuned to vibrate exactly 11 times as rapidly as ut^ — it is the lltli harmonic of that note, but does not correspond precisely to any note of the diatonic scale. It has 2816 vibrations, and is related to utQ as 11 : 8. The two remainders will now be 768 and 1280, which are the respective fre- quencies of sol^^ and mir,. I will first sound those notes on two other forks, that you may know beforehand what to listen for. Now, on striking the two shrill forks in rapid succession, the two beat-tones are heard. If I select, instead of the 11th harmonic, the 13th harmonic of ut^, vibrating 3328 times in the second, to be sounded along with ut^, I shall produce the same two beat-tones as in the preceding case ; but mi^ = 1280 is now the inferior one, corresponding to the positive remainder, while sol^ = 768 is the superior tone, corresponding to the negative remainder. It is certainly a striking corroboration of Dr. Koenig's view that the beat-tones actually heard in these last two experiments should come out precisely alike, though on the old view, that the combination tones were simply the summational and differential tones, one would have been led to expect the sounds in the two experiments to be quite different. 216 Professor Silvanus P. Thompson [June 13, Oue other example I will give you of a beat-tone belonging to the second period. The two primary notes are given by the forks ut^ = 1024 and re^ = 2304. The beat-tone which you hear is uf.. = 256, which corresponds to the positive remainder. I may here mention that a mathematical investigation,* which only appeared a month ago from the pen of Professor W. Voigt, entirely confirms the views of Dr. Koenig as to the non-existence of the supposed summational tones, and the existence of those which accord with the two remainders. It will be convenient to draw up in tabular form the results just obtained. These may be considered as abbreviations of the much more extended tables drawn up by Dr. Koenig, which hang upon the walls, and which are to be found in his book, ' Quelques Experiences d'Acoustique.' TABLE II. Sounds of Pkimary Beats. Primary Tones. Uts 1024 2304 Eatio. 8 : 9 8 : 15 8 : 12 8 : 11 8 : 13 4 : 9 Inferior Beat-tone. Superior Beat-tone. 256 1024 i 768 ( mi in.. .280 256 So far we have been dealing with primary beats and beat- tones ; but there are also secondary beats and secondary beat-tones, which are produced by the interference of primary beat-tones. An example of a secondary beat is afforded by the following experiment. Recurring to the preceding table of experiments, it may be observed that when the two shrill notes uIq, sol^, giving the interval of the fifth, are sounded together, the inferior and superior beat-tones are both present, and of the same pitch. If, now, one of the two forks is lightly loaded with pellets of wax to put it out of adjustment, we ♦ " Ueber den Zusammenklaiig zweier einfacher Tone." ' Gcttinger Nach- richten,' No. 5, 1890. 1830.] 071 the Physical Foundation of Music. 217 shall get beats, not between the primary tones, but between the beat- tones. Suppose we add enough wax to reduce the vibration of solg from 3072 to 3070. Then the positive remainder is 1022, and the negative remainder is 1026; the former being ut^ flattened two vibrations, the latter the same note sharpened to an equal amount. As a result there will be heard four beats per second — secondary beats. Similarly the intervals 2 : 5, 2 : 7, if slightly mistuned, will, like the fifth, yield secondary beats. Or, to put it in another way, there may be secondary beats from the ( mistuned) beat-tones that are related (as in our experiment) in the ratio 1:1, or from those in the ratios 3 : 4, 3 : 5, 4 : 7, and so forth. I have given you an example of secondary beats ; now for an example of a secondary beat-tone. This is afforded by one of the previous experiments, in which were sounded iUq, and the 11th har- monic of ut^. In this experiment, as in that which followed with the 13th harmonic, two (primary) beat-tones were produced, of 768 and 1280 vibrations respectively. These are related to one another by the intervals 3:5. If we treat these as tones that can themselves interfere, they will give us for their positive remainder the number 256, which is the frequency of uti. As a matter of fact, if you listen carefully, you may, now that your attention has been drawn to it, hear that note, in addition to the two primary tones and the two beat-tones to which you listened previously. In von Helmholtz's " Tonemptindungen," he expresses the opinion that the distinctness with which beats are heard depends upon the narrowness of the interval between the primary tones, saying that they must be nearer together than a minor third. But, as we have seen, using bass sounds of a sufficient degree of intensity and purity, as is the case with those of the massive forks, beats can be heard with every interval from the mistuned unison up to the mistuned octave. Even the interval of the fifth, uti to sol^, gave strongly-marked beats of 32 per second. When this number is attained or exceeded, the ear usually begins to receive also the effect of a very low, continuous tone, the beats and the beat -tone being simultaneously perceptible up to about 60 or 70 beats, or as a roughness up to 128 per second. If, using forks of higher pitches but of narrower interval, one produces the same number of beats, the beat-tone is usually more distinct. Doubtless this arises from the greater true intensity of the sounds of higher pitch. With the object of pursuing this matter still more closely. Dr. Koenig constructed a series of 12 forks of extremely high pitch, all within the range of half a tone, the lowest giving s^e and the highest ut^. The frequencies, and the beats and beat-tones given by seven of them, are recorded in Table III. The first of these intervals is a diatonic semitone ; the second of them is a quarter-tone ; the third is an eighth of a tone ; neverthe- less, a sensitive ear will readily detect a difference of pitch between the two separate sounds. The last of the intervals is about half a comma. 218 Professor Silvanus P. Thompson TABLE III. [June 13, Frequencies of Forks. Ratio. Beats (Calcd.). Resulting Sound. ^ "^^ and ''^ I I 4096 3840 5 16 : 15 256 ut^ 3968 .. 32 : 31 128 tit^ 4032 .. 64 : 63 64 ut^ 4048 .. 256 : 253 48 sol _ 4056 .. 512 : 507 40 1 „ 4064 .. 128 : 127 32 ut 1 4070 .. 158 : 157 26 These forks are excited by striking tliem with a steel hammer. Some of the resulting beat-tones will be heard all over the theatre ; but, in the case of the very low tones of 40 and 32 vibrations, only those who are close at hand will hear them. The case in which there are 26 beats is curious. Most hearers are doubtful whether they perceive a tone or not. There is a curious fluttering eflect, as though a tone were there, but not continuously. We have seen, then, that the beat-tones correspond in pitch to the number of the beats ; that they can themselves interfere, and give secondary beats ; and that the same number of beats will always give the same beat-tone irrespectively of the interval between the two primary tones. What better proofs could one desire to support the view that the beat-tones are caused, as Dr. Young supposed, by the same cause as the beats, and not, as von Helmholtz maintains, by some other cause ? Yet there are some further points in evidence which are of significance, and lend additional weight to the proofs already adduced. Beats behave like primary impulses in the following respect, that when they come with a frequency between 32 and 128 per second, they may be heard, according to circumstances, either discontinuously or blending into a continuous sensation. It has been objected that, whereas beats imply interference between two separate modes of vibration arising in two separate organs, combination-tones, whether summational, or differential, or any other, must take their origin from some one organ or portion of vibratile matter vibrating in a single but more complex mode. To this objection an experimental answer has been returned by Dr. Koenig in the following way. He takes a prismatic bar of steel, about 9 inches in length, and files it to a rectangular section, so as to give, when it is struck at the middle of a face to evoke transversal vibrations, a sound of some well-defined pitch. By carefully adjusting the sides of the rectangular section in proper proportions, the same 1890.] on the Physical Foundation of Music. 219 steel bar can be made to give two different notes when struck in the two directions respectively parallel to the long and short sides of the rectangle. A set of such tuned steel bars are here before you. Taking one tuned to the note of utg = 2048, with re^ = 2304, 1 give you the notes separately by striking the bar with a small steel hammer when it is lying on two little bridges of wood, first on one face, then on the other face. If, now, I strike it on the corner, so as to evoke both notes at once, you immediately hear the strong boom of w^3 = 256, the inferior beat- tone. If I take a second bar tuned to utg and s^g = 3840, you hear also ut^, this time the superior beat-tone. If I take a bar tuned to ut^ and the 11th harmonic of ut^ (in the ratio 8 : 11), you hear the two beat-tones sol^ and mi^ (in ratios of 3 and 5 respec- tively) precisely as you did when two sej^arate forks were used instead of one tuned bar. Dr. Koenig goes beyond the mere statement that beats blend to a tone, and lays down the wider proposition that any series of maxima and minima of sounds of any pitch, if isochronous and similar, will always produce a, tone the pitch of which corresponds simply to the frequency of such maxima and minima. A series of beats may be regarded as such maxima and minima of sound ; but there are other ways of producing the effect than by beats. Let me illustrate some of these to you. If a shrill note, produced by a small organ-pipe or reed, be con- veyed along a tube, the end of which terminates behind a rotating disk pierced with large, equidistant apertures, the sound will be periodically stopped and transmitted, giving rise, if the intermittences are slow enough, to effects which closely resemble beats, but which, if the rotation is sufficiently rapid, blend to a tone of definite pitch. Dr. Koenig uses a large zinc disk with 16 holes, each about 1 inch in diameter. In one set of experiments this disk was driven at 8 revolu- tions per second, giving rise to 128 intermittences. The forks used were all of different pitches from w^3 = 256 to w^7 = 4096. In all cases there was heard the low note ut2 corresponding to 128 vibrations per second. In another series of experiments, using forks ut2 and w^g, the number of intermittences was varied from 128 to 256 by increasing the speed, when the low note rose also from ut^ to ut^. From these experiments it is but a, step to the next, in which the intensity of a tone is caused to vary in a periodic manner. For this purpose Dr. Koenig has constructed a siren-disk (Fig. 1), pierced with holes arranged at equal distances around seven concentric circles ; but the sizes of the holes are made to vary periodically from small to large. In each circle are 192 equidistant holes, and the number of maxima in the respective circles was 12, 16, 24, 32, 48, 64, and 96. On rotating this disk, and blowing from behind through a small tube opposite the outermost circle, there are heard, if the rotation is slow, a note corresponding to the number of holes passing per second, and a beat corresponding to the number of maxima per second. With more rapid rotation two notes are heard — a shrill one, and another 220 Professor Silvanus P. Thompson [June 13, 4 octaves lower in pitch, the latter being the beat-tone. On moving the pipe so that wind is blown successively through each ring of apertures, there is heard a shrill note, which is the same in each case, and a second note (corresponding to the successive beat-tones) which rises by intervals of fourths and fifths from circle to circle. Fig. 1. • • ••••:.v^ .•• .,••-. •» . ,•'•• ••*.. *•••. *•. ••. .♦• .• ,. ♦.. ••. •. . ,. .•• •., •. •. Siren Disk, with apertures varying periodically in size. These attempts to produce artificially the mechanism of beats were, however, open to criticism ; for in them the phase of the individual vibrations during one maximum is the same as that of the individual vibrations in the next succeeding maximum ; whereas in the actual beats produced by the interference of two tones the phases of the individual vibrations in two successive maxima differ by half a vibration; as may be seen by simple inspection of the Fig. 2. Siren Disk, pierced to imitate mechanism of beats. curves corresponding to a series of beats. When this difierence was pointed out to Dr. Koenig, he constructed a new siren-disk (Fig. 2), having a similar series of holes of varying size, but spaced out so as to correspond to a difference of half a wave between the sets. With this disk, beats are distinctly produced with slow rotation, and a beat-tone when the rotation is more rapid. 1890.] on the Physical Foundation of Music. 221 Finding this result from the spacing out of apertures to corre- spond in position and magnitude to the individual wavelets of a complex train of waves, it occurred to Dr. Koenig that the phenomena of beats and beat-tones might be still more fully reproduced if the edge of the disk were cut away into a wave-form corresponding precisely to the case of the resultant wave produced by the composi- tion of two interfering waves. Accordingly, he calculated the wave- forms for the cases of several intervals, and, having set out these Fig. 3. 'sA _..••" j2q "•••.. ^l 6* \ ^^ Wave-disk giving beats and beat-tone. Fig. 4. v^ .<:• 184 ° 64 ° " ° = , ^ />• % / ° . e ^ / : o ^- \. '■■■■< ;; = -';;;° Wave-disk, giving beats and beat-tone. curves around the periphery of a brass plate, cut away the edge of the plate to the form of the desired wave. Two such wave-disks, looking rather like circular saws with irregular teeth, are depicted in Figs. 3 and 4. These correspond to the respective intervals 8 : 15 222 Professor Silvanus P. TJiompson [June 13, and 8 : 23. A number of sncli wave-disks corresponding to other intervals lie upon the table ; these two will, however, suffice. In the first of these the curve is that which would be obtained by setting out around the periphery a series of 120 simple sinusoidal waves, and a second set of 64 waves, and then compounding them into one resultant wave. In order to permit of a comparison being made with the simple component sounds, two concentric rings of holes have been also pierced with 120 and 64 holes respectively. Regarding these two numbers as the frequency of two primary tones, there ought to result beats of frequency 8 (being the negative remainder corresponding to the superior beat). An interior set of 8 holes is also pierced, to enable a comparison to be made. To experiment with such wave-disks they are mounted upon a smoothly running whirling-table, and wind from a suitable wind-chest is blown against the waved edge from behind, through a narrow slit set radially. In this way the air-pressures in front of the wave-edge are varied by the rush of air between the teeth. It is a question not yet decided how far these pressures correspond to the values of the ordinates of the curves. This question, which involves the validity of the entire prin- ciple of the wave-siren, cannot here be considered in detail. Suffice it to say that for present purposes the results are amply convincing. The wave-disk (Fig. 3) has been clamped upon the whirling-table, which an assistant sets into rotation at a moderate sjDeed. I blow first through a small pipe through one of the rows of holes, then through the other. The two low notes sound out separately, just a seventh aj)art. Then I blow through the pipe with a slotted mouth-piece against the waved edge ; at once you hear the two low notes interfering, and making beats. On increasing the speed of rotation the two notes become shrill, and the beats blend into a beat- tone. Notice the pitch of that beat-tone : it is precisely the same as that which I now produce by blowing through the small pipe against the ring of 8 holes. A\ ith the other wave-disk, having 184 and 64 holes in the two primary circles, giving a wave-form corresponding to the interval 8 : 23, the effects are of the same kind, and when driven at the same speed it gives the same beat-tone as the former wave-disk. It will be noted that in each of these two cases the frequency of the beat-tone is neither the difference nor the sum of the frequencies of the two primary tones. A final proof, if such were needed, is afforded by an experiment, which, though of a striking character, will not necessarily be heard by all persons present, being only well heard by those who sit in certain positions. If a shrill tuning-fork is excited by a blow of the steel mallet, and held opposite a flat wall, part of the waves which it emits strike on the surface, and are reflected. This reflected system of waves, as it passes out into the room, interfere with the direct system. As a result, if the fork, held in the hand, be moved toward the wall or from it, a series of maxima and minima of sound will successively reach an ear situated in space at any point near the line 1890.] on the Physical Foundation of Music. 223 of motion and will be heard as series of beats ; tbe rapidity with which, they succeed one another being proportional to the velocity of the movement of the fork, the fork I am using is ut^, which gives well-marked beats, slow when I move my arm slowly, quick when I move it quickly. There are limits to the speed at which the human arm can be moved, and the quickest speed that I can give to mine fails to make the beats blend to a tone. But if I take soZ^, vibrating 1^ times as fast, and strike it, and move it away from the wall with the fastest sj^eed that my arm will permit, the beats blend into a short low growl, a non-uniform tone of low pitch, but still having true continuity. This first portion of my discourse may then be summarised by saying that in all circumstances where beats, either natural or artificial, can be produced with sufficient rapidity, they blend to form a beat-tone of a pitch corresj)onding to their frequency. I now pass to the further part of the researches of Dr. Koenig which relates to the timbre of sounds. Prior to the researches of Dr. Kcenig, it had been supposed that in the reception by the ear of sounds of complex timbre the ear took no account of, and indeed was incapable of perceiving, any differences in phase in the constituent partial tones. For example, in the case of a note and its octave sounded together, it was supposed and believed that the sensation in the ear, when the difference in phase of the two com- ponents was equivalent to one-half of the more rapid wave, was the same as when that difference of phase was one-quarter, or three- quarters, or zero. I had myself, in the year 1876, shown reason for holding that the ear does nevertheless take cognizance of such differences of phase. Moreover, the peculiar rolling or revolving effect to be noticed in slow beats is a proof that the ear perceives some difference due to difference of phase. Dr. Koenig is, however, the first to put this matter on a distinct basis of observation. That such differences of phase occur in the tones of musical instruments is certain : they arise inevitably in every case where the sounds of subdivision are such that they do not agree rigidly with the theoretical harmonics. Fig. 5 depicts a graphic record taken by Dr. Koenig from a vibrating steel wire, in which a note and its octave had been simultaneously excited. The two sounds were scarcely preceptibly different from their true interval, but the higher note was just sufficiently sharper than the true harmonic octave to gain about one wave in 180. The graphic trace has in Fig. 5 been split up into 5 pieces to facilitate insertion in the text. It will be seen that as the phase gradually changes, the form of the waves undergoes a slow change from wave to wave. Now, it is usually assumed that in the vibrations of symmetrical systems, such as stretched cords and open columns of air, the sounds of subdivision agree with the theoretical harmonics. For examj)le, it is assumed that when a stretched string breaks up into a nodal vibration of four parts, each of a quarter its length, the vibration is 224 Professor Sihanus P. Thompson [June 13, precisely four times as rajnd as the fundamental vibration of tlie string as a whole. This would be true if the string were absolutely uniform, homogeneous, and devoid of rigidity. Strings never are 60 ; and even if uniform and homogeneous, seeing that the rigidity Fig. 5. Graphic Record of Vibrations of Steel Wires. of a string has the effect of maldng a short piece stiffer in proportion than a long piece, cannot emit true harmonics as the sounds of sub- division. In horns and open organ-pipes the width of the column (which is usually neglected in simple calculations) affects the frequency of the nodal modes of vibration. Wertheim found the partial tones of pij)es higher than the supposed harmonics. Dr. Koenig found with an open organ-pij)e, about Ih feet long, that the eighth partial tone (or sound of subdivision) was a whole major tone higher than the theoretical eighth harmonic, and nearly agreed with the ninth harmonic of the fundamental tone! Further, there are the researches of Lord Eayleigh on the tones of bells, in which the sounds of subdivision are most extraordinarily inharmonious ; afford- ing us probably the reason why concerted hand-bell music is so unendurable. I do not know what the musicians present would say to such chords * as "^E 01* 7) They are given by Lord Eayleigh as representing resi^ectively the sounds emitted by two of the bells of the peal at Terling. * Tlie signs + or — signify tliat tlie actual tones were respfctively a httle sharixT or a little Hatter than the note as written in the staif notation. 1890.] on the Physical Foundation of Music, 225 These things being so, it is manifestly insufficient to assume, as von Helmholtz does in his great work, that all timbres possess a purely periodic character ; with the necessary corollary that all timbres consist merely in the presence, with greater or less intensity, of one or more members of a series of higher tones corresponding to the terms of a Fourier-series of harmonics. When, therefore, following ideas based on this assumption, von Helmholtz constructs a series of resonators, accurately tuned to correspond to the terms of a Fourier-series (the first being tuned to some fundamental tone, the second to one of a frequency exactly twice as great, the third to a frequency exactly three times, and so forth), and applies such resona- tors to analyse the timbres of various musical and vocal sounds, he is trying to make Nature fit to an ideal system which Nature does not herself follow. He is trying to make his resonators pick up things which in many cases do not exist — upper partial tones which are exact harmonics. If they are not exact harmonics, even though they exist, his tuned resonator does not hear them, or only hears them imperfectly, and he is thereby led into an erroneous appreciation of the sound under examination. Further, when in pursuance of this dominant idea he constructs a system of electro-magnetic tuning-forks, accurately tuned to give forth the true mathematical harmonics of a fixed series, thinking therewith to reproduce artificially the timbres not only of the various musical instruments but even of the vowel sounds, he fails to repro- duce the supposed efifects. The failure is inherent in the instrument ; for it cannot reproduce those natural timbres which do not fall within the circumscribed limits of its imposed mathematical principle. Nature does not sort men out into rigidly defined sets, one set exactly four feet high, another set exactly five feet high, another exactly six feet high. Neither does she, in the vibrations of strings, reeds, and air-columns impose rigid mathematical relations between the funda- mental notes and the sounds of subdivision, though in many cases such mathematical relations are approximately attained. Harmony depends, beyond contest, on the approximate fulfilment of exact mathematical relations, and it is the grand achievement of von Helm- holtz to have shown us why this is so. But the question of timbre involves the more subtle question of the minuter details of vibration by virtue of which the sound of a notfe in one instrument differs from that of the same note in an instrument of another kind, and depends therefore on the mechanism of the small vibrating parts. In these matters of delicate detail the natural departures from mathematical relations assert themselves. He who neglects these departures, or tries to square them to his preconceived theory, misses one of their most important characteristics, and can only render an imperfect account of them. Nothing is more certain than that in the tones of instruments, particularly in those of such instruments as the harp and the piano- forte, in which the impulse, once given, is not sustained, the relations Vol. XIII. (No. 84.) q 226 Professor Silvanus P. Thompson [June 13, between the component partial tones are continually changing, both in relative intensity and in phase. The wavelets, as they follow one another, are ever changing their forms ; in other words, the motions are not truly periodic — their main form may recur, but with modifi- cations ever changing. To estimate the part j)layed in such phenomena by mere differ- ences of phase — to evaluate, in fact, the influence of phase of the constituents upon the integral effect of a compound sound — Dr. Koenig had recourse to the wave-siren^ an earlier invention of his own, of which the wave-disks which have already been shown are examples. In the first place, Dr. Koenig proceeded synthetically to construct the wave-forms for tunes consisting of the resultant of a set of pure harmonics of gradually decreasing intensity. The composition of complex wave-form out of simple waves belonging to a Fourier- series has long been a familiar subject to students of acoustics ; and instruments have been devised by Wheatstone and others to produce them mechanically. Of such devices one of the most elegant is the curve-drawing machine of Mr. A. Stroh, here on the table, which he has kindly lent me, together with a number of curves produced by its means. "With this beautiful little machine it is possible to draw curves compounded of any of the first eight waves of a harmonic series, in various phases and of various amplitudes. In Dr. Kcenig's synthetic study he began by drawing to scale the separate waves of the different orders. The curves of these, up to the tenth member of the series, were carefully compounded graphi- cally : first with zero difference of phase, then wdth all the upper members shifted on one quarter, then with a difference of a half- wave, then with with a difference of three-quarters. The results are shown in the top line of curves in Fig. 6, wherein it will be noticed that the curve for difference of phase = i is like that for zero differ- ence, but reversed, left for right ; and that the curve for difference of phase = J is like that for difference = J, but inverted. Now, according to von Helmholtz, the sounds of all these four curves should be precisely alike, in spite of their differences of form and position. To test the matter, these carefully-plotted curves were set out upon the circumference of a cylindrical baud of thin metal, the edge being then cut away, leaving the unshaded portion, the curve being re})eatcd half a dozen times, and meeting itself after passing round the circumference. For convenience, the four curves to be comjjared are set out upon the separate rims of two such metallic cylindrical hoops, which are mounted upon one axis, to which a rapid motion of rotation can be imparted, as shown in Fig. 7. Against the dentel- lated edges of these rims, wind can be blown through narrow slits connected to the wind-chamber of an organ-table. In the apparatus (Fig. 7) the four curves in question are the four lowest of the set of six. It will be obvious that, as these curves pass in front of the slits from which wind issues, the maximum displacement of air will result 1890.] on the Physical Foundation of Music. Fig. 6. 227 Synthesis of "Wave-forms. Fig. 7. Wave-forms set out to act as Sirens. Q 2 228 Professor Silvanus P. Tliomjpson [June 13, when the slit is least covered, or when the point of greatest depression of the curve crosses the front of the slit. The negative ordinates of the curves correspond therefore approximately to condensations. Air is now being supplied to the slits ; and when I open one or other of the valves which control the air-passages, you hear one or other of the sounds. It must be audible to every one present that the sound is louder and more forcible with a difference of phase of \ than in any other case, that produced with £ difference being gentle and soft in tones, whilst the curves of phase 0 and ^ yield tones of intermediate quality. Dr. Koenig found that, if he merely combined together in various phases a note and its octave (which was indeed the instance examined by me binaurally in 1876), the loudest resultant sound is given when the phase difference of the combination is \, and the mildest when it is £. Returning to Fig. 6, in the second line are shown the curves which result from the superposition of the odd members only of a harmonic series of decreasing amplitude. On comparing together the curves of the four separate phases, it is seen that the form is identical for phases 0 and ^, which show rounded waves, whilst for phases \ and '^ the forms are also identical, but with sharply angular outline. These two varieties of curve are set out on the two edges of the highest metallic circumference in the apparatus depicted in Fig. 7. The angular waves are found to yield a louder and more strident tone than the rounded waves, though according to von Helm- holtz, their tones should be alike. A much more elaborate form of compound wave-siren (Fig. 8) was constructed by Dr. Koenig for the synthetic study of these phase- relations. Upon a single axis, one behind the other is mounted a series of 16 brass disks, cut at their edges into sinusoidal wave- forms. These represent a harmonic series of 16 members of de- creasing amplitude, there being just sixteen times as many small sinuosities on the edge of the largest disk as there are of large sinuosities on that of the smallest disk. A photograph of the ap- paratus* is now thrown upon the screen. Against the edge of each of the 16 wave-disks wind can be separately blown through a slit. This instrument, therefore, furnishes a fundamental sound with its first fifteen pure harmonics. It is clear that any desired combina- tion can be obtained by opening the appropriate stops on the wind-chest ; and there are ingenious arrangements to vary the phases of any of the separate tones by shifting the positions of the slits. The brass tubes, which terminate in 15 mouth-piece slits, are connected to the wind-chest by flexible rubber tubes. The mouth- piece tubes are so mounted that they can be displaced laterally in curved slots concentric with the disks. By the aid of templates * It is described fully by Dr. Koenig in his volume ' Quelques Expe'riences,* and was figured and described in * Nature,' vol. xxvi. p, 277. 1890.] on the Physical Foundation of Music. 229 cut out in comb-fashion, and screwed, as shown in Fig. 12, to a lever handle, the mouth-pieces, or any set of them can be displaced at will, producing any pre-arranged difference of phase. Fig. 9 shows the Fig. 8. Koenig's Compound Wave-siren for synthetic researches on the quality of Compound Tones. way in which the 15 movable slits are arranged with respect to the wave-disks and to the one fixed slit of the fundamental note ; they are set in two radial lines for convenience of grouping, and so that Q 3 230 Professor Silvanus P. Thompson [June 13, each is opposite the crest of the wave of its own wave-disk ; all the slits being simultaneously closed. This corresponds in Dr. Koenig's nomenclature to a phase of |; minimum flow of air occurring Fig. 9. Positions of the Slits in front of the Wave-disks for combining the Sounds with Phase-difference f . Fig. 10. Position of the Slits for Phase-difference \. Fig. 11. Position of the Slits for Phase-difference J. simultaneously for all the components. Suppose now it is desired to change the phase so that the slits shall all be open simultaneously, all that is necessary is to move forward the slits of alternate 1890.] on the Physical Foundation of Music. 231 members of tlie series, as shown in Fig. 10. This is done by a special template. Fig. 11 shows the positions required for phase of J. Fig. 12 shows the template for zero phase. To produce this there will be no movement required for the fourth, eighth, and twelfth members of the movable set, but the intermediate ones will Fig. 12. Position of the Shts for Phase-difference 0. need to be shifted by J, J, and f of their respective waves. When this set of positions is attained the condensation is increasing at the same moment for all the component waves, and reaches its mean values simultaneously. In experimenting the practice is to listen first to the combined sound with the undisplaced slits, and then, suddenly raising the lever, observe the change in the resultant sound. The following are the chief results obtained with this instrument. If we first take simply the fundamental tone and its octave together, the total resultant sound has the greatest intensity when the differ- ence of phase 8 = ^ (i. e. when the maximum displacement of air occurs at the same instant for both waves) ; and at the same time the whole character of the sound becomes somewhat graver, as if the fundamental tone predominated more than in other phases. The intensity is least when 8 = j. If, however, attention is concentrated on the octave note while the phase is changed, its intensity seems about the same for 8 = ;J as for 8= J, but weaker in all other positions. The compound tones formed only of odd members of the series have always more power and brilliancy of tone for phase differences of \ and |, than for 0 and J ; but the quality for \ is always the same as for |, and the quality for 0 is always the same as for J. This corresponds to the peculiarity of the corresponding wave-form, of which the fourth line of curves in Fig. 6 is an example. For com- pound tones corresponding to the whole series, odd and even, there is, in every case, minimum intensity, brilliancy, and stridence with 232 Professor Silvanus P. Thompson [June 13, 8 = j, and maximum with 8 = ^. Inspection of the first and third lines of curves in Fig. 6 shows that in these wave-forms that phase which is the most forcible is that in which the maximum displacement, and resulting condensation, is sudden and brief. Observing that wave-forms in which the waves are symmetrical — steeper on one side than on the other — are produced as the resultant of a whole series of compounded partial tones, it occurred to Dr. Koenig to produce from a perfect and symmetrical sinusoidal wave- curve a complex sound by the very simple device of turning into an oblique position the slit through which the wind was blown against it. In Fig. 13 is drawn a simple symmetrical wave-form, eglnjprtv. If a Fig. 13. Eflfect of Tiltins: the Slit. series of such vs^ave-forms is passed in front of a vertical slit, such as ah, B. perfectly simple tone, devoid of upper partials, is heard. But by inclining the slit, as at ab\ the same effect is produced as if the wave-form had been changed to the oblique outline e'g'l'n'p'r't'v', the slit all the while remaining upright. But this oblique form is pre- cisely like that obtained as resultant of a decreasing series of partial tones (Fig. 6, a). If the slit be inclined in the same direction as the for- ward movement of the waves, the quality produced is the same as if all the partial tones coincided at their origin, or with S = 0 ; while if inclined in the opposite direction the quality is that corresponding to 8 = J. It is easy to examine whether the change of phase produces any effect on the sound. Before you is a simple wave-disk, and air is being blown across its edge through a slit. On tilting the slit forward to give 8 = 0, you hear a purer and more perfect sound ; and on tilting it back, giving 8 = J, a sound that is more nasal and forcible. All the preceding experiments agree then in showing that differences of phase do produce a distinct effect upon the quality of compound tones : what then must we say as to the effect on the 1890.] on the Physical Foundation of Music. 233 timbre of the presence of upper partial tones or sounds of subdivision that do not agree with any of the true harmonics ? A mistuned harmonic — if the term is permissible — may be looked upon as a harmonic which is undergoing continual change of phase. The mistuned octave which yielded the graphic curve of Fig. 5 is a case in point. The wavelets are continually changing their form. It is certain that in a very large number of musical sounds, instrumental and vocal, such is the case. It was whilst experimenting with his large compound wave-siren that Dr. Koenig was struck by the circumstance that under no con- ditions, and by no combination of pure harmonics in any proportion of intensity or phase could he reproduce any really strident timbres of sound, like those of harmonium reeds, trumpets, and the like ; nor could he produce satisfactory vowel qualities of tone. Still less can these be produced satisfactorily by von Helmholtz's apparatus with electro-magnetic tuning-forks, in which there is no mode of vary- ing the phases of the components. The question was therefore ripe for investigation, whether, for the production of that which the ear can recognise as a timbre, a definite unitary quality of tone, it was necessary to suppose that all the successive wavelets should be of similar form. Or, if the forms of the successive wavelets are con- tinually changing, is it possible for the ear still to grasp the result as a unitary sensation ? If the ear could always separate impure harmonic or absolutely anharmonic partials from their fundamental tone, or if it always heard pure harmonics as an indistinguishable part of the unity of the timbre of a fundamental, then we might draw a hard and fast line between mere mixtures of sound and timbres, even as the chemist dis- tinguishes between mere mixtures and true chemical compounds. But this is not so : sometimes the ear cannot unravel from the in- tegral sensation the inharmonious partial ; on the other hand, it can often distinguish the presence of truly harmonious ones. Naturally, something will depend on the training of the ear ; as is the case with the conductor of an orchestra, who will pick out single tones from a mixture of sounds which to less perfectly trained ears may blend into a unitary sensation. Dr. Koenig accordingly determined to make at least an attempt to determine synthetically how far the ear can so act, by building up specific combinations of perturbed harmonics or anharmonic partials, giving rise to waves that are multiform, as distinguished from the uniform waves of a true periodic motion. The wave-siren presented a means of carrying this attempt to a result. On the table before me lie a number of wave-disks constructed with this aim. These I will now set into rotation by aid of a silent-running water-motor, and will blow against them by means of a wind-chest, which supplies air to the slit at a sufiiciently great and steady pressure. But I ought to warn you that these experiments are intended for the laboratory rather than for the lecture theatre, and only those who sit in the 234 Professor Silvanus P. Thompson [June 13, immediate front of the apparatus will hear the resultant sounds properly. Upon the edge of the first of the series there has been cut a curve graphically compounded of 24 waves as a fundamental, together with a set of four perturbed harmonics of equal intensity. The first har- monic consists of 49 waves (2 X 24 -j- 1) ; the second of 75 waves (3 X 24 + 8) ; the third of 101 (4 X 24 + 5) ; the fourth of 127 (5 X 24 -}- 7). The resulting curve possesses 24 waves, no two of them alike in form, and some highly irregular in contour. The efi'ect of blowing air through a slit against this disk is to produce a disagreeable sound, quite lacking in unitary character, and indeed suggesting intermittence. The second wave-disk is constructed with the same perturbed harmonics, but with their amplitudes diminishing in order. Tliis disk produces similar etfects, but with more approach to a unitary character. In the third disk there are also 24 fundamental waves, but there are no harmonics of the lower terms, the superposed ripples being perturbed harmonics of the hfth, sixth, and seventh orders. Their numbers are 6 x 24 -j- 6 ; 7 X 24 + 7 ; and 8 X 24 -f- 8 ; being, in fact, three harmonics of a fundamental 25. This disk gives a distinctly dual sort of sound ; for the ear hears the fundamental quite separate from the higher tones, which set themselves to blend to a unitary effect. There is also an intermittence corresponding to each revolution of the disk, like a beat. The fourth disk resembles the preceding ; but the gap between the fundamental and the three perturbed harmonics has been filled by the addition of three true harmonics. This disk is the first in this research which gives a real timbre, though it is a peculiar one : it preserves, however, a unitary character, even when the slit is tilted in either direction. The 24 waves in this disk all rake forward like the teeth of a circular saw, but with multiform ripples upon them. The quality of tone becomes more crisp when the slit is tilted so as to slope across the teeth, and more smooth when in the reverse direction. The fifth disk, which is larger, has 40 waves at its edge ; these are cut with curves of all sorts, taken haphazard from various com- binations of pure harmonics in all sorts of proportions and varieties, no two being alike, the maxima and minima of the separate waves being neither isochronous nor of equal amplitude. This disk gives an entirely unmusical effect, amid which a fundamental tone is heard, accompanied by a sort of rattling sound made up of intermittent and barely recogTiisable tones. The sixth disk is derived from the preceding by selecting eight only of the waves, and repeating them five times around the periphery. In this case each set of eight acts as a single long curve, giving beats, with a slow rotation, and a low tone (accompanied always by the rattling mixture of higher tones) when the speed is increased. 1890.] on the Physical Foundation of Music. 233 The seventh disk was constructed by taking 24 waves of perfect sinusoidal form, and superposing upon them a series of small ripples of miscellaneous shapes and irregular sizes, but without essentially departing from the main outline. This disk gives a timbre in which nothing can be separated from the fundamental tone, either with vertical or tilted slit. The eighth and last disk consists of another set of 24 perfect waves, from the sides of which irregular ripples have been carved away by hand, with the file, leaving, however, the summits and the deepest parts of the hollows untouched, so that the maxima and minima are isochronous and of equal amplitude. This disk gives also a definite timbre of its own, a little raucous in quality, but still distinctly having a musical unity about it. We have every reason, therefore, to conclude that the ear will recognise as possessing true musical quality, as a timbre, a combina- tion in which the constituents of the sound vary in their relative intensity and phase from wave to wave. What, then, is a timbre f Dr. Kcenig would be the first to recog nise that these experiments, though of deepest interest, do not afford a final answer to the question. We may not yet be in a position to frame a new definition as to what constitutes a timbre, but we may at least conclude that, whenever that definition can be framed, it will at least include several varieties, including the non-periodic kinds with multiform waves, as well as those that are truly periodic with uniform waves. We must not on that account, however, rush to the conclusion that the theory of von Helmholtz as to the nature of timbre has been overthrown. The corrections introduced into lunar theory by Hansen and Newcomb have not overturned the splendid generalisations of Newton. What we can and must confess is that we now know that the acoustic theory of von Helmholtz is, like the lunar theory of Newton, correct only as a first approximation. It has been the distinctive merit of Dr. Koenig to indicate to us the magni- tude of the correcting terms, and to supply us not only with a rich store of experimental facts but with the means of prosecuting the research synthetically beyond the point to which he himself has attained. Fascinating as is the pursuit of such questions, one cannot con- clude these researches without pausing to enquire how much nearer they have brought us to the ultimate explanation of the power which music exercises upon us. And it must be confessed frankly that the discovery of the physical foundations of the science leaves us very much where we were before. For music, though a science, is before all an art, and can be interpreted only by the artist. Science has nothing to say concerning the vast range of musical impressions, which are purely associative in their character. No analysis, how- ever searching, will explain away the thrill that runs through us as we listen to some simple phrase or motif which recalls the stately pre- lude, the inspiring theme, the passionate andante, the gay barcarolle, 236 Prof. TJiompson on Physical Foundation of Music. [June 13/90. the massive triumphal march, or the wailing miserere. The horn of Siegfried summons us to Briinhilde's rock, quite irrespective of the upper partial tones which accompany its fundamental tone. We may try to analyse our sensations with endless metaphysical re- finements : we may investigate their physical causes by the most careful dissection of the waves and wavelets with which the musician's hand and instrument flood our listening ears — and we are not a whit nearer either to composing music ourselves or to comprehending its intrinsic beauty and power. We might as well suppose that we could become painters by going through a course of chemical analysis of the paints employed by a Watts or a Herkomer. True, a knowledge of the chemistry of pigments will assist the artist by sparing him blunders and giving him something more than empirical rules to guide him in the mixing of his paints. So likewise, a knowledge of the physical basis of music may help the musician by lifting him above merely empirical rules, which, like that forbidding consecutive fifths, are founded on no rational basis, being deliberately violated by the builder of every organ, and set aside by every great composer. But, make him a musician, never. Analysis, though it is an instinctive faculty of the mind, is not art. Of some arts indeed, it may be said that analysis is death ; but only of those which have been based on falsehood or superstition. Art that is true fears nothing from analysis; it is beyond and above its reach. And music, the most refined, the most subtle, the most spiritual of the arts, defies analysis more efiectually than any. Our enquiry leaves its emotional and spiritual power untouched, unchanged. Some things there are which lose their charm when touched by the finger of enquiry : their spell is snapt ; their magic vanishes into thin air. Not so is it with music : — " For music, which is as a voice, A low voice calling fancy, as a friend, To the green woods in the gay summer-time, Seeing we know emotions strange by it Not else to be revealed . . . • ... is earnest of a Heaven." [S. P. T.] IRojjal jftt!3titution of dS^xtat ISxitairt. WEEKLY EVENING MEETING, Friday, January 23, 1891. Sir Frederick Bramwell, Bart. D.C.L, F.E.S. Honorary Secretary and Vice President, in the Chair. The Right Hon. Sir Edward Fry, Lord Justice of Appeal, F.E.S. F.S.A. F.L.S. M.BJ. British Mosses. (Abstract.) I CANNOT without an apology address the Royal Institution on this subject. I can make no pretence to speak with authority ; I speak only as a learner who has devoted to the subject some leisure from amidst avocations of a very different kind. But the pleasure I have derived from the study, the sense, whenever I am in the country, that I am surrounded with a world of variety and beauty of which I was formerly only dimly conscious, and the hope of communicating some of this pleasure to others may, I hope, furnish some apology for my venturing to speak on the subject. Classification. — Without entering into any question as to the best classification of the mosses, or the relative systematic value of the dif- ferent groups, the following table, which is arranged in an ascending rank, will be sufficient to show the position of the mosses in the vegetable kingdom, and the principal groups into which they may be divided : — TABLE A. Vascular Cryptogams Muscinese Musci Sphagnaceai HepaticesB Series. /' Pleurocarpse I Acrocarpae Anomalese Orders. ( Stegocarpse \ Cleistocarpgo J SchizocarpsB \ HolocarpaB Examples, Hypnum Polytriclium Pbascum Andrsea Archidium I Jungermanniacese \ Marchantiacese Algae, &c. From this table it will be gathered that the mosses, using that word in its wide signification, stand at the head of the cellular cryptogams, and that above them are the vascular cryptogams, of which the ferns are one of the best-known groups. From these vascular cryptogams the mosses are, however, separated by a distance which Goebel has described as a chasm " the widest with which we are acquainted in the whole vegetable kingdom." Vol. XIII. (No. 85.) r 238 Lord Justice Fry [Jan. 23, From the table it will be further seen that the larger group of the Muscinea3 divides itself into three principal smaller groups ; the Hepatica) or liverworts, the SphagnacesB or turf mosses, and the Musci or true mosses — urn-mosses, as they have been called, from the form of their capsule. Passing over the other subdivisions, it may be observed that the Acrocarpous mosses are those which carry their capsules at the end of the axis of growth, whilst the Pleurocarpous mosses bear their fructification on stalks, more or less long, proceed- ing from the sides of the axis. Amongst these Pleurocarpous mosses occurs the old genus Hypnum (broken up by modern systematists into several genera), the largest of all the genera in these islands or in Europe — a vast group which occupies amongst mosses something like the place which the Agarics occupy amongst the Fungi. Number of British S'pecies. — If we were to try and ascertain the number of the British Muscineae from the systematists of some few years ago, like Hooker and Wilson, the species would number be- tween 500 and 600 ; but according to the views of more recent writers, the number would probably rise to something between 800 and 900. The true mosses are the most numerous, the turf-mosses by far the fewest. Date of Flora. — "What is the date of this moss flora of Britain ? Two ancient collections enable us to give some reply to the question. In an interglacial bed near Crofthead, in Kenfrewshire, eleven species of moss were discovered, and with one possible exception all are well-defined British species of the present day. If we take Mr. Wallace's chronology, and hold that 80,000 years have passed since the Glacial epoch disappeared, and 200,000 years since the Glacial epoch was at its maximum, we may perhaps give from 100,000 to 150,000 years for the age of this little collection. Out of the eleven mosses discovered, seven belong to the genus Hypnum, or the family Hypnaceae. This collection, then, is evidence, so far as it goes, (1) that the existing moss flora is as old as the interglacial epoch ; (2) that the Hypnaceae were as dominant then as now : and (3) that the specific forms have remained constant since that epoch. Another collection of fourteen mosses has been discovered in a drift in the Clyde valley above the Boulder drift, and tends to confirm the previous conclusions ; as all the species are existing, all now inhabit the valley of the Clyde, and the HypnaceaB are still pre- dominant, though not in so great a proportion as in the Eeufrewshire bed. The fossil remains of mosses are not numerous, nor for the most part very ancient. Heer inferred their existence in the Liassic period, from the presence of remains of a group of small Coleoptera, the existing members of which now live amongst mosses — an inference which seems not very strong. But recently the remains of a moss have been found in the Carboniferous strata at Commentry, in France. It appears to be closely allied to the extant Polytrichura, the most highly-developed genus of mosses ; so that we have here a 180LJ on British Mosses. 239 phenomenon like that which occurs in reference to the Equisetacese and Lycopodiaceie, viz. that the earliest fossil species known belong to very highly-developed forms of the group. Life-History. — The following table (p. 240) is intended to illustrate the life-history of a moss in its fullest and in its abbreviated courses, and to bring this history into comparison with that of the ferns. Attention should first be drawn to the second column, which shows the life history in its fullest form. It will be seen that it starts with a spore and returns to a spore. From (1) the spore, which is a simple cell, proceeds (2) the protonema, a line of cells, extending by transverse divisions, so that it consists of single cells joined end to end to one another — an organism indistinguishable from the hypha of an Alga. At points this hypha throvrs off lateral branches which are always of less diameter than the principal ones. There is thus produced a tangled mat of fibres, running on or near the surface of the ground, and often coloured by chlorophyll. It is the green stuff so often seen in flower-pots which have been allowed to get too damp. At points in the primary hypha individual cells begin to divide in a new fashion — not by transverse septa as before, but by septa differently inclined, so as to produce the rudiments of leaves ; and the direction of growth changes from horizontal to vertical. Thus is formed (3) the hud, which by growth gives rise to (4) the moss plant ; on this plant, some- times in close proximity to one another, sometimes in different parts of the same plant, sometimes on different plants, are formed (a) the female cell or archegonium, and (b) the antheridia or male organs, the antherozoids proceeding from which seek and find and fertilise the archegonium. This completes the first part of the life of the plant, the oophytic generation which results in a single sexual cell, viz. the fertilised archegonium. From this cell arises the next generation, consisting of the sporogone or stem bearing the capsule and the capsule itself, in which without fertilisation are produced spores. The plant has thus started with the spore, an asexual cell, reached the point where its whole future is gathered up in a sexual cell, which has produced an organism again producing an asexual cell : we started with a spore, and have returned to a spore ; we have travelled round a circle, divisible into two parts or generations, one sexual, the other asoxual ; and we have therefore a case of alternation of genera- tions. To make this statement more clear, it may be observed that a generation is here spoken of as that part of the life of an organism which intervenes between the two points at which its whole future is gathered up into one cell ; that such a cell is sexual when it is the result of the combination of two previously existing and independent cells ; that such a cell is asexual when it is not the result of such combination ; that an alternation of generation exists, whenever in the complete cycle of existence or life-history there are two points at which the whole organism is reduced to a single cell, and when the forms of the organism in the two intervals of its development are B 2 240 Lord Justice Fry [Jan. 28, p a P (SB ^ e3 r—t Ph &. ^ CQ 05 ^ M t» ® © ^ -2 ^ — P » 00 rt o PC) o -1-1 o (3^ T3 S 3. 2 o _ P « 2 .— r « «-> C3 w sa, ,P ^ CQ P :iQ ft P OQ o o o 02 w -•-=< t^ H Q^ -S S !z; oo ^^ ^ p CS OS 02 O (u ^ •l-H M.M.F. Copper Iron Diagrams illustrating the symmetry in relation between electromotive force and electric current, and magnetomotive force and magnetic induction. ring stand as a symbol for a copper or conductive circuit. Let the blue ring stand for an iron or magnetic circuit. If we introduce into the conductive circuit an impulsive or alternating electromotive force, we are well aware that the interlinked iron circuit, by increasing the self-induction of the conductive circuit, hinders the change of current strength in it by introducing a hack electromotive force of self-induction. Consider now the iron circuit. If we intro- duce into that magnetic circuit an impulsive or alternating magneto- motive force by interlinking it with some turns of a magnetising 1891.] on Electro-magnetic Bepulsion. 311 current, the effect of tlie copper or conductive circuit, which is linked with the iron or magnetic current, is similarly to introduce a hack magnetomotive force into the magnetic circuit by reason of the magnetic field set up by the secondary current generated in that copper or conducting circuit. In other words, the secondary current induced in the copper circuit by any change in the magnetomotive in the iron circuit is in such a direction that it operates to oppose that primary magnetomotive force, chiefly, however, at the spot where the copper circuit passes round the iron. The general result may be stated to be that the action of the interlinked copper circuit is to cause the magnetic induction in the iron circuit to leak across through the air and partly to escape, passing through the secondary circuit. This escape of induction is called magnetic leakage, and the induced current set up in the closed secondary circuit is the cause of this magnetic leakage. There is a symmetry in the relations of magnetomotive force and the magnetic induction and electromotive force and electric current, and we can, as Faraday pointed out long ago, make the symmetry complete, if we suppose the two interlinked magnetic and electric circuits immersed in an imperfectly conducting medium. If, then, we throttle a magnetic circuit, such as a laminated iron bar with copper coils closed upon themselves, and place a magnetising coil at one end, the closed conducting circuits hinder the rise of magnetic induction in the bar ; in other words, they give it what may be called magnetic self-induction. If the source of magnetism is a rapidly-reversed pole, the consequences of this delay or " lag " in the induction is that a series of alternating magnetic poles are always travelling with retarded speed up the bar, and these may be considered to be represented by tufts of lines of magnetic force which spring out from and move laterally up the bar. If the bar is not laminated and not throttled, the eddy currents set up in the mass of the bar itself act in the same way, and operate to resist the rise of induction in the bar and to delay the propagation of magnetism along it. Hence we must think of such a throttled bar, when embraced by a magnetising coil at one end, as surrounded by laterally moving bunches of lines of magnetic force, which move up the bar. Each reversal of current in the magnetising coil calls into existence a fresh magnetic pole at the one end of the bar, which is, as it were, pushed along the bar to make room for the pole of opposite name, which appears the next instant behind it. When an iron disc is held near such a laminated und throttled bar, these laterally moving lines of force induce poles in the disc which travel after the inducing poles, and hence the disc is continually pulled round. If the disc is a copper disc, the laterally moving lines of magnetic force induce eddy currents in the disc, and these, by the principle already explained, create a repulsion between the pole and the part of the disc in which the eddy currents are set up. § 14. The progression of alternate poles along a bar can be investigated by means of an experiment due to Mr. A. Wright. 312 Professor J. A. Fleming [March 6, Two laminated straight iron bars (Fig. 16) are throttled at intervals with secondary circuits, and have wound on one extremity a mag- netising coil. The two bars are jilaced near ea'^h other and parallel. The coils are so connected that the poles at any instant in the ends of the two bars are of similar name. An alternate current is sent through the coils joined in series. Under these circumstances a series of alternate poles of similar names run up the bar parallel with one another. A small, soft iron needle hung at any place between the bars sets itself parallel to the bars, because at any instant poles of similar names are abreast of one another at any spot in the length of the bars. If, however, we shift one bar lengthways back- wards or forwards through a certain distance, so as to bring opposite Fig:. 16. S N S tsl Ni////iii 11 III III N Niy///1 11 N N N N S N S N mi II III N S V= Nl Mr. Wright's experiments with throttled and alternately magnetised bars. poles abreast of each other throughout their journey up the bars, we shall find a position such that the soft iron needle will set at right angles to the bars when hung at any point in the space between them. The distance by which we have to shift the one bar backwards of the other to effect the change is evidently half a magnetic wave length, and knowing the frequency of the alternations we can readily arrive at a measure of the velocity of propagation of these altt- mate poles in the bar. This velocity is evidently numerically equal to the product of the frequency and wave length so obtained. § 15. A very pretty apj)licatiou of the above principle has been made in the electric meter of Messrs. Wright aud Ferranti for measuring alternating currents. Before me stands one of these meters. It consists of a pair of vertical electro-magnets, with laminated iron cores, and each magnet bears at the toj) a curved horn of laminated iron which is throttled by copper rings. These curved horns, springing from the magnets, embrace and nearly touch 1891.] on Electro-magnetic Bepulsion. Fm. 17. 313 Plan and general view of Wright-Ferranti self-starting alternating motor working a fan. 314 Professor J, A. Fleming [Marcli 6, a light iron-rimmed wheel, free to turn in the centre. The actions just explained drive the wheel round, when the magnet coils are traversed by an alternating current. The iron wheel carries on its shaft a set of mica vanes, which retard the wheel by air friction. Under the opposing influences of this retardation and the electro- magnetic rotation forces, the wheel takes a certain speed corres- ponding to different current strengths in the magnetic coils, and hence the total number of revolutions of the wheel in a given time, as recorded by a counter, serves to determine the total quantity of alternating current which has passed through the meter. A motor (Fig. 17) working a fan is also here exhibited, the operation of which depends on the same facts. In the case of the motor the iron-rimmed wheel has its tyre closed with copper sheet to aid the action. § 16. The rotation of iron discs can be shown also by means of a badly-designed transformer. If a closed laminated iron ring (Fig. 18), like the one before me, is wound with a Fig. 18. couple of conducting circuits, such an ar- rangement constitutes a transformer. If these two circuits are wound on opposite sides of the iron ring, the previous explana- tions will enable you to perceive that the arrangement will be productive of great magnetic leakage across the iron circuit. In designing transformers for practical work, one condition amongst others which must be held in view is to so arrange the conductive and magnetic circuits that a great magnetic leakage of lines of force across the air does not take place. If, however, this leakage exists, it indicates that the secondary circuit ^th^^'ttlldiro^^Snt^au^^^ ^^ ^^* getting the full benefit of the induc- rotation oraTlrSrdfs? *ion created by the primary. To detect it placed near the secondary we have merely to hold near the iron circuit coil. a little balanced or pivoted iron disc, and if it is set in rapid rotation, as you observe in this case, it indicates that there are laterally-moving lines of magnetic force outside the iron, which have escaped from the iron in consequence of the back magneto-force of the secondary circuit. § 17. Time would fail me if I were to attempt to enlarge on the practical applications of the scientific principles which these experi- ments disclose to us. They are a fertile field both for the investigator seeking to add to the sum total of existing knowledge, or to the inventor in search of applications in electrical technology for such acquired facts. Ingenious minds, and that of Prof. Elihu Thomson foremost amongst them, are busy in seeking to turn these facts to account in the construction of alternating current motors. One of the simplest of these is shown in principle in the diagram now on the screen (Fig. 19). The coils C are traversed by an alter- 1891.] on Electro-magnetic Bepulsion. 315 nating current, and are placed on either side of a drum armature wound over with three sets of insulated wire coils, the terminals of the coils coming to insulated sections of a commutator. The func- tions of this commutator are to keep one coil, B, on short circuit during the time when it is in such positions relatively to the field coils C that the induced current in the closed coil causes it to be repelled by the field coils, and as each successive coil on the armature becomes in turn the active coil, rotation is kept up. A motor, made by Prof. Thomson, based on these principles,^but with some additions, is on the table, and on turning the current into it it speedily starts and gets up considerable speed. The details of the actual construc- tion are a little less simple than in the diagram shown, because the Fig. 19. Diagram illustrating elementary form of alternating-current motor. motor is made to start by sending the external current into the armature by means of a commutator and brushes. When, however, the proper speed is attained, the armature coils are automatically short-circuited, and the motor continues to run in virtue of the current induced by the field-magnet in the armature coils. This is by no means, however, the last word said on this portion of the applications, and I think we may shortly look to Prof. Thomson to give us further and more perfect methods of utilising these facts in the construction of self-starting alternating motors. § 18. For the opportunity of exhibiting to you this evening these remarkable experiments, I am personally indebted to Prof. Elihu Thomson, both for constructing and sending the apparatus we have used. Part of these appliances have now an historical value, and have been presented by him to the Eoyal Institution. For the use 316 Prof. Fleming on Electro-magnetic Bepulsion. [March 6, of the rest I desire to record my obligations and thanks. Illus- trative as these experiments are of important facts in connection with the use of alternating currents, they have a special value at the present time. In the opening year of next century, when we celebrate the centenary of the first practical production by Volta, in 1801, of the electric current, we shall find ourselves in the presence of the fact that almost every large city is ramified by a subterranean network of copper conductors for the distribution of electric energy as a necessary of modern life ; and although it may be dangerous to express too confident a view on the direction which the progress of electrical invention may take, yet it does not seem improbable that the alternating current will be doing a considerable share of that work. It is, therefore, not only as a contribution to a comprehension of the vagaries of these alternating currents that the phenomena we have shortly studied are worthy of attention, but also as being, perhaps, the avenue of approach to a further possession of valuable knowledge, enlarging our view^s, and capable, without doubt, of being minted into the current coin of useful an5 ingenious applications.* [J. A. F.] * For the loan of the blocks, illustrating the foregoing reprint, the author is indebted to the#Editor of the Electrician. 1891.] Dr. Felix Semon on the Culture of the Singing Voice. 317 WEEKLY EVENING MEETING, Friday, March 13, 1891. Sir James Crichton Browne, M.D. LL.D. F„R.S. Treasurer and Vice-President, in the Chair. Felix Semon, M.D. F.R.C.P. The Culture of the Singing Voice, The subject selected for to-night's discourse is so large that within the limited time at my disposal it will be obviously impossible to do justice to it in all its branches. Under these circumstances two ways are open : either to cast a hurried glance over the whole subject, or rather to select a few points of special interest from amongst the multitude of questions with which it is beset, and to dwell on these at somewhat greater length. The latter course appears to me the preferable one, and I shall follow it, but before entering upon the subject itself I am anxious to touch upon the reasons which have induced me to select this particular sulgect, and to define my own position with regard to it. If it be true, as no doubt generally speaking it is, that occupation with science and art is an ennobling thing, an imperfect study of the physiology of the singing voice constitutes a sorry exception to that rule. Whilst in previous times the culture of the singing voice was conducted upon purely empirical but good rules, such as had gra- dually and logically developed themselves from the accumulated experience of many schools of singing, ever since the discoveries of modern physiology have been popularised, and especially since the laryngoscope has been introduced and believed to elucidate all ques- tions connected with the production and cultivation of the singing voice, a very bitter war has been raging, in which practically every- body's hand has been against his neighbour. Dogmatic rules, irre- spective of actual facts, have been laid down as to the hygiene of the vocal organs, the question of registers has been and is at the present time as hotly discussed as ever, and untenable theories have been raised with regard to the capability of the laryngoscope to decide the most intricate and difficult questions concerned in the production of the singing voice. Now, I have always taken, since I have occupied myself with these questions, the one view that nothing could be more detrimental to the true interests of the noble art of singing than to be led astray by well-meaning but over-enthusiastic adapters of incomplete physio- logical facts into a wrong groove under the impression that the rules Vol. XIII. (No. 85.) y 318 Dr. Felix Semon [March 13, which were preached were so firmly based upon facts of unimpeach- able scientific accuracy that nothing remained to the professors of the art itself but to bow before the superior wisdom of the theorist ; and I make bold to say that such a superior wisdom does not exist with regard to tbis question. Probably I of all persons shall least be suspected of underrating the value and the importance of the laryngoscope, and I firmly hope and believe that with further long continued and careful studies this valuable little instrument will help us in the future to further elucidate a great many questions concerning the production and culture of the singing voice, about which at the present we are still completely in the dark. At the same time it canuot be strongly enough insisted upon that the millenium has not yet come, and that at the present time the claims of the laryngoscope to teach and lay down the rules for really reasonable and scientific training of the singing voice are by no means completely established. This may be very disappointing to a good many of my hearers, who jDOSsibly have expected that I would join the ranks of those who know everything about the culture of the singing voice from i^hysio- logical principles, but if it be true, as no doubt it is, that the very foundation of every knowledge consists in the fact that one knows the limitation of one's knowledge, I think that some good may be done by simply strictly defending those claims which are justified and refuting those which are based upon insufficient and solitary experience of one or of a few cases. This will be the point of view from which I sliall to-night approach my subject. As to my legiti- mation I only have to add that for a good many years I have had unusual opportunities of seeing the results of faulty training of the singing voice ; that I have always taken a special interest in the study of the nervous mechanism by which the production of song is governed, and that I have for many years made experimental re- searches in that particular line ; and finally, that I have had the good luck for many years of having been associated by ties of friendshij) with a great many of the leading singers and teachers of singing of our age. Upon such basis I wdll venture to-night to give a few of the results of my own experiences coupled with results of literary study and of the scientific and important work of an American friend of mine, Dr. French, of Brooklyn, through whose kindness I am in the position to-night of showing you some of the most interesting and remarkable facts concerning the production of the singing voice graphically, and which have been recently elucidated by means of instantaneous photograj)hy. The organ in which the singing voice is produced being the larynx, it will be indispensable to give a short description of the anatomical configuration of that part, which I shall strive to keep as free from technicalities as possible. The larynx consists of a frame- work of cartilages which are joined to one another by means of ligaments and joints, and which allow to all the parts very free 1891.] on the Culture of the Singing Voice. 319 movements towards one another by means of muscles attached to them. Additionally the larynx as a whole can be very freely moved in various directions through the instrumentality of other muscles connecting it with the parts both above and below it. The larynx forms the top of the windpipe, which again is the beginning of the bronchial tubes, which branch off from its lower part and gradually spread into more and more twigs around which are arranged tlie con- stituent parts of the lungs, which form the bellows for the blast of air necessary for the pei-formance of vocal functions. Above, the larynx opens into the throat and the cavities of the mouth, nose, and its accessory cavities, and the naso-pharyngeal space, which serve as a resonator for the vocal vibrations which are produced in the larynx itself. The larynx is lined with a mucous membrane contiguous with that of the neighbouring parts. This mucous membrane in the larynx itself forms two folds, situated one above the other ; the upper of these two reduplications, which is not itself at all concerned in the formation of sound, retains all the characteristics of common mucous membrane. Formerly these upper folds — as there is one on each side of the larynx — were called the ialse vocal cords, but this misleading name has latterly almost entirely been given up in favour of the more significant expression, ventricular bands. The lower reduplications are much more im23ortant, and are inserted in front into the receding angle of the biggest laryngeal cartilage (the thyroid), wliich in the male sex forms outwardly the so-called Adam's aj)plc. Posteriorly they are inserted into two small cartilages called the arytenoid cartilages, which, by means of an articulation or joint, can move very freely and in various directions on the surface of the second large laryngeal cartilage, the cricoid. Theso lower folds of mucous membrane form the so-called true vocal cords and have lost to a great extent the common characteristics of mucous membrane, which are principally rej)laced by numberless elastic fibres in part running parallel to one another, but in part interwoven in the most various directions with one another. These fibres are of unequal length, some of them being inserted in the most f)rojectirjg j)art of the arytenoid cartilages, which has been called the vocal j)i'^^cess, whilst other ones extend very considerably further backwards and are inserted along the body of the arytenoid cartilage itself. This elastic tissue being the sounding element, by the vibrations of which pri- marily sound is engenrlered, it is very likely, as Signer Manuel Garcia first pointed out, that it is through the unequal length of these fibres that the enormous range of the human voica is rendered possible. The muscles through which the vocal cords are set in motion, and which indeed regulate the mechanism of the sound produced in the larynx, are subdivided into three groups : the abductors, the adductors, and the tensors of the vocal cords. Of these the two last groups, i.e. the adductors and tensors, are always in unison, whilst their action is antagonistic to that of the abductors. The function Y 2 320 Dr. Felix Semon [March 13, of the latter muscles consists in keeping the vocal cords during respiration so far asunder from one another that the narrowing of the tube, which is actually produced by the interpolation of the larynx into the respiratory apparatus, is neutralised to the necessary extent, whilst the adductors and tensors as a rale serve only the voluntary and purposive function of phonation, as in speaking and in singing, and are employed only in a secondary fashion for some of the reflex acts of respiration, such as laughing and coughing. All these muscles, i. e. the respiratory as well as the phonatory muscles, receive their nerve supply from two small nerves, the superior laryngeal and the recurrent laryngeal nerves. The superior laryngeal only supplies the tensors of the vocal cords, the cricothyroid muscles, with motor fibres, whilst the recurrent is distributed to the adductor as well as to the abductor muscles. It is still an open question whether the recurrent is ultimately derived from the sjnnal accessory or the vagus nerve, both being cranial nerves, the centres of which are situated in the medulla oblongata. The researches of Terrier, Buret, Munk, Krause, Horsley, and myself have shown that the medulla is not the ultimate seat from which impulses are dis- tributed along the motor paths just sketched to the laryngeal muscles, but that there is for the purposive function which the larynx serves, viz. for phonatiou, a distinct centre in the surface or cortex of the brain, situated in the foot of the ascending frontal gyrus, just behind the lower end of the precentral sulcus. It is a very interesting and noteworthy phenomenon, that Professor Horsley and I have only been able to find (except in the cat) a definite area of representation of the action of the vocal cords in the cortex of the brain for the intentional purposive movements of the vocal cords, such as are used in speaking and singing. On stimulation of this area on one side, both vocal cords directly come together (i. e. are adducted), and remain, so long as the stimulation lasts, in the position which they assume when used for either of the last-named purposes. It is never possible, according to our researches, to produce an action of one cord alone, they always act bi-laterally and symmetrically. Equally impossible is it w^hen one looks at the larynx of a human being, of a monkey, or of a dog during the act of phonation, i. e. when the cords are being brought together and put into the proper degree of tension, to make out any difference in time between these two actions. Tension and adduction apparently occur absolutely simultaneously, or at least our retina is not able to distinguish any point of time between the order of execution of these two movements. Only in the cat can it be seen that the mewing is produced by the vocal cords first being brought together, i.e. by the act of adduction being performed, and then, after a measurable interval tension, i. e. elongation of tlie vocal cords, occurring. All this may seem rather much of a scientific reSnement, and only in remote, if any, connection with the subject of to-night's discourse. In reality, however, it is easy to show that this connection is a very 1891. J on the Culture of the Singing Voice, 321 intimate and a very necessary one. Nothing could be more fallacious than the often heard comparison between the teaching of the voice and that of the hand, as in violin or in piano playing. The mechanism which governs the muscles of our fingers, though by no means capable of producing finer variations and differentiations than that of the larynx, yet is infinitely more under the influence of the will than that of the last-named part. We can, by a process of perfectly conscious cerebration, teach not only the muscles of one hand, whilst those of the other remain absolutely quiet, to perform certain movements according to will, but this difierentiation goes to such refinement that we can actually educate individual muscles of individual fingers to a degree of independence which does not exist at all in the child or in the uneducated adult. All this is done, I repeat, by a process of conscious cerebration. Very different, however, from this is the action of the vocal cords in speaking and in singing. Not only is it impossible to the greatest singer to move one vocal cord without the other at the same time executing the same movements (in this respect, nlso, the vocal cords differ from even the movements of the eyes), but nobody can by a process of conscious cerebration move one laryngeal muscle without the other. This is rendered an absolute fact both by observation of the human being with the laryngoscope and by experiments upon animals. All the comparisons, therefore, of the development of the laryngeal muscles with those of the hand fall to the ground, and all the elaborate anatomico-physiological directions met with in more than one book of instruction for the student of singing must be referred to the realm of bewildering phantasmagoria. The rational training of the singing voice can only as yet proceed upon the basis of empirical experience, not uj)on that of theoretical deductions as to the action of the individual adductor muscles and upon equally theoretical directions as to their individual use. The means by which the movements of the vocal cords and indeed the larynx can be observed during the act of singing is the laryngo- scope, first introduced for physiological purposes by Signer Manuel Garcia, and afterwards brought into use for the study of laryngeal disease by Czermak and Tiirck. This instrument consists of a little round mirror, which, after having been properly warmed, is introduced into the throat of the person under observation in such a manner that it forms an angle of 45° with the horizon, its upper margin resting against the base of the uvula. If now from a powerful source of light horizontal rays are thrown on to the mirror, which is held in the open mouth of the person in the position just described, according to the principles of physiological optics these rays are directed in a vertical direction downwards, and illuminate the larynx, which is just below the point where the mirror is held. The rays are in turn reflected upwards into the mirror and thence into the eye of the observer, which is situated at an equal height and close to the source 322 Dr. Felix Semon [Marcli 13, of illumiiiatini. The picture thus resulting during qniet respiration you see here on the screen. (Demonstration.) Now, what I am particularly anxious to say as the result of long observation is that whilst you can, as just showu, see in this way the larynx in its entirety, and whilst you can judge with certainty ;is to any pathological change that may exist therein, not even the most cxperiencdd larjngologist can say from mere laryngoscopic examina- tion whether the larynx he sees is in any way that of a siuger or not. Of course he will be able to pronounce that, if there are any organic congenital or acquired defects in the ai;atomical configuration of the jiart, the owner of this organ will be incapable of producing musical sound, but if he sees merely a normally constituted larynx, it is absolutely impossible for hiui to say whether this belongs to the greatest singer living or to a person absolutely unendowed with the faculty of producing melodious sounds. I can assure my hearers that the laryrges of some of the greatest living singers look so common-place that nobody seeing one of these organs without knowing who its owner is would ever venture for a moment to believe that this could be the organ tj which he has been indebted for many a time of the highest artistic pleasure, whilst, on the other hand, magnificent looking larynges are frequently found in the possession of individuals who not only are utterly unmusical, but at the same time incaj^able of pioducing anything like an average singing voice. Nor is it possible, from the mere aspect of a laiynx, to say with absolute certainty even so much as what tlie general cluirncter of the singing voice prcduced by it may be. It is perfectly true that in the majority of cases soprani and tenors have comparatively S2)eaking short and narrow vocal cords, whiL; those of contralti aud bassi are broad and long. But to this rule so many exceptions occur that anybody who trusts blindly to this sign will be exposed to very frequent mistakes. To give but one example, I have never seen any larger and longer vocal cords than those of a well-known tenor who has often enchanted London audiences, whilst I am perfectly certain that every larjngologist who was asked without knowing anything about the owner to pronounce merely from the larynx, would pro- nounce tliis vocal organ, if at all exercised for singing, to be that of a basso profundo. I mention this point more i)articularly because it has more than once occurred in ray practice that students have been brought to me in order that I should decide from laryngoscopic examination what the true character of their voice was, a demand which, as 1 think 1 have just shown, it is absolutely impossible to comply with. But the general gist of the foregoing remarks is to show that an instrument which unfortunately fails to give us any clue as to the very elementary points just mentioned with regard to the character of the voice of the j^erson examined, can certainly not claim to have laid down on its authority the rules for singing 1891.] on the Culture of the Singing Voice. 323 in the dogmatic fashion in which this has repeatedly been done of late. Having so far given a very cursory anatomical outline of the conditions in which we are here interested, I now come to the physiological aspect of the question. The long mooted question whether the human voice was to be compared to a wood, a string, or a reed instrument has at last been definitely decided in favour of the last-named view ; though even at present timid attempts are made from time to time to revive the flute or the violin theory. In reality, however, the larynx is best to be compared to an organ pipe, the reed being rej)resented by the two vocal cords, which being anatomically absolutely identical with one another, and being simultaneously put into vibrations by the blast of air coming from the lungs, entirely correspond to the reed of the organ pijDe ; sound being produced, of course, by the vibrations of the cords, which are communicated to the column of air above and below the vibrating reed. According to the quantity of air coming from the lungs, more or less amplitude is given to the vibrations, as the result of which the tone gets more or less strength. The character of the sound thus emitted is no doubt influenced to a very considerable degree by the configuration of the larynx and the composition of the vibrating reeds, but the exact manner in which this influence is exercised is at the present time still an absolutely unknown entity. What is quite certain, however, is that the character of the voice is very greatly varied by the anatomical configuration of and the changes possible in the throat and mouth.* According to the laws of acoustics, three fundamental laws come here into question : 1. The number of vibrations of the cords determines the pitch of the note. 2. The amplitude of the vibrations determines, as already mentioned, the strength of the note. 3. The form of the vibrations determines the timbre or quality of the voice. These laws briefly indicate the most important qualities of the sound, viz. purit}', strength, and timbre. The iutra-laryngeal movements, i^ e. the proper degree of tension of the vocal cords determining, as has just been said, the pitch of the note, the purely technical training of the voice and the purity of the notes naturally dej^end upon the movements of the larynx proper, and more particularly upon the intralaryngeal changes during the emission of the sound. The dynamics of the voice, on the other hand, the crescendo and decresceiido, &c., depend upon the intensity of the movements of the thorax, of the diaphragm, and of the lungs. Finally, the colour or timbre of the voice is rendered variable by * The brief summary here given I have borrowed mainly from Julius Stock- hausen's ' Gesangsteclmik imd Stimmbilduug.' 324 Dr. Felix Semon [Marcli 13, the different positions of the parts forming the resonator, i. e. the tongue, the lips, the palate, and the epiglottis. What we call '■ exwressiou " in singing is, therefore, the result of a combination of the action of the bellows on the one, and of the resonator on the other, hand. (Demonstration ) There are, of course, almost numberless particular qualities of the voice upon which I should like to enter here at greater length, as the definition and discussion of each of them possess a particular fas- cination of their ovra, such as the compass, the volume, the sustained power, the tellingness, the certainty, the freshness, the intonation, facility, &c., of the voice, but time will not allow me to do so. I can only refer my hearers to a most charming little book cf Dr. Walsh's, called ' Dramatic Singing,' in which, although I do not agree with everything that the distinguished author states, and esj)ecially not with his curious manner of estimating the individual qualities of the voice, they will find a most fascinating description of all those individual qualities, and ample food for thought concerning the almost incredible multitude of points which enter into the composition of dramatic singing, couched in the most elegant and most picturesque language. Coming now to the question of the culture of the singing voice itself, two elements are absolutely necessary for proficiency, viz. first, a certain amount of natural material, and, second, a good ear. With regard to the first, this ought to be, as it were, a truism, but, indeed, it is not. Often enough people mistake the inclination for the gift^ and confound their love of singing with the decision of devoting themselves to it. I see numbers of students deficient in the very elements of vocal niaterial, who nevertheless have formed so grave and momentous a decision as the devotion of their lives to the practice of singing. There is a general tendency, under such circumstances, to attribute the failure to some "disease" of the vocal organs, or, if the word "disease" be not pronounced, at any rate to "weakness." The physician, seeing many of these ailments, cannot help asking himself what want of judgment can have induced such peoj)le to fight against impossibilities. As a rule there is no disease at all, but simple deficiency of the indispensable elementary material. I think it an act of kindness to warn such people against an uphill fight, in which, with the rarest exceptions, they cannot be successful. Cer- tainly it is not my desire to discourage ardent lovers of music from training their voices, however small, so long as they merely intend to use them for their own or their immediate friends' pleasure, but matters are widely diflerent when one sees young persons, who in other walks of life might earn a decent livelihood, struggling under the greatest difiiculties against unfavourable circumstances of every conceivable sort, and all this in order to cultivate a 2)ractically non- existent singing voice. Valuable years are often thus lost, and it is finally with a leeliug of des]iair and bitterness that such people, after 1891.] on the Culture of the Singing Voice. 325 lost years of labour, gain the conviction that they would have done much better to devote themselves from the very commencement to a different career. Would that every student of music, or those responsible for the selection of a career, might keep before their minds that in singing there are but few, very few indeed, who ever reach the top of the ladder, and that those who lag behind often enough carry the conviction of the futility of their endeavours throughout their lives ! I trust that the foregoing thoughts will not be interpreted in the sense as if I wished to encourage only those who are endowed with very large and beautiful material to devote themselves to the noble art of singing. In many cases even in originally weak vocal organs by rational training really astounding improvement can be produced ; others even with small material may, if husbanding their resources, and if intelligent enough not to aspire to impossibilities, achieve very fair success with limited means. Thus, it is a curious thing to find that often very small voices, i. e. small both in compass and in strength, yet are endowed with that all-important quality of the singing voice, viz. a sympathetic timbre, which is utterly denied to much larger or more flexible voices. Indeed this sympathetic timbre of the voice often goes hand in hand with conditions of an otherwise disqualifying character, such as a certain veil over the notes, a very small compass, a very deficient strength of tone ; yet if such people understand the great secret, that it is better, as was said of Henrietta Sonntag, to have a small genre, but to be great in that genre, than to a' tempt impossibilities, they may on the concert platform be very successful. Thus I know myself of several singers, both ladies and gentlemen, whose voices aie very small indeed, but who, being endowed with the sympathetic quality of timbre, having cultivated their voices in the most rational manner, and limiting their work to the interpretation of a high class of musical lyrics, to such a degree enchant their public that the smallness of the means by which their successes are achieved is comj^letely forgotten in the intellectual delight whiclt they give to their hearers. But the warning note I tried to sound before was merely direct(d against_^the loss of valuable time in cases of utter absence of any of those qualities of the voice which could endear its owner to a musical public. The next indispensable factor for cultivating the singing voice is the possession of a good musical ear. Now, with regard to the musical ear there are almost as many different senses in which that expression may be taken, as there are with regard* to the expression ** musical" in general. Thus it is perfectly well known that, whilst in some persons the musical ear is by a generous gift of nature, even if entirely untutored, yet endowed with the keenest qualities of perception and of action based upon that perception, other people equally intelligent are entirely deprived of any natural endowment in this particular direction, and have, as the saying goes, absolutely 326 Dr. Felix Semon [March 13, " no ear for music." Now this may mean a great many different things. Some people have no ear for pitch, others not for melody. The former will not hear even the most abominable flat or sharp singing, the latter will never recognise even the most catching melodies however often they may have heard them. Upon the tympana of other ones music makes a directly painful im2)ression. A third class has absolutely no sense of rhythm and cannot distin- guish a march from a waltz ; again, others, and here we come to the subject now under consideration, though having a keen enough perception of music, and boing ready enough to detect faults in others, are utterly unaware eitlier of the quality or of the pitch of their own voices. No doubt many of those present to-night will remember instances within their own experience in which some professional singer or amateur has judged very harshly certain defects in another singer's voice, being apparently utterly unaware that he himself had the faults against which he vociferated, in a much higher degree than the object of his attack. In other cases singers who will most acutely hear any fiat singing in another are utterly incapable of a2)prehending that tbey themselves sing flat, and finally, there is one class, who, though they themselves are aware of their own singing flat, are quite incapable of correcting the fault and of singing in pitch and in unison with other voices or with accompanying instruments. Instances of these j)oints will bo familiar to my hear -rs. The causes of all these deficiencies, which are of tlje most serious importance for the career of any professional singer, are no doubt to be found in the highest cerebral centres ; the imperfection of jjer- ception being due either to those afi'erent fibres which carry the impression of sound to the auditory centre or to congenital defect of the centre itself, whilst the impossibility of singing in pitch, though the singer himself is painfully conscious of his not doing so, must be due to some mischief within the paths which lead from the auditory to the phonatory centre. Defects of this sort are in part to some extent remediable through the aid of long continued training. In such cases it must be assumed that certain nerve cells originally not intended or only intended in a minor degree for the conveyance of the imi)ressious now under discussion, have been educated up to higher functions, in the same way in which we see that after the destruction of the speech centre in the left hemisjihere, the corre- sponding part in the right hemisphere may be, though almost always in an imperfect way, educated up to take the original duties of its fellow in the left hemisphere. In the great majority (f cases, however, either all training remains without efi'.ct, or the results are so small in proportion to the labour spent that the game is hardly w'orth the candle. This is a point of the very highest imjiortance. I have already previously mentioned that the training of the voice cannot be compared to the training of the hand for the purposes of piano or violin playing, inasmuch as the training of the latter is mostly performed in the shape of conscious voluntary acts ; whilst 1891.] on the Culture of the S'mgingVoice. 327 the training of the voice is of an infinitely more instinctive character and guided mainly by auditory impressions. But few persons have got such an absolute sense of tonality that they are at any moment ready to produce a note in the correct pitch without having first received a hint from some musical instrument. If the guide be taken away, i. e. if the auditory mechanism and the fibres connecting the auditory and phonatory apparatus be acting imperfectly, the whole training will needs be of au infinitely more difficult, very frequently of a finally imperfect character. Proofs of this may practically be seen any day both on the operatic stage and on the concert platform. A good musical ear, therefore, I should isay, is an indispensable adjunct for the 2:)rofessi{)nal career of a singer. Supposing now that both the indispensable amount of vocal material and the good ear be present, one question foremost naturally presents itself: when to begin proper training? With regard to this question, I iim decidedly of opinion that serious vocal training should not be begun in either sex as a rule before the sixteenth year of age, though it must be understood that there may be exceptions to this rule, both in favour of an earlier and <)t' a later commencement of vocal studies. The reason of this decided opinion consists in a consideration of the physiological conditions of the larynx during its development. In the period of adolescence the larynx undergoes very considerable changes. In boys especially a very sudden and very considerable enlargement of all the cartila- ginous framework occurs, accompanied by more or less acute con- gestion of the mucous membrane. Tlie considerable elongation of the vocal c irds which takes place at the same time, in a number of cases undoubtedly goes on so gradually that the muscles governing their movements adapt themselves insensibly to the altered condition of matters, and the transition both of the speaking and of the sino'ino' voice may be equally insensible and gradual. In by far the larger number of cases, however, the co-operation between all the factors necessary to produce the voice, especially in singing, often enough even in simple speaking, is not so imperceptibly established. The whole apparatus, as it were, temporarily gets out of gear and only alter a considerable period the diti'erent elements constituting it learn instinctively to adapt themselves to the suddenly altered anatomical conditions. The practical illustration of what I mean is given by that hated period in the life of many a boy called the breakinf: of the voice. Supposing now that a boy had had a sweet child's voice and that this voice had been utilised in choir singing, on the stage, in oratorio, or elsewhere, too often the exigencies of life make it very desirable that such a boy, who has to some extent contributed towards the support of his family by the gift of Nature bestowed upon him, should continue his singing over the period allotted to the child's voice by Nature ; whilst in other cases masters who do not know enough of the physiological changes taking place in the larynx might be inclined •328 Br. Felix Semon [Marcli 13, to continue the training of a favourite pupil's voice into this period of disturbance, during which physiological rest is absolutely wanted. The result in most cases will bo lasting loss of voice ; inasmuch as all the organs here concerned are of such a delicate nature that once hopelessly overstrained they are not likely ever to return to normal conditions. I am perfectly well aware that different opinions exist on this question ; that some singers as well as some laryngologists have expressed themselves in favour of a continued training through the period of adolescence, and that so and so many cases are quoted in which such a training has been continued throughout this trying period without any lasting harm resulting, the pupil on the contrary finally attaining eminence in the vocal profession. To all this I simply reply that I do not doubt the occurrence of exceptions, but that such exceptions the more confirm the rule, and that if a census were taken with regard to the number of those voices which have baen irretrievably ruined by premature vocal training during the period of adolescence in proportion to those in which no harm has resulterl, undoubtedly a large excess on the side of harm having resulted would be shown. Indeed a census of this nature has been taken by Messrs. Behnke and Browne in their little work, ' The Child's Voice,' and the result based upon collective investigation, in which a very large number of competent physiological authorities, teachers of singing and singers took part, iucontrovertibly points in the same direction in which my observations are going. All I can say is that if I had a child, boy or girl, gifted with an exceptionally fine voice, I should not allow it even to make the experiment. If a voice is really worth training, be it for professional use or for private amusement only, it is certainly worth — provided that external circumstances permit — having from the very beginning a very good teacher. No greater mistake, I think, could be made than to confide so comj)lex an apparatus as the vocal one is, at first for so- called elementary tuition to the tender mercies of a teacher, who has not the faintest idea either of the j)hysiology of the vocal organs or of the recognised and valuable modes of educating this apparatus, and who, by wrong tuition, either hopelessly spoils all the material that has been confided to him, or at any rate engenders bad habits, wrong muscular combinations, wrong habitudes of the sounding board of the voice, which afterwards only with the greatest j^ossible difiicul- ties can be eradicated even by the most competent successor he may have. The necessity of selecting from the very beginning of the pupil's vocal carter a really good teacher, is too obvious to be insisted upon at length. A really good master of singing will first of all take infinite pains to ascertain the true character of the pupil's voice. He will not make the mistake, but too often committed, of educating a contralto as a soprano or a baritone as a tenor, simply because there are a few fine high notes in the pui^il's voice ; nor will he at all 1891.] on the Culture of the Singing Voice. 329 purposely develop one part of the range of the pupil's voice at the expense of the others. He will build upon the material that he finds, not impose hypothetical or self-made laws ujDon it, and he will sub- ordinate his own likings to the natural exigencies of the whole character and nature of the pupil's voice. No more pernicious thing could be imagined than to look npou flexibility as the highest triumph to be achieved in a pujDil whose voice is the prototype of a heroic tenor, or, on the other hand, to force a J)^^P^1 to sing Brahms' or Schubert's most dramatic songs whilst the nature of her voice would show to any perfectly unbiassed ear that her true vocation was that of a coloratura singer. This brings me to the final part of my discourse, to the vexed question of the registers. I need not say that this question alone could be made the subject, not of one, but of a whole course of lectures, and that it will be impossible in the short space of time still lett me to do anything like adequate justice to it, or merely to mention all the points which here demand consideration. At the same time the question is of such transcendental importance fur the rational cultiva- tion of the singing voice that it cannot in a discourse on this subject be altogether passed over in silence ; and I avail myself of the oppor- tunity of alluding to it the more readily because, as stated in the beginning of my discourse, through the kindness of Dr. French, I am in a position to illustrate the question by the aid of the unassailable testimony of the photographic camera. It is well known that if any singer, but especially an untutored one, sings the ascending scale, the ear of the musical listener per- ceives after a series of tones which are different from one another only so far as the pitch is concerned, suddenly at one point or another of the gamut a notable difference in timbre, strength, and character. The point at which this change occurs is called the " break in the voice," and this change is much more noticeable in some classes of voices than in others. It is most developed in the tenor voice, in which the transition from the chest to the so-called falsetto voice is obvious even to less musical ears. A break of this character, accord- ing to the opinion of many authorities, occurs only once in the range of the voice, and these authorities Jbroadly divide the entire compass into the "chest" and "head" registers. In the opinion of others, however, there are not one but several breaks in the voice, and accordingly not two but three or more registers, the term "register" by common consent being applied to that series of consecutive tones which is produced by one and the same relative position of the laryn- geal apparatus, whilst only in the tension and approximation of the vocal cords do minute variations occur. What each of these registers exactly is, how it is produced, how one is changed into the other, what exactly is the manner in which our will influences the change, &c., we are not yet, I make bold to say, in a position to know precisely, though I am perfectly avvare that some authorities think that they know all about it, and that it 330 Dr. Felix Semon [Marcli 13, has been definitely stated which of the adductor muscles is, as it has been called, the "leadin^:;" muscle for each register. A theory of this character has been developed in a very attractive little book by Dr. Michael, of Hamburg, entitled ' The Formation of the Registers in Singing.' The author, whilst claiming that each register is distinguished by one of the adductor muscles specially presiding over its functions, positively states that for the production of each sound the co-operation of all laryngeal muscles up to a certain degree is necessary, and that on complete disablement of a single muscle only, complete loss of voice must necessarily ensue. Statements of this character show how dangerous it is to make too bold and absolute assertions in this whole question. According to the nature of things it is quite imaginable that certain of tlie adductor muscles may be concerned more in the formation of one, others in the formation of another register, but to make, as Dr. Michael has done, ahsolute and general conclusions from a few cases of paralysis of one laryngeal muscle or another in singers, as to the exact function of each of them in the j)roduction of the register, is quite inadmissible, as I am in a position to show at once. A distinguished tenor, whose case is known to several British laryngologists, had the misfortune a few years ago of entirely losing his voice from a tumour in his neck, jn-essing upon the left recurrent laryngeal nerve and completely paralysing the left vocal cord. Not only the singing but even the sj)eaking voice was entirely lost in the beginning of the illness. Under apj)ropriate treatment the tumour almost disappeared, and certain fibres of the recurrent laryngeal nerve recovered, whilst other ones had already been irretrievably damaged. The result of all this was that his left vocal cord was finally immov- ably fixed in the jiosition of phonation. In this position it remains up to the present day, i. e. it is not the least abducted wlien the patient inspires, and there cannot be the least doubt that the left abductor muscle is as comjjletely paralysed and unable to fulfil its natural functions as it possibly could be. Yet this gentleman at the present time is able not merely to sing and to sing high chest as well as falsetto notes, but the voice, according to the statements of many who have heard him before and after his severe illness, has entirely regained its former character, power, and comjiass. This case at once disposes of two theories which have been brought forward as if they were unassailable facts, namely, first of the state- ment just mentioned, and secondly of the frequently heard assertion that in paralysis of the abductors the possibility of producing high notes is lost. Another point also associated with the question of registers and of the greatest possible importance for tlie rational cultivation of the singing voice, is that, whether in voices of identical character, say for instance contralto voices, the break always occurs in one and the same note of the sjale, or whether the exact note on which it takes place varies in dilFerent individuals. I hope that the number of the 1891.] on the Culture of the Singing Voice. 331 theorists among teachers of singing, who on preconceived ideas believe that it always occurs on one and the same point and who, in accord- ance with this belief, force the whole natural mechanism of their pupils' voices into their theoretical formulae, is only a small one. But no doubt such teachers exist, and more than once I have heard statements from pupils who come to consult me, to the eifect that ever since they studied with Mr. So-and-so, and since they were told that they had been wrongly taught with regard to the break in their voice, and that they must begin to use the head voice or the falsetto voice, either higher or lower than so far they had been accustomed to take it, they f3t a great sense of fatigue after practising, and that they distinctly thought they had suffered with regard to the character of their voice. There can be nothing more dangerous, I venture to say, than any mistake with regard to this point, i. e. any interference with the lavys of nature, which in this question, I have not the least doubt, vary in every individual case. There is no such thing as an absolute point on which the voice breaks, in auy class of singers. No doubt the break occurs in one and the same class of voice more or less in the neighbourhood of a certain note, for instance, in contralto voices the lower break as a rule occurs about the neighbourhood of E or F on the line, but no doubt there are many voices in which it occurs either at E flat or on the other hand at F sharp, and that the voice in which it occurs at the higher part should now be forced into a lower break because that corresponds with the theoretical ideas of the master, would be a simply unpardonable mistake. The whole question of the registers is at the present time being so ably treated by my friend, Dr. French, of Brooklyn, who earned general and well deserved applause by a paper he read on that subject on the occasion of last year's International Medical Congress at Berlin, that I only wish I could in conclusion of tliis discourse read to you verbatim the whole of it and show you all those splendid photographs by mea,ns of which he illustrated it. But unfortunately the time still left to me is so short that I must limit myself to giving you a part only of his lecture in his own words, and to more briefly deal with the remainder. Dr. French at the onset of his enquiries started from the very just idea that the movements of the glottis are often so rapid that the eye cannot appreciate them, or rather so numerous that the mind will not retain them in the order of their occurrence. It is estimated that the human eye can open and shut in the tenth part of a second, but an impression formed upon the retina in that time lacks detail, while an image of the interior of the larynx in all its detail may be fully and clearly impressed upon the sensitive plate in the hundredth part of a second. Those movements which the eye fails to appreciate may easily be defined by taking a series of photographs at different stages, which being viewed consecutively clearly shows such move- ments in their entirety. 332 Dr. Felix Semon [March 13, For fully six years Dr. French with unremitting perseverance has perfected the art of taking instantaneous photographs of the larynx in singing. Only those who saw his initial results and those obtained about 1883 and 1884: by contemporaneous workers, such as Messrs. Behnke and Browne, can appreciate the enormous progress he has made within that time and the value of the results thus obtained. In spite of this he has, according to his own statements, net yet permitted himself to formulate a theory of the action of the larynx in singing, for even now, after large numbers of studies Lave been made by him, he says that the camera is constantly revealing new processes in the action of the vocal cords in every part of the scale, and that the movements of the larynx in a much larger number of subjects must be revealed, grouped, and recorded before definite conclusions can be drawn. The fact that there are relatively but few subjects in whose larynges the anterior insertions of the vocal cords can be seen throughout the range, adds greatly to the difficulties of this investigation. In order to find one satisfactory subject a large number have to be examined, which necessarily takes much time, and renders the progress of the study very slow. At Berlin Dr. French exhibited a series of photographs taken of the larynges of four female singers, which showed how the changes are made in the action of the glottis from one register to the other in the variations and the pitch of the voice. These series were taken consecutively, and therefore fairly represent the marked variations in the movements of the various structures which occur in different larynges. The description of the first series I give in Dr. French's own words as follows : — " The first pair of photographs is the first of a series which will be shown of the larynx of a well-known professional contralto singer. Fig. 1. 1891.] on the Culture of the Singing Voice. 333 Tho voice is of excellent quality. The first pair was taken while F sharp, treble clef, third line below staff, was being sung ; and the second while she was singing E above. These are one of the lowest and highest notes of her lower register. In the photograph repre- senting the lowest note it can be seen that the vocal cords are (^uite short and wide, and that with the exception of the anterior fourth the ligamentous part of the cartilaginous glottis is open, and the slit between the vocal bands is linear in shape. As the voice ascends the scale the vocal cords increase in length and decrease in width, until at the highest note of the register they may be seen to have become considerably longer. It can also be observed that the ligamentous portion of the glottis is still open to the same relative extent, and that the cartilaginous portion has opened to its full extent. In the photograph representing the lower note the anterior faces of the arytenoid cartilages can be seen. The epiglottis, though not well illuminated, seems to have risen as the voice ascended the scale ; the vocal cords have increased in length at least |th of an inch in seven notes. The compass of the voice of this singer is about two octaves and a half, therefore at that rate of lengthening the vocal cords would increase nearly half an inch if their length was progressively increased while singing up the scale from the lowest to the highest note. This progressive increase in length does not, however, occur, and the reason will be apparent in the next pair of photographs, which show the changes which take place in the larynx at the lower break in the voice, which in this subject occurs at F sharp, treble clef, first space." Fig. 2. E m " The changes which occur at this point are extremely interesting and instructive in the transition from the lower to the middle register, from E to F sharp. In the voice of. this subject the vibratory portions of the vocal cords are shortened about the ^\yth of an inch. The Vol. XIII. (No. 85.) ' z 334 Dr. Felix Semon [March 13, anterior insertions of the cords can be seen in both photographs, therefore the actual difference in the length of the bands can be appreciated. The vocal cords have not only become shorter, but they appear to be subject to a much higher degree of tension. The cartilaginous glottis is closed, and the aperture in the ligamentous portion has been much reduced in size. The laws which govern the pitch in both string and reed instruments will aid us in explaining this change. Though the tone is higher, and the degree of stretching less than in the note below, the tension is increased, and the aperture through which the air passes is much narrower." " The anterior, posterior, and lateral dimensions of the larynx are shown to have been considerably decreased when the voice broke into the register above. The voice acquired a very different quility, which continued in gradual elevation of pitch throughout the register." As marked a change as this in the mechanism of the vocal cords in females is, Dr. French believes, only found in the larynges of con- tralto singers. " As the singer ascends the scale above the break at F sharp the vocal cords are increased in length, and the chink gradually enlarges, as shown in the next pair. The first photograph is of the larynx Fig. 8. while singing F sharp, treble clef, first space, the note on which the lower break occurred, and the second while singing D, treble clef, fourth line, which is the highest note in the middle register of the voice of this singer. The difference in the length of the vocal cords and width of the chink of the glottis as the voice mounts from the lowest to the highest note of the middle register is clearly shown. Again, as the vocal bands increase in length in this register, their tension is apparently decreased." " Now the voice mounts one note higher — that is, to E, treble clef, fourth space — and as it does so a distinct change in the quality of 1891.] on the Culture of the Singing Voice. 335 the voice is heard, and the second change in the mechanism of the vocal cords occurs. The changes which take place in the larynx at the upper break in the voice of this singer are shown in the next pair. The first photo represents the larynx while singing D, treble clefj fourth line, the note immediately preceding the break, and the Fig 4. ^'-tr fm mui second shows the change which occurred while singing E, the next note above. A very decided change in the mechanism of the vocal cords is apparent. These ligaments have grown higher and narrower, and the chink which in the note before the break can be seen to be linear in shape and quite wide, after the break becomes considerably reduced in both length and width. Not only is the cartilaginous portion of the glottis closed in the note after the break, but also a small portion of the ligamentous glottis immediately adjoining it. The chink appears to be closed to the same extent in front as it was while producing the note immediately preceding it. There is, there- fore, stoj)-closure in front and behind, which leaves a slit in the middle of the glottis measuring a little more than half the length of the vocal cords. In addition to these changes, it may be observed that the epiglottis is depressed and the arytenoid cartilages have again receded. As this is the highest note which this subject is capable of singing with ease, we cannot study the action of the vocal cords in the production of tones in the upper register." " It may be remembered that in this larynx the vocal cords increase in length from the low F sharp to the E above. At the next note higher they began to increase in length again until D above was reached, and at E, the note next above, they were again suddenly shortened. It will be instructive to determine the degree to which the vocal cords were lengthened, and at what point in the scale they were longest. We saw that in the lower register the vocal cords were longest in the production of the highest note, and in the middle 336 Dr. Felix Scmon [March 13, register they were also longest while the highest note was being sung. By comparing the photographs representing these notes it can be seen that the vocal cords were as long, if not the longest, while the highest note of the lower register was being sung. In this subject the vocal cords increase in length in each register, but they had as great a length in the lower as, in either register above, if not greater. It is generally thought that the pitch is raised by the vocal cords increasing progressively in tension and length. In regard to length this is true in some cases, while in others it is only true as aj)plied to a register, not to the whole voice." In the second case, photographs of which were shown by Dr. French at Berlin, but of which he unfortunately could not send me copies, because the photographs of the larynx of this subject, though clear and strong enough for satisfactory exhibition upon the screen, were too weak for a direct reproduction by the photo-engraving jjrocess, the action of the larynx was in many respects the reverse of that just examined. In it the cartilaginous glottis did not appear to begin to open until the highest notes were reached. In the lower register the chink of the glottis decreased instead of increasing in size as the voice ascended. At the lower break the vocal cords were increased instead of decreased in length, and the chink of the glottis increased instead of decreasing. Again, the vocal cords attained their greatest length at the highest note in the voice of this subject, which corresponded to about the highest note of the middle register, whilst in the larynx before examined the chink of the glottis increased in size, and the vocal cords increased in length, as the voice ascended in each register. I should the more have liked to show the photo- graphs illustrating this condition, inasmuch as the subject was also a contralto singer, and as the demonstration would have materially aided in strengthening the position that the action of the glottis in singing, even in voices belonging to the same class, varies very considerably. The next series of photograj)hs, I am selecting from Dr. French's collection, illustrates the action of the glottis in singing, of a well- trained soprano singer, who possesses the extraordinary range of four octaves, the voice being of excellent quality. The first pair of photographs represent one of the lowest and the highest notes of the lower register of this singer's voice. As the voice mounts the scale the vocal cords increase in length and the cartilaginous portion of the glottis increases in size ; the arytenoid cartilages recede from the anterior wall of the larynx. In the neighbourhood of C sharp a change in the quality of the voice was heard. Dr. French lays jmrticular stress upon the fact that the change could be heard in the ncighhourlwod of C sharp, for the note at which the break occurred varied considerably in this subject. In some of the runs it occurred at C sharp ; in others at D or E. Not knowing exactly where it would occur, it was difficult to get a satisfactory idea of the nature of the change in the laryugoscoi)ic mirror. lie therefore took 1891.] oil the Culture of the Singing Voice. 337 pliotographs while the subject sang each note from A below to the A above. An examination of the negatives revealed the break at D, a Fig. 5. photograph of the larynx while singing which is shown in the next pair, together with one while singing the note immediately pre- ceding it. Fig. 6. From this point the vocal cords are gradually increased in length and decreased in width as the voice mounts the scale in the middle register, as is seen in the following pair. This pair represents the lowest and highest notes of the middle register of this subject. 338 Br. Felix Semon Fig. 7. [March 13, At the next note higher, F sharp, treble clef, top line, another change in the quality of the voice occurred, and with it a change in the laryngeal mechanism, which is displayed in the next pair of photographs. The voice has broken into the upper or head register Fig. 8. and the chancje in the mechanism is decided. The vocal cords are reduced in length and appear to be narrower. The edges of the cords are closer together, only a narrow linear slit being left between them ; the capitula Santorini are tilted backward and the cartilaginous portion of the glottis is nearly or quite closed. The position of tlie epiglottis is about the same as when j)roduciug the note before the break. The opinion prevails that in the production of tones in the upper register some portion of the edges of the vocal cords are in contact or pressed tightly together ; in other words, that stop-closure occurs. 1891.] on the Culture of the Singing Voice. 339 Here the anterior fourth of the glottic chink is closed, but the same amount of ch)sure in the same position may be seen in the larynx singing the note before the break. Now the voice mounts to high C sharp. The next pair shows the Fig. 9. Ojlt Jfi larynx while singing that note, and also the note on which the voice broke into the head register. In that representing G sharp it can be seen that the whole of the cavity of the larynx is smaller, and that the vocal cords and the chink of the glottis are narrower. The vocal cords appear to be much shorter, but as the anterior ends are covered by the cushion of the epiglottis, it is impossible to say how much shortened they really are. The arytenoid cartilages are closer together and are inclined further forward in the high than in the low notes of this register. The mucous membrane covering the lateral walls of the larynx is wrinkled, showing that during the production of this high note it is not capable of contracting to a sufficient extent to present a smooth surface. In the high note even the contact between the vocal cords, which can be seen in the lowest head note, and which we saw occur in the production of notes in the middle register, has disappeared, and there is a clear linear space between the vocal cords the entire length of the glottis. The next pair represents high C sharp and a still higher note in the subject of this voice, F sharp. In that representing F sharp we may observe that the cavity of the larynx is greatly contracted, the epiglottis is not so high as when C sharp was sung, in fact the four walls of the larynx are crowded towards the centre and the epiglottis is curled inward, the arytenoid cartilages arc almost if not quite in contact, the vocal cords are very short and look like threads. The most surprising revelation made in this picture is that there is no 340 Dr. Felix Semon [March 13, stop-closure. It is possible that there was slight contact between the edges of the vocal cords at the posterior portion of the glottis, but in Fig. 10. F^ if*. Dr. French's opinion air was passing between the edges of the cords the entire length of the glottis when this photograph was taken. From the revelations made in the photographs of the glottis of difterent persons while head tones were being sung. Dr. French comes to the conclusion that contact of the vocal cords in the first 5 or 6 tones of the head register does not occur in half the number of cases. Reluctantly I refrain from further following Dr. French in his interesting lecture. His argument of course gets the more convincing tlie more examples of the variety of ways in which the larynx acts in the cases of different singers are brought forward and illustrated by means of the camera. Time, however, will not allow me to do so, and I can only give the most important conclusions regarding tlie action of the glottis in female singers at which he finally arrives. They are as follows : — " 1. The larynx may act in a variety of ways in the production of the same tones or registers in different individuals." " 2. The rule, which, however, has many exceptions, is that the vocal cords are short and wide, and the ligamentous and cartilaginous portions of the glottis are open in the production of the lower tones ; that as the voice ascends the scale the vocal cords increase in length and decrease in width. The aperture between the posterior portions of the vocal cords incr(;ascs in size, the capitula ISantorini are tilted more and more forward, and the epiglottis rises until a note in the neighbourhood of E, treble clef, first line, is reached. The cartila- ginous glottis is then closed, the glottic chiid^ becomes much narrower and linear in shape, the capitula Santorini are tilted backward and the epiglottis is depressed." 1891.] on the Culture of the Singing Voice, 341 " When the vocal bands are shortened in the change at the lower break in the voice, it is mainly due to closure of the cartilaginous portion of the glottis, the ligamentous portion not usually being affected. If, therefore, the cartilaginous glottis is not closed there is usually no material change in the length of the vocal cords." " As the voice ascends from the lower break the vocal cords increase in length and diminish in width, the posterior portion of the glottic chink opens more and more, the capitula Santorini are tilted forward and the epiglottis rises until, in the neighbourhood of E, treble clef, fourth space, another change occurs. The glottic chink is then reduced to a very narrow slit ; in some subjects extending the whole length of the glottis ; in others closing in front or behind in both. Not only is the cartilaginous glottis always closed, but the ligamen- tous glottis is, I believe, invariably shortened. The arytenoid cartilages are tilted backward, and the epiglottis is depressed. As the voice ascends in the head register the cavity of the larynx is reduced in size, the arytenoid cartilages are tilted forward and brought closer together, the epiglottis is depressed and the vocal cords decreased in length and breadth. If the posterior part of the ligamentous portion of the glottis is not closed in the lower, it is likely to be in the upper notes of the voice." The series of photographs which were shown by Dr. French were not selected to prove any preconceived ideas ; they simply represent the variations which will be met with in any four consecutive studies. It is, however, scarcely to be wondered at that the theories regarding the action of the glottis in singing differ so widely, especially those based upon the study of one subject or of a few. Dr. French personally is of opinion that the female voice has three registers, and considers it quite probable that in voices with exceptional ranges there are four registers. At the same time, he says that sufficient evidence has not yet been obtained to make this demonstrable. I am glad to have been able to show that this, the latest achieve- ment of abstract science, so fully corroborates the views held by competent teachers of singing as to the enormous variety in producing the singing voice, and I can only, in conclusion of my discourse, express, together with my warmest thanks to Dr. French for having allowed me to illustrate my opinions by aid of the results of his perseverance and industry, the conviction that that teacher will be the most successful one who individualises in every single case confided to his care, remembering how delicate the mechanism is which is entrusted to him and how easily mischief may be wrought by wrong training, whilst that pupil will the most probably reap the best fruits of his studies who aims only at perfecting that which has been given to him by Nature, not at achieving what is impossible according to physiological laws. [F. S.] Vol. XIII. (No. 85.) 2 a 342 General Monthly Meeting. [April 6, WEEKLY EVENING MEETING, Friday, Marcli 20, 1891. Basil Woodd Smith, Esq. F.R.A.S. F.S.A. Vice-President, in the Chair. Professor Victor Horsley, F.R.S. B.S. F.R.C.S. M.B.I. Fullerian Professor of Physiology, R.I. Hydrophobia, (No Abstract.) GENERAL MONTHLY MEETING, Monday, April 6, 1891. Sir James Crichton Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. William Boyle Barbour, Esq. M.P. The Right Hon. Lord Randolph Churchill, M.P. C. E. H. Chadwyck-Healey, Esq. Q.C. Mrs. C'. E. H. Chadwyck-Healey, William Frederick Hamilton, Esq. LL.D. William Robert Lake, Esq. The Rev. Edward G. C. Parr, M.A. Thomas Slingsby Tanner, Esq. Charles Humphrey Wingfield, Esq. Latham Augustus Withall, Esq. were elected Members of the Royal Institution. The Special Thanks of the Members were returned for the following Donations to the Fund for the Promotion of Experimental Research : — £ s. Ludwig Mond, Esq 100 0 Lachlan M. Rate, Esq 50 0 Charles Hawksley, Esq. (for new Optical Lantern) 50 0 Alfred Bray Kempe, Esq. (do.) 5 5 David Edward Hughes, Esq. (do.) 2 2 George Berkley, Esq. (^<^-) ^ ^ Basil Woodd Smith, Esq. (do.) 5 5 Edward Pollock, Esq. (do.) 2 2 Sir Frederick Bramwell, Bart. (do.) 10 10 Sir Frederick Abel (do.) 5 0 Professor Dewar (do.) 10 10 Sir James Crichton Browne (do.) 5 5 Warren W. de la Rue, Esq. (do.) 10 10 Wm. Chandler Roberts- Austen, Esq. (do.) 5 5 1891.] General Monthhj Meeting. 343 The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FROM Accademia dei Lincei, Reale, Roma — Atti, Serie Quarta : Kendiconti. 1" Semes- tre, Vol. VII. Fasc. 1-6. 8vo. 1891. Atti, Anno 43, Sess. 4% 5% 6*. 4to. 1891. Atti, Serie Quarta, Anno CCLXXXIII.-CCLXXXV. 4to. 1886-8. Academy of Natural Sciences, PMladelphia — Proceedino^s, 1890, Part 2. 8vo. Antiquaries, Society of — Archseologia, 2nd Series, Vol. II. Part 1. 4to. 1890. Proceedings, Vol. XIII. No. 2. 8vo. 1890. Aristotelian Society — Proceedings, Vol. I. No. 4, Part 1. 8vo. 1891. Asiatic Society of Bengal — Journal, Vol. LVIII. Part 1, No. 3; Part 2, No. 5; Vol. LIX. Part 2, Nos. 2, 3. 8vo. 1889-90. Proceedings, Nos. 4-10. 8vo. 1890. Astronomical Society, Boyal — Monthly Notices, Vol. LI. No. 4. 8vo. 1891. British Architects, Boyal Institute of — Proceedings, 1891, Nos. 10, 11. 4to. Brymner, Douglas, Esq. {the Archivist) — Report on Canadian Archives, 1890. 8vo. Cambridge Philosophical Society — Transactions, Vol. XV. Part 1. 4to. 1891. Proceedings, Vol. VII. Part 3. 8vo. 1891. Canadian Institute — Transactions, Vol. I, Part 1, No. 1. 8vo. 1890. Chemical Industry, Society of — Journal, Vol. X. No. 2. 8vo. 1891. Chemical Society — Journal for March, 1891. 8vo. Civil Engineers' Institution — Minutes of Proceedings, Vol. CIII. 8vo. 1891. Cracovie, V Academic des Sciences — Bulletin, 1891, No. 2. 8vo. Daivson, G. M. Esq. LL.D. F.G.S, (the Author) — Note on the Geological Structure of the Selkirk Range. 8vo. 1891. Dax, Soci^te de Borda — Bulletin, Quinzieme Anne'e. 3me et 4me Trimestre Svo. 1890. Editors — American Journal of Science for March, 1891. 8vo. Analyst for March, 1891. 8vo. Athenaeum for March, 1891. 4to. Brewers' Journal for March, 1891. 4to. Chemical News for March, 1891. 4to. Chemist and Druggist for March, 1891. Svo. Electrical Engineer for March, 1891. fol. Engineer for March, 1891. fol. Engineering for March, 1891. fol. Horological Journal for March, 1891. Svo. Industries for March, 1891. fol. Iron for March, 1891. 4to. Ironmongery for March, 1891. 4to. Murray's Magazine for March, 1891. Svo. Nature for March, 1891. 4to. Open Court for March, 1891. 4to. Photographic News for March, 1891. Svo, Public Health for March, 1891. Svo. Revue Scientifique for March, 1891. 4to. Telegraphic Journal for March, 1891. fol. Zoophilist for March, 1891. 4to. Florence Biblioteca Nazionale Centrale — Bolletino, Nos. 124-126. Svo. 1891. Indice Cataloghi, Codici Palatini IV. Vol. II. Fasc. 3. Svo. 1891. FranTdin Institute— J owcnol, No. 783. Svo. 1891. Geographical Society, Royal — Proceedings, New Series, Vol. XIII. Nos. 3, 4. Svo. 1891. Georgofili, Reale Accademia — Atti, Quarta Serie, Vol. XIII. Disp. 3^ Svo. 1890. Harlem, Societe Hollandaise des Sciences — CEuvres Completes de Christiaa Huygens, Tome 3. Correspondance, 1660-1661. 4to. 1890. 2 A 2 344 General Monthly Electing. [April 6, Harris, John, Efq. (the Author) — The Laws of Force and Motion. 4to. 1890. Johns HopTihis L'i/irers/ow Sun Visible Spectra, with notes on the method of Photographing tlie Eed End of the Spectrum, fol. 1890. Manchester Geological Society — Transactions, Vol. XXI Parts 2-5. 8vo. 1890-1. Ministry of Public WorJcs, Rome — Giornale del Genio Civile, 1891, Fasc. 1". And Designi. fol. 1891. Morris, David K. Esq. (the Author) — Notes of a Thousand Men. 8vo. 1891. Neiv York Academy of Sciences — Transactions, Vol. IX. Nos. 3-8. 8vo. 1889-90. Annals, Vol. IV. (index) ; Vol. V. Nos. 4-8. 8vo. 1890. North of England Institute of Alining and Mechanical Engineers — Keport of the French Commission on the Use of Explosives in the presence of Fire-damp in Mines. Part 3. 8vo. 1891. Odontologiral Society of Great Britain — Transactions, Vol. XXIII, Nos. 4, 5. New Series. 8vo. 1891. Pennsijlvania Geological Survey — Dictionary of Fossils, Vols. II. III. 8vo. 1889. Atlases to Report, 1889. 8vo. Report on Oil and Gas Fields. 8vo. 1890. Pharmacmtical Society of Great Britain — ^^Journal, INIarch, 1891. 8vo. Prince, C. Leeson, Esq. F.R.A.S. F.R.Met.Soc. — Summary of a Meteorological Journal for 1890. Rathhone, E. P. Esq. {the Editor) — The Witwatersrand Mining and Metallurgical Review, Nos. 13, 14. 8vo. 1891. Richards, Admiral Sir G. H. K.C.B. F.R.S. (the Conservator) —'Reiport on the Navigation of the River Mersey, 1890. 8vo. 1891. Rochester Academy of Science — Proceedings, Vol. I. Part 1. 8vo. 1890. Rothschild, F. C von, Esq. — Die Einrichtung nnd Verwaltung der F. C. von Rothschild'schen offentlichen Bibliotek (1887-90), von Dr. Christ Wilh. Berghreflfer. 8vo. 1891. Royal Institution of Cornwall — Journal, Vol. X. Part 2. 8vo. 1891. Royal Society of London — Proceedings, No. 297. 8vo. 1891. Royal Society of New South Wales — Jouinal and Proceedings, Vol. XXIV. Part 1. 8vo. 1890. Saxon Society of Sciences, Royal — Mathematisch-physischen Classe : Abhandlun- gen. Band XVI. No. 3 ; Band XVII. Nos. 1, 2. 8vo. 1891. Berichte, 1890, Nos. 2-4. 8vo. 1891. Scottish Society of Arts, Royal — Transactions, Vol. XII. Part 4. 8vo. 1891. Selborne Society— Nature Notes, Vol. II. No. 15. 8vo. 1891. Smithsonian Institution — Annual Report, 1888. 8vo. 1890. National Museum Report, 1888. 8vo. 1890. Societe Archxologique du Midi de la France — Bulletin, No. 5. 8vo. 1890. Society of Architects— Proceedings, Vol. III. Nos. 7, 8, 9. 8vo. 1891. Society of ^r^s— Journal for March, 1891. 8vo. United Service Institution, Royal — Journal, No. 157. 8vo. 1891. Vereins zur Beforderung des Gewerhfleisses in Preussen — Verhandlungen, 1891 : Heft 2, 3. 4to. Wells, Sir T. Spencer, Bart. F.R.C.S. M.R.I, (the Author)— M.odiexn Abdominal Surgery. (The Bradshaw Lecture.) 8vo. 1891. Wild, Dr. H. (the Director) — Annalen des Physikalischen Central-Observatoriums, Theil II. January, 1889. 4to. Wright & Co. Messrs. J. (the Publishers)— Lectiuea on Diabetes. By Robert Saundby, M.D. 8vo. 1891. Medical Annual, 1891. 8vo. 1891.] Sir W. Thomson on Electric and Magnetic Screening. 345 WEEKLY EVENING MEETING, Friday, April 10, 1891. William Crookes, Esq. F.E.S. Vice-President, in the Chair. Sib William Thomson, D.C.L. LL.D. Pres. R.S. M.B.I, Electric and Magnetic Screening. There are five kinds of screening against electric and magnetic influences, which are quite distinct in our primary knowledge of them, but which must all be seen in connected relation with one another when we know more of electricity than we know at present : — I. Electrostatic screening ; II. Magnetostatic screening ; III. Varia- tional screening against electromotive force ; IV. Variational screening against magnetomotive force ; V. Fire-screens and window-blinds or shutters. I. Electrostatic screening is of fundamental significance throughout electric theory. It has also an important place in the history of Natural Philosophy, inasmuch as consideration of it led Faraday from Snow Harris's crudely approximate but most interestingly sug- gestive doctrine of non-influence of unopposed parts and action in parallel straight lines betv\'een the mutually visible parts of mutually attracting conductors, to his own splendid theory of inductive attrac- tion transmitted along curved lines of force by specific action in and of the medium intervening between the conductors. A continuous metallic surface completely separating enclosed air from the air surrounding it acts as a perfect screen against all electro- static influence between electrified bodies in the portions of air so sej)arated. This proposition, which had been established as a theorem of the mathematical theory of electricity by Green, in the ninth article of his now celebrated essaj^,* was admirably illustrated by Faraday, by the observations which ^ he made inside the wooden cube covered all around with wire netting and bands of tinfoil, which he insulated within this lecture-room ij *' I went into the cube and lived in it ; and, using lighted candles, electrometers, and all other tests of electrical states, I could not find the least influence upon them, or indication of anything particular given by them, though all the time the outside of the cube was powerfully charged, and large sparks and brushes were darting off from every point of its outer surlace." * See pp. 14 and 48 of the reprint edited by Ferrers, t 'Experimental Kescarclics,' 1173-1174. 346 Sir William Thomson [April 10, The doctrine of electric images is slightly alluded to, and an illustrative experiment performed, showing the fixing of an electric image. The electroscope used for the experiments is an electrified pith ball, suspended by a varnished double-silk fibre of about 9 or 10 feet long. Figs. 1-4 represent experimental illustrations, in which the pith ball, positively electrified, experiences a force due to electrified bodies, optically screened from it by a thin sheet of tin- plate. In Figs. 1 and 2 the pith ball is attracted round a corner by a stick of rubbed sealing-wax, and in Figs. 3 and 4 repelled round a corner by a stick of rubbed glass. In Fig. 2 the sealing-wax seems to repel the pith ball, and in Fig. 4 rubbed glass seems to attract it. Fig. 1. -® Fig. 2. Fig. 3. ©--• Fig. 4. This experiment constituted a very palpable illustration of Faraday's induction in curved lines of force. In the present lecture some experimental illustrations were given of electrostatic screening by incomplete plane sheets and curved surfaces of continuous metal, and of imperfectly conducting material, such as paper, slate, wood, and a sheet of vulcanite, moist or dry, window glass at ordinary temperatures in air of ordinary moisture, and by perforated metal screens and screens of network, or gratings of parallel bars. 1891.] on Electric and Magnetic Screening. 347 The fixing of an electric image is shown in two experiments : (1) the image of a stick of sealing-wax in a thin plane sheet of vulcanite, moistened, warmed, and dried under the electric influence by the application and removal of a spirit-lamp flame ; (2) the glass jar of a quadrant electrometer with a rubbed stick of sealing-wax held projecting into it, while the outer surface is moistened, warmed, and dried by the application and removal of a ring of flame produced by cotton wick wrapped on an iron ring and moistened in alcohol. Fig. 5 is copied from a diagram of Clerk Maxwell's to illustrate screening by a plane grating of parallel bars of approximately circular Fig. 5. cross section, with distance from centre to centre twelve times the diameter of each bar.* It represents the lines of force due to equal quantities of opposite electricities on the grating itself, and a parallel plane of continuous metal (not shown in the diagram) at a distance from the grating of not less than one and a half times the distance from bar to bar. The shading shows the lines of force for the same circumstances, but with oval bars instead of the small circular bars of Maxwell's grating. It is interesting to see how every line of force ends in a bar of the grating, none straying to an iu finite distance beyond it, which is necessarily the case when the quantities of elec- tricity on the gratiug and on the continuous plane are equal and opposite. If an insulated electrified body, with electricity of the same name as that of the grating, for example, is brought up from below, it experiences no electric force differing sensibly from that which would be produced by its own inductive effect on the grating, till it is within a less distance from the grating than the distance from bar to bar, when it experiences rejjulsion or attraction, according as it is under a bar of the grating or under the middle of a space between two bars. If there be a parallel metal plane below the grating, kept * 'Electricity and Magnetism,' vol. 1. art. 203, fig. xiii. 348 Sir William Thomson [April 10, at the same potential as the grating, it takes no sensible proportion of the electricity from the grating, and experiences no sensible force when its distance from the grating exceeds a limit depending on the ratio of the diameter of each bar to the distance from bar to bar. The mathematical theory of this action was partially given by Maxwell,* and yesterday I communicated an extension of it to the Eoyal Society. II. Magnetostatic screening by soft iron would follow the same law as electrostatic screening, if the magnetic susceptibility of the iron were infinitely great. It is not great enough to even approximately ffl V////////////////?777P. ^s^ss^sss^s^^^s^^^ssssss^s^s^^^ V//?//////////////ZZ, Fig. 6. fulfil this condition in any practical case. The nearest aj^proach to fulfilment is presented when we have a thick iron shell completely enclosing a hollow space, but the thickness must be a considerable proportion of the smallest diameter, not less than -j^^^, perhaps, for iron of ordinary magnetic susceptibility to produce so much of screen- ing effect that the magnetic force in the interior should be anything less than 5 per cent, of the force at a distance outside, when the shell is placed in a uniform magnetic field. The accompanying diagram, Fig. 6, representing the conning-tower of H.M.S. ' Orlando,' and the position of the compass within it, has been kindly sent to me by Captain Creak, R.N., for this lecture, by permission of the Controller * Arts. 203-205. 1891.] on Electric and Magnetic Screening. 349 of the Navy. It gives an interesting illustration of magnetic screen- ing effect by the case of a belt of iron, 1 foot thick, 5 feet high, and 10 feet in internal diameter, with roof and floor of comparatively thin iron. Captain Creak informs me that the average horizontal com- ponent of the magnetic directing force on the compass in the centre of this conning-tower is only about one-fifth of that of the undisturbed terrestrial magnetism. An evil practice, against which careful theoretical and practical warnings were published two or three years ago,* and which is now nearly, though, I believe, not at this moment quite thoroughly, stopped, of what is called single wiring in the electric lighting of ships, has been fallaciously defended by various bad reasons, among them an erroneous argument that the ship's iron produced a sufficient screening effect against disturbance of the ship's compasses, by the electric light currents, when that plan of wiring is adopted. The argument would be good for a ship 60 feet broad and 30 feet deep, if the deck and hull were of iron 3 feet thick. As it is, mathematical calculation shows that the screening effect is quite small in comparison with what the disturbance of the compass would be if the ship and her decks were all of wood. Actual observation, on ships electrically lighted on the single wire system by some of the best electrical engineers in the world, has shown, in many cases, disturbance of the compass of from 3 degrees to 7 degrees, produced by throwing off and on the groups of lights in various parts of the ship, which are thrown on and off habitually in the evenings and nights, in ordinary and neces- sary practice of sea-going passenger ships. When the facts become known to shipowners, single wiring will never again be admitted at sea unless the alternating current system of electric lighting is again adopted. But, although this system was largely used when electric lighting was first introduced into ships, the economy and other advan- tages of the direct-current system are so great that no one would think of using the alternate system for the trivial economy, if any economy there is, in the single wire, as compared with the double insulated wire system. An interesting illustration of a case in which iron, of any thick- ness, however great, produces no screening effect on an electric current, steady or alternating, is shown by the accompanying diagram, Fig. 7, which represents in section an elecT;ric current along the axis of a circular iron tube, completely surrounding it. Whether the tube be long or short, it exercises no screening effect whatever. A single circular iron ring, supported in the air, with its plane perpendicular to the length of a straight conductor conveying an electric current, produces absolutely no disturbance of the circular endless lines of magnetic force which surround the wire ; neither does any piece of * See ' The Electrician,' vol. xxiii. p. 87. Paper read before the Institution of Electrical Engineers, by Sir "William Thomson, "On the Security against Disturbance of Ships' Compasses by Electric Lighting Appliances." 350 Sir William Thomson [April 10, iron, wholly bounded by a surface of revolution, with a straight conductor conveying electricity along its axis. A screen of imperfectly conducting material is as thorough in its action, when time enough is allowed it, as is a similar screen of metal. But if it be tried against rapidly varying electrostatic force. Fig. 7. its action lags. On account of this lagging, it is easily seen that the screening etfect against periodic variations of electrostatic force will be less and less, the greater the frequency of the variation. This is readily illustrated by means of various forms of idiostatic electro- meters. Thus, for example, a piece of paper supported on metal in metallic communication with the movable disc of an attracted disc electrometer annuls the attraction (or renders it quite insensible) a few seconds of time after a difference of potential is established and kept constant between the attracted disc and the o23posed metal plate, if the paper and the air surrounding it are in the ordinary hygro- metric conditions of our climate. But if the instrument is applied to measure a raj)idly alternating difference of potential, with equal differences on the two sides of zero, it gives very little less than the same average force as that found when the paper is removed and all other circumstances kept the same. Probably, with ordinary clean white paper in ordinary hygro metric conditions, a frequency of alternation of from 50 to 100 per second will more than suffice to render the screening influence of the paper insensible. And a much 1891.] on Electric and Magnetic Screening. 351 less frequency will suffice if the atmosphere surrounding the paper is artificially dried. Up to a frequency of millions per second, we may safely say that, the greater the frequency, the more perfect is the annulment of screening by the paper ; and this statement holds also if the paper be thorouohly blackened on both sides with ink, although possibly in this condition a greater frequency than 50 to 100 per second might be required for practical annulment of the screening. Kow, suppose, instead of attractive force between the two bodies separated by the screen, as our test of electrification, that we have as test a faint spark, after the manner of Hertz. Let two well insulated metal balls. A, B, be placed very nearly in contact, and two much larger balls, E, F, placed beside them, with the shortest distance between E, F sufficient to prevent sparking, and with the lines joining the centres of the two pairs parallel. Let a rapidly alternating difierence of potential be produced between E and F, varying, not abruptly, but according, we may suppose, to the simple harmonic law. Two sparks in every period will be observed between A and B. The interposition of a large paper screen between E, F, on one side, and A, B, on the other, in ordinary hygrometric con- ditions, will absolutely stop these sparks, if the frequency be less than, perhaps, 4 or 5 per second. With a frequency of 50 or more, a clean white paper screen will make no perceptible difference. If the paper be thoroughly blackened with ink on both sides, a frequency of something more than 50 per second may be necessary ; but some moderate frequency of a few hundreds per second will, no doubt, suffice to practically annul the effect of the interposition of the screen. With frequencies up to 1000 million per second, as in some of Hertz's experiments, screens such as our blackened paper are still perfectly transparent, but if we raise the frequency to 500 million million, the influence to be transmitted is light, and the blackened paper becomes an almost perfect screen. Screening against a varying magnetic force follows an opposite law to screening against varying electrostatic force. For the present I pass over the case of iron and other bodies possessing magnetic susceptibility, and consider only materials devoid of magnetic sus- ceptibility, but possessing more or less of electric conductivity. However perfect the electric conductivity of the screen may be, it has no screening efficiency against a steady magnetic force. But if the magnetic force varies, currents are induced in the material of the screen which tend to diminish the magnetic force in the air on the remote side from the varying magnet. For simplicity, we shall suppose the variations to follow the simple harmonic law. The greater the electric conductivity of the material, the greater is the screening efi'ect for the same frequency of alternation ; and, the greater the frequency, the greater is the screening effect for the same material. If the screen be of copper, of specific resistance 1640 sq. cm. per second (or electric diffusivity 130 sq. cm. per second), and with frequency 80 per second, what I have called the " mhoic effectivt^ 352 Sir William Thomson [April 10, thickness"* is 0*71 of a cm.; and the range of current intensity at depth n x 0 • 71 cm. from the surface of the screen next the exciting magnet is c— " of its value at the surface. Thus (as €^ = 20-09) the range of current intensity at depth 2 '13 cm. is ^^Q of its surface value. Hence we may expect that a sufficiently large plate of copper of 2 J cm. thick will be a little less than perfect in its screening action against an alternating magnetic force of frequency 80 per second. Lord Kayleigh, in his " Acoustical Observations/'f after referring to Maxwell's statement, that a perfectly conducting sheet acts as a barrier to magnetic force, J describes an experiment in which the interi)osition of a large and stout plate of copper between two coils renders inaudible a sound which, without the copper screen, is heard by a telephone in circuit with one of the coils excited by electro- magnetic induction from the other coil, in which an intermittent current, with sudden, sharp variations of strength, is produced by a " microphone clock " and a voltaic battery. Larmor, in his paper on " Electromagnetic Induction in Conducting Sheets and Solid Bodies "§ makes the following very interesting statement: — "If we have a sheet of conducting matter in the neighbourhood of a magnetic system, the effect of a disturbance of that system will be to induce currents in the sheet of such kind as will tend to prevent any change in the conformation of the tubes [lines] of force cutting through the sheet. This follows from Lenz's law, which itself has been shown by Helmholtz and Thomson to be a direct consequence of the conservation of energy. But if the arrangement of the tubes [lines of force] in the conductor is unaltered, the field on the other side of the conductor into which they pass (supposed isolated from the outside spaces by the conductor) will be unaltered. Hence, if the disturbance is of an alternating character, with a period small enough to make it go through a cycle of changes before the currents decay sensibly, we shall have the conductor acting as a screen. " Further, we shall also find, on the same principle, that a rapidly rotating conducting sheet screens the space inside it from all magnetic action which is not symmetrical round the axis of rotation." Mr. Willoughby Smith's experiments on " Yolta-electric induc- tion," which he described in his inaugural address to the Society of Telegraph Engineers of November 1883, afforded good illustration of this kind of action with copper, zinc, tin, and lead, screens, and with different degrees of frequency of alternation. His results with iron are also very interesting : they showed, as might be expected, comparatively little augmentation of screening effect with augmenta- tion of frequency. This is just what is to be expected from the fact * ' Collected Papers,' vol. 3, art. oil. § 35. t rhil. Mag. 1882, first half-year. X ' Electricity and Magnetism,' § G6o. § Phil. Mag. 1884, llrst half-year. 1891.] on Electric and Magnetic Screening. 353 that a broad enougli and long enough iron plate exercises a large magneto-static screening influence ; which with a thick enough plate, will be so nearly complete that comparatively little is left for aug- mentation of the screening influence by alternations of greater and greater frequency. A copper shell closed around an alternating magnet produces a screening effect which on the principle stated above we may reckon to be little short of perfection if the thickness be 2j cm. or more, and the frequency of alternation 80 per second. Suppose now the alternation of the magnetic force to be produced by the rotation of a magnet M about any axis. First, to find the effect of the rotation, imagine the magnet to be represented by ideal magnetic matter. Let (after the manner of Gauss in his treatment of the secular perturbations of the solar system) the ideal magnetic matter be uniformly distributed over the circles described by its different points. For brevity call I the ideal magnet symmetrical round the axis, which is thus constituted. The magnetic force throughout the space around the rotating magnet will be the same as that due to I, compounded with an alternating force of which the component at any point in the direction of any fixed line varies from zero in the two opposite directions in each period of the rotation. If the copper shell is thick enough, and the angular velocity of the rotation great enough, the alternating component is almost annulled for external space, and only the steady force due to I is allowed to act in the space outside the copper shell. Consider now, in the space outside the copper shell, a point. P rotating with the magnet M. It will experience a force simply equal to that due to M when there is no rotation, and, when M and P rotate together, P will experience a force gradually altering as the speed of rotation increases, until, when the speed becomes sufficiently great, it becomes sensibly the same as the force due to the symme- trical magnet I. Now superimpose upon the whole system of the magnet, and the point P, and the copper shell, a rotation equal and opposite to that of M and P. The statement just made with reference to the magnetic force at P remains unaltered, and we have now a fixed magnet M and a point P at rest, with reference to it, while the copper shell rotates round the axis around which we first supposed M to rotate. A little piece of apparatus, constructed to illustrate the result experimentally, was submitted to the Royal Institution and shown in action. The copper shell is a cylindric drum, 1 • 25 cm. thick, closed at its two ends with circular discs 1 cm. thick. The magnet is sup- ported on the inner end of a stiff wire passing through the centre of a perforated fixed shaft which passes through a hole in one end of the drum, and serves as one of the bearings ; the other bearing is a rotating pivot fixed to the outside of the other end of the drum. The accompanying sections, drawn to a scale of three-fourths full size, explain the arrangement sufficiently. A magnetic needle outside, 354 Sir William Tliomson [April 10, deflected by the fixed magnet when the drum is at rest, shows a great diminution of the deflection when the drum is set to rotate. If the Fig. 8. 1891.] on Electric arid Magnetic Screening. 355 (triple compound) magnet inside is reversed, by means of the central wire and cross bar outside, shown in the diagram, the magnetometer outside is greatly affected while the copper shell is at rest ; but scarcely affected perceptibly while the copper shell is rotating rapidly. When the copper shell is a figure of revolution, the magnetic force at any point of the space outside or inside is steady, whatever be the speed of rotation ; but if the shell be not a figure of revolution, the steady force in the external space observable when the shell is at rest becomes the resultant of the force due to a fixed magnet inter- mediate between M and I compounded with an alternating force with amplitude of alternation increasing to a maximum, and ultimately diminishing to zero, as the angular velocity is increased without limit. If M be symmetrical, with reference to its northern and southern polarity, on the two sides of a plane through the axis of rotation, I becomes a null magnet, the ideal magnetic matter in every circle of which it is constituted being annulled by equal quantities of positive and negative magnetic matter being laid on it. Thus, when the rota- tion is sufficiently rapid, the magnetic force is annulled throughout the space external to the shell. The transition from the steady force of M to the final annulment of force, when the copper shell is sym- metrical round its axis of rotation, is, through a steadily diminishing force, without alternations. When the shell is not symmetrical round its axis of rotation, the transition to zero is accompanied with alter- nations as described above. When M is not symmetrical on the two sides of a plane through the axis of rotation, I is not null ; and the condition approximated to through external space with increasing speed of rotation is the force due to I, which is an ideal magnet symmetrical round the axis of rotation. A very interesting simple experimental illustration of screening against magnetic force may be shown by a rotating disc with a fi.xed magnet held close to it on one side. A bar magnet held with its magnetic axis bisected perpendicularly by a plane through the axis of rotation would, by sufficiently rapid rotation, have its magnetic force almost perfectly annulled at points in the air as near as may be to it, on the other side of the disc, if the diameter of the disc exceeds con- siderably the length of the magnet. The magnetic force in the air close to the disc, on the side next to the magnet, will be everywhere parallel to the surface of the disc. [W. T.] 356 Annual Meeting. [May 1, ANNUAL MEETING, Friday, May 1, 1891. Sir James Criohton Browne, M.D. LL.D. F.K.S. Treasurer and Vice-President, in the Chair. The Annual Report of the Committee of Visitors for the year 1890, testifying to the continued prosperity and efficient management of the Institution, was read and adopted. The Eeal and Funded Property now amounts to above 83,000Z. entirely derived from the Contributions and Donations of the Members. Fifty- six new Members were elected in 1890. Sixty-three Lectures and Nineteen Evening Discourses were delivered in 1890. The Books and Pamphlets presented in 1890 amounted to about 285 volumes, making, with 561 volumes (including Periodicals bound) purchased by the Managers, a total of 846 volumes added to the Library in the yearc Thanks were voted to the President, Treasurer, and the Honorary Secretary, to the Committees of Managers and Visitors, and to the Professors, for their valuable services to the Institution during the past year. The following Gentlemen were unanimously elected as Officers for the ensuing year : President — The Duke of Northumberland, E.G. D.C.L. LL.D. Treasurer — Sir James Crichton Browne, M.D. LL.D. F.E.S. Secretary — Sir Frederick Bramwell, Bart. D.C.L. F.E.S. M. Inst. C.E. Managers. Sir Frederick Abel, K.C.B. D.C.L. F.R.S. George Berkley, Esq. M. Inst. C.E. Colonel Sir Archibald C. Campbell, Bart. M.P. Sir James N. Douglass, F.R.S. M.Inst. C.E. Sir Dyce Duckworth, M.D. LL.D. F.R.C.P. Sir Douglas Galton, K.C.B. D.C.L. LL.D. F.R.S. William Huggins, Esq. D.C.L. LL.D. F.R.S. David Edward Hughes, Esq. F.R.S. Ludwig Mond, Esq. F.C.S. Edward Pollock, Esq. John Rae, M.D. LL.D. F.R.S. William Chandler Roberts-Austen, Esq. C.B. F R S Hon. Rollo Russell, F.M.S. Basil Woodd Smith, Esq. F.R.S. F.S.A. C. Meymott Tidv, Esq. M.B. A.C.S. Visitors. Alfred Carpmael, Esq. Michael Carteighe, Esq. F.C.S. Andrew Ainslie Common, Esq. F.R.S. F.R.A.S. James Farmer, Esq. J. P. George Herbert, Esq. Frederick John Horniman, Esq. F.L.S. Thomas John Maclagan, M.D. James Mansergh, Esq. M. Inst. C.E. John W. Miers, Esq. Lachlan ^lackintosh Rate, Esq. MA. Benjamin Ward Richardson, M.D. LL.D. F.R.S. George John Romanes, Esq. M.A. LL.D. F.R.S. Arthur William Riicker, Esq. M.A. F.R.S. Joseph Wilson Swan, Esq. Thomas Edward Thorpe, Esq. Ph.D. F.R.S. 1891.] Mr. James Edmund Harting on Hawks and Hawking. 357 WEEKLY EVENING MEETING, Friday, May 1, 1891. Sir James Criohton Browne, M.D. LL.D. F.H.S. Treasurer and Vice-President, in the Chair. James Edmund Harting, Esq. F.L.S. F.Z.S. Hawks and Hawking, The result of many years' experience has been to convince me that the art of Falconry (as all the old writers term it), that is, the art of taming and training birds of prey for the chasf, and teaching them to exercise their natural instinct for our amusement and benefit, is really a noble art ; and that the power which has been given to man to exert " dominion over the fowls of the air," when properly exercised, is the greatest and most wonderful form of control which can be exerted by man over the lower animals. On looking into the literature of the subject, and it is pretty ex- tensive, comprising more than 300 volumes in fourteen or fifteen languages, two points are particularly striking: — First, the great antiquity of Falconry ; and, secondly, its wide-spread practice. In the East, Falconry has been traced back to a period long anterior to the Christian era, and we may form some idea of its antiquity from Sir Henry Layard's discovery of a bas-relief amongst the ruins of Khorsabad, in which a falconer is represented carrying a hawk upon his fist. From this it is to be inferred that hawking was practised there some 1700 years B.C. In China it was known even at an earlier date than this, for in an old Japanese work, of which a French translation appeared at the beginning of the present century, it is stated that falcons were amongst the presents made to princes in the time of the Hia dynasty, which commenced in the year 2205 B.C. It would occupy too much time on Jhe present occasion to discuss the origin of Falconry, on which a very great deal might be said. Suffice it to remark that from the East it was introduced into Europe, and from Europe, long afterwards, into England. On looking into the history of Falconry in Europe, one figure of a great falconer in the middle ages stands out prominently, namely, the Emperor Frederick II. of Germany, who died in 1250. He had seen something of hawking in the East, and in 1239, on his return from a Crusade which he had undertaken the year before, when he was crowned King of Jerusalem and Sicily, he brought with him, from Syria and Arabia, several expert falconers with their hawks, and spent much of his leisure time in learning from them the secret of Vol. XIII. (No. 85.) 2 b 858 Mr. James Edmund Harting [May 1, their art, which he considered the noblest and most worthy of all the arts. The excellent treatise which he composed in Latin, 'Dearte venandi cum Avibus,' was the first which appeared in the West, and is still one of the best which exists. In the Middle Ages the Germans were great falconers ; so also were the French, and the natives of Brabant, of whom a celebrated Spanish falconer in 1383 wrote that they were the best falconers in the world. To a less extent the art was practised in Spain and Italy during many centuries, and books were written in all these countries, by those who had become proficient in the art and were fired with the enthusiasm of their success. The kings of Norway and Denmark preferred hunting to hawking, but rendered good service to the sister sport by procuring, from various jiarts of Scandinavia, the celebrated gerfalcons of Northern Europe, which were held in the highest esteem by those to whom they were sent as presents. Although the precise date of the introduction of hawking into England cannot now be ascertained, we know, from several sources, Soc/efy— Journal for April, 1891. 8vo. Cracovie, V Academic des Sciences— Bnllttin, 1891, No. 3. 8vo. Crisp, Frank, Esq. LL.B. F.L.S. &c. M.R J.— Journal of the Royal Microscopical Society, 1891, Part 2. 8vo. East India Association— J omnal, Vol. XXIII. No. 1. 8vo. 1891. Editors — American Journal of Science for Apiil, 1891. 8vo. Analyst for April, 1891. 8vo. Athenaeum for April, 1891. 4to. Brewers' Journal for April, 1891. 4to. Chemical News for April, 1891. 4tu. Chemist and Druggist for April, 1891. 8vo. Electrical Engineer for April, 1891. fol. Engineer for April, 1891. fol. Engineering for April, 1891. fol. Horological Journal for April, 1891. 8vo. Industries for April, 1891. fol. Ironfor April, 1891. 4to. Ironmongery for April, 1891. Ito. Monist for April, 1891. 8vo. Murray's Magazine for April, 1891. 8vo. Nature for April, 1891. 4 to. Open Court for April, 1891. 4to. Photographic News for April, 1891. 8vo. Public Health for April, 1891. 8vo. Revue Scientifique for April, 1891. 4to. Telegraphic Journal for April, 1891. fol. Zoophilist for April, 1891. 4to. 364 General MontJdy Meeting. [May 4, Electrical Engineers Institution — Journal, No. 92. 8vo. 1891. Florence Bihlioteca Nazionale CentraJe — Bolletino, Nos. 127, 128. Svo. 1891. Franklin Institute — Journal, No. 784. Svo. 1891. General Steam Navigation Company — Handbook of Information. Svo. 1891. Geological Institute, Imperial, Vienna — Jahrbucli, Band XL. Heft 1, 2. Svo. 1890. Abhandlungen. Band XIV. 4to. 1890. Verhandlungen, 1891, No3. 2-4. Svo. G'eoZoj^u-aZ iSoc/e^?/— Quarterly Journal, No. 186. Svo. 1891. Georgofili, Reale Arcademie — Atti, Quarta Serie, Vol. XIV. Disp. 1". Svo. 1891. Horticultural Society, J?o?/aZ— Journal, Vol. XIII. Part 1. Svo. 1891. Institute of Breicing — Transactions, Vol. IV. Nos. 3, 4, 5, 6. Svo. Ih91. Iron and Steel Instiiide — Journal for 1890, Pai t 2. Svo. Kovalevshy, M. Edouard cle {the Author) — L'Enseignement de I'Agriculture dans les e'coles norniales et primaiies en France. 4to. 1891. Linnean S'ciety — Journal, Nos 187, 1S8. Svo, 1891. Mancliester Geological /Socte^?/— Transactions, Vol. XXI. Part G. Svo. 1891. Manchester Literary and Philosophical Society — Memoirs and Proceedings, Vol. IV. No. 3. Svo. 1890-91. Massnroli, Guiseppe, Esq. (the Author) — Grande Inscription de Nabuchodonosor. Svo. 1890. Odontological Society of Great Britain — Transactions, Vol. XXIII. No. 6. New Series. Svo. 1891. Percival, Messrs. and Co. {the Publishers) — The Economic Keview, Vol. I. No. 1. Svo. 1891. Pharmaceutical Society of Great Britain — Journal, April, 1891. Svo. Rathbone, E. P. Esq. {the Editor) — Tlie Witwatersrand Mining and Metallurgical Review, Nos. 15, 16. Svo. 1891. Bio de Janeiro, Museu Nacional — Archivos do Museu Nacional, Vol. VII. 4to. 1887. Le Museu Nacional de Rio de Janeiro por Ladislau Netto. Svo. 1889. Bio de Janeiro. Observatoire Imperiale de — Revista, No. 2. Svo. 1891. Boyal Irish Academy — Transactions, Vol. XXIX. Part 15. 4to. 1891. Boyal Society of London — Proceedings, No. 298. Svo. 1891. Selborne Society— Mature Notes, Vol. II. No. 16. Svo. 1891. Society of Architects — Proceedings, Vol. III. No. 10. Svo. 1891. Society of -4Ws— Journal for April, 1891. Svo. St. Petersburg Academic Imperiale des Sciences — Bulletin (Nouvelle Serie), Tome II. No. i. 4to. 1891. Statistical Society, Boycd — Journal, Vol. LIV. Part 1. Svo. 1891. Teyler Museum — Archives, Serie II. Vol. III. 5« Partie. Svo. 1890. United Service Institution, Boyal — Journal, No. 158. Svo. 1891. Vereins zur Bejbrderung des Gewerbjieisses in Preussen — Verhandlungen, 1891 : Heft 4. 4to. Victoria Institute — Transactions, No. 95. Svo. 1S91. Willing and Co. Messrs. {the Publishers) — Willing's British and Irish Press Guide Svo. 1891. Yorkshire Archxological and Topographical Association — Journal, Parts 43, 44. Svo. 1891. Zoological Society of London — Proceedings, 1890, Part 4. Svo. 1891. 1891.] Professor W. Uamsay on Liquids and Gases. 365 WEEKLY EVENING MEETING, Friday, May 8, 1891. Sir Frederick Bramwell, Bart. D.C.L. F.R.S. Honorary Secretary and Vice-President, in the Chair. Professor W. Ramsay, Ph.D. F.R.S. M.B.L Liquids and Gases. Almost exactly twenty years ago, on June 2nd, 1871, Dr. Andrews, of Belfast, delivered a lecture to the Members of the Royal Institution in this Hall, on " The Continuity of the Gaseous and the Liquid states of Matter." He showed in that lecture an experiment which I had best describe in his own words : — " Take, for example, a given volume of carbonic acid at 50^ Centigrade, or at a higher temperature, and expose it to increasing pressure till 150 atmospheres have been reached. In the process its volume will steadily diminish as the pressure augments ; and no sudden diminution of volume, without the application of external pressure, will occur at any stage of it. When the full pressure Las been applied, let the temperature be allowed to fall until the carbonic acid has reached the ordinary temperature of the atmosphere. During the whole of this operation no break of continuity has occurred. It begins with a gas, and by a series, of gradual changes, presenting nowhere any abrupt alteration of volume or sudden evolution of heat, it ends with a liquid. " For convenience, the process has been divided into two stages, the compression of the carbonic acid and its subsequent cooling. But these operaticms might have been performed simultaneously if care were taken so to arrange the application of the pressure and the rate of cooling that the pressure should not be less than seventy-six atmospheres when the carbonic acid has cooled to 31°." I am able, through the kindness of Dr. Letts, Dr. Andrews* successor at Belfast, to show you this experiment, with the identical piece of apparatus used on the occasion of the lecture twenty years ago. I must ask you to spend some time to-night in ctmsidering this remarkable behaviour ; and in order to obtain a correct idea of what occurs, it is well to begin with a study of gases, not, as in the case you have just seen, exposed to high pressures, but under pressures not differing greatly from that of the atmosphere, and at temperatures which can be exactly regulated and measured. To many here to-night such a study is unnecessary, owing to its familiarity, but I will ask such of my audience to excuse me, in order that I may tell my story from the beginning. 366 Professor W, Hamsay [May 8, Generally speaking, a gas, when comjDressed, decreases in volume to an amount equal to that by which its pressure is raised, provided its temperature be kept constant. This was discovered by Eobert Boyle in 1660. (In 1661 he presented to the Eoyal Society a Latin translation of his book ' Touching the Spring of the Air and its Effects.') His words are : — " 'Tis evident that as common air, when reduced to half its natural extent, obtained a sj^riug about twice as forcible as it had before ; so the air, being thus compressed, being further crowded into half this narrow room, obtained a spring as strong again as that it last had, and consequently four times as strong again as that of common air." To illustrate this, and to show how such relations may be expressed by a curve, I will ask your attention to this model. We have a piston, fitting a long glass tube. It confines air under the pressure of the atmosphere, that is, some 15 lb. on each square inch of area of the piston. The pressure is supposed to be registered by the height of the liquid in the vertical tube. On increasing the volume of the air, so as to double it, the pressure is decreased to half its original amount. On decreasing the volume tu half its original amount the pressure is doubled. On again halving, the j)ressure is again doubled. Thus, you see, a curve may be traced, in which the relation of volume to pressure is exhibited. Such a curve, it may be remarked incidentally, is termed a hyperbola. We can repeat Boyle's experiment by pouring mercury into the open limb of this tube containing a measured amount of air. On causing the level of the mercury in the open limb to stand 30 inches (that is the height of the barometer) higher in the open limb than the closed limb, the pressure of the atmosphere is doubled, and the volume is halved. And on trebling the pressure of the atmosphere the volume is reduced to one-third of its original amount, and on adding other 30 inches of mercury the volume of the air is now one quarter of that which it originally occupied. It must be remembered that here the temperature is kept constant; that it is the temperature of the surrounding atmosphere. Let us next examine the behaviour of a gas when its temperature is altered ; when it becomes hotter. This tube contains a gas, air, confined by mercury, in a tube surrounded by a jacket or mantle of glass, and the vapour of boiling w^ater can be blown into the space between the mantle and the tube containing the air, so as to heat the tube to 100^, the temperature of the steam. The temperature of the room is 17° C, and the gas occupies 290 divisions of the scale. On blowing in steam the gas expands, and on again equalising pressure it stands at 373 divisions of the scale. The gas has thus expanded from 290 to 373 divisions, i. e. its volume has increased by 83 divisions, and the temperature has risen from 17° to 100°, i. e. through 83 degrees. This law of the expansion of gases was discovered almost simultaneously by Dalton and Gay-Lussac in 1801. It usually 1891.] on Liquids and Gases. 867 goes by the name of Gay-Lussac's law. Now, if we do not allow the volume of the gas to increase, we shall find that the pressure will increase in the same proportion that the volume would have increased had the gas been allowed to expand, the pressure having been kept constant. To decrease the volume of the gas, then, according to Boyle's law, will require a higher initial pressure, and if we were to represent the results by a curve we should get a hyperbola, as before, but one lying higher as regards pressures. And so we should get a set of hyperbolas for higher and higher temperatures. We have experimented up to the present with air, a mixture of two gases, oxygen and nitrogen; and the boiling-point of both of these elements lies at very low temperatures, — 184° and — 193*1° respectively. The ordinary atmospheric temperature lies a long way above the boiling-points of liquid oxygen and liquid nitrogen at the ordinary atmospheric pressure. But it is open to us to study a gas, which, at the ordinary atmosf)heric temperature exists in the liquid state ; and for this purpose I shall choose water-gas ; in order that it may be a gas at ordinary atmospheric pressure, however, we must heat it to a temperature above 100° C, its boiling-point. This tube contains water-gas at a temperature of 105° C. ; it is under ordinary pressure, for the mercury columns are at the same level in both the tube and in this reservoir, which communicates with the lower end of the tube by means of the india-rubber tubing. The temperature, 105°, is maintained by the vapour of chlorobenzene, boiling in the bulb sealed to the jacket, at a pressure lower than that of the atmosphere. Let us now examine the effect of increasing pressure. On raising the reservoir, the volume of the gas is diminished, as usual, and nearly in the ratio given by Boyle's law ; that is, the volume decreases in the same proportion as the pressure increases. But a change is soon observed ; the pressure soon ceases to rise ; the distance between the mercury in the reservoir and that in the tube remains constant, and the gas is now condensing to liquid. The pressure continues constant during this change, and it is only when all the water-gas has condensed to liquid water that the pressure again rises. After all gas is condensed, an enormous increase of pressure is necessary to cause any measurable decrease in volume, for liquid water scarcely yields to pressure, and in such a tube as this no measurements could be attempted with success. Representing this diagrammatically, the right-hand part of the curve represents the compression of the gas, and the curve is, as before, nearly a hyperbola. Then comes a break, and great increase in volume occurs without rise of pressure, represented by a horizontal line. The substance in the tube here consists of water-gas in presence of water ; the vertical, or nearly vertical, line represents the sudden and great rise of pressure, where liquid water is being slightly compressed. The pressure registered by the horizontal line 368 Professor W. Hamsay [May 8, is termed the " vapour- pressure " of water. If now the temperature were raised to 110° we should have a greater initial volume for the water-gas. It is compressible, by rise of the mercury, as before, the relation of pressure to volume being, as before, represented on the diagram as an approximate hyperbola ; and, as before, condensation occurs when volume is sufficiently reduced ; but this time at a higher pressure. We have again a horizontal portion, rej)resenting the pressure of water-gas at 110^ in contact with liquid water; again a 1891.] on Liquids and Gases. 369 sharp angle, where all gaseous water is condensed ; and again a very steep curve, almost a straight line, representing the slight decrease of volume of water, produced by a great increase of pressure. And should we have similar lines for 120^ 130°, 140^ 150°, and for all temperatures — such lines are called isothermal lines, or shortly, " isothermals," or lines of equal temperature, and represent the relations of pressure to volume for different temperatures. Dr. Andrews made similar measurements of the relations between the pressure and volumes of carbon dioxide, at pressures much higher than those I have shown you for water. But I prefer to speak to you about similar results obtained by Professor Sydney Young and myself with ether, because Dr. Andrews was unable to work with carbon dioxide free from air, and that influenced his results. For example, you see that the meeting-points of his hyperbolic curves with the straight lines of vapour-pressures are curves and not angles. That is caused by the presence of about 1 part of air in 5U0 parts of carbon dioxide ; also, the condensation of gas was not perfect, for he obtained curves at the points of change from a mixture of liquid and gas to liquid. We, however, were more easily able to fill a tube with ether, free from air, and you will notice that the points I have referred to are angles, not curves. Let me first direct your attention to the shapes of the curves in the figure, which represents such relations of volume, temperature, and pressure in the case of ether. As the temperature rises, the vapour-pressure lines lie at higher and higher pressures, and the lines tliemselves become shorter and shorter. And finally, at the temperature 31° for carbon dioxide, and at 125° for ether, there ceases to be a horizontal portion at all ; or, rather, the curve touches the horizontal at one point in its course. That point corresponds to a definite temperature, 195° for ether; to a definite pressure, 27 metres of mercury, or 35*6 atmospheres ; and to a definite volume, 4 • 06 cubic centimetres per gram of ether. At that point the ether is not liquid, and it is not gas ; it is a homogeneous substance. At that temperature ether has the appearance of a blue mist. The strias mentioned by Dr. Andrews and by other observers are the result of unequal heating, one portion of the substance being liquid and another gas. You see the appearance of this state on the screen. When a gas is compressed, it is heated. Work is done on the gas, and its temperature rises. If I compress the air in this syringe forcibly, its temperature rises so high that I can set a j)iece of tinder on fire, and by its help explode a little gunpowder. If the ether at its critical point be compressed, by screwing in the screw, it is some- what warmed, and the blue cloud disappears. Conversely, if it is expanded a little by unscrewing the screw, and increasing its volume, it is cooled, and a dense mist is seen accompanied by a shower of ether rain. This is seen as a black fog on the screen. I wish also to direct your attention to what happens if the volume 370 Professor W. Ramsay [May 8, given to the ether is greater than the critical volume. On increasing the volume, you see that it boils away, and evaporates completely ; and also what happens if the volume be somewhat less than the critical volume ; it then expands as liquid, and completely fills the tube. It is only at a critical volume and temperature that the ether exists in the state of blue cloud, and has its critical pressure. If the volume be too great, the pressure is below the critical pressure ; if too small, the pressure is higher than the critical pressure. Still one more point before we dismiss this experiment. At a temperature some degrees below the critical temperature, the menis- cus, i. e. the surface of the liquid is curved. It lias a skin on its surface ; its molecules, as Lord Kayleigh has recently exj)lained in this room, attract one another, and it exhibits surface tension. Raise the temperature, and the meniscus grows flatter ; raise it further, and it is nearly flat, and almost invisible ; at the critical temperature it disappears, having first become quite flat. Surface-tension therefore disappears at the critical point. A liquid would no longer rise in a narrow capillary tube ; it would stand at the same level outside and inside. It was suggested by Professor James Thomson and by Professor Clausius, about the same time, that if the ideal state of things were to exist, the passage from the liquid to the gaseous state should be a continuous one, not merely at and above the critical point, but below that temperature. And it was suggested that the curves shown in the figure, instead of breaking into the straight line of vapour-pressure, should continue sinuously. Let us see what this conception would involve. On decreasing the volume of a gas, it should not liquefy at the point marked B on the diagram, but should still decrease in volume on increase of pressure. This decrease should continue until the j)oint E is reached. The anomalous state of matters should then occur, that a decrease in volume should be accomj^anied by a decrease of pressure. In order to lessen volume, the gas must be exposed to a continually diminishing pressure. But such a condition of matter is of its nature unstable, and has never been realised. After volume has been decreased to a certain point F, decrease of volume is again attended by increase of pressure, and the last part of the curve is continuous with the realisable curve representing the compression of the liquid above D. Dr. Sydney Young and I succeeded by a method which I shall briefly describe in calculating the actual position of the unreali sable portions of the curve. They have the form pictured in the figure (shaded portion). The rise from the gaseous state is a gradual one ; but the fall from the liquid state is abrupt. Consider the volume 14 cubic centimetres per gram on the figure. The vertical equivolume line cuts the isothermal lines for the 1891.] on Liquids and Gases. 371 temperatures 175°, 180°, 185°, 190°, and so on, at certain definite pressures, which may be read from a properly constructed diagram. AVe can map the course of lines of equal volume, of which the instance given is one, using temperatures as ordinates and pressures as abscissaB. We can thus find the relations of temperature to pressure for certain definite volumes, which we may select to suit our convenience ; say, 2 c.c. per gram, 3, 4, 5, 6, and so on. Now all such lines are straight. That is, the relation of pressure to temperature, at constant volume, is one of the simplest ; pressure is a linear function of tem- perature measured on the absolute scale. Expressed mathematically, p = h t — a, where h and a are constants, depending on the volume chosen, and varying with each volume. But a straight line may be extrapolated without error, and so having found values for a and h for such a volume as 6 c.c. per gram, by help of experiments at temperatures higher than 195°, it is possible by extrapolation to obtain the pres- sures corresponding to temperatures below the critical point 195°, in a simple manner. But below that temperature the substance at volume 6 is in practice partly liquid and partly gas. Yet it is possible by such means to ascertain the relations of pressure to temperature for the unrealisahle portion of the state of a liquid, that is, we can deduce the pressure and temperature corresponding to a continuous change from liquid to gas. And in this manner the sinuous lines on the figure have been constructed. It is possible to realise experimentally certain portions of such continuous curves. If we condense all gaseous ether, and, when the tube is completely filled with liquid, carefully reduce pressure, the pressure may be lowered considerably below the vapour pressure corresponding to the temperature of ebullition without any change, further than the slight expansion of the liquid resulting from the reduction of pressure — an expansion too small to be seen with this apparatus. But on still further reducing pressure sudden ebullition occurs, and a portion of the liquid suddenly changes into gas, while the pressure rises quickly to the vapour-pressure corresponding to the temperature. If we are successful in expelling all air or gas from the ether in filling the tube, a considerable portion of this curve can be experimentally realised. The first notice of this appearance, or rather, of one owing its existence to a precisely similar cause, is due to Mr. Hooke, the cele- brated contemporary of Boyle. It is noted in the account of the Proceedings of the Royal Society, on November 6th, 1672, that " Mr. Hooke read a discourse of his, containing his thoughts of the experiment of the quicksilver's standing top-full, and far above the 29 inches ; together with some experiments made by him, in order to determine the cause of this strange phenomenon. He was ordered to prepare those experiments for the view of the Society." And on 372 Professor W. Ramsay [May 8, November IStli, "The experiment for the high suspension of quick- silver being called for, it was found that it had failed. It was ordered that thicker glasses should be provided for the next meeting." There can be no doubt that this behaviour is caused by the attrac- tion of the molecules of the liquid for each other. And if the temperature be sufficiently low, the pressure may be so reduce^ that it becomes negative — that is, until the liquid is exposed to a strain or pull, as is the mercury. This has been experimentally realised by M. Berthelot, and by Mr. Worthington, the latter of whom has succeeded in straining alcohol at the ordinary temj^erature with a pull equivalent to a negative pressure of 25 atmospheres, by completely tilling a bulb with alcohol and then cooling it. The alcohol in con- tracting strains the bulb inwards, and finally, when the tension becomes very great, parts from the glass with a sharp " click." To realise a portion of the other bend of the curve, an experiment has been devised by Mr. John Aitken. It is as follows: If air (that is space, for the air plays a secondary part) saturated with moisture be cooled, the moisture will not deposit unless there are dust-particles on which condensation can take place. It is not at first evident how this corresponds to the compressing of a gas without condensation. But a glance at the figure will render the matter plain. Consider the isothermal (175') 75^ for ether at the point marked B. If it were possible to lower the temperature to 160^ without condensation, keeping volume constant, pressure ^vould fall, and the gas would then be in the state represented on the isothermal line 160^ at G ; that is, it would be in the same condition as if it had been compressed without condensation. You saw that a gas, or a liquid, is heated by compression ; a piece of tinder was set on fire by the heat evolved on compressing air. You saw that condensation of ether was brought about by diminution of pressure ; that is, it was cooled. Now if air be suddenly expanded it will do work against atmospheric pressure, and will cool itself. This globe contains air ; but the air has been filtered carefully through cotton-wool, with the object of excluding dust-particles. It is satu- rated with moisture. On taking a stroke ol the pump, so as to exhaust the air in the globe, no change is evident ; no condensation has occurred, although the air has been so cooled that the moisture should condense, were it possible. On repeating the operation with the same globe after admitting dusty air — ordinary air from the room — a slight fog is produced, and owing to the light behind, a circular rainbow is seen; a slight shower of rain has taken place. There are comparatively few dust-particles, because only a little dusty air has been admitted. On again repeating, the fog is denser; there are more particles on which moisture may condense. One point more and I have done. Work is measured by the distance or height through which a weight can be raised against the force of gravity. The British unit of work is a foot-pound, that is, a pound raised through one foot ; that ol the metric system is one gramme 1891.] on Liquids and Gases. 373 raised througli one centimetre. If a pound be raised through two feet, twice as much work is done as that of raising a pound through one foot, and an amount equal to that of raising two pounds through one foot. The measure of work is then the weight, multiplied by the distance through which it is raised. When a gas expands against pressure it does work. The gas may be supposed to be confined in a vertical tube, and to propel a piston upwards against the pressure of the atmosphere. If such a tube has a sectional area of one square centimetre, the gas in expanding a centimetre up the tube lifts a weight of nearly 1000 grams through one centimetre (for the pressure of the atmosphere on a square centimetre of surface is nearly 1000 grams) ; that is, it does 1000 units of work, or ergs. So the work done by a gas in expanding is measured by the change of volume multiplied by the pressure. On the figure the change of volume is measured horizontally, the change of pressure vertically. Hence the work done is equivalent to the area on the diagram A B C D. If liquid as it exists at A change to gas as it exists at B, the substance changes its volume, and may be made to do work. This is familiar in the steam-engine, where work is done by water expand- ing to steam, and so increasing its volume. The pressure does nor alter during this change of volume if sufficient heat be supplied, hence the work done during such a change is given by the rectangulat area. Suppose that a man is conveying a trunk up to the first storey of a house, he may do it in two (or perhaps a greater number of) ways. He may put a ladder up to the drawing-room window, shoulder his trunk, and deposit it directly on the first floor. Or he may go down the area stairs, pass through the kitchen, up the kitchen stairs, up the first flight, up the second flight, and down again to the first storey. The end result is the same ; and he does the same amount of work in both cases, so far as conveying the weight to a given height is con- cerned ; because in going downstairs he has actually allowed work to be done on him by the descent of the weight. Now the liquid in expanding to gas begins at a definite volume ; it evaporates gradually to gas without altering pressure, heat being of course communicated to it during the change, else it would cool itself ; and it finally ends as gas. It increases its volume by a definite amount at a definite pressure, and so does a definite amount of work ; this work might be utilised in driving an engine. But if it pass continuously from liquid to gas, the starting-point and the end point are both the same as before. An equal amount of work has been done. But it has been done by going down the area- stair, as it were, and over the round I described before. It is clear that a less amount of work has been done on the left- hand side of the figure than was done before ; and a greater amount on the right-hand side ; and if I have made my meaning clear, you will see that as much less has been done on the one side, as more has been done on the other ; that is, that the area of the figure B E H Vol. XIII. (No. 85,) 2 c 374 Professor W. Bamsay on Liquids and Gases. [May 8, must be equal to that of the figure A F H. Dr. Young and I have tried this experimentally, that is, by measuring the calculated areas; and we found them to be equal. This can be shown to you easily by a simple device, namely, taking them out and weighing them. As this diagram is an exact representation of the results of our experi- ments with ether, the device can be put in practice. We can detach these areas which are cut out in tin, and place one in each of this j^air of scales, and they balance. The fact that a number of areas thus measured gave the theoretical results, of itself furnishes a strong support of the justice of the conclusions we drew as regards the forms of these curves. To attempt to explain the reasons of this behaviour would take more time than can be given to-night ; moreover, to tell the truth, we do not know them. But we have at least partial knowledge ; and we may hope that investigations at present being carried out by Professor Tait may give us a clear idea of the nature of the matter, and of the forces which act on it, and with which it acts, during the continuous change from gas to liquid. [W. E.] 1891.] Professor G. D. Liveing on Crystallisation. 375 WEEKLY EVENING MEETING, Friday, May 15, 1891. Sir James Criohton Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Professor G. D. Liveing, M.A. F.R.S. Crystallisation. There is something very fascinating about crystals. It is not merely the intrinsic beauty of their forms, their picturesque grouping, and the play of light upon their faces, but there is a feeling of wonder at the power of nature which causes substances in passing from the fluid to the solid state to assume regular shapes bounded by plane faces, each substance with its own set of forms, with faces arranged in characteristic symmetry ; some, like alum, in perfect octahedra, and others, like blue vitriol, in shapes which are regularly oblique. It is this power of nature which will be the subject of this discourse. I hope to show that crystalline forms with all their regularity and symmetry are the outcome of accepted mechanical principles. I shall invoke no peculiar force, but only such as we are already familiar with in other natural phenomena. In fact, I shall call in only the same force that produces the rise of a liquid in a capillary tube, and the surface tension at the boundary of two substances which do not mix. Whether this force is different from gravity I shall not stop to inquire. Any attractive force which for small masses, such as we suppose the molecules of matter to be, is only sensible at insensible distances, is sufficient for my purpose. We know that the external form of a crystal is intimately con- nected with its internal structure, with the chemical nature, the arrangement and the motions, of the molecules. This internal struc- ture betrays itself in the cleavages with which every one is familiar in mica and selenite, which extend to the minutest parts, so that when calc-spar is crushed, even the dust consists of tiny rhombs. It is still better seen in the optical characters. The regular crystals, like common salt, give no double refraction, while those less regular refract doubly, and indicate different degrees of symmetry by their action on polarised light. These familiar facts suggest that it is the internal structure which determines the external form. As a starting-point for considering that structure I assume that crystals are made up of molecules, and that in the solid state the molecules have little freedom ; that they are always within the range of each other's influence, and cannot change their relative places. Nevertheless, these molecules must be in constant and very rapid motion. Not only will they communicate heat to colder bodies which touch them, but they are always radiating, which means that they are 2 c 2 376 Professor G. D. Liveing [May 15, always producing waves in the ether at the rate of many billions a second. We are sure that they have a great deal of eneTgy, and if they cannot move far they must have very rapid vibratory motion. It is reasonable to suppose that the parts of each molecule swing backwards and forwards through, or about, the centre of mass of the molecule. The average distance to which the parts swing will give the average dimensions of the molecule. Dalton fancied that he had proved that the atoms of the chemical elements must be spherical, because there was no assignable cause why they should be longer in one dimension than another. I rather invert the argument. I see no reason why the excursions of the parts of a molecule from the centre of mass should be equal in every direc- tion. I assume, as the most general case, that these excursions are unequal in different directions, and since the movements must be symmetrical with reference to the centre of mass, they will in general be included within an ellipsoid, of which the centre is the centre of mass. Here I may, perhaps, guard against a misconception. Chemists are familiar with the notion of complex molecules, and most of us figure to ourselves a molecule of common salt as consisting of an atom of sodium and an atom of chlorine held together by some sort of force, and it may be imagined that these atoms are the parts of the molecules which I have in mind. That, however, is not my notion. I am paradoxical enough to disbelieve altogether in the existence of either sodium or chlorine in common salt. Were my audience a less philo- sophical one, I could imagine the retort on many a lip — " Why, you can get sodium and chlorine out of it, and you can make it out of sodium and chlorine." But, no ; you cannot get either sodium or chlorine out of it WT.thout first adding something which seems to me of the essence of the matter. You can get neither sodium nor chlorine from it without adding energy. Nor can you make salt out of those elements without subtracting energy. My point is that the energy is of the essence of the molecule. Each kind of molecule has its own kind of motion ; and in this I think most physicists will agree with me. The chemists will agree with me in thinking that all the mole- cules of the same element or compound are alike in mass, and in the space they occupy at a given temperature and pressure. The only further assumption I have to make is that the form of the ellipsoid, the relative length of its axes, is on tlie average the same for all the molecules of the same substance. This implies that the distances of the excursions of the parts of the molecule depend upon its con- stitution, and are, on the average, the same in similarly constituted molecules under similar circumstances. I have now come to the end of my postulates. I hope they are such as you will readily concede. I want you to conceive of each molecule that its parts are in extremely rapid vibration, so that it occupies a larger space than it would occupy if its parts were all at rest ; and that the excursions of the parts about the centre of mass 1891.] on Crystallisation. 377 are, on tlie average, at a given temperature and pressure, comprised within a certain ellipsoid : that the dimensions of this ellipsoid are the same for all molecules of the same chemical constitution, but different for different kinds of molecules. We have next to consider how these molecules will pack them- selves in passing from the fluid state, in which they can and do move about amongst themselves, into the solid state, in which they have no sensible freedom. If they attract one another according to any law, and for my purpose gravity will suffice, then the laws of energy require that for stable equilibrium the potential energy of the system shall be a minimum. This is the same, in the case we are considering, as saying that the molecules shall be packed in such a way that the distance between their centres of mass shall be the least possible, or as many of them as possible be packed into a given space. In order to see how this packing will take place, it will be easiest to consider the case in which the axes of the ellipsoids are all equal — that is, when the ellipsoids happen to be spheres. The problem is then reduced to finding how to pack the greatest number of equal spherical balls into a given space. It is easy to reduce this problem to that of finding how the spheres can be arranged so that each sphere shall be touched by as many as possible of its neighbours. In this way the cornered spaces between the spheres, the spaces not occupied, are reduced to a minimum. Now, you can arrange balls so that each is touched by twelve others, but not by more than twelve. This, then, will be the arrangement which the molecules will naturally assume. Fig. 1. We may do this apparently in two ways. We may begin with arranging balls on a flat surface so that each is touched by six others, as in Fig. 1. We may then place a ball so that it rests on three, a, 6, c, 378 Professor G. D. Liveing [May 15, in the figure, and may place six others, touching it, and resting in the six adjacent triangular spaces which are black in the figure. Above these we can again place three more so as to touch the first. If we complete the pile we get a triangular pyramid, as in Fig. 2. Or we Fig. 2. may begin by arranging balls on the flat, as in Fig. 3, so that each is touched by four others. We may then place one ball so as to rest on four, such as a, Z), c, d, in the figure. Then place four others, touching it, in the four adjacent square-shaped openings which are shaded in the figure. Above these, in places corresponding to a, h, c, d, four more may be placed so as to touch the first. If the pile be completed it will form a four-sided pyramid, as in Fig. 4. Fig. 3. Fig. 4. Although this arrangement seems at first sight difierent from that in Fig. 2, it is not so ; for it will be seen that in the faces of the pyramid of Fig. 2 the arrangement is that of Fig. 3, while in the faces of the pyramid in Fig. 4 the arrangement is that of Fig. 1. Fig. 2 is really part of Fig. 4 turned over on its side. Before proceeding to the packing of ellipsoids, let us consider 1891.] on Crystallisation. 379 how this packing of the spheres will affect the external form. And here I must bring in the surface tension. We are familiar with the effects of this force in the case of liquids, and if we adopt the usual theory of it we must have a surface tension at the boundary of a solid as well as at the surface of a liquid. I know of no actual measures of the surface tension of solids. But Quincke has given us the surface tensions of a number of substances at temperatures near their points of solidification. The surface tension of most of the solids are probably greater than these, since surface tension usually diminishes with increase of temperature. Table of Surface Tensions of Substances near their Temperatures of SoUdification, in dynes per lineal centimetre, after Quincke. Platinum 1,658 Gold 983 Zinc 860 Tin ' .. 587 Mercury 577 Lead 448 Silver 419 Bismuth 382 Potassium 364 Sodium 253 Antimony 244 Borax 212 Sodium carbonate 206 Sodium chloride 114 Water 86-2 Selenium 70*4 Sulphur 41-3 Phosphorus 41 '1 Wax 33-4 We have evidently to do here with an agency which we cannot neglect. In all these cases the measured tension is at a surface bounded by air, and is such as tends to contract the surface. We have then at the boundary between a crystallising solid and a fluid, gas or liquid, out of which it is solidifying, a certian amount of potential energy ; and by the laws of energy the condition of equilibrium is that this potential energy shall be a minimum. The accepted theory of surface tension is that it arises from the mutual attractions of the molecules. The energy will therefore be a mini- mum for a surface in which the molecules are as closely set as possible. Now if you draw any surface through a heap of spherical balls arranged so that each is touched by twelve others, you will find that the surfaces which have the greatest number of centres of the balls in unit area are all plane surfaces ; and those for which the concentration is greatest are the faces of a regular octahedron, next those of a cube, next those of a rhombic dodecahedron, and so on for the other planes which follow the crystallographic law of indices. Taking the concentration in the faces of the cube as unity, those of other forms will be Octahedron .. 1-1547 Eikositessarahedron .. -4083 Dodecahedron .. -7071 Triakisoctahedron . . .. -3333 Tetrakishexahedron .. -4472 It must not be supposed that these figures give the surface energies. We have at present no means of determining the exact magnitudes of. 380 Professor G. D. Liveing [May 15, the surface energies. What we can assert is that greater concentra- tion means in general less surface energy. Hence when the molecules are spherical the bounding surface tends to be that of a regular octahedron. But we have another point to consider. Since the solid must be a closed figure, there will be edges where the bounding planes meet each other. At these edges the surface tensions will have a resultant tending to compress the crystal, and there must be a corresponding resultant pressure on the opposite side. It follows from this that if one pair of faces are developed on one side of a crystal a parallel pair must in general be developed on the opposite side, and if one face of a form, be it cube, octahedron, or other form, be developed, all the faces of that form will, as a rule, be developed. But there is yet another point to be taken into account. The sur- face energy may become less in two ways ; one by reducing the tension per unit of surface, and the other by reducing the total surface for the same quantity of matter. When a liquid separates from another liquid, as chloroform from a solution of chloral hydrate by adding an alkali, or a cloud from moist air, the liquid assumes the form which for a given mass has the least surface, that is the drops are spherical. If you cut off the projecting angles, and plane away the projecting edges of a cube or octahedron, you bring it nearer to a sphere, and diminish the surface per unit volume. And if diminution of the total surface is not compensated by the increase of the surface energy on the truncations, there will be a tendency for the crystal to grow with such truncations. The like will be true in more complicated combinations. There will be a tendency for such combinations to form provided the surface energy of the new faces is not too great as compared with that of the first formed faces. But it does not always hapj)en that an octahedron of alum developes truncated angles. This leads to another point. To pro- duce a surface in a homogeneous mass requires a supply of energy, and to produce a surface in the interior of any fluid is not easy. Air may be supersaturated with aqueous vapour, or a solution super- saturated with a salt, and no cloud or crystals be formed in the interior, unless there is some discontinuity in the mass, specks of dust or something of the kind. When solid matter separates from a solution, a certain amount of energy is available from the change of state, and supplies the surface energy of the new solid. The amount of this available energy is proportional to the mass of solid separated. But since the surface varies as the square of the diameter, while the mass varies as the cube of the diameter, the amount of energy available when the mass is very minute may be insufficient. In fact, a very small mass of solid might be squeezed into liquid again by its own surface energy. It will be easier to add to a surface already formed, even if that surface be one of less energy than that of the new solid, than it is to break the con- tinuity of the fluid. Hence we find that crystals often form on the 1891.] on Crystallisation. 381 side of the vessel, or at the top where the liquid meets the air. But it is easiest of all to add to a surface of the same energy as that of the crystal. The additional energy required will then be only for the extension of the surface. This explains why dropping a crystal into a supersaturated solution starts crystallisation. Large crystals grow more readily than small ones because the extension of surface, that is the addition of energy, for a given addition of mass is less in the former. Also it is easier to add to the faces already formed than to develop new faces. While speaking of the difficulty of creating a new surface in the interior of a mass, the question of cleavage suggests itself. It is plain that in dividing a crystal we create a new surface on each of the two parts, each with its own surface energy. The division must there- fore take place most readily where that surface energy is a minimum. Hence I infer that the principal cleavage of a crystal made up of molecules for which the vibrations are comprised within spherical spaces will be octahedral. As a fact, we find that the greater part of substances which crystallise in what is called the regular system, have an octahedral cleavage. But not all ; there are some which have a cubical cleavage such as rock salt and galena, and a very few like blende have the principal cleavage dodecahedral. These I have to explain. I may, however, first observe that some substances, like fluor spar, which have a very distinct octahedral cleavage, are rarely met with in octahedral crystals, but usually in the cubic form. In regard to this we must remember that the surface energy depends upon the nature of both the substances which meet at the common surface, their electrical state, their temperature, and other circumstances. It is a well known fact that the form assumed by a salt on crystallising is affected by the character of the solution. Thus, alum, which from a solution in pure water lakes the octahedral form, from a solution neutralised with potash takes the cubic form. It is therefore quite possible that, under the circumstances in which the natural crystals of fluor spar were formed, the surface energy of the cubical faces was less than that of the octahedral, although when we experiment upon them in the air it is the other way. The closeness of the molecules in the surface of the solid will determine the surface energy so far as the solid alone is concerned ; but though this may be the most important factor of the result, the molecules of the fluid in contact with the crystal have their effect too. But to return to cubic and dodecahedral cleavages. If we suppose the excursions of the parts of the molecule to be greater in some one direction than in the others, the figure within which the molecule vibrates will be a prolate spheroid ; if it be less, an oblate spheroid. Now if such spheroids be packed as close as possible, each can be touched by twelve others, and they can be packed just as the spheres were, provided their axes be all parallel. It matters not what the orientation of the axes may be so far as the closeness of packing goes. 382 Professor G. D. Liveing [May 15, so long as their parallelism is maintained ; but the orientation will aifect very mucli the symmetry of the crystal. If we suppose the spheroids to be oblate, and arrange them as in Fif^ure 1, with their axes perpendicular to the plane of that figure, and place the next layer in those triangular openings which are white in the figure, and complete the pyramid, the magnitude of the three angles at the apex of the pyramid will depend on the relative flatness of the spheroids. In case the length of the axis of the spheroids is half their greatest diameter, these three angles will be right angles, and the whole heap of molecules will have a cubic symmetry, and in the faces of the cubes the concentration will be a maximum, and therefore the surface energy a minimum, and the easiest cleavage will be cubic. If the concentration in the cubic faces be 1 * 0000, that in the octahedral faces will be 0 • 5774, and that in the dodecahedral 0 • 7071. We have here the case of crystals like rock salt and galena. Suppose, however, we start with the arrangement of Figure 3, and keep the axes per- pendicular to the plane of that figure ; and suppose, further, that the biggest diameter of the spheroids is greater than the length of the axis in the ratio of the diagonal to the side of a square, we shall again get a heap with a cubic symmetry ; but in this case the maxi- mum concentration will be in the faces of the dodecahedron, and we have the case of blende in which the easiest cleavage is dodeca- hedral. In order to see what the symmetry will be in other cases, we may look at the problem from another point of view. Suppose a cube made up of spherical molecules to be subject to a uniform stress perpendicular to one face of the cube, so that all the spheres are strained, either by extension or compression, into spheroids, we should get that dia^^onal of the octahedron which was parallel to the stress either lengthened or shortened, but the symmetry about that diagonal would remain as before. We should get a crystal of the pyramidal system. If the spheroids were prolate and sufficiently elongated, the easiest cleavage would be perpendicular to the axis as in potassium ferro- cyanide and apophyllite. If the spheroids were oblate the funda- mental octahedron would be more obtuse, and if obtuse enough the easiest cleavage would be in faces parallel to the axis of symmetry. Attain, if the stress, instead of being perpendicular to one face of the cube, were parallel to a diagonal of the cube, the cube would become a rhombohedron, and the spheres would become spheroids with their axes parallel to the axis of the rhombohedron. If the spheroids were prolate the rhombohedron would be acute, and the easiest cleavage perpendicular to the axis as we find it in beryl and many other crystals. If the original cube were formed of spheroids with their axes half the length of their greatest diameters, and the stress parallel to the axes were such as to alter the length of the axes only a little, we should get crystals with a rhombohedral cleavage like calcite. The crystals like beryl almost always exhibit hexagonal forms, six- sided prisms and pyramids. To explain this I would observe that if 1891.] on Crystallisation. 883 we start with spheroids arranged as in Figure 1, with their axes perpendicuhir to the plane of that figure, and place three others touching that marked a ; there are two ways in which we can do this. We may place the three either in the white or in the black triangles. The two positions difier in such a way that you pass from one to the other by turning the three spheroids as a whole through 180°. The relation is that of twin crystals. If a crystal wore growing by addition to the face which we suppose represented iu Figure 1, it would be as likely that one arrangement should be taken as the other so far as the middle part of the face is concerned. But a crystal built up of such alternate layers of twins v/ould have ridged and furrowed faces, that is faces of extra surface-tension, except in the case of hexagonal forms. For hexagonal forms are no way altered by being turned through two right angles. There will there- fore be a tendency for such forms to grow unless the rhombohedral faces have a much less surface energy. Hexagonal forms have also less surface per unit of volume than rhombohedrons, and lend them- selves to the formation of nearly globular crystals, with a minimum of total surface, as is often seen in pyromorphite. Recurring to the cube of spheres, if it be subject to a stress in a direction not parallel to an edge or diagonal, we shall get an arrange- ment of spheroids which will give forms of less symmetry. Also if it be subject to two uniform stresses at right angles to one another the spheres will become ellipsoids and may be taken to represent the molecules in the most general case. The degrees of symmetry, and the directions of most easy cleavage, may be woi^ked out on the lines already indicated, and will be found to correspond with those observed in nature. Bravais long ago suggested arrangements of the molecules corresponding to the symmetry, and Sohncke has extended his suggestions, but neither has assigned any mechanical reason why the molecules should so arrange themselves. They also supposed different arrangements for different kinds of symmetry. I have endeavoured to give a sufficient reason for the positions taken by the molecules and to show that out of the one arrangement by which the molecules are packed as closely as., is possible all the varieties of symmetry will arise. M. Curie also has, before me, pointed out that differences of surface tension will determine the relative sizes of different faces ; but he has not pointed out that the same principle determines that the faces shall be planes, and that similar edges and angles shall be similarly modified, or that the law of indices in the relations of different forms is a direct consequence of it. We are able now, I think, to understand the interesting facts brought forward by Prof. Judd in a discourse which he delivered at the Eoyal Institution in the early part of this year. It does not matter how long a crystal has been out of the solution or vapour in which it was formed, the surface tension remains 384 Professor G. D. Liveing [May 15, the same, and it must grow on its old faces if replaced in the same medium. Also if it have any part broken off, the tension of the broken surface will, if it be not a cleavage face, be greater than on a face of the crystal, and in growing, the laws of energy necessarily cause it to grow in such a way as to reduce the potential energy to a minimum, i. e. to replace the broken surface by the regular planes of less surface energy. The formation of what have been called " negative crystals " by fusion in the interior of a mass, is due to the same principle. If the mass is crystalline in structure the surfaces of least energy will be most easily produced in the inside as well as on the outside. We see a very similar result in the development of crystalline form by the action of solvents, as of acids on metals. The substance acted on must be crystalline in its molecular arrangement internally, though its external figure may have been derived from the shape of the vessel or other cause. If this is the case, and if the acid is not so strong as to dissolve the metal rapidly, there must be a tendency for those parts of the surface for which the energy is greatest to be most easily removed. The result is to leave a crystalline form with surfaces of minimum energy, as we see in Widmanstatt figures, a tin plate acted on by dilute aqua regia, and many such cases. In fact, the solution of solids in liquids is very closely and directly connected with the surface tension. One of many facts connected with crystallisation is that the same substance in one crystalline form may be soluble in a liquid in which it is not soluble when it has another crystalline form. It is probably the low surface energy of one form of crystals of sulphur which makes them insoluble in carbon disulphide, and this low surface energy may be an electric effect. It is not difficult to understand that the same molecules may give rise to crystals of different degrees of symmetry, according to the orientation of the axes, and the orientation of the axes may very well depend on the distribution of the mass within the molecule, or the molecules may in one case contain a greater number of chemical atoms than in the other. With different crystalline forms of the same kind of sub- stance we shall in general have different surface energies, and a surface of great energy will be attacked by a solvent when one of less energy will resist it. I pointed out that the law of symmetry, the development of all the faces of any form, and the similar modification of all corresj)onding edges and angles, is in general necessary in order to give equilibrium under the action of the surface tensions. But we often find crystals with only half the modifications required for symmetry. In such cases the surface tensions must produce a stress in the interior tending to deform the crystal. When the crystal was in process of formation there was necessarily equilibrium, and there must have been a pressure equal and opposite to this effect of the surface tension. There are various ways in which we may suppose that such a force 1891.] on Crystallisation. 385 would arise; for instance, the electric field miglit produce a stress in opposition to the aggregation of the molecules in the closest possible way, and then the crystal would develop such faces as would give rise to an equal and opposite stress. The presence of molecules of some other material, difi'erent from those forming the bulk of the crystal, might cause a similar eifect, so might inequalities of temperature. In the case of an electric stress, or one due to inequalities of tem- perature, when the electric stress, or the inequality of temperature was removed, the crystal would be left with an internal strain, because the stress due to the want of symmetry must be met by an equal pressure. Crystals of this sort generally betray the internal strain, either by developing electricity of opposite kinds at the two ends when they are heated, or cooled ; or they affect polarised light, rotating the plane of polarisation. That these effects are really due to the state of internal strain is proved because tourmalines, and other crystals, which are pyro-electric when unsymmetrical, show no such property when symmetrically grown ; and sodium chlorate when in solution, quartz when fused, and so on, lose their rotatory power. On the other hand there are many substances which in solution show a rotatory power, and as a rule such substances produce unsymmetri- cally developed crystals. This is well seen in the tartrates. The constitution of the molecules must naturally be such that they will not, without some strain, form crystals, and equilibrium in the crystal is attained by the opposing stress arising from want of symmetry in the surface tensions. In all such crystals the rotatory power disappears either in whole or in part when the substance crystallises. It is impos- sible however, in biaxal crystals to tell whether there is rotation or not. According to Des Cloizeaux the only crystal formed from a liquid having rotatory power, which shows rotation in the solid state, is strychnine sulphate. This substance forms crystals like prussiate of potash, double square pyramids with the two apices truncated. Its rotatory power in the crystalline form is much stronger than in the liquid form. The crystals are not hemihedral, and the rotatory power is not due to any stress arising from want of symmetry in surface tensions. Effects more or less analogous to those due to the stress arising from unsymmetric development may be produced in crystals by external pressure. Thus a piece of rock salt, which in its natural state has no action on polarised light, when compressed in a vice will change the plane of polarisation. Also a cleavage slice of potassium ferrocyanide which is uniaxal, may, by compression, be made to give in convergent polarised light the two eyes and elliptic rings of a biaxal crystal. 386 Professor G. D. Liveing on Crystallisation. [May 15, Explanation of the Plate. Fig. 4 shows half of a regular octahedron formed of a pile of spherical balls, and Fig. 5 shows part of a face of a dodecahedron produced by truncating one edge of Fig. 4. In this it is seen that in the plane of the dodecahedral face each ball is touched by only two others. Fig. 6 shows the triangular pyramid formed of oblate spheroids, which becomes one corner of a cube when the ratio of the diameters of the spheroids is 2 : 1, but one corner of a rhombohedron if the ratio is greater or less. Figs. 7, 8. and 9 represent lialves of octahedra formed of prolate spheroids. In Fig. 7 the axes are perpendicular to the base, and the octahedron has pyramidal symmetry. In Fig. 8 the axes are parallel to one edge of the base, and the octahedron has right prismatic symmetry. In Fig. 9 the axes are in planes parallel to one edge of the base, but inclined to that edge, and the octahedron is oblique. [G. D. L.] Fig 4 Fig 5. Tig -7. 1891.] Prof. Ewing on the Molecular Process in Magnetic Induction. 387 WEEKLY EVENING MEETING, Friday, May 22, 1891. David Edward Hughes, Esq. F.E.S. Vice-President, in the Chair. Professor J, A. Ewing, M.A. B.Sc. F.E.S. PROFESSOR OF APPLIED MECHANICS AND MECHANISM IN THE UNIVERSITY OF CAMBRIDGE. The Molecular Process in Magnetic Induction. Magnetic induction is the name given by Faraday to the act of becoming magnetised, which certain substances perform when they are placed in a magnetic field. A magnetic field is the region near a magnet, or near a conductor conveying an electric current. Throughout such a region there is what is called magnetic force, and when certain substances are placed in the magnetic field the magnetic force causes them to become magnetised by magnetic induction. An effective way of producing a magnetic field is to wind a conducting wire into a coil, and pass a current through the wire. Within the coil we have a region of comparatively strong magnetic force, and when a piece of iron is placed there it may be strongly magnetised. Not all substances possess this property. Put a piece of wood or stone or copper or silver into the field, and nothing noteworthy happens ; but put a piece of iron or nickel or cobalt and at once you find that the piece has become a magnet. These three metals, with some of their alloys and compounds, stand out from all other sub- stances in this respect. Not only are they capable of magnetic induction — of becoming magnets while exposed to the action of the magnetic field — but when withdrawn from the field they are found to retain a part of the magnetism they acquired. They all show this property of retentiveness, more or less. In some of them this residual magnetism is feebly held, and may be shaken out or other- wise removed without difficulty. In others, notably in some steels, it is very persistent, and the fact is taken advantage of in the manufacture of permanent magnets, which are simply bars of steel, of proper quality, which have been subjected to the action of a strong magnetic field. Of all substances, soft iron is the most susceptible to the action of the field. It can also, under favourable conditions, retain, when taken out of the field, a very large fraction of the magnetism that has been induced — more than nine-tenths — more, indeed, than is retained by steel ; but its hold of this residual mag- netism is not firm, and for that reason it will not serve as a material for permanent magnets. My purpose to-night is to give some account of the molecular process through which we may conceive magnetic induction to take place, and of the structure which makes residual magnetism possible. 388 Professor J. A. Ewing [May 22, When a piece of iron or nickel or cobalt is magnetised by induction, the magnetic state permeates the whole piece. It is not a superficial change of state. Break the piece into as many fragments as you please, and you will find that every one of these is a magnet. In seeking an explanation of magnetic quality we must penetrate the innermost framework of the substance — we must go to the molecules. Now, in a molecular theory of magnetism there are two possible beginnings. We might suppose, with Poisson, that each molecule becomes magnetised when the field begins to act. Or we may adopt the theory of Weber, which says that the molecules of iron are always magnets, and that what the field does is to turn them so that they face more or less one way. According to this view, a virgin piece of iron shows no magnetic polarity, not because its molecules are not magnets, but because they lie so thoroughly higgledy-piggledy as regards direction that no greater number point one way than another. But when the magnetic force of the field begins to act, the molecules turn in response to it, and so a preponderating number come to face in the direction in which the magnetic force is applied, the result of which is that the piece as a whole shows magnetic polarity. All the facts go to confirm Weber's view. One fact in particular I may mention at once — it is almost conclusive in itself. When the molecular magnets are all turned to face one way, the piece has clearly received as much magnetisation as it is capable of. Accordingly, if Weber's theory be true, we must expect to find that in a very strong magnetic field a piece of iron, or other magnetisable metal, becomes saturated, so that it cannot take up any more mag- netism, however much the field be strengthened. This is just what happens : experiments were published a few years ago which put the fact of saturation beyond a doubt, and gave values of the limit to which the intensity of magnetisation may be forced. When a piece of iron is put in a magnetic field, we do not find that it becomes saturated unless the field is exceedingly strong. A weak field induces but little magnetism ; and if the field be strength- ened, more and more magnetism is acquired. This shows that the molecules do not turn with perfect readiness in response to the deflect- in" magnetic force of the field. Their turning is in some way resisted, and this resistance is overcome as the field is strengthened, so that the magnetism of the piece increases step by step. What is the directing force which prevents the molecules from at once yielding to the deflecting influence of the field, and to what is that force due? And again, how comes it that after they have been deflected they return partially, but by no means wholly, to their original places when the field ceases to act ? I think these questions receive a complete and satisfactory answer when we take account of the forces which the molecules necessarily exert on one another in consequence of the fact that they are magnets. We shall study the matter by examining the behaviour of 1891]. on the Molecular Process in Magnetic Induction. 389 groups of little magnets, pivoted like compass needles, so that each is free to turn except for the constraint which it suffers on account of the presence of its neighbours. But first let us see more particularly what happens when a piece of iron or steel or nickel or cobalt is magnetised by means of a field the strength of which is gradually augmented from nothing. We may make the experiment by placing a piece of iron in a coil, and making a current flow in the coil with gradually increased strength, noting at each stage the relation of the induced magnetism to the strength of the field. This relation is observed to be by no means a simple one : it may be represented by a curve (Fig. 1), and an Fig. 1. inspection of the curve will show that the process is divisible, broadly, into three tolerably distinct stages. In the first stage (a) the magnetism is being acquired but slowly: the molecules, if we accept Weber's theory, are not responding readily — they are rather hard to turn. In the second stage (6) their resistance to turning has to a great extent broken down, and the piece is gaining magnetism fast. In the third stage (c) the rate of increment of magnetism falls off: we are there approaching the condition of saturation, though the process is still a good way from being completed. Further, if we stop at any point of the process, such as P, and gradually reduce the current in the coil until there is no current, and therefore no magnetic field, we shall get a curve like the dotted line PQ, the height of Q showing the amount of the residual mag- netism. If we make this experiment at a point in the first stage (a), we shall find, as Lord Rayleigh has shown, little or no residual mag- netism ; if we make it at any point in the second stage (6), we shall find very much residual magnetism ; and if we make it at any point Vol. XITI. (No. 85.) 2 d o'JO Professor J. A. Ewing [May 22, in tbe third stage (c), we sball find only a little more residual mag- netism than we should have found by making the exjieriment at the end of stage h. That jiart of the turning of the molecules which goes on in stage a contributes nothing to the residual magnetism. That })art which goes on in stage c contributes little. But that part of the turning which goes on in stage h contributes very njuch. In some sjiecimcns of magnetic metal we find a much sharper separation of the three stages than in others. By applying strain in certain ways it is possible to get the stages very clearly separated. Fig. 2, a beautiful instance of that, is taken from a paper by Mr. Fig. 2. Nagaoka — one of an able band of Jai)anese workers who are bidding fair to repay the debt that Japan owes for its learning to the West. It shows how a piece of nickel which is under the joint action of puU and twist becomes magnetised in a growing magnetic field. There the first stage is exceptionally j^rolouged, and the second stage is extraordinarily abruj^t. The bearing of all this on the molecular theory will bo evident when we turn to these models, consisting of an assemblage of little pivoted magnets, which may be taken to represent, no doubt in a very crude way, the molecular structure of a magnetisable metal. I have here some large models, where the pivoted magnets are pieces of sheet steel, some cut into short flat bars, others into diamond shapes with ])ointed ends, others into shapes resembling mushrooms or nmbrellas, and in these the magnetic field is produced by means of a coil of in- sulated wire wound on a large wooden frame below the magnets. Some of these are arranged with the pivots on a gridiron or lazy-tongs of jointed wooden bars, so that we may readily distort them, and vary the distances of the pivots from one another, to imitate some of the ctfects of strain in the actual solid. But to display the experiments U) a hii'gc audience a lantern model will fcrvc best. In this one the 1891.] on the Molecular Process in Magnetic Induction. 391 magDcts are got by taking to pieces numbers of little pocket compasses. The pivots are cemented to a glass plate, through which the light })asses in such a way as to project the shadows of the magnets on the screen. The magnetic force is apj)lied by means of two coils, one on either side of the assemblage of magnets and out of the way of the light, which together produce a nearly uniform magnetic field through- out the whole group. You see this when I make manifest the field in a well-known fashion, by dropping iron filings on the plate. We shall first put a single pivoted magnet on the plate. So long as no field acts it is free to point anyhow — there is no direction it prefers to any other. As soon as I apply even a very weak field it responds, turning at once into the exact direction of the applied force, for there was nothing (beyond a trifling friction at the pivot) to prevent it from turning. Now try two magnets. I have cut off the current, so that there is at present no field, but you see at once that the pair has, so to speak, a will of its own. I may shake or disturb them as I please, but they insist on taking up a j)osition (Fig. 3) with the north end of one as close as possible to the south end of the other. If disturbed they return to it : this configuration is highly stable. Watch what happens when the magnetic field acts with gradually growing strength. At first, so long as the field is weak (Fig. 4), there is but little deflection ; Fm. P. Fig 4. but as the deflection increases it is evident that the stability is being lost, the state is getting more and more critical, until (Fig. 5) the tie that holds them together seems to break, and they suddenly turn, with violent swinging, into almost perfect alignment with the magnetic force H. Kow 1 gradually remove the force, and you see that they are slow to return, but a stage comes when they swing back, and a comj)lete removal of the force brings them into the condition with which we began (Fig. 3). If we were to picture a piece of iron as formed of a vast number of such i^airs of molecular magnets, each jiair far enough from its ueigh- O T-, i) 392 Professor J. A, Eiinng [May 22, hours to be practically out of reacli of tlieir magnetic influence, we might deduce many of the observed magnetic pro2:)erties, but not all. In particular, we should not be able to account for so much residual magnetism as is actually found. To get that, the molecules must Fig. 5. make new connections when the old ones are broken ; their relations are of a kind more complex than the quasi-matrimonial one which this experiment exhibits. Each molecule is a member of a larger community, and has probably many neighbours close enough to atiect its conduct. We get a better idea of what happens by considering four magnets (Fig. 6). At first, in the absence of deflecting magnetic force, they group themselves in stable pairs — in one of a number of possible Fig. 7. combinations. Then — as in the former case — when magnetic force is applied, they are at first slightly deflected, in a manner that exactly tallies with what I liave called the stage a of the magnetising process. Next comes instability, 'i'he original ties break up,*^and the magnets 1891.] on the Molecular Process in Magnetic Induction, 393 swing violently round ; but finding a new possibility of combining (Fig. 7), they take to that. Fimilly, as the field is further strengthened Fig. 8. Fig. 9. they are drawn into perfect alignment with the applied magnetic force (Fig. 8). We see the same three stages in a multiform group (Figs, 9, 10, 1 1). 394 Professor J. A. Eiving [May 22, At first, the group, if it has been shuffled by any casual disturbance, arranges itself at random in lines that give no resultant polarity. A weak force produces no more than slight quasi-elastic deflections ; a stronger force breaks up the old lines, and forms new ones more favourably inclined to the direction of the force (Fig. 10). Avery strong force brings about saturation (Fig. 11). In an actual piece of iron there are multitudes of groups lying variously directed to begin with— perhaps also different as regards the spacing of their members Some enter the second stage while Fig. 10. Fig. 11. others are still in the first, and so on. Hence, the curve of mag- netisation does not consist of peifectly sharp steps, but has the rounded outlines of Fig. 1. Notice, again, how the behaviour of these assemblages of ele- mentary magnets agrees with what I have said about residual mag- netism. If we stop strengthening the field before the first stage is passed — before any of the magnets have become unstable and have tumbled round into new places — the small deflection simply dis- appears, and there is no residual effect on the configuration of the 1891.] on the Molecular Process in Magnetic Induction. 395 group. But if we carry the process far enough to have unstable deflections, the effects of these persist when the force is removed, for the magnets then retain the new grouping into which they have fallen (Fig. 10). And again, the quasi- elastic deflections which go on during the third, stage do not add to the residual magnetism. Notice, further, what happeus to the group if after applying a magnetic force in one direction and removing it, I begin to apply force in the opposite direction. At first there is little reduction of the residual polarity till a stage is reached when instability begins, Fig. 12. Cyclic reversal of magnetisation in (A a) annealed iron wire, (b b) the same piece hardened by stretching. and then reversal occurs with a rush. We thus find a close imitation of all the features that are actually observed when iron or any of the other magnetic metals is carried through a cyclic magnetising process (Fig. 12). The effect of any such process is to form a loop in the curve which expresses the relation of the magnetism to the mag- netising force. The changes of magnetism always lag behind the 396 Professor J. A. Ewing [May 22, changes of magnetising force. This tendency to lag behind is called magnetic hysteresis. We have a manifestation of hysteresis whenever a magnetic metal has its magnetism changed in any manner through changes in the magnetising force, unless, indeed, the changes are so minute as to be confined to what I have called the first stage (a, Fig. 1). Residual magnetism is only a particular case of hysteresis. Hysteresis comes in whatever be the character or cause of the magnetic change, provided it involves such deflections on the part of the molecules as make them become unstable. The unstable move- ments are not reversible with respect to the agent which produces them — that is to say, they are not simply undone step by step as the agent is removed. We know, on quite independent grounds, that when the mag- netism of a piece of iron or steel is reversed, or indeed cyclically altered in any way, some work is spent in performing the operation — energy is being given to the iron at one stage, and is being recovered from it at another ; but when the cycle is taken as a whole, there is a net loss, or rather a waste of energy. It may be shown that this w^aste is proportional to the area of the loop in our diagrams. This energy is dissipated ; that is to say, it is scattered and rendered useless : it takes the form of heat. The iron core of a transformer, for instance, which is having its magnetism reversed with every pulsation of the alternating current, tends to become hot for this very reason ; indeed, the loss of energy which happens in it, in conse- quence of magnetic hysteresis, is a serious drawback to the efficiency of alternating-current systems of distributing electricity. It is the chief reason why they require much more coal to be burnt, for every unit of electricity sold, than direct-current systems require. The molecular theory shows how this waste of energy occurs. When the molecule becomes unstable and tumbles violently over, it oscillates and sets its neighbours oscillating, until the oscillations are damped out by the eddy currents of electricity which they generate in the surrounding conducting mass. The useful work that can be got from the molecule as it falls over is less than the work that is done in replacing it during the return portion of the cycle. This is a simple mechanical deduction from the fact that the move- ment has unstable phases. I cannot attempt, in a single lecture, to do more than glance at several places where the molecular theory seems to throw a flood of light on obscure and complicated facts, as soon as we recognise that the constraint of the molecules is due to their mutual action as magnets. It has been known since the time of Gilbert that vibration greatly facilitates the process of magnetic induction. Let a piece of iron be briskly tapped while it lies in the magnetic field, and it is found to take up a large addition to its induced magnetism. Indeed, if we examine the successive stages of the process while the iron is kept vibrating by being tapped, we find that the first stage (a) has practi- 1891.] on the Molecular Process in Magnetic Induction. 397 Fig. 13. cally disappeared, and tliere is a steady and rapid growth of mag- netism almost from the very first. This is intelligible enough. Vibration sets the molecular magnets oscillating, and allows them to break their primitive mutual ties and to respond to weak deflecting forces. For a similar reason vibration should tend to reduce the residue of magnetism which is left when the magnetising force is removed, and this, too, agrees with the results of observation. Perhaps the most eflfective way to show the influence of vibration is to apply a weak magnetising force first, before tapping. If the force is adjusted so that it nearly but not quite reaches the limit of stage (a), a great number of the molecular magnets are, so to speak, hovering on the verge of instability, and when the piece is tapped they go over like a house of cards, and magnetism is acquired with a rush. Tapping always has some effect of the same kind, even though there has been no special adjustment of the field. And other things besides vibration will act in a similar way, precipitating the break-up of molecular groups when the ties are already strained. Change of temperature will sometimes do it, or the application or change of mechanical strain. Suppose, for instance, that we apply pull to an iron wire while it hangs in a weak magnetic field, by making it carry a weight. The first time that we put on the weight, the magnetism of the wire at once increases, often very greatly, in consequence of the action I have just described (Fig. 13). The molecules have been on the verge of turning, and the slight strain caused by the weight is enough to make them go. Remove the weight, and there is only a com- paratively small change in the magnet- ism, for the greater part of the molecular turning that was done when the weight was put on is not undone when it is taken ofi^. Reapply the weight, and you find again but little change, though there are still traces of the kind of action which the first application brought about. That is to say, there are some groups of molecules which, though they were not broken up in the first application of the weight, yield now, because they have lost the support they then obtained from neigh l)ours that have now entered into new combinations. Indeed, this kind of action may often be traced, always diminishing in amount, during several Effects of loading, unloading, and reloading a soft iron wire in a weak magnetic field. 398 Professor J. A. Ewing [May 22, successive applications and removals of the load (see Fig. 13), and it is only when the process of loading has been many times repeated that the magnetic change brought about by loading is just opposite to the magnetic change brought about by unloading. Whenever, indeed, we are observing the effects of an alteration of physical condition on the magnetism of iron, we have to distinguish between the primitive effect, which is often very great and is not reversible, and the ultimate effect, which is seen only after the molecular structure has become somewhat settled through many repetitions of the process. Experiments on the effects of temperature, of strain, and so forth, have long ago shown this distinction to bo exceedingly important : the molecular theory makes it perfectly intelligible. Further, the theory makes plain another curious result of experi- ment. When we have loaded and unloaded the iron wire many times over, so that the effect is no longer complicated by the primitive action I have just described, we still find that the magnetic changes which occur while the load is being put on are not simply undone, step by step, while the load is being taken off. Let the whole load be divided into several parts, and you will see that the magnetism has two different values, in going up and in coming down, tor one and the same intermediate value of the load. The changes of magnetism lag behind the changes of load : in other words, there is hysteresis in the relation of the magnetism to the load (Fig. 14). This is because some of the molecular groups are every time being broken up during the loading, and re-established during the unloading, and that, as we saw already, involves hysteresis. Consequently, too, each loading and unloading requires the expenditure of a small quantity of energy, which goes to heat the metal. Moreover, a remarkably interesting conclusion follows. This hysteresis, and consequent dissipation of energy, will also happen though there be no magnetisation of the piece as a whole: it depends on the fact that the molecules are magnets. Accordingly, we should expect to find — and experiment confirms this* — that if the wire is loaded and unloaded, even when no magnetic field acts and there is no magnetism, its physical qualities which are changed by the load will change in a manner involving hysteresis. In particular, the length must be less for the same load during loading than during unloading so that work may be wasted in every cycle of loads. There can be no such thing as perfect elasticity in a magnetisable metal, unless, indeed the range of the strain is so very narrow that none of the molecules tumble through unstable states. This may have something to do with the fact, well known to engineers, that numerous repetitions of a straining action, so slight as to be safe enough in itself, have a dangerous effect on the structure of iron or steel. * See Phil. Trans. 1885, p. GU. 1891.] on the Mclecular Process in Magnetic Induction. 399 Another tiling on which the theory throws light is the phenomenon of time-lag in magnetigation. When a piece of iron is put into a steady magnetic field, it does not take instantly all the magnetism Fig. 14. Hysteresis in the changes of magnetism produced by applying and remoA'ing load. that it will take if time be allowed. There is a gradual creeping up of the magnetism, which is most noticeable when the field is weak and whenlhe iron is thick. If you will watch the manner in which a group of these little magnets breaks up when a magnetic force is applied to it, you will see that the process is one that takes time. The first molecule to yield is some outlying one which is comparatively unattached — as we may take the surface molecules in the piece of iron 400 Professor J. A. Ewing [May 22, to be. It falls over, and then its neighbours, weakened by the loss of its support, follow suit, and gradually the disturbance propagates itself from molecule to molecule throughout the group. In a very thin piece of iron — a fine wire, for instance — there are so many surface molecules, in comparison with the whole number, and con- sequently so many points which may become origins of disturbance, that the breaking up of the molecular communities is too soon over to allow much of this kind of lagging to be noticed. Effects of temperature, again, may be interpreted by help of the molecular theory. When iron or steel or nickel is heated in a weak magnetic field, its susceptibility to magnetic induction is observed to increase, until a stage is reached, at a rather high temperature, when the magnetic quality vanishes almost suddenly and almost completely. Fig. 15, from one of Hopkinson's papers, shows what is observed as the temperature of a piece of steel is grad ually raised. The sudden loss of magnetic quality occurs when the metal has become red-hot ; the Fig. 15. C 1400 - " ^ /200 - _ t '000 - ■ ^ aoQ - O CL f:< 600- ^<^ 400- 100 200 300 400 Temperature 500 600 700° C Effects of rising temperature on the magnetic inductive capacity of steel (Hopkinson). magnetic quality is recovered when it cools again sufficiently to cease to glow.^ Now, as regards the first effect— the increase of suscepti- bility with increase of temperature —I think that is a consequence of two independent effects of heating. The structure is expanded, so that the molecular centres lie further aj^art. But the freedom with which the molecules obey the direction of any applied magnetic force is increased not by that only, but perhaps even more by their being thrown into vibration. When the magnetic field is weak heating consequently assists magnetisation, sometimes very greatly, by hasten- ing the passage from stage a to stage h of the magnetising process. And it is at least a conjecture worth consideration whether the sudden loss of magnetic quality at a higher temperature is not due to the vibra- tions becoming so violent as to set the molecules spinning, when, of course, their pcdarity would be of no avail to produce magnetisation. We know, at all events, that when the change from tlie magnetic to the non-magnetic state occurs, there is a profound molecular change, 1891.] on the Molecular Process in Magnetic Induction. 401 and heat is absorbed which is given out again when the reverse change takes place. In cooling from a red heat, the iron actually extends at tlie moment when this change takes place (as was shown by Gore), and so much heat is given out that (as Barrett observed) it reglows, becoming brightly red, though just before the change it had cooled so far as to be quite dull. [Experiment, exhibiting retraction and reglow in cooling, shown by means of a long steel wire, heated to redness by the electric current.] The changes which occur in iron and steel about the temperature of redness are very complex, and I refer to this as only one possible direction in which a key to them may be sought. An interesting illustration of the use of these models has reached me, only this morning, from New York. In a paper just published in the Electrical World * Mr. Arthur Hoopes supports the theory I have laid before you by giving curves which show the connection, deter- mined experimentally, between the resultant polarity of a group of little pivoted magnets and the strength of the magnetic field, when the field is applied, removed, reversed, and so on. I shall throw these curves upon the screen, and, rough as they are, in consequence of the limited number of the magnets, you see that they succeed remarkably well in reproducing the features which we know the curves for solid iron to possess. It may, perhaps, be fairly claimed that the models whose behaviour we have been considering have a wider application in physics than merely to elucidate magnetic processes. The molecules of bodies may have polarity which is not magnetic at all — polarity, for instance due to static electrification — under which they group themselves in stable forms, so that energy is dissipated whenever these are broken up and rearranged. When we strain a solid body beyond its limit of elasticity, we expend work irrecoverably in overcoming, as it were, internal friction. What is this internal friction due to but the breaking and making of molecular ties ? And if internal friction is to be ascribed to that, why not also the surface friction which causes work to be spent when one body rubs upon another ? In a highly suggestive passage of one of his writings, | Clerk Maxwell threw out the hint that many of the irreversible processes of physics are due to the breaking up and reconstruction of molecular groups. These models help us to realise Maxwell's notion, and, in studying them to-night, I think we may claim to have been going a step or two forward where that great leader pointed the way. [J. A. E.] * Reprinted in the Electrician of May 29tli, 1891. t ' Eiicyc. Bi'it.' Art. '• Constitution of Bodies." 402 3Ir. David Gill [May 29, WEEKLY EVENING MEETING, Friday, May 29, 1891. William Hug gins," Esq. D.C.L. LL.D. F.R.S. Vice-President, in the Chair. David Gill, Esq. LL.D. F.R.S. Her Majesty's Astronomer at the Cape of Good Hope. An Astronomer s Worh in a Modern Observatory. The work of Astronomical Observatories has been divided into two classes, viz. Astrometry and Astrophysics. The first of these relates to Astronomy of precision, that is to the determination of the posi- tions of celestial objects ; the second relates to the study of their physical features and chemical constitution. Some years ago the aims and objects of these two classes of observatories might have been considered perfectly distinct, and, in fact, were so considered. But I hope to show that in more recent years their objects and their processes have become so interlaced that they cannot with advantage be divided, and a fully equipped modern observatory must be understood to include the work both of Astrometry and Astrophysics. In any such observatory the principal and the fundamental instru- ment is the transit circle. It is upon the position in the heavens of celestial objects, as determined with this instrument or with kindred instruments, that the whole fair superstructure of exact astronomy rests; that is to say, all that we find of information and prediction in our nautical ahnanacs, all that we know of the past and can predict of the future motions of the celestial bodies. Here is a very small and imperfect model, but it will serve to render intelligible the photograph of the actual instrument which will be subsequently projected on the screen. [Here the lecturer de- scribed the adjustments and mode of using a transit circle.] We are now in a position to understand photographs of the instru- ment itself. But first of all as to the house in which it dwells. Here, now on the screen, is the outside of the main building of the Eoyal Observatory, Cape of Good Hope. I select it simply because being the observatory which it is my privilege to direct, it is the one of which I can most easily procure a series of photographs. It was built during the years 1824-28, and like all the observatories built about that time, and like too many built since, it is a very fair type of most of the things which an observatory should not be. It is, as you see, an admirably solid and substantial structure, innocent of any architectural charm, and so far as it affords an excellent dwelling- place, good library a';commodation, and good rooms for computers, no 1891.] on An Astronomer s Work in a Modern Observatory. 403 fault can be found with it. But these very qualities render it unde- sirable as an observatory. An essential matter for a j)erfect observa- tory should be the possibility to equalise the internal and the external temperature. The site of an instrument should also be free from the immediate surroundings of chimneys or other origin of ascending currents of heated air. Both these conditions are incompatible with thick walls of masonry and tbe chimneys of attaclied dwelling houses, and therefore, as far as possible, I have removed the instruments to small detached houses of their own. But tbe transit circle still remains in the main building, for, as will be evident to you, it is no easy matter to transport such an instrument. The two first photographs show the instrument, in one case pointed nearly horizontally to the north, the other pointed nearly vertical. Neither can show all parts of the instrument, but you can see the massive stone piers, weighing many tons each, whidi, resting on the solid blocks 10 feet below, support the pivots. Here are the counter- weights which remove a great jjart of the weight of the instrument from the pivots, leaving only a residual pressure sufficient to enable the pivots to preserve the motion of the instrument in its proper jjlane. Here are the microscopes by which the circle is read. Here the opening through which the instrument views the meridian sky. The observer's chair is shown in this diagram. His work appears to be very simple, and so it is, but it requires special natural gifts — patience and devotion, and a high sense of the importance of his work — to make a first-rate meridian observer. Nothing apparently more monotonous can be well imagined if a man is " not to the manner born.'* Having directed this instrument by means of the setting circle to the required altitude, he clamps it there and waits for the star which he is abf)ut to observe to enter the field. This is what he sees. [Artificial transit of a star by lantern.] As the star enters the field it passes wire after wire, and as it passes each wire he presses the key of his chronograph and records the instant automatically. As the star passes the middle wire he bisects it with tlie horizontal web, and again similarly records on his chronograph the transit of the star over the remaining wehs. Then he reads otf the microscopes by which the circle is read, and also the barometer and thermometer, in order afterwards to be able to calculate accurately the effect of atmospheric refraction on the observed altitude of the star ; and then his observation is finished. Thus the work of the meridian observer goes on, star after star, hour after hour, and night after night ; and, as you see, it differs very widely from the popular notion of an astronomer's occupation. It presents no dreamy contemj^lation, no watching for new stars, no unexpected or startling phenomena. On the contrary, there is beside him the carefully prepared observing-list for the night, the jDreviously calculated circle setting for each star, allowing just sufficient time for the new setting for the next star after the readings of the circle for the previous observation. 404 Mr. David Gill [May 29, After four or five hours of this work the observers have had enough of it ; they have, perhaps, observed fifty or sixty stars, they determine certain instrumental errors, and betake themselves to bed, tired, but (if they are of the right stuff) happy and contented men. At the Cape we employ two observers, one to read the circle and one to record the transit. Four observers are employed, and they are thus on duty each alternate night. Such is the work that an outsider would see were he to enter a working meridian observatory at night, but he would find out if he came next morning that the work was by no means over. By far the largest part has yet to follow. An obser- vation that requires only two or three minutes to make at night, requires at least half an hour for its reduction by day. Each obser- vation is aflected by a number of errors, and these have to be deter- mined and allowed for. Although solidly founded on massive i)ier8 resting on the solid rock, the constancy of the instrument's position cannot be relied upon. It goes through small periodic changes in Level in Collimation and in Azimuth, which have to be determined by proper means, and the corresponding corrections have to be com- puted and applied ; and also there are other corrections for refrac- tion, &c., which involve computation and have to be applied. But these matters would fall more properly under the head of a special lecture upon the transit instrument. I mention them now merely to explain why so great a part of an astronomer's work comes in the daytime, and to dispel the notion that his work belongs only to the night. One might very well occupy a special lecture in au account of the peculiarities of what is called personal equation — that is to say, the difiereut time which elapses for difierent observers between the time when the observer believes the star to be upon the wire and the time when the finger responds to the message which the eye has conveyed to the brain. Some observers always press the key too soon, some always too late. Some years ago I discovered, from observations to which I will subsequently refer, that all observers press the chrono- graph key either too soon for bright stars or too late for faint ones. Other errors may, and I am sure do, arise both at (Treenwich and the Cape from the impossibility of securing uniformity of outside and inside temperature in a building of strong masonry. The ideal observatory should be solid as possible as to its foundations, but light as possible as to its roof and walls — say, a light framework of iron covered with canvas. But it would be undesirable to cover a valuable and permanent instrument in this way. But here is a form of observatory which realises all that is required, and which is eminently suited for permanent use. The walls arc of sheet iron, which readily acquire the temperature of the outer air. The iron walls are protected from direct sunshine by wooden louvres, and small doors in the iron walls admit a free circu- lation of air. The revolving roof is a light framework of iron covered with well-painted papier mache. 1891.] on An Astronomer^ s Worlc in a Modern Observatory. 405 The photograpli now on the screen shows the interior of the observatory, and this brings me to the description of observations of an entirely different class. In this observatory the roof turns round on wheels, so that any part of the sky can be viewed from the tele- scope. This is so because the instrument in this observatory is intended for purposes which are entirely different from those of a transit circle. The transit circle, as we have seen, is used to determine the absolute positions of the heavenly bodies ; the helio- meter to determine with greater precision than is possible by the absolute method the relative positions of celestial objects. To explain my meaning as to absolute and relative positions :- It would, for example, be a matter of very little importance if the absolute latitude of a point on the Eoyal Exchange or the Bank of England were one-tenth of a second of arc (or ten feet) wrong in the maps of the Ordnance Survey of England — that would constitute a small absolute error common to all the buildings on the same map of a part of the city, and common to all the adjoining maps also. Such an error, regarded as an absolute error, would evidently be of no importance if every point on the map had the same absolute error. There is no one who can say at the present moment whether the absolute latitude of the Eoyal Exchange — nay, even of the Koyal Observatory, Greenwich — is known to ten feet. But it would be a very serious thing indeed if the relative positions on the same map were ten feet wrong here and there. For example, if of two points marking a frontage boundary on Cornhill one were correct, the other ten feet in error — what a nice fuss there would be ! what food for lawyers ! what a bad time for the Ordnance Survey Oifice ! Well, it is just the same in astronomy. We do not know, we probably never shall know with certainty, the absolute places of even the principal stars to yV^^ ^^ ^ second of arc. But To^^ ^^ ^ second of arc in the measure of some relative position would be fatal. For example, in the measurement of the sun's parallax an error of yV*-'^ ^^ ^ second of arc means an error of 1,000,000 miles, in round numbers, in the sun's distance; and it is only when we can be quite certain of our measures of much smaller quantities than y o^h of a second of arc, that we are in a posi- tion to begin seriously the determination of such a problem as that of the distances of the fixed stars. For these problems we must use differential measures, that is measures of the relative positions of two objects. The most perfect instrument for such purposes is the heliometer. Lord McLaren has kindly sent from Edinburgh, for the purposes of this lecture, the parts of his heliometer which are necessary to illustrate the principles of the instrument. This instrument is the same which I used on Lord Crawford's expedition to Mauritius, in 1874. It was also kindly lent to me by Lord Crawford for an expedition to the Island of Ascension to observe the opposition of Mars, in 1877. In 1879, when I went to Vol. XIIL (No. 85 ) 2 e 406 Mr. David Gill [May 29, the Cape, I acquired the instrument from Lord Crawford, and carried out certain researches with it on the distances of the fixed stars. In 1887, when the Admiralty provided the new heliometer for the Cape Observatory, this instrument again changed hands. It became the property of Lord McLaren. I felt rather disloyal in parting with so old a friend. We had spent so many happy hours together, we had shared a good many anxieties together, and we knew each other's iceaknesses so well. But my old friend has fallen into good hands, and has found another sphere of work. The principle of the instrument is as follows. [The instrument was here explained.] There is now on the screen a picture of the new heliometer of the Cape Observatory, which was mounted in 1887, and has been in constant use ever since. It is an instrument of the most refined modern construction, and is probably the finest apparatus for refined measurement of celestial angles in the world. [Here were explained the various parts of the instrument in relation to the model, and the actual processes of observation were illustrated by the images of artificial stars projected on a screen.] Here, again, there is little that conforms to the popular idea of an astronomer's work ; there is no searching for objects, no contemplative watching, nothing sensational of any kind. On the contrary, every detail of his work has been previously arranged and calculated before- hand, and the prospect that lies before him in his night's work is simply more or less of a struggle with the difficulties which are created by the agitation of the star images, caused by irregularities in the atmospheric refraction. It is not upon one night in a hundred that the images of stars are perfectly tranquil. You have the same effect in an exaggerated way when looking across a bog on a hot day. Thus, generally, as the images are approached, they appear to cross and recross each other, and the observer must either seize a moment of comparative tranquillity to make his definitive bisection, or he may arrive at it by gradual approximations till he finds that the vibrating images of the two stars seem to pass each other as often to one side as to the other. So soon as such a bisec- tion has been made the time is recorded on the chronograph, then the scales are pointed on and printed off, and so the work goes on, varied only by reversals of the segments and of the position circle. Generally, I now arrange for 32 such bisections, and these occupy about an hour and a half. By that time one has had about enough of it, the nerves are somewhat tired, so are the muscles of the back of the neck, and, if the observer is wise, and wishes to do his best work, he goes to bed early and gets up again at two or three o'clock in the morning, and goes through a similar piece of work. In fact this must be his regular routine night after night, whenever the weather is clear, if he is engaged, as I have been, on a large programme of work on the parallaxes of the fixed stars, or on observations to deter- mine the distance of the sun by observations of minor planets. 1891.] on An Astronomer's Work in a Modern Observatory. 407 I will not speak now of tliese researclies, because they are still in progress of execution or of reduction. I would rather, in the first place, endeavour to complete the picture of a night's work in a modern observatory. We pass on to celestial photography, where astrometry and astro- physics join hands. Here on the screen is the interior of one of the new photographic observatories, that at Paris. [Brief description.] Here is the exterior of our new photographic observatory at the Cape. Here is the interior of it, and the instrument. [Brief description.] The observer's work during the exposure is simply to direct the telescope to the required part of the sky, and then the clockwork nearly does the rest — but not quite so. The observer holds in his hand a little electrical switch with two keys ; by pressing one key he can accelerate the velocity of the driving screw by about 1 per cent., and by pressing the other he can retard it 1 per cent. In this way he keeps one of the stars in the field always perfectly bisected by the cross wires of his guiding telescope, and thus corrects the small errors produced partly by changes of refraction, partly by small unavoidable errors in cutting the teeth of the arc into which the screw of the driving shaft of the clockwork gears. The work is monotonous rather than fatiguing, and the com- panionship of a pipe or cigar is very helpful during long exposures. A man can go on for a watch of four or five hours very well, taking plate after plate, exposing each, it may be, forty minutes or an hour. If the night is fine a second observer follows the first, and so the work goes on the greater part of the night. Next day he develops his plate and gets something like this. [Star cluster.] Working just in this way, but with the more humble apparatus which you see imperfectly in the picture now on the screen, we have with a rapid rectilinear lens by Dallmeyer of 6 inches aperture photographed at the Cape during the past six years the whole of the southern hemisphere from 20° of south declination to the south pole. The plates are being measured by Professor Kapteyn, of Groningen, and I expect that in the course of a year the whole work containing all the stars to 9J magnitude (between 200,000 and 300,000 stars) in that region will be ready for publication. This work is essential as a preliminary step for the execution in the southern hemisphere of the great work inaugurated by the Astrophotographic Congress at Paris in 1887, the last details of which were settled at our meeting at Paris in April last. What we shall do with the new apparatus perhaps I may have the honour to describe to you some years hence, after the work has been done. We now come to an important class of astronomical work more purely astrophysical, for the illustration of which I can no longer appeal to the Cape, because I regret to say that we are not yet pro- vided with the means for its prosecution. I refer to the use of the spectroscope in astronomy, and especially to the latest developments 2 E 2 408 Mr. David Gill [May, 29, of its use for the accurate measurement of the velocity of the motions of stars in the line of sight.* It is beyond the province of this lecture to enter into history, but it is impossible not to refer to the fact that the chief impulse to astronomical work in this direction was given by Dr. Huggins, our chairman to-night — nay, more, except for the early contributions of Fraunhofer to the subject, Dr. Huggins certainly is the father of sidereal spectroscopy, and that not in one but in every branch of it. He has devised the means, pointed the way, and, whilst in many branches of the work he still continues to lead the way, he has of necessity left the development of other branches to other hands. From an astrometer's point of view the most important advance that has been made in spectroscopy of recent years is the sudden development of jirecision in the measures of star motion in the line of sight. The method remained for fifteen or sixteen years quite undeveloped from the condition in which it left the hands of Dr. Huggins, and certainly no progress in the accuracy attained by Dr. Huggins was made till the matter was taken up by Dr. Vogel at Potsdam. At a single step Dr. Vogel has raised the precision of the work from that of observations in the days of Ptolemy to that of the days of Bradley — from the days of the old sights and pinnules to the days of telescopes. Therefore I take a Potsdam observation as the best type of a modern spectroscopic observation for description, especially as I have recently visited Dr. Vogel at Potsdam, and he has kindly given me a photograj)h of his spectroscope, as well as of some of the work done with it. A photograph of the Potsdam spectroscope attached to the equa- torial is now on the screen. [Description.] The method of observation consists simply in inserting a small photographic plate in the dark slide, directing the telescope to the star, and keeping the image of the star continuously on the slit during an exposure of about an hour ; and this is w'hat is obtained on develop- ment of the picture. If the star remained perfectly at rest between the jaws of the slit the spectrum would be represented by a single thread of light, and of course no lines would be visible upon such a thread ; but the observer intentionally causes the star image to travel a little along the slit during the time of exj)osure, and so a spectrum of sensible width is obtained. (Fig. 1.) You will remark how beautifully sharp are the faint lines in this spectrum. Those who have tried to observe the spectrum of Sirius in the ordinary way know that many of these fine lines cannot be seen or measured with certainty. The reason is that on account of irregularities in atmospheric refraction, the image of a star in the * The older metliorls enabled us to measure motions at riglit angles to the line of sight, but till the spectroscope came we could not measure motions in tlie line ot" sight. Fig. 1. Fig. 2. a Aurigse. d o 3 o E? .is m a o a, October. December. March. Fig. 3. 1891.] on An Astronomer'' s Worh in a Modern Observatory. 409 telescope is rarely tranquil, sometimes it shines brightly in the centre of the slit, sometimes barely in the slit at all, and the eye becomes puzzled and confused. But the photographic eye is not in the least disturbed ; when the star image is in the slit, the plate goes on record- ing what it sees, and when the star is not in the slit the plate does nothing, and it is of no consequence whatever how rapidly these alternate appearances and disappearances recur. The only difference is that when the air is very steady and the star's image, therefore, always in the slit, the -exposure takes less time than when the star is unsteady. That is one reason why the Potsdam results are so accurate. And there are many other reasons besides, into which I cannot now enter. What, however, it is very important to note is this, that we have here a method which is to a great extent independent of the atmo- spheric disturbances which in all other departments of astronomical observation have imposed a limit to their precision. Accurate astro- spectroscopy, therefore, may be pushed to a degree of perfection which is limited only by the optical aid at our disposal and by the sensibility of our photographic plates. And now I think we have sufficiently considered the ordinary pro- cesses of astronomical observation to illustrate the character of the work of an astronomer at night ; the picture should be completed by an account of his work by day. But to go into that matter in detail would certainly not be within the limits of this lecture. It is better that I should in conclusion touch upon some recent remarkable results of these day and night labours. It is these after all that most appeal to you, it is for these that the astronomer labours, it is the prospect of them that lightens the long watches of the night and gives life to the otherwise dead bones of mechanical routine. Let us take first some spectroscopic results. To explain their meaning let me remind you for a moment of the familiar analogy between light and sound. The pitch of a musical note depends on the rapidity of the vibra- tions communicated to the air by the reed or string of the musical instrument that produces the note, a low note being given by slow vibrations and a high one by quick vibrations. Just in the same way red light depends on relatively slow vibra- tions of ether, and blue or violet light on relatively quick vibrations. Well, if there is a railway train rapidly approaching one, and the engine sounds its whistle, more waves of sound from that whistle will reach the ear in a second of time, than would reach the ear were the train at rest. On the ether hand, if the train is travelling at the same rate away from the observer, fewer waves of sound will reach his ears in a second of time. Therefore an observer beside the line should observe a distinct change of pitch in the note of the engine whistle as the train passes him, and as a matter of fact such a change of pitch can be and has been observed. Just in the same way, if a source of light could be moved rapidly 410 Mr. David Gill [May 29, enough towards an observer it would become bluer, or if away from him it would become more red in colour. Only it would require a change of velocity in the moving light of some thousands of miles per second in order to render the difference of colour sensible to the eye. The experiment is, therefore, not likely to be frequently shown at this lecture table ! But the spectroscope enables such changes of colour to be measured with extreme precision. Here on the screen is the most splendid illustration of this that exists at present, viz. copies of three negatives of the spectrum of a Aurigas, taken at Potsdam in October and December of 1888, and in March 1889. (Fig. 2.) The white Hue (the picture being a positive) represents the bright line Hy given by the artificial light of hydrogen, the strong black line in the picture of the star spectrum corresponds to the black absorption line which is due to hydrogen in the atmosphere of the star. Why is it that the artificial hydrogen line does not correspond with the stellar line in these three pictures ? The answer is, either the star is moving towards or from the earth in the line of sight, or the earth is moving from or towards the star. But in December the earth in its motion round the sun is moving at right angles to the direction of a Aurigae, why then does not the stellar hydrogen line agree in position with the terrestrial hydrogen line ; the simple explanation is that a Aurigee is moving with respect to the sun. In what way is it moving ? Well, that also is clear : the stellar line is displaced towards the red end of the spectrum, that is to say the star light is redder than it should be in consequence of a motion of recession ; this proves that the star is moving away from us, and measures of the photograph show the rate of this motion to be 15 J miles per second. We also know that in October the earth in its motion round the sun is moving towards a Aurigae nearly at the same rate as we have just seen that a Aurigas is running away from the sun. Consequently, at that time, their relative motions are nearly insensible, because both are going at the same rate in the same direction, and we find accordingly in October, that the positions of the stellar and artificial hydrogen lines perfectly correspond. Finally, in March, the earth in its motion round the sun is moving away from a Aurigae, and as a Aurigae is also running away from the sun the star-light becomes so much redder than normal that the stellar hydrogen line is shifted completely to one side of the hydrogen and artificial line. The accuracy of these results may be proved as follows : — If we measure all the photographs of a Aurigae which Dr. Vogel has obtained we can derive from each a determination of the relative velocity of the motion of the star with respect to our earth. Of course these velocities are made up of the velocity of motion of a Aurigae with respect to the sun (which we may reasonably assume to be a uniform velocity) and the velocity of the earth due to 1891.] on An Astronomer's Work in a Modern Observatory. 411 a Auriga — Potsdam. Date. Observed Relative Motion of Earth and Star. Miles per sec. Motion of Earth. Concluded Motion, Star Relative to the Sun. 1888. October 22nd .. .. + 2-5 - 13-0 + 15-5 „ 24th .. .. + 31 - 12-4 + 15-5 „ 25th .. .. + 3-1 - 12-4 + 15-3 28th .. .. + 2-5 - 11-8 + 14-3 November 9th . . -I- 6-8 - 8-7 4- 15-5 December 1st + 11-8 - 31 + 14-9 „ 13th .. .. + 14-9 + 0-6 + 14-3 1889. • January 2nd + 20-5 + 6-8 + 13-7 February 5th + 32-9 + 14-3 + 18-6 March 6th 4 34-2 + 16-8 + 17-4 a Auriga — Greenwich. Date. Observed Relative Motion of Earth and Star. Miles per sec. Motion of Earth, Concluded Motion, Star Relative to the Sun, 1887. January 26th + 16-4 + 12-6 + 3-8 February 16th .. + 34-4 + 15-9 + 18-5 October 22nd . . . . + 39-8 - 13-5 + 52-3 „ 25th .. .. + 25-4 - 13-0 + 38-4 „ 29th .. .. + 40-6 - - 121 + 52-7 1888. -, December 7th . . + 29-0 - 1-2 + 36-2 1889. February 15 th .. .. + 23-8 + 16-0 + 7-8 March 5th + 20-3 + 17-1 + 3-2 September 17th . . + 18-6 - 13-3 + 33-3 19th.. .. + 21-8 - 16-7 + 38-5 25th.. .. + 24-8 - 16-5 + 41-3 November 25th . . + 24-5 - 4-9 + 29-4 4.12 Mr. David Gill [May 29, its motion round the sun. But the velocity of the earth's motion in its orbit is known with an accuracy of about one five-hundredth part of its amount, and therefore, within that accuracy, we can allow precisely for its effect on the relative velocity of the earth and a AurigsB. When we have done so we get the annexed results for the velocity of the motion of a Aurigse with respect to the sun. You see by the annexed table how beautifully they agree in the Potsdam results, and how comparatively rough and unreliable are the results obtained by the older method at Greenwich. I believe that in a few years, at least in a period of time that one may hope to see, we shall not be content merely to correct our results for the motion of the earth in its orbit only, and so test our observations of motion in the line of sight, but that we shall have arrived at a certainty and precision of working which will permit the process to he reversed, and that we shall be employing the sjjectroscope to determine the velocity of the earth's motion in its orbit, or in other words to determine the fundamental unit of astronomy, the distance of the sun from the earth. I will take as another example one recent remarkable spectro- scopic discovery. Miss Maury, in examining a number of photographs of stfUer spectra taken at Harvard College, discovered that in the spectrum of P Aurigas certain lines doubled themselves every two days, becoming single in the intermediate days. Accurate Potsdam observations confirmed the conclusion. The picture on the screen (Fig. 3) shows the spectrum of ^ AurigaB photographed on November 22 and 25 of last year. In the first the lines are single, in the other every line is doubled. Measures and discussion of a number of these photographs have shown that the doubling of the lines is perfectly accounted for by the supposition of two suns revolving round each other in a period of four days, each moving at a velocity of about 70 miles a second in its orbit. When one star is approaching us and the other receding, the lines in the spectrum formed by the light of the first star will be moved towards tl;e blue end of the spectrum, those in the spectrum of the second star towards the red end of the S23ectrum. Then, as the two stars come into the same line with us, their motions become at right angles to the line of sight, and their two spectra, not being affected by motion, will perfectly coincide ; but then, after the stars cross, their spectra again separate in the opposite direction, and so they go on. Thus by means of their spectra we are in a position to watch and to measure the relative motions of two objects that we can never see apart ; nay more, we can determine not only their period of revolution but also the velocity of their motions in their orbits. Now, if we know the time that a body takes to complete its revolution, and the velocity at which it moves, clearly we know the dimensions of its orbit, and if we know the dimensions of an orbit we know what attrac- 1891.] on An Astro7iomer's Work in a Modern Observatory. 413 tive force is necessary to compel the body to keep in that orbit, and thus we arc able to weigh these bodies. The components of /? AurigaB are two suns, which revolve about each other in four days ; they are only between 7 and 8 millions of miles (or one-twelfth of our distance from the sun) apart, and if they are of equal weight they each weigh rather over double the weight of our sun. I have little doubt that these facts do not represent a permanent condition, but simply a stage of evolution in the life-history of the system, an earlier stage of which may have been a nebular one. Other similar double stars have been discovered both at Potsdam and at Cambridge, U.S., stars that we shall never see separately with the eye aided by the most powerful telescope ; but time does not permit me to enter into any account of them. I pass now to another recent result that is of great cosmical interest. The Cape photographic star charting of the southern hemisphere has been already referred to. In comparing the existing eye estimates of magnitude by Dr. Gould with the photographic determinations of these magnitudes, both Professor Kapteyn and myself have been greatly struck with a very considerable systematic discordance between the two. In the rich parts of the sky, that is in the Milky Way, the stars are systematically photographically brighter by com- parison w^ith the eye observations than they are in the poorer part of the sky, and that not by any doubtful amount but by half or three- fourths of a magnitude. One of two things was certain, either that the eye observations were wrong, or that the stars of the Milky Way are bluer or whiter than other stars. But Professor Pickering, of Cambridge, America, has lately been making a complete photographic review of the heavens, and by placing a prism in front of the telescoj)e he has made pictures of the whole sky like this. [Here two examples of the plates of Pickering's spectroscopic Durchmusterung were exhibited on the screen.] He has discussed the various types of the spectra of the brighter stars, as thus revealed, according to their distribution in the sky. He finds thus that the stars of the Sirius type occur chiefly in the Milky Way, whilst stars of other types are fairly divided over the sky. Now stars of the Sirius type are very white stars, very rich rela- tive to other stars in the rays which act most strongly on a photo- graphic plate. Here then is the explanation of the results of our photographic star-charting, and of the discordance between the photo- graphic and visual magnitudes in the Milky Way. The results of the Cape charting further show that it is not alone to the brighter stars that this discordance extends, but it extends also-, though in a rather less degree, to the fainter stars of the Milky Way. Therefore we may come to the very remarkable conclusion that the Milky Way is a thing apart, and that it has been developed perhaps in a different manner, or more probably at a different and probably later epoch from the rest of the sidereal universe. 414 Mr. David Gill [May 29, Here is another interesting cosmical revelation wliicli we owe to photography. You all know the beautiful constellation Orion, and many in this theatre have before seen the photograph of the nebula which is now on the screen, taken by Mr. Roberts. Here is another photograph of the same object taken with a much longer exposure. You see how over-exposed, in fact, burnt out, the brightest part of the picture is, and yet what a wonderful develop- ment of faint additional nebulous matter is revealed. But I do not think that many persons in this room have seen this picture, and probably very few have any idea what it represents. It is from the original negative taken by Professor Pickering, with a small photographic lens of short focus, after six hours' exposure in the clear air of the Andes, 10,000 feet above sea-level. The field embraces the three well-known stars in the belt of Orion on the one hand, and /? Orionis (Eigel) on the other. You can hardly recognise these great white patches as stars ; their ill-defined character is simply the result of excessive over-exposure. But mark the wonders which this long exposure with a lens of high intrinsic brilliancy of image has revealed. Here is the great nebula, of course terribly over-exposed, but note its wonderful fainter ramifications. See how the whole area is more or less nebulous, and surrounded as it were with a ring fence of nebulous matter. This nebulosity shows a special concentration about /S Orionis. Well, when Professor Pickering got this wonderful picture, know- ing that I was occupied with investigations on the distances of the fixed stars, he wrote to ask whether I had made any observations to determine the distance of (3 Orionis, as it would be of great interest to know from independent evidence whether this very bright star was really near to us or not. It so happens that the observations were made, and their definitive reduction has shown that /S Orionis is really at tbe same distance from us as are the faint comparison stars. /3 Orionis is, therefore, probably part and parcel of an enormous system in an advanced but incomplete state of stellar evolution, and that what we have seen in this wonderful picture is all a part of that system. I should explain what I mean by an elementary or by an ad- vanced state of stellar evolution. There is but one theory of celestial evolution which has so far survived the test of time and com- parison with observed facts, viz. the nebular hypothesis of Laplace, Laplace supposed that the sun was originally a huge gaseous or nebulous mass of a diameter far greater than the orbit of Neptune. I say originally^ do not misunderstand me. We have finite minds ; we can imagine a condition of things which might be supposed to occur at any particular instant of time however remote, and at any particular distance of space however great, and we may frame a theory beginning at another time still more remote, and so on. But we can never imagine a theory beginning at an infinite distance of time or at 1891.] on An Astronomer'' s Work in a Modern Observatory. 415 an infinitely distant point in space. Thus, in any theory which man with his finite mind can devise, when we talk of originally we simply mean at or during the time considered in our theory. Now, Laplace's theory begins at a time, millions on millions of years ago, when the sun had so far disentangled itself from chaos, and its component gaseous particles had by mutual attraction so far coalesced as to form an enormous gaseous ball, far greater in diameter than the orbit of the remotest planet of our present system. The central part of this ball was certainly much more condensed than the rest, and the whole ball revolved. There is nothing improbable in this hypothesis. If gaseous matter came together from different parts of space such coalition would unquestionably occur, and as in the meeting of opposite streams of water or of opposite currents of wind, vortices would be created and revolution about an axis set up such as we are familiar with in the case of whirlpools or cyclones. The resultant would be rotation of the whole globular gaseous mass about an axis. Now this gaseous globe begins to cool, and as it cools it necessarily contracts. Then follows a necessary result of contraction, viz. the rotation becomes more rapid. This is a well-known fact in dynamics, about which there is no doubt. Thus, the cooling and the contracting go on, and simultaneously the velocity of rotation becomes greater and greater. At last the time arrives when, for the outside particles, the velocity of rotation becomes such that the centrifugal force is greater than the attractive force, and so the outside particles break off and form a ring. Then, as the process of cooling and contraction proceed still further, another ring is formed, and so on, till we have finally a succession of rings and a condensed central ball. If from any cause the cooling of any of these rings does not go on uniformly, or if some of the gaseous matter of the ring is more easily liquefied than others, then probably a single nucleus of liquid matter will be formed in that ring, and this nucleus will finally by attraction absorb the whole of the matter of which the ring is composed — at first as a gaseous ball with a condensed nucleus, and this will finally solidify into a planet. Or, meanwhile, this yet unformed planet may repeat the history of its parent sun. By contraction, and consequent accele- ration of its rotation, it may throw ofif one or more rings, which in like manner condense into satellites like our moon, or those of Jupiter, Saturn, Uranus, or Neptune. Such, very briefly outlined, is the celebrated nebular hypothesis of Laplace. No one can positively say that the hypothesis is true, still less can any one say that it is untrue. Time does not permit me to enter into the very strong proofs which Laplace urged in favour of its acceptance. But I beg you for one moment to cast your imaginations back to a period of time long antecedent to that when our sun had begun to disentangle itself from chaos, and when the fleecy clouds of cosmic stuff had but commenced to rush together. What should we see in such a case were there a true basis for the theory of Laplace? 416 3Ir. David Gill on An Astronomer's Work. [May 29, Certainly, in the first place, we should have a huge whirlpool or cyclone of cosmic gaseous stuff, the formation of rings, and the con- densation of these rings into gaseous globes. Remembering this, look now on tliis v;onclerful photograph of the nebula in Andromeda, made by Mr. Roberts. In the largest telescopes this nebula appears simply as an oval patch of nearly uniform light, with a few dark canals through it, but no idea of its true form can be obtained, no trace can be found of the significant story which this photograph tells. It is a picture that no human eye unaided by photography has ever seen. It is a true picture drawn without the intervention of the hand of fallible man, and uninfluenced by his bias or imagination. Have we not here, so at least it seems to me, a picture of a very early stage in the evolution of a star cluster or sun-system — a phase in the history of another star-system similar to that which once occurred in our own — millions and millions of years ago — when our earth, nay, even our sun itself, " was without form and void," and " darkness was on the face of the deep." During this lecture I have been able to trace but very imperfectly the bare outlines of an astronomer's work in a modern observatory, and to give you a very few of its latest results — results which do not come by chance, but by hard labour, and to men who have patience to face dull daily routine for the love of science — to men who realise the imperfections of their methods and are constantly on the alert to improve them. The mills of the astronomer grind slowly, and he must be infinitely careful and watchful if he w^ould have them like the mills of God, to grind exceeding small. I think he may well take for his motto these beautiful lines : — " Like the star Which shines afar, "Without haste, "Without rest, Let each man wheel With steady sway, Eonnd the task Wliich rules the day, And do his best." [D. G.] 1891.] Professor A. W. Hiicker on Magnetic Bocks. 417 WEEKLY EVENING MEETING, Friday, April 17, 1891. Edward Feankland, Esq. D.C.L. LL.D. F.R.S. Vice-President, in the Chair. Professor A. W. HDgker, M.A. F.R.S. M.B.I. Magnetic Bocks. The cause of terrestrial magnetism is still unknown, and the problem of attempting to discover it is not rendered more easy by the fact that a solution may be looked for in either of two different directions. On the one hand the earth is partly composed of magnetic material, and if vast masses of this were permanently magnetised, the principal phenomena observed upon the surface might be produced. On the other hand, we know that different points on the earth's crust are at different electrical potentials, and it is conceivable that the directive forces exerted on the magnet might be due to a world-wide system of earth currents. Both theories are beset with difficulties, and at present we are accumulating facts, in the hope that a clue to an explanation may hereafter be found. A mere dry record of observations is, however, hardly a subject for a lecture, and I should not have mooted the question if there had not been another problem, related to, though differing from that of terrestrial magnetism, with regard to which it is perhaps possible to form an opinion as to the direction in which the balance of evidence inclines. If the magnetic declination be determined at a number of stations scattered all over the surface of the globe, lines can be drawn through those places at which the deviation from true north is the same. If the scale of the map on which they are depicted is small, and if the distances between the stations are measured in scores or in hundreds of miles, these isogonal lines are smooth curves ; but if the number of stations be multiplied, and the scale on which the results are represented increased, the curves are found to be irregular, and to be complicated by unexpected bends and twists. These irregularities must be due to disturbing magnetic forces, produced by local causes, which deflect the needle from its normal direction ; and if the number of stations be sufficiently great there is no difficulty in sifting out the disturbing from the normal forces and determining with approximate accuracy the directions in which they act. If this is done, the question may be asked whether these local peculiarities are due to rock magnetism or to earth currents. There is no reason why both should not in some cases coexist, but as there \ 418 Professor A. W. Biicker [April 17, are, as I think, weighty reasons for believing that rock magnetism is often the principal cause, I propose to discuss them. Permanent magnetisation of the rocks may perhaps be discarded as the cause of disturbances which extend over large areas. Basaltic columns are often strongly magnetised, but then magnetisation is irregular. At a short distance the opposite poles would neutralise each other's effects, and widespreading effects are most likely due to the inductive influence of the earth acting on widespread masses. The evidence for this may be summed up as follows : — In some cases, as in that of the cliffs on the Hudson Eiver and at Snake Hill (New Jersey), the mass is apparently polarised at the upper and lower extremities, as it would be if magnetised by the earth. Clear indications of this fact are, however, often difficult to obtain, as they are masked by local permanent magnetism. A more certain test can be applied in the case of less strongly magnetic rocks if the instruments can be placed in their neighbour- hood, but on non-magnetic soil. These conditions are satisfied by the Malvern Hills, and they are found to attract the north pole of a magnet, which is consistent with the view that they are magnetised inductively. Again, over large districts, the centres of which are marked by the outcrop of basaltic rocks, the magnetic forces tend towards the centre, which is again what would occur if the rocks which appear on the surface are the uppermost portions of a much larger mass magnetised by the inductive influence of the earth. This state of things is observed in the south and west of Scotland and in Antrim. Lastly, Captain Creak, F.E.S., has shown that islands in the northern and southern hemispheres attract the north and south poles of the magnet respectively. The only question that remains is whether the presence of rocks similar to those which exist on the surface would suffice to account for the observed surface disturbances. To test this the magnetic permeabilities of a number of specimens of basalt kindly supplied by Professor Judd have been determined. Assuming (1) that magnetite becomes non-magnetic at the same temperature as iron, (2) that its magnetic properties are not affected by great pressures, (3) that the temperature at which iron ceases to be magnetic is reached at a depth of 12 miles, (4) that large sheets of magnetic rock exist between the surface and this depth, the areas of which are of the same dimensions as those of the regions of high vertical force which exist in the United Kingdom, (5) that the magnetic susceptibilities of these rocks vary between the mean of those of 13 sj)ecimens from the Island of Mull (0' 00163), and of 34 sj)ecimens from the west of Scotland (0* 00271), it is found that a fair agreement exists between the results of calculation and of observation, and that there is no doubt that the calculated and observed disturbances are of the same order of magnitude. All these facts then accord well with the theory that local and 1891.] on Magnetic BocJcs. 419 regional magnetic disturbances are due to the inductive action exerted by the earth's magnetic field on rocks. It is, however, necessary to discuss the arguments which can be brought forward on the other side of the question. The neighbourhood of Melton Mowbray is the source of a consider- able magnetic disturbance. Mr. Preece, F.R.S., was good enough to cause an earth-current survey to be made between the post offices in that district. The earth currents appeared in all cases to run out from Melton. This might raise a doubt as to whether the currents were not largely due to small differences between the earth plates causing them when connected to act as a battery. If this is so the differences of potential to which the earth currents are due must be less than those due to the plates. If, however, we assume that real earth currents were measured the directions were not in all cases such as would produce the observed deviations of the magnet. The potential differences were also much less than those which at Greenwich produce or are at least connected with similar deflections of the needle. The difference is not small. If in both cases the earth currents are the cause, equal potential dif- ferences must produce at Greenwich magnetic effects a hundred times less powerful than those produced at Melton Mowbray. Perhaps, however, the strongest argument against the earth- current theory is based on Captain Creak's generalisation as to the magnetic properties of islands. If opposite poles are attracted in the two hemispheres, disturbance currents must circulate round the island in opposite directions. No adequate physical cause has been suggested why current eddies of contrary directions of circulation should be produced in the two hemispheres. If then we accept the view that the balance of evidence at present inclines towards the rock theory, it is evident that in a survey of magnetic disturbances the lines towards which the magnet is at- tracted are in general loci of nearest approach of the magnetic rocks to the surface, or of centres of highest magnetic susceptibility, or of both of these combined. It is thus possible that from such observations we may learn something as to the distribution of basic rocks at depths far below those which ordinary geological methods can reach. It is therefore interesting to note that the results obtained in the United Kingdom have received a remarkable confirmation from France. Correspond- ing to a ridge (or locus of attraction) which runs south from Reading and enters the channel near Chichester, is another which emerges from the channel almost exactly oj)posite to it and passes to the south of Paris. The southern termination is not yet known, but the magnetic disturbance increases as the latitude diminishes. There can be little doubt that a well-marked locus of attraction for the north pole of the needle runs from Reading to the south of Paris. [A. W. R.] 420 General Monthly Meeting. [June 1, WEEKLY EVENING MEETING, Friday, April 24, 1891. The Eight Hon. Earl Percy, F.S.A. Vice-President, in the Chair. The Eev. Canon Aingee, M.A. LL.D. Euphuism — Past and Present, [No Abstract.] GENEEAL MONTHLY MEETING, Monday, June 1, 1891. Sir James Crichton Browne, M.D. LL.D. F.E.S. Treasurer and Vice-President, in the Chair. E. W. Peregrine Birch, Esq. William Edmonds, Esq. Nicholas Eumorfopoulos, Esq. Mrs. Charles Hoare, Mrs. Edward Singleton, Harold Swithinbank, Esq. were elected Members of the Eoyal Institution. The Special Thanks of the Members were returned for the following Donation to the Fund for the Promotion of Experimental Eesearch : — ■ Mrs. Priestley .. £21 The following Letter, recommended by the Managers to be sent to the Members, was read and approved : — "RoTAL Institution, Albkmarlb Street, W., " 1st June, 1891, ^ „ " Centenary of the Biiih of Michael Faraday. " I am directed by the Managers to inform you that His Eoyal Highness the "Prince of Wales has fixed 4 o'clock, on Wednesday, tlie 17th June, for the " delivery by Lord Rayleigh of the first of the two Lectures in connectioa with " this Centenary, and that Friday evening, the 26th June, at 9 o'clock, has been " appointed for the second of these Lectures, which will be given by Professor " Dewar. 1891.] General Monthhj Meeting. 421 "With the view of insuring the comfort of those Meiubers attending, the Man- " agers find it will be necessary to confine the invitations to ' friends ' to one person "for each jMember attemling. '• To facilitate the arrangements, I am directed to request that you will be good "enough to let me know, not later than Thursday morning, the 11th June, "whether you propose to be present at one, or at both, of these Lectures, and " whether you wish a card for a friend (to be introduced personally by you) for *' the Lecture of the 17th iust., or for the Lecture of the 26th, or for both. " I am, Sir, " Your obt dient Servant, "Fkederick Bramwell, " Boniirary Secretary. The Presents received since tlie last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FROM The Secretary of State for India — Catalogue of Birds in the Museum of Hon. East Imlia Company, Vols. L II. 8vo. 1854-58. Catalogue of Mammalia (ditto). 8vo. 1851. Catalogue of Lepidopterous Insects (ditto), Vols. I. II. 8vo. 1857-59. Ahel, Sir Frederic]:, K.G.B. F.li.S. D.C.L. 3LU.L {the ^«^/ior)— Presidential Address delivered at the Iron and Steel Institute, May 6th, 1891. 8vo. Accademia. del Lincei, Reale, Roma — Atti, Serie Quarta : Eendiconti. 1" Semes- tre, Vol. VIL Fasc. 8. 8vo. 1891. Atti, Serie Quarta, Anno CCLXXV.-CCLXXVI. 4to. 1888-89. Academy of Natural Sciences, Philadelphia — Proceedhigs, 1890, Part 3. 8vo. American Philosophical Society — Pioceedings, No. 134. 8vo. 1890. Astronomical Society, Royal — Montlily Notices, Vol. LI. No. 6. 8vo. 1891. Banhers, Institute of — Journal, Vol. XII. Part 5. 8vo. 1S91. Bavarian Academy of Sciences — Abhandlungeu, Band XVII. Abth. 2. 4to. 1891 Almanaeh fur 1890. British Architects, Royal Institute of — Proceedings, 1891, Nos. 14, 15. 4 to, British Association for Advancement of Science — Keport of Meeting at Leeds, 1890. 8vo. Canada, Geological and Natural History Survey o/~Contributions to Canadian Palaontoh)gy, Vol. III. 4to. 1891. Canadian Institute — Transactions, Vol. I. Part 2, No. 2. 8vo. 1891. Fuurth Annual Report, 1890-91. 8vo. Time Reckoning for the 20th Century. By S. Fleming, LL.D. C.E. 8vo. 1889. Carey, Colonel William^ C.B. B.A. (the Author) — The Crustacean Diving Dress 12mo. 1891. Chemical Industry, Society of — Journal, Vol. X. No. 4. 8vo. 1891. Chemical Society — Journal for May, 1891. 8vo. Cracovie, V Academic des Sciences — Bulletin, 1891, No. 4. 8vo. Editors — American Journal of Science for May, 1891. 8vo. Analyst for May, 1891. 8vo. Athenseum for May, 1891. 4to. Brewers' Journal for May, 1891. 4to. Chemical News for May, 1891. 4to. Chemist and Druggist for May, 1891. 8vo. Electrical Engineer for May, 1891. fob Engineer for May, 1891. fob Engineering for May, 1891. fob Horological Journal for May, 1891. 8vo. Industries for May, 1891. fol. Iron for May, 1891. 4to. Ironmongery for May, 1891. 4to. Vol. XIII. (No. 85.) 2 f 422 General Monthly Meeting. [June 1, Murray's Magazine for May, 1891. 8vo, Nature for May, 1891. 4to. Open Court for May, 1891. 4to. Photographic News for May, 1891. 8vo. Public Health for May, 1891. 8vo. Eevue Scientifique for May, 1891. 4to. 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Kansas Academy of Sciences — Transactions, Vol. XII. Part 1, 8vo. 1890. Linnean Society — Journal, No. 193. 8vo. 1891. Mechanical Engineers' Institution — Proceedings, 1891. No. 1. 8vo. Meriden Scientific Association — Transactions, Vol. IV, 8vo. 1889-90. Murray, John, Esq. (the Publisher) — Dictionarv of Greek and Eomau Antiquities. Edited by Dr. W. Smith and others. Vol. II. 8vo. 1891. National Life-boat Institution, Boyal— Annual Report, 1891. 8vo. Newberry Library {Chicago), Trustees of the — Proceedings of the Trustees for year ending January 5, 1891. 8vo. North of England Institute of Mining and Mechanical Engineers — Transactions, Vol. XXXIX. Parts 1, 2 ; Vol. XL. Part 1. 8vo. 1891. Odontological Society of Great Britain — Transactions, Vol. XXIII. No. 7. New Series. 8vo. 1891. Pharmaceutical Society of Great Britain— J onrna]. May, 1891. 8vo. Physical Society of London — Proceedings, Vol. XL Part 1. 8vo. 1891. Rio de Janeiio, Observatoire Imptriale de — Revista, Nos. 3, 4. 8vo. 1891. Boyal Botanic Society of London — Quarterly Record, 1S8')-1890. 8vo. Boyal Society of Antiquaries of Ireland — Journal, Vol. I. Fifth Series, No. 5. 8vo. 1891. St. Petersburg Academic Imperiale des Sciences —'Memoires, Tome XXXVIII. Nos. 2, 3. 8vo. 1891. Sanitary Institute — Transactions, Vol. XL 8vo. 1891. Selborne Society— 'is htme Notes, Vol. II. No. 17. 8vo. 1891. Smithsonian Institution— ^m\t\iiionia.n Miscellaneous Collections, Vol. XXXIV. Nos. 1-3. 8vo. 1890. Society of Architects — Proceedings, Vol. III. No. 11. Svo. 1891. Society (f Arts — Journal for INIay, 1891. 8vo. Tnrpin, Eugene, Esq. {the Author) — The Truth on Melinite. 8vo. 1890. United Service Institution. Boyal — Journal, No. 159. 8vo. 1891. University of London— Ci\\en<\uv, 1891-92. 8vo. Upsal University — Bulletin de I'Observatoire Meteorologique, Vol. XXII. 4to. 1890-91. Vertins zur Befurderung des Gewerbfeisses in Preussen — Verhandlungen, 1891 : Heft 5. 4to. 1891.] Dr. C. Waldstcin on Discovery of the " Tomb of Aristotle:' 423 EXTRA EVENING MEETING, Tuesday, Jime 2, 1891. David Edward Hughes, Esq. F R.S. Vice-President, in the Chair. Charles Waldstein, Esc^. Ph.D. Litt.D. L.H.D. The Discovery of the " Tomb of Aristotle:' Dr. Charles Waldstein said that during the excavations carried on at Eretria, in Eubcea, by the American Archasological School of Athens under his direction, the discovery of a tomb stands foremost. This tomb is of great magnitude and splendour, and, by a process of inference, from data which, taken singly, might appear minute or insignificant but assume a new aspect when they are found to be interdependent and to converge to a common centre, he is led to believe to be that of the great philosopher Aristotle. IJr. Waldstein contributed a short account of his discoveries to the ' Nineteenth Century ' for May, which may be said to be only of a preliminary character, and in which he confined himself mainly to a narrative of the excavations and to the negative aspects of the question and the objections which might fairly be urged against the hypothesis that on this spot were interred the philosopher's remains. In the meantime Dr. Waldstein has been engaged in literary and epigraphical researches to enable him to arrive at a final conclusion on the subject. These investigations are not yet completed, and he hopes to ransack all the principal libraries in Europe in search of literary or other indicia which may go to support or destroy the theory. It should be premised that Dr. Waldstein went to Eretria with no thought of such a discovery. He knew that it was a place of great historical importance and antiquity, and he knew also that there were dispersed among the clandestine dealers in antiquities at AtLens many objects which could be traced to that ancient city, so familiar to students of Herodotus and Thucydides. Even if it be found that the explorer is mistaken, there can be no doubt of the great value and interest of the ancient remains which have been disinterred, and of the light which they reflect on an interesting period of Hellenic history and culture. It would be remembered, he said, that Eretria and Chalcis were the two great commercial cities of Eubcea, and every reader of Thucydides was familar with the rivalry which so long subsisted between Eretria and Athens. Its position was on the Euripus, with a beautiful hilly landscape behind, and the mountains of Attica opposite on the other side of the channel. Especial attention was drawn to Eretria by the discovery at Chalcisj in 1869, of a long inscription referring to the former city, 2 F 2 424 Dr. Charles Waldstein [June 2, tlie date of wliicli lay between the years 340 and 278 b.o. This document embodied a formal contract for the execution of a work resembling that which in our ow^n times has been done by the Bedford Level Commissioners. It recited that an engineer, Chaere- phanes by name, contracted with the Eretrians to drain their marshes. He was himself to bear the cost of the work on condition that he was to be allowed to cultivate the reclaimed land for ten years at an annual rental of 30 talents, or about 7000Z. The work was to be completed in four years. In case of war the ten years' lease was to be prolonged by a like period. There were also provisions for the compensation of persons whose land might be taken for the making of reservoirs or sluices, and the concession was to continue in the heirs of Chaerephanes, and the latter was to find sureties for the due execution of the works. This was one of the many indications of the richness of Euboea as a field for archaeological research, and would be found to have an incidental bearing upon the question at issue. At the beginning of the present year Dr. Waldstein, having obtained a concession from the Greek authorities, proceeded from Athens to Eretria for the purpose of excavating the theatre and of digging out tombs, and in particular of discovering if he could, the temple of Artemis Amarysia. As is well known, the Greeks were in the habit of burying their dead outside the city walls, and at Eretria there was a continuous succession of graves running in different direc- tions from the ancient city. These graves were of different periods, some as late as the Roman period, and many of the persons buried were foreigners. Out of 26 inscriptions he found that no fewer than eight referred to strangers and sojourners in the land. In the course of his excavations he came upon the most beautiful of all the family tombs which has yet been discovered. The lecturer had described the difficulties which he encountered in the labour of excavation in the article above referred to, and, in fact he and his associates had three times to give up the attempt. In the course of his narrative he gave an interesting account of Greek writing materials — fxeXav ypacfuKov, for ink, KoXa/xos ypacftLKoSy a pen — being the materials used for permanent records on papyrus ; whilst the cTTt'Aos or ypacfiU was the stylus used for writing notes of transient importance on waxed tablets. He had already in the article referred to described the statuettes and ornaments and other things, including the only extant metal pen, so far as he knew, which had been found in Greece. As before mentioned. Dr. Waldstein, in his contribution to the * Nineteenth Century,' had dealt in a sceptical spirit with his own discovery. He now argued the affirmative side of the question, and indicated the considerations which induced him to believe that in the family tomb which he had discovered once reposed the Stagirite's remains. According to the best authorities, Aristotle died at Chalcis in 332 B.C., of disease in the stomach, at the age of 63 years. The 1891.] on the Discovery of the '^ Tomb of Aristotle." 425 stories that he committed suicide by drinking hemlock and that he drowned himself in the Euripus, in consequence of disappointment at not being able to discover the cause of the ebb and flow of the tide, were both discredited by Zeller and the best authorities. But it would be asked, as he died at Cbalcis, how came he to be buried at Eretria, which was some 12 miles distant from the city of Chalcis ? One answer to this objection was that in the Macedonian period the name Chalcis was sometimes used for the whole island of Eubcea, so completely had it eclipsed its former rival Eretria. Strabo described Chalcis as ra TrpioTela Kac ixrirp6TroXius mixtures, and finds a close accordance between these numbers and the explosion rates of the same mixtures. He concludes that the explosive wave is propagated by the impact of the products of combustion of one layer upon the unburnt gases in the next layer, and so on to the end of the tube at the rate of movement of the products of combustion themselves. If his theory is true, it accounts not only for the extreme rapidity of explosion of gaseous mixtures, and gives us the means of calculating the maximum velocity obtainable with any mixture of gases, but it also affords us information on the specific heats of gases at very high temperatures, and it explains the phenomena of detonation whether of gases or of solid or liquid explosives. 446 Professor Harold B. Dixon [June 12, Table I. shows tlie explosion rates found by Bertbelot, compared with the theoretical velocity of the products of combustion : — TABLE I. Berthelot's Expebimetns. Gaseous Mixture. Velocity in Metres per Second. Theoretical. Found. H, + O Hydrogen and oxygen. 2830 2810 N^O Hs + Hydrogen and nitrous oxide. CO + o Carbonic oxide and oxygen. 2250 2284 1940 1090 CO + Carbonic oxide and nitrous oxide. N^O 1897 1106 CH, + O, Marsh gas and oxygen. CjH, + Oe Ethylene and oxygen. 2427 2287 2517 2210 C2N2 + O, Cyanogen and oxygen. C2H2 4- O5 Acetylene and oxygen. 2490 2195 2660 2482 CO + H, + O. Carbonic oxide, hydrogen, and oxygen .} 2236 2008 Two points in Table I. favoured the view that Bertbelot might have here given the true theory of explosions : first, the close coinci- dence between the rates of explosion of hydrogen both with oxygen and nitrous oxide with the calculated mean velocities of the products of combustion ; and secondly, the great discordance between the found and calculated rates for carbonic oxide with both oxygen and nitrous oxide. I had previously discovered that pure carbonic oxide cannot be exploded either with pure oxygen or pure nitrous oxide. The discordance found by Bertbelot was what I should have expected from my own experiments. A consideration of Berthelot's results, published in full in the ' Annales de Chimie,' led me to think it would be useful to repeat and extend these experiments. My objects were chiefly: (1) to deter- mine as accurately as possible the rate of the explosion-wave for 1891.] on the Bate of Explosions in Gases, 447 some well-known mixtures ; (2) to measure the rate of the explosion wave in carbonic oxide with different quantities of steam ; and (3) to determine the influence of inert gases on the propagation of the wave. 1. The results obtained with hydrogen and oxygen, with hydrogen and nitrous oxide, and with marsh gas and oxygen in exact proportions for complete combustion, were in close accordance with the mean results of Berthelot ; for ethylene, acetylene, and cyanogen my numbers differed appreciably, but in no case differed by more than 7 per cent, from the rates observed by Berthelot : — TABLE II. Velocity of Explosion in Metkes per Second. H^ + O Berthelot. Dixon. Hydrogen and oxygen 2810 2821 Hydrogen and nitrous oxide Hg + Ng 0 2284 2305 Marsh gas and oxygen CH, + 0, 2287 2322 Ethylene and oxygen C^H. + O^ 2210 2364 Acetylene and oxygen C^H^ + O, 2482 2391 Cyanogen and oxygen 0^ N, + 0, 2195 2321 The general agreement between these measurements left no room for doubt about the substantial accuracy of Berthelot's experiments. The formula he gives does, therefore, express with a close degree of approximation the rates of explosion of many gaseous mixtures. 2. The formula fails for the explosion of carbonic oxide with oxygen or nitrous oxide. This was to be expected if, in the detona- tion of carbonic oxide in a long tube, the oxidation is effected indirectly by means of steam, as it is in the ordinary combustion of the gas. Measurements of the rate of explosion of carbonic oxide and oxygen in a long tube showed that the rate increased as steam was added to the dry mixture, until a maximum velocity was attained when between 5 and 6 per cent, of steam was present. 3. When electrolytic gas was mixed with an excess of either hydrogen or oxygen the rate of explosion was found to be altered ; the addition of hydrogen increasing the velocity, the addition of oxygen diminishing it. The addition of an inert gas nitrogen, incapable of taking part in the chemical change, produced the same effect as the addition of oxygen — one of the reacting substances — only the retarding effect of nitrogen was less marked than that of an equal volume of oxygen. The retardation of the explosion-wave 448 Professor Harold B. Dixon [June 12, caused by the addition of an inert gas to electrolytic gas evidently, therefore, depends upon the volume and the density of the gas added. In the following table the retarding effect of oxygen and nitrogen, on the explosion of electrolytic gas, is compared: — TABLE III. Eate of Explosion of Electrolytic Gas with Excess of Oxygen and Nitrogen. Volume of oxygen added \ to H2 + 0 / Rate. 0, 2328 O3 1927 1690 0. 1281 Volume of uitrogen added "1 to H2 + 0 / Rate. Nx 2426 N3 2055 1822 N, I think it a fair inference from these facts to conclude, when the addition of a gas to an explosive mixture retards the rate of explosion by an amount proportional to its volume and density, that such added gas is inert as far as the propagation of the wave is concerned, and that any change which it may undergo takes place after the wave- front has passed by — in other words, is a secondary change. This principle has been applied to determine whether, in the combustion of gaseous carbon, the oxidation to carbonic acid is effected in one or two stages — an important question, on which there is little experimental evidence. If, for instance, in the combustion of a hydrocarbon, or of cyanogen, the carbon is first burnt to carbonic oxide, which subsequently is burnt to carbonic acid, the rate of the explosion-wave should correspond with the carbonic oxide reaction, in this case the primary reaction ; whereas, if the carbon of these gases burns to carbonic acid directly, in one stage, then the rate of the explosion-wave should correspond with the complete reaction. Now, if we adopt Berthelot's formula as a working hypothesis, we can calculate the theoretical rates of explosion of marsh gas, ethylene, or cyanogen : Q) on the supposition that the carbon burns directly to COg, and (2) on the supposition that the carbon burns first to CO, and the further oxidation is a subsequent or secondary reaction. On the first supposition, if 100 represents the rate of explosion of these three gases burning to carbonic oxide, the addition of the oxygen required to burn the gases to carbonic acid should increase the rate of explosion : — Marsh Gas. Ethylene. Cyanogen. Calculated rate of explosion when burnt to CO2 } 104 103 107 Whereas if these gases really burn first to carbonic oxide, and the 1891.] on the Bate of Explosions in Gases. 449 9 extra oxygen is inert in propagating the explosion-wave, then the addition of this inert oxygen would diminish the rate of explosion : — Marsh Gas. Ethylene, Cyanogen. Calculated rate of explosion when burnt 1 q2 88 87 to CO with inert oxygen present . . J The experiments show that if 100 be taken as the rate of explosion when the oxygen is only sufficient to burn the carbon to carbonic oxide, the following are the rates found when oxygen is added sufficient to burn the carbon to carbonic acid: — Marsh Gas. Ethylene. Cyanogen. Bates found 94 92 84 The results are, therefore, in favour of the view that, in the explosion of these gases, the carbon is first burnt to carbonic oxide. But stronger evidence on this point is obtained by comparing the explosion rate of these gases (1) when fired with oxygen sufficient to burn the carbon in them to carbonic acid, and (2) when nitrogen is substituted for the oxygen in excess of that required to burn the carbon to carbonic oxide. We have seen that oxygen added to electrolytic gas hinders the explosion more than nitrogen. In pre- cisely the same way oxygen added to a mixture of equal volumes of cyanogen and oxygen hinders the explosion more than the same volume of nitrogen. The conclusion we must come to is that the oxygen added to the mixture expressed by the formula C2 N2 -|- O2 is as inert (so far as the propagation of the explosion- wave is concerned) as oxygen added to the mixture expressed by the formula H2 + 0. The same phenomena occur in the explosion of marsh gas, ethylene, and acetylene. In all these cases the substitution of nitrogen for the oxygen required to burn the carbon from carbonic oxide to carbonic acid increases the velocity of the explosion. These facts seem only consistent with the view that the carbon burns directly to carbonic oxide, and the formation of carbonic acid is an after-occurrence. Finally, the rates of explosion of cyanogen and the hydro- carbons, when their carbon is burnt to carbonic oxide, have been found greater than the velocities calculated from Berthelot's formula. This accords with the observation previously made that the rate of explosion of electrolytic gas with excess either of hydrogen or oxygen is far higher than the calculated rate. It would seem probable that the theoretical rates as calculated by Berthelot should be modified, in spite of the close agreement which his numbers show. I think the low rates found, when hydrogen, marsh gas, cyanogen, &c., are exploded with equivalent proportions of oxygen, depend partly on the carbon burning to carbonic oxide and partly on the dissociation of the steam at the high temperature. If the formula is modified in these respects, velocities can be calculated which agree with the experimental results where dissociation does not occur. 450 Pro/. H. B.Dixon on the Bate of Exj^losions in Gases. [June 12, I suggest the following modifications : (1) the specific heats should be taken at constant volume instead of at constant pressure ; (2) the density of the gas should be taken as the mean of the burnt and unburnt molecules, instead of that of the burut molecules alone ; and (3) a correction should be made for the alteration of volume by the chemical reaction, which in some cases increases, in others diminishes, the volume. The rates so calculated agree with the explosion rates of cyanogen when burnt to carbonic oxide either by oxygen, nitrous oxide, or nitric oxide ; with the explosion rates of hydrogen and oxygen with a large excess either of hydrogen, oxygen, or nitrogen ; with the explosion rates of ethylene and acetylene with oxygen and a large excess of nitrogen ; and, lastly, with the explosion rates of hydrogen and chlorine with an excess of hydrogen. In conclusion, I would say that these experiments have amply confirmed the truth of Berthelot's statement that the explosion-wave is a " specific constant " for every gaseous mixture ; that it has been shown that the rate of explosion depends upon the primary reaction occurring, and that the determination of the rate may throw some light on what is now so obscure — the mode in which chemical changes are brought about ; and, finally, that it does not seem impossible that a connection between the rate of the molecules and the rate of the explosion may be worked out, which will give us some definite information on points of high interest in the theory of gases. [H. B. D.] 1891.] General Monihhj Meeting. 451 GENERAL MONTHLY MEETING, Monday, July 6, 1891. Sir James Cbichton Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Henry Claudius Ash, Esq. Henry T. C. Knox, Esq. John George Mair-Rumley, Esq. M. Inst. C.E. were elected Members of the Royal Institution. The Special Thanks of the Members were returned to Miss Jane Barnard, Dr. J. H. Gladstone, the Rev. A. R. Abbott, Mr. T. F. Deacon, Mr. A. Blaikley, and others, for the loan of the valuable and interesting Collection of Faraday Memorials shown in the Library on the occasion of the two Lectures on June 17th and 26th given in commemoration of the Faraday Centenary. The Special Thanks of the Members were returned to Sir Frederick Abel, K.C.B. for his valuable present of an CErtling Balance, and to Mr. Ludwig Mond, for his donation of £100 towards expenses connected with the Faraday Centenary Commemoration. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FEOM Academy of Natural Sciences, Philadelphia — Proceedings, 1891, Part 1. 8vo. Accademia dei Lincei, Reale, Roma — Atti, Serie Quarta ; Rendiconti. 1° Semes- tre, Vol. Vir. Fasc. 9. 8vo. 1891. American Academy of Arts and Sciences — Proceedings, New Series, Vol. XVII. 8vo. 1890. Astronomical Society, Boyal — Monthly Notices, Vol. LI. No. 7. 8vo. 1891. Bankers, Institute of — Journal, Vol. XII. Part 6, 8vo. 1891. British Architects, Boyal Institute of — Proceedings, 1890-1, Nos. 16, 17. 4to. Buckton, George B. Esq. F.jR.S. M.R.L (the Author) — Monograph of the British Cicadse or Tettigidse, Part 6. 8vo. 1891. California State Mining Bureau — Tenth Annual Report for 1890. 8vo. With Maps. Chief Signal Officer, U.S. Army — Annual Keport for 1890. 8vo. 1890. Chemical Industry, Society of — Journal, Vol. X. No. 5. 8vo. 1891. Chemical Society — Journal for June, 1891. 8vo. Civil Engineers' Institution — Proceedings, Vol. CIV. 8vo. 1891. Cornwall Polytechnic Society, Boyal — Annual Eeport for 1890. 8vo. Cortie, the Bev. A. L. (the Author) — Note on the Spectrum of the Sun-spot of Juoe, 1889. 8vo. Further Note, with a correction. 8vo. Cracovie, V Academic des Sciences — Bulletin, 1891, No. 5. 8vo. 452 General Monthly Meeting. [July 6, Crisp, FranTx, Esq. LL.B. F.L.S. &c. M.R.L — Journal of the Koyal Microscopical Society, 1891, Part 3. 8vo. Cutter, Drs. E. and J. A. (the J?t^/jors)— Heartrest Sanatory. 4to. 1891. East India Association— ^onvx\Q\, Vol. XXIII. No. 2. 8vo. 1891. Editors — American Journal of Science for June, 1891. 8vo. Analyst for June, 1891. 8vo Athenseum for June, 1891. 4to. Brewers' Journal for June, 1891. 4to. Chemical News for June, 1891. 4to. Chemist and Druggist for June, 1891. 8vo. Electrical Engineer for June, 1891. fol. Engineer for June, 1891. fol. Engineering for June, 1891. fol. Horological Journal for June, 1891. 8vo. Industries for June, 1891. fol. Iron for June, 1891. 4to. Ironmongery for June, 1891. 4to. Murray's Magazine for June, 1891. Svo. Nature for June, 1891. 4to. Open Court for June, 1891. 4to. Photographic News for June, 1891. Svo. Public Health for June, 1891. 8vo. Eevue Scientifique for June, 1891. 4to. Telegraphic Journal for June, 1891. fol. Zoophilist for June, 1891. 4to. Florence Bihlioteca Nazionale Ce?zfm7e— Bolletino, Nos. 131, 132. Svo. 1891. Franhlin Institute — Journal, No. 786. Svo. 1891. Geneva, Society de Physique et d'Eistoire Naturelle — Me'moires, Tome XXXI. Partie 1. 4to. 1890-1. Geographical Society, Royal — Proceedings, Vol. III. Nos. 6, 7. Svo. 1891. Great Eastern Railway Company — The Kivers and Broads of Norfolk and Suffrlk. Svo. 1891. New Holidays in Essex. Svo. 1891. The Log of the Lalage. Svo. 1889. Johns Hopk-ins University — University Circulars, No. 89. 4to. 1891. American Cliemical Journal, Vol. XIII. No. 5. Svo. 1891. Menshrugghe, G. Van der, Esq. (the Author) — Sur un particularite curieuse des Cours d'Eau. Svo. 1891. La surface Commune a deux Liquid es. 3rd Part. Svo. 1891. Meteorological Society, Royal — Quarterly Journal, No. 78. Svo. 1891. Meteorological Record, No. 39. Svo. 1 890. Ministry of Public WorJiS, Rome— Gioinale del Genio Civile, 1891, Fasc. 2-4. Svo. And Designi. fol. 1891. Odontological Society of Great .Brttozji— Transactions, Vol. XXIII. No. 8. New- Series. Svo. 1891. Parker, E. W. Esq. (the Author) — Diphtheria; its nature and treatment. Svo. 1891. Pharmaceutical Society of Great Britain — Journal, June, 1801. Svo. Bathhone, E. P. Esq. (the Editor)— The Witwatersrand Mining and Metallurgical Eeview, No. 17. Svo. 1891. Royal Irish ^car7ew?/— Transactions, Vol. XXIX. Part 16. 4to. 1891. Proceedings, 3rd Series, Vol. I. No. 5. Svo. 1891. Ror/oZ /Soc/e/?/ o/ ioncZon— Proceedings, No. 299. Svo. 1891. Saxon Society of Sciences, i?o?/aZ— Mathematische-Physischen Classe: Abhandlungen, Band XVII. Nos. 3, 4. 4to. 1891. Berichte, 1891, No. 1. Svo. 1891. Science and Education Library, South Kensington 3lMSfMm— Catalogue of the Science Library. Svo. 1891. 1891.] General Monthly Meeting. 453 Sidgreaves, the Eev. W. (the Author)— Results of Meteorological and Magnetical Observations, 1889-90. 8vo. 1890. Society of Architects — Proceedings, Vol. III. No, 12. 8vo. 1891. Society of Arts — Journal for June, 1891. 8vo. Thompson, Sir Henry, F.R.CS. M.B.I. &c. {the Juf/ior)— Modern Cremation. 2nd Edition. 8vo. 1891. United Service Institution, Royal — Journal, No. 160. 8vo. 1891. Wright & Co. Messrs. John (the Publishers)— Foithcawl as a Health Resort. By Robert C. Hunter. 8vo. 1891. Zoological Society of London — Proceedings, 1891, Part 1. 8vo. 1891. Transactions— Vol. XIII. Parts 1, 2. 4to. 1891. Vol. XIII. (No. 85.) 2 h 454 General Monthly Meeting. [Nov. 2, GENERAL MONTHLY MEETING, Monday, November 2, 1891. Sir James Crichton Browne, M.D. LL.D. F.R.S. Treasurer ancl Vice-President, in the Chair. George Frederick Deacon, Esq. M. Inst. C.E. Miss Henriette Hertz, Arthur Walter Mills, Esq. Robert Mond, Esq. B.A. F.R.S.E. Joseph Shaw^, Esq. D. Hack Tuke, M.D. F.R.C.P. Lieut.-Col. H. S. S. Watkin, C.B. R.A. William Henry White, Esq. C.B. F.R.S. M. Inst. C.E. were elected Members of the Royal Institution. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. : — FROM The Secretary of State for India — Great Trigonometrical Survey of India, Vol. XIV. 4to. 1890. The Governor-General of India — Geological Survey of India: Memoirs, Vol. XXIV. Part 3. 8vo. 1891. Rfcords, Vol. XXIV. Parts 1-3. 8vo. 1891. Index to first 20 vols of the Records, 186S-1887. 8vo. 1891. Accademia dei Linrei, Reale, Rorna — Atti, Serie Quarta : Rendieonti. 1° Semes- tre, Vol. VII. Fasc. 10-12. 2' Semestie, Vol. VII. Fasc. 1-6. 8vo. 18j1. Memorie, Vol. VIII. 4to. 1891. Academy of Natural Sciences, Philadelphia — The Priority in demonstrating the Toxic Effect of Matter accompanying the Tubercle Bacillus and its Nidus. 8vo. 1891. Agricultural Society of England, Royal — Journal, Vol. II. Part 3. 8vo. 1891. Ainerican Philosophical Society — Proceedings, No. 135. 8vo. 1891. Asiatic Society of Bengal— Fioceedings, Nos. II.-VI. 8vo. Is91. Journal, Vol. LIX. Part 1, Nos. III.-IV. Part 2, No. IV. Part 2, Supplement, No. 2. Vol. LX. Part I. No 1. Part II. No. 1. 8vo. 1891. Astronomical Society, Royal — Monthly Notices, Vol. LI. Nos. 8, 9. 8vo. 1891. Bankers, Institute o/— Journal, Vol. XII. Purt 7. 8vo. 1891. Bavarian Academy of Sciences — Sitzuug.^berichte, l!S91. Heft 1, 2. 8vo. Belgium, Royal Academy of Sciences — Memoires Couronne's, Tomes L.-LI. 4to, 1889, 90. Memoires Cuuronn^s. Collection in 8vo. Tomes XLIII.-XLV. 8vo, 1889-91. Bulletins, 3'°« i^erie. Tomes XVIII.-XXI. 8vo. 1889-91. Annuaire. 1890-91. 8vo. 1890-91. Catalogue de la Bibliotheque, Partie II. 8vo. 1890. Boston Soiety of Natural History — Proceedings, Vol. XXV. Part 1. 8vo. 1891. Bowman, Sir William, Bart. LL.D. F.R.S. M.R.I, {the Author)— FrRua Cornells Donders, 1819-1889. 8vo. 1891. (Pro.-ee. lings of Rovul Society.) Briti.Ii Architects, Royal Institute o/— Proceedings, 1891, Nos. 18-20 ; 1891-2, No. 1. 4to. British Museum Trustees — Ancient Greek Inscriptions, Parts 2, 3. fol. 1883-90. Cuneiform Inscriptions of Western Asia, Vol. IV. fol. 1891. Egyptian Texts from the CoflSn of Amamu. fol. 1886. 1891.] General Monthly Meeting. 455 British Museum Trustees — continued. Facsimiles of Epistles of Clement of Rome. fol. 1856. Photojzritphs of the Papyrus of Ntbseni. fol. 1886. Catalogue of Engl'sh Coins. Vol. I. 8vo. 1887. Catal gue of Greek Coins : Peloponnesus, Attica, Corinth, Pontus, &c. 4 vols. 8vo. 1887-9. Catalogue of Persian Coins. 8vo. 1887. Catalogiieof Additions to MRS. 1876-87. 2 vols. 8vo. 1882-9. Cafalo^rue of Ancient MSS. Part I. (Greek), fol. 1881. Catalogue of Seals in TNISS. Department, Vol. I. 8vo. 1887. Cat ilogue of Persian MSS. Vol. III. 4to. 1883. Catalogue of Printed Maps, Plans, and Charts. 2 vols. 4to. 1885. Catalogue of Prints and Drawings, Vol IV. 1761-1770. 8vo. 1883. • Catalogue of Early Prints ((German and Fleniisli). Vol. II. 8vo, 1883. Britsh Museum (Natural History) — Catalogue of Birds, Vol. XIX. 8vo. 1891. Catalngu(^ of Fossil Binls. 8vo. 18JI. Illustrations of Lepidoptera Hcterocera, Part VIII. 4to. 1891. List of British Oligoceiie an 1 Eocene Mollusca. 8vo 1891. Buckton, George B. Esq. F.R.S. M.R.I, (the Author) — Monograph of the British Cicadge or Tettigidse, Part 7. 8vo. 1891. Cali/onnn, University of— Fu\'\ici\t'\ons, 1890-91. 8^o. Canada. Geological and Natural History Surrey o/— Contributions to Canadian Palte-ntology, Vol. I. Part 3. 8vo. 1891. Annu .1 Kepoit, Vol. IV. New Series. 8vo. 1890. Cnssell (i: Co. Messrs. (the Publishers) — Howard's Art of Reckoning. 8vo. 1891. Chemical Industry Society of — Journal, Vol. X. Nos. 6, 7. 8vo. 1891. Chemical Society — Journal for July-Oct. 1891. 8vo. C>ty of London C(^Z/^.ge-Calendar, 1891-92. 8vo. 1891. Civil Engineers^ Institution — Proceedings, Vol. CVI. 8vo. 1891. Subject Index, LIX.-CVI. 1879-91. 8vo. 1891. Engineering Education. 8vo. 1891. Clarke, William Harrison, Esq. (the Author) — The Civil Service Law. 8vo. 1891. Cliiiic(d ^o«Vi?/— Transaet'onj., Vol. XXIV. 8vo. 1891. ' Colonial Institute, BoyaZ- Proceedings, Vol. XXII. 8vo. 1890-91. Cooper Union, Trustees of the (New York, U.S.A.) — Annual Report. 8vo. 1891. Cracovie, V Academic des Sciences — Bulletin, 1891, No. 6. 8vo. Crisp, Frank, Esq. LL.B. F.L.S. &c. M.R.I. — Journal of the Royal Microscopical Society, 1891, Part 4. 8vo. East India Associidion—Joarn'.\\, Vol. XXIII. No. 4, 8vo. 1891. Editors — Ameriean Journal of Science for July-Oct. 1891. 8vo. Analyst for July-Oct. 1891. 8vo. Athenaeum for July-Oct. 1891. 4to. Brewers' Journal for July-Oct. 1891. 4to. Chemical News for July-Oct. 1891. 4to. Chemi.'^t and Druggist for July-Oct. 1891. - 8vo. Electrical Engineer for July-Oct. 1891. fol. Engineer for July-Oct. 1891. fol. Engineering for July-Oct. 1891. fol. Horological Journal for July-Oct. 1891. 8vo. Industries for July-Oct. 1891. fol. Iron for July-Oct. 1891. 4to. Ironmongery for July-Oct. 1891. 4to. Monist for July-Oct. 1891. 8vo. Murray's Magazine for Julv-Oct. 1891, 8vo. Nature for July-Oct. 1891.' 4to. Open Court for July-Oct. 1891. 4to, Photographic News for July-Oct. 1891. 8vo. Revue Scientifique for July-Oct. 1891. 4to. Telegraphic Journal for July-Oct. 1891. fol. Zoophilist for July-Oct. 1890. 4to. 2 H 2 456 General Monthly Meeting, [Nov. 2, EJeotrical Engineers, Institution of — Journal, No. 94. 8vo. 1891, Florence Bihlioteca Nazionale Geidrale — Bolletino, Nos. 133-140. 8vo. 1891. Franklin Institute — Journal, Nos. 788-790. 8vo. 1891. Fraser, Colonel A. T. R.E. M.B.I, (the Author) — Darkness and Light in the Land of Egypt. 8vo. 1891. I^etters on Indian Finance and Thorough Cultivation. By Sir A. Cotton. 8vo. 1887-91. Geographical Society, Royal — Proceedings, Vol. III. Nos. 8-11. 8vo. 1891. Geological Institute, Imperial, Vienna — Verhandlungen, 1891, Nos. 8-13. 8vo. Abhandlungen, BandXV. Heft 3. 4to. 1891. Geological Society — Quarterly Journal, Nos. 187, 188. 8vo. 1891. Georgofili, Beale Accademia — Atti, Quarta Serie, Vol. XIV. Disp. 2, 3. 8vo. 1891. Harlem, Societe Hollandaise des Sciences — Archives Neerlandaises, Tome XXV. 2nie l^ivraison. 8fo. 1891. Ilazell, Watson, ^ Viney (the Publishers) — Hazell's Annual for 1891. 8vo. Hicks, E. L. J^sq. (the Author)— ^The Collection of Ancient Marbles at Leeds. 8vo. 1890. (Journal of Hellenic Studies, Vol. XI.) Horticultural Society, Boyal — Journal, Vol. XIII. Part 2. 8vo. 1891. Huggins, William, Esq, D.GL. LL.D, F.B.S. M.R.I, (the ^M^/iorJ— Presidential Address to British Association, Cardiff Meeting, 1891. 8vo. Institute of Brewing— T-TrsLUsactlonSt Vol. IV. No. 8. 8vo. 1891. Iron and Steel Institute — Journal for 1891. 8vo. Jahlonowski'sche Gesellschaft, Leipzig — Preisschriften, XVIII. 4to. 1891. Jenkins, Bev. Canon B. C. M.A. (the Author) — Pre-Tridentine Doctrine. 8vo. 1891. Johns Hopkins University — University Circulars, No. 91, 4to. 1891. American Chemical Journal, Vol. XIII. No. 6. 8vo. 1891. Langley, S. P. Esq. (the Author) — Eecherches experimentales aerodynamiques. 4to. 1891. (Comptes Bendus.) Linnean Society— Journal, Nos. 148, 176, 194, 197. 8yo. 1891. Transactions: Botany, Vol. IIX- Parts 2, 3. 4to. 1891. Zoology, Vol. V. Parts 4-7. 4to.. 1890-91. Proceedings, August, 1891. 8vo. Madras Government Central Museum— '^ei^ort, 1890-91. fol. 1891. Major, Frederick, Esq. (the Author) — Special and Atomic Energy, Part III. 'Heat.' 8vo. 1891. Manchester Geological Society — Transactions, Vol. XXL Parts 7-10. 8vo. 1891. Manchester Literary and Philosophical Society — Memoirs and Proceedings, Vol. IV. Nos. 4, .5. 8vo. 1890-91. Mechanical Engineers' Institution— FroceeiWngs, 1891, Nos. 2-3. 8vo. Meteorological O^oe— Quarterly Weather Eeport, 1880, Parts 3, 4, 8vo. 1891. Monthly Weather Report, 1887, May-December. 8vo. 1891. • Hourly Means, 1887. 8vo. 1891. Mt'teorological Observations at Stations of the Second Order, for 1887. Svo. 1891. Cyclone Tracts in the South Indian Ocean, fol. 1891. Meteorological Society, Boyal — Quarterly Journal, No. 79. 8vo. 1891. Meteorological Record, No. 40. Svo. 1891. Ministry of Public Works, i2o m-e—Giornale del Geuio Civile, 1891, Fasc. 5-8. Svo. And Designi. fol. 1891. Montt, Pedro, Esq. (the Author) — Exposition of the Illegal Acts of Ex-Presiden.t Bulmaceda. Svo. 1891. Morize, H. Esq. (the Author) — Ebauche d'unc Climatologie du Bresil, Svo. 1891. Musical Association — Proceedings, 17th Session, 1890-91. Svo. 1891, North of England Institute of Mining and Mechanical Engineers — Transactions, Vol. XXXVIII. Part 6 ; Vol. XL. Parts 2, 3. Svo. 1891. Nova Scotian Institute of Science — Proceedings and Transactions, Vol VII. Part 4. Svo. 1890. JHessrs. Partridge, S. W. & Co. (the Publishers) — Henry M. Stanley. By Arthur aioutefiore". Svo. 1890. 1891.] General Monthly Meeting. 457 Fharmadeuticat Saeiety of Great 2?nYSfeZ6ome>S'oc?'ef 2/ -Nature Notes, Vol. II. Nos. 19,20. 8to. 1891. Smithsonian Institution — Smithsonian Miscellaneous Collections, Vol. XXXIV. Nos. 4, 5. 8vo. 1891. Contributions to Knowledge, Vol. XXVII. fol. 1891. Annual Report, 1889, Part I. 8vo. 1890. Society of Arts — Journal for July-Oct. 1891, 8vo. St. Bartholomew's Hospital — Statistical Tables fofr 1890. 8to. Statistical Society, Royal— J ouruid, Vol. LIV. Parts 2,- 3. 8vo. 1891. Tacchini, Professor P. Hon. Mem. R.I. (the Author) — Memorie delia So'cieta degli Spettroscopisti Italiani, Vol. XX. Disp. 7A. 4to. 1891. Tasmania^ Royal Society — Proceedings for 1890. 8vo. 1891. Tei/Zer MtseMm— Archives, Se'rie II. Vol. III. Part 6. 8vo. 1891. Toronto University — Papers. 1890-91. 8vo. United Service InstitUtioni Royal — Joufnal, Nos. 161-164. Svo. 1891. United States Navy — General Information Series No. X. Svo. 1891. University Correspondence CoZ/eg^e— ^Calendar, 1891-92. Svo. Upsal, Roijal Society of Sciences— 'Noysl Acta, Series 3, Vol^ XIV. Fasc. 2. 4ta.- 1891. Vereins zur Beforderung des GeWerhfleises in Preussen — Veihandluugen, 1891 : Heft 6-8. 4to. Victoria Institute — Transactions,- I^o. 96. Svo. 1891. Wild, Dr. H. (the Director) — Annalen der Physikalischen Central-Observatoriums, 1890. Theill. Svo. 1891. Wright d: Co. Messrs. John (the Publishers)— The Practice of Hypnotic Suggestion,- By G. C. Kingsbury, M.D. Svo. 1891. Zoologiccd Society of LoncZon— Proceedings, 1891, Part II. Svo. 1891, 458 General Monthly Meeting. [Dec. 7, GENEEAL MONTHLY MEETING, Monday, December 7, 1891. Sir James Crichton Browne, M.D. LL.D. F.E.S. Treasurer and Vice-President, in the Chair, Lorentz Albert Groth, Esq. John Imray, Esq. M.A. M. Inst. C.E. George Stillingfleet Johnson, Esq. F.C.S. John List, Esq. M. Inst. C.E. Mrs. Douglas Powell, James Shand, Esq. M. Inst. C.E. Mrs. Thomas Threlfall, were elected Members of the Royal Institution. The Special Thanks of the Members were returned for the following Donations to the Fund for the Promotion of Experimental Research : — Professor Dewar (For Structural Alterations) .. £200 Mr. Ludwig Mond (For New Pressure Pump) .. £120 The Honorary Secretary reported that the late Mr. J. P. Stocker, M.B.I. had bequeathed £100 to the Eoyal Institution. The following Lecture Arrangements were announced : — On Life in Motion, or the Animal Machine. By Professor John G. McKendkick, M.D. LL.D. F.R.S. Proft ssor of Physiology in the Univer.-ity of Glasgow. Six Lectures (adapted to a Juvenile Auditory), on Dec. 29 {Tuesday), Dec. 31, 1891; Jan. 2, 5, 7, 9, 1892. On The Structure and Functions of the Nervous System. The Brain. By Professor Victor Horsley, F.R.S. B.S. F.R.C.S. M.R.I. Fullerian Professor of" Physiology, R.I. Twelve Lectures on Tuesdays, Jan. 19, 26, Feb. 2, 9, 16, 23, March 1, 8, 15, 22, 29, April 5. On Some Aspects of Greek Sculpture in Relief. By A. S. Murray, Esq. LL.D. F.S.A. Keeper of Greek and Roman Antiquities at the British Museum. Three Lectures on Thursdays, Jan. 21, 28, Feb. 4. On Some Recent Biological Discoveries. By Professor E. Ray Lan- kester, M.A. LL.D. F.R.S. Three Lectures on Thursdays, Feb. 11, 18, 25. On The Progress of Romance in the Middle Ages. By Professor W. P. Ker, M.A. Professor of English Literature in University College, London. Three Lectures on Thursdays, March 3, 10, 17. On Epidemic Waves. By B. Arthur Whitelegge, M.D. B.Se. Three Lectures on Thursdays, March 24, 31, April 7. 1891.] General Monthly Meeting. 459 On The Induction Coil and Alternate Current Transformer. By Professor J. A. Fleming, M.A. D.Sc. M.R.L Three Lectures on Saturdays, Jan. 23, 30, Feb. 6. On Matter : At Best and in Motion. By The Right Hon. Lord Rayleigh, M.A. D.C.L. F.R.S. M.R.L Professor of Natural Philosophy, R.I. Six Lectures on Saturdays, Feb. 13, 20, 27, March 5, 12, 19. On Dramatic Music, from Shakespeare to Drtden. (The Play, the Masque, &,nd the Opera.) (With Illustrations.) By Professor J. F. BbIdge, Mus. Doc. I'hree Lectures on Saturdays, March 26, April 2, 9. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz. ; — FROM i'he Governor-General of India — Geological Survey of India: Palseontologica Indica, Series XIIL Vol. IV. Part 2. fol. 1890. Memoirs, Vol. XXIIL 4to. 1891. The French Government — Documents Ine'dits sur I'Histoire de France : Lettres du Cardinal Mazarin. Par A. Cheruel. Tome VI. 1653-1655. 4to. 1890. Comptes des Batiments du Roi, sous le Regno de Louis XIV. Par J. Guiffrey. Tome 3«. 4to. 1891. Aecademia dei Linrei, Reale, Boma — Atti, Serie Quarta : Rendiconti. 2° Semes- tre, Vol. VII. Fasc. 7^ 8. 8vo. 1891. Atti. Anno 43, Sess. 7a; Anno 44, Sess. 1. 4to. 1890-91. Memorie, Vol. IX. Partie 2^ 4to. 1891. Academy of Natural Sciences, Philadelphia — Proceedings, 1891, Part 2. 8vo. American Association for the Advancement o/zSe/ence— Proceedings, 39th Meeting, Indianapolis, 1890. 8vo. 1891. Antiquaries;, Society of — Proceedings, Vol. XIIL No. 3, 8vo. 1890-91. Ai chseologia. Second Series. Vol. II. 4to. 1890. Aristotelian Society — Proceedings, Vol. I. No. 4, Part 2. 8vo. 1891. Asiatic Society of Great Britain, Boyal — Journal for October, 1891. Svo. Bankers, Institute of — Journal, Vol. XII. Part 8. Svo. 1891. Bavarian Academy of Sciences — Neue Annalen, Band II. 4to. 1891. Boston Society of Natural History — Proceedings, Vol. XXV. Part 2. Svo. 1891. British Architects, Royal Institute of — Proceedings, 1891-2, Nos. 2-4. 4to. Calendar, 1891-2. Svo. Cambridge Philosophical Society — Proceedings, Vol. VII. Part 4. Svo. 1891. Canadian Inf-titute — Transactions, Vol. II. Part 1, No. 3. Svo. 1891. Chemical Industry, Society of — Journal, Vol. X. No. 10. Svo. 1891. Chemical Society — Journal tor November, 1891. Svo. Cracovie, V Academic des Sciences — Bulletin, 1891, No. 7. Svo. Bax, Societe de Borda — Bulletin, seizieme annee, 1^^-^^, Trimestre. Svo. 1891. Devonshire Association for the Advancement of Science, Literature, and Art — Report and Transactions, Vol. XXIIL Svo. 1891. Devonshire Domesday, Part 8. Svo. 1891. Editors — American Journal of Science for November, 1891. Svo. Analyst for November, 1891. Svo. Athenaeum for November, 1891. 4to. Brewers' Journal for November, 1891. 4to. Chemical News for November, 1891. 4to. Chemist and Druggist for November, 1891. Svo. Educational Review, New Series, Vol. I. No. 1. Svo. 189L Electrical Engineer for November, 1891. fol. Engineer for November, 1891. fol. Engineering for November, 1891. fol. 460 General Monthly Meeting, [Dec. 7, Editors — continued. Horological Journal for November, 1891. 8vo. Industries for November, 1801. fol. Iron for November, 1891. 4to. Ironmongery for November, 1891. 4to. Monist for November, 1891. 8vo. Murray's Magazine for November, 1891. Svo. Nature for November, 1891. 4to. Open Court for November, 1891, 4to. Photographic News for November, 1891. 8vo. Kevue Scientifique for November, 1891. 4to. Telegraphic Journal for November, 1891. fol. Zoophilist for November, 1891. 4to. Ex-Lihris Society — Journal for December, 1891. 4to. Florence Bihlioteca Nazionale Centrale — Bolletino, Nos. 141, 142. 8vo. 1891. Indice e Cataloghi, Vol. I. Fasc. 3 ; Vol. II. Fasc. 4. 8vo. 1891. FranUin Institute — Journal, No. 791. 8vo. 1891. Geographical Society, Boyal — Proceedings, Vol. XIII. No. 12. 8vo. 1891. Geological Institute, Imperial, Vienna — Verhandlungen, 1891, No. 14. 8vo. Jahrbuch, Band XL. Heft 3, 4; Band XLI. Heft 1. 8vo. 1891. Greville, Edward, Esq. J.P. {the Editor) — The Year Book of Australia, 1886, 1889, and 1890. 8vo. Historical Society, Royal — Transactions, New Series, Vol. V. 8vo. 1891. Howard Association — Penological and Preventive Principles. By W. Tallack. 8vo. 1889. Institute of Brewing — Transactions, Vol. V. No. 1. 8vo. 1891. Johns Hopkins University — University Circulars, Nos. 92, 93. 4to. 1891. American Chemical Journal, Vol. XIV. Nos. 2-4. 8vo. 1891. American Journal of Philology, Vol. XI. No. 4 ; Vol. XII. No. 1. Svo. 1891. Studies in Historical and Political {Science, Ninth Series, Nos. 1-8. Svo. 1891. Lawes, Sir John Bennet, Bart. LL.D. F.R.S. (the Author)— Field and other Ex- periments conducted at Rothamsted, Herts, fol. 1891. Linnean Society— Journal, Nos. 149, 150, 195. Svo. 1891. Longmans & Co. Messrs. (the Publishers) — The Principles of Chemistry. By D. Mendeleef. Translated by G. Kamensky and A. J. Greenaway. 2 vols. Svo. 1891. Manchester Geological Society— Trsmaactions, Vol. XXI. Part 11. Svo. 1891. Meteorological Office — Daily Weather Charts of the Arabian Sea (June 1885). 4to. 1891. Charts of the Indian Ocean adjacent to Cape Gardafui. fol. 1891. Ministry of Public Worhs, Rome — Giornale del Genio Civile, 1891, Fasc. 9. Svo. And Designi. fol. 1891. New York Academy of Sciences — Annals, Vol. V. Extra, Parts 1-3. Svo. 1891. Transactions, Vol. X. Parts 2-6. Svo. 1890-91. Odontological >Soc?ef!/— Transactions, Vol. XXIV. No. 1. Svo. 1891. Pharmaceutical Society of Great Britain — Journal, November, 1891. Svo. Radcliffe Library — Catalogue of Books added to Library during 1890. 4to. 1891. Ramsay, William, Esq. Ph.D. F.R.S. M.R.I. (the Author)— A System of Inorganic Chemistry. Svo. 1891. Rio de Janeiro, Observatoire Imperial de — Eevista, No. 9. Svo. 1891. Saxon Society of Sciences, Royal — Mathematische-Physischen Classe : Abhandlungen, Band XVII. No. 6. 4to. 1891. Philologisch-Historischen Classe ; Abhandlungen, Band XIII. No. 2. 4to. 1891. Soci^i^ Arch€ologique du Midi de la France — Bulletin, Serie in Svo, Nofl. 6-7. 1890-91. Society of Architects— Tioceedings, Vol. IV. Nos. 1, 2. Svo. 1S91. 1891.] General Monthly Meeting. 461 Society of ^r^s— Journal for November, 1891. 8vo. St. Petershourg Academie Imperiale des Sciences — Bulletin, Tome XXXIV. No. 2. 4to. 1891. Surgeon- General's Office, U.S. Army — Index Catalogue of the Library, Vol. XII. 4to. 1891. United Service Institution, Royal — Journal, Nos. 165, 166. 8vo. 1891. United States Department of Agriculture — ^North American Fauna, Part 5. 8vo, 1891. Monthly Weather Eeview for July and August, 1891. 4to. Special Keport of Chief of Weather Bureau. 8vo. 1891. Vereins zur Beforderung des Gewerhfleises in Preussen — Verhandlungen, 1891 : Heft 9. 4to. Wild, Henry, Esq. F.B.S. (the Author) — The Phenomena of Terrestrial Magnetism. 4to. 1891. Zoological Society of London — Proceedings, 1891, Part 3. 8vo. 1891. Transactions, Vol. XIII. Part 3. 4to. 1891. 462 The Faraday Centenary. [June 17, THE FAKADAY CENTENARY.* Wednesday, June 17, 1891. H.E.H. The Peince of Wales, K.G. F.K.S. Vice-Patron, in the Chair. There were also present — The Duke of Northumberland (President), Lord Morris, Sir William Thomson (Pres. R.S.), Sir George Stokes, M.P. Sir William Grove, Count Tornielli (the Italian Ambassador), Sir Frederick Leighton, Sir James Crichton Browne, Sir Joseph Lister, Sir Frederick Abel, Sir William Bowman, Sir Archibald Geikie, Sir Henry Roscoe, M.P. Sir Somers Vine, Sir Frederick Bramwell, Professor Dewar, and Professor Horsley. The Prince of Wales opened the proceedings with the following address : — Ladies and Gentlemen, — ^I can well remember that two-and-twenty years ago I had the high privilege of presiding at a meeting here. That meeting was a very large one, and included many of the most eminent scientific men of the day. Among those present on that occasion, I remember, were the illustrious chemist, Professor Dnmas, Sir Edward Sabine, Sir Roderick Murchison, Sir Henry Holland, a very old per- sonal friend of mine. Dr. Bence Jones, Mr* Warren de la Rue, and many others, who 1 regret to say have now passed away. The object of our meeting on that occasion was to select a suitable memorial to the memory of the great Faraday, the eminent chemist and philosopher, who, I may say, was also the founder of modern electricity. As you are well aware, the fine statue by Foley, which is in the hall below, was, we thought, a suitable memorial to that great man. As for myself personally, 1 feel proud to think that in the days of my boy- hood my brother and myself used to attend his chemical lectures here about Christmas time, and I shall ever remember the admirable and lucid way in which he delivered those lectures to us who were mere boys, and gave us a deep interest in chemistry, which we kept up for many years, and which I had the opportunity of practising at the "University of Oxford. I can only regret that I have not since had the time to pursue that interesting science. To-day is a memorable day, for this year we celebrate the centenary of the birth of that great man ; and we all of us have reason to feel grateful that two such eminent men as Lord Rayleigh and Professor Dewar should have consented to give lectures on the work of the great Faraday. I have only now to beg Lord Rayleigh to give us his address. Lord Rayleigh said that the man whose name and work they were * Michael Faraday, born 22nd September, 1791. 1891.] The Faraday Centenary. 463 celebrating was identified in a remarkable degree with the history of this Institution. If they could not take credit for his birth, in other respects they could hardly claim too much. During a connection of fifty-four years, Faraday found tbere his opportunity, and for a large part of the time his home. The simple story of his life must be known to most who heard him. Fired by contact with the genius of Davy, he volunteered his services in the laboratory of the Institution. Davy, struck with the enthusiasm of the youth, gave him the desired opportunity, and, as had been said, secured in Faraday not the least of his discoveries. The early promise was indeed amply fulfilled, and for a long period of years by his discoveries in chemistry and electricity Faraday maintained the renown of the Royal Institution and the honour of England in the eye of the civilised world. He should not attempt in the time at his disposal to trace in any detail the steps of that wonderful career. The task had already been per- formed by able hands. In their own ' Proceedings' they had a vivid sketch from the pen of one whose absence that day was a matter of lively regret. Dr. Tyndall was a personal friend, had seen Faraday at work, had enjoyed opportunities of watching the action of his mind in face of a new idea. All that he could aim at was to recall, in a fragmentary manner, some of Faraday's great achievements, and, if possible, to estimate the position they held in contemporary science. Whether they had regard to fundamental scientific import, or to practical results, the first place must undoubtedly be assigned to the great discovery of the induction of electrical currents. He proposed first to show the experiment in something like its original form, and then to pass on to some variations, with illustrations from the be- haviour of a model, whose mechanical properties were analogous. He was afraid that these elementary experiments would tax the patience of many who heard him, but it was one of the difiiculties of his task that Faraday's discoveries were so fundamental as to have become familiar to all serious students of physics. The first experiment required them to establish in one coil of copper wire an electric current by completing the communication with a suitable battery; that was called the primary circuit, and Faraday's discovery was this : That at the moment of the starting or stopping of the primary current in a neighbouring circuit, in the ordinary sense of the words completely detached, there was a ten- dency to induce a current. He had said that those two circuits were perfectly distinct, and they were distinct in the sense that there was no conducting communication between them, but, of course, the im- portance of the experiment resided in this — that it proved that in some sense the circuits were not distinct ; that an electric current circulating in one does produce an effect in the other, an effect which is propagated across a perfectly blank space occupied by air, and which might equally well have been occupied by vacuum. It might appear that that was a very simple and easy experiment, and of course it was so in a modern laboratory, but it was otherwise at 464 The Faraday Centenary. [June 17, the time when Faraday first made it. With all his skill, Faraday- did not light upon the truth without delay and difficulty. One of Faraday's biographers thus wrote: — "In December 1824, he had attempted to obtain an electric current by means of a magnet, and on three occasions he had made elaborate and unsuccessful attempts to produce a current in one wire by means of a current in another wire, or by a magnet. He still persevered, and on August 29, 1831 — that is to say, nearly seven years after his first attempts — he obtained the first evidence that an electric current induced another in a different circuit." On September 23rd, he writes to a friend, R. Phillips: "I am busy just now again with electro-magnetism, and think I have got hold of a good thing, but cannot say ; it may be a weed instead of a fish that, after all my labour, I at last haul uj)." We now know that it was a very big fish indeed. Lord Rayleigh proceeded to say that he now proposed to illustrate the mechanics of the question of the induced current by means of a model (see figure), the first idea of which was due to Maxwell. The one actually employed was a combination known as Huygens's gear, invented by him in connection with the winding of clocks. Two similar pulleys, A B, turn upon a piece of round steel fixed horizontally. Over these is hung an endless cord, and the two bights carry similar pendant pulleys, C, D, from which again hang weights, E, F. The weight of the cord being negligible, the system is devoid of potential energy ; that is, it will balance, whatever may be the vertical distance between C and D. Since either pulley, A, B, may turn independently of the other, the system is capable of two inde- pendent motions. If A, B turn in the same direc- tion and with the same velocity one of the pendant pulleys, C, D rises, and the other falls. If, on the other hand, the motions of A, B are equal and opposite, the axes of the pendant pulleys and the attached weights remain at rest. In the elec- trical analogue the rotatory velocity of A corre- sponds to a current in a primary circuit, that of B to a current in a secondary. If, when all is at rest, the rota- tion of A be suddenly started, by force applied at the handle or otherwise, the inertia of the masses E, F opposes their sudden move- ' ment, and the consequence is that the pulley B turns backwards, i. e. in the opposite direction to the rotation imposed upon A. This is the current induced in a secondary circuit when an electromotive- force begins to act in the primary. In like manner, if A, having been for some time in uniform movement, suddenly stops, B enters into motion in the direction of the former movement of A. This is 1891.] The Faraday Centenary. 465 the secondary current on the break of the current in the primary circuit. It might perhaps be supposed by some that the model was a kind of trick. Nothing could be further from the truth. The analogy of the two things was absolutely essential. So far was this the case that precisely the same argument and precisely the same mathematical equations proved that the model and the electric currents behaved in the way in which they had seen them behave in the experiment. That might be considered to be a considerable triumph of the modern dynamical method of including under the same head phenomena the details of which might be so different as in this case. If they had a current which alternately stopped and started, and so on, for any length of time, they, as it were, produced in a permanent manner some of the phenomena of electrical induc- tion ; and if it were done with sufficient rapidity it would be evident that something would be going on in the primary and in the secondary circuit. The particular apparatus by which he proposed to illustrate those effects of the alternating current was devised by a skilful American electrician. Prof. Elihu Thomson, and he had no doubt it would be new to many. The alternating current was led into the electro-magnet by a suitable lead ; if another electric circuit, to be called the secondary circuit, was held in the neigh- bourhood of that, currents would be induced and might be made manifest by suitable means. Such a secondary circuit he held in his hand, and it was connected with a small electric glow-lamp. If a current of sufficient intensity were induced in that secondary circuit it would pass through the lamp, which would be rendered incan- descent. [Illustrating,] It was perfectly clear there was no con- juring there ; the incandescent lamp brightened up. One of the first questions which presented itself was, what would be the effect of putting something between ? Experimenting with a glass plate, he showed there was no effect, but when they tried a copper plate the lamp went completely out, showing that the copper plate was an absolute screen to the effect, whatever it might be. Experiments of that kind, of course in a much less developed and striking form, were made by Faraday himself, and must be reckoned amongst some of his greatest discoveries. Before going further, he might remark on what strong evidence they got in that way of the fact that the propagation of the electric energy which, having its source in the dynamo downstairs, eventually illuminated that little lamp, was not merely along the wires, but was capable of bridging over and passing across a space free from all conducting material, and which might be air, glass, or, equally well, vacuum. Another kindred effect of a striking nature, devised by Prof. Elihu Thomson, consisted in the repulsive action which occurred between the primary current circulating around a magnet and the current induced in a single hoop of aluminium wire. Illustrating this by experiment, he showed that the repulsion was so strong as to throw the wire up a considerable height. Those effects were com- 466 The Faraday Centenary. [June 17, monly described as dependent upon the mutual induction between two distinct circuits, one being that primarily excited by a battery or other source of electricity, while the other occurred in a detached circuit. Many surprising effects, however, depended on the reactions ■which took ])lace at different parts of the same circuit. One of these he illustrated by the decomposition of water under the influence of self-induction. About the time the experiments of which he had been speaking were made, Faraday evidently felt uneasiness as to the soundness of the views about electricity held bj his contemporaries, and to some extent shared by himself, and he made elaborate experiments to remove all doubt from his mind. He re-proved the complete identity of the electricity of lightning and of the electricity of the voltaic cell. He evidently w^as in terror of being misled by words which might convey a meaning beyond what facts justified. Much use was made of the term " poles " of the galvanic battery. Faraday was afraid of the meaning which might be attached to the word "pole," and he introduced a term since generally substituted, *' electrode," which meant nothing more than the way or path by which the electricity was led in. " Electric fluid " was a term which Faraday considered dangerous, as meaning more than they really knew about the nature of electricity, and as was remarked by Maxwell, Faraday succeeded in banishing the term " electric fluid " to the region of newspaper paragraphs. Diamaguetism was a subject upon which Faraday worked, but it would take him too long to go into that subject, though he must say a word or two. Faraday found that whereas a ball of iron or nickel or cobalt, when placed near a magnet or combination of magnets, would be attracted to the place where the magnetic force was the greatest, the contrary occurred if for the iron was substituted a corresponding mass of bismuth or of many other substances. The experiments in diamag- netism were of a microscopic character, but he would like to illustrate one position of Faraday's, developed years afterwards by Sir Wm. Thomson, and illustrated by him in many beautiful experi- ments, only one of which he now proposed to bring before them. Supposing they had two magnetic poles, a north pole and a south pole, with an iron ball between them, free to move along a line perpendicular to that joining the poles, then, according to the rule he had stated, the iron ball would seek an intermediate position, the place at which the magnetic force was the greatest. Consequently, if the iron ball be given such a position, they would find it tended with considerable force to a central position of equilibrium ; but if, instead of using opposite poles, they used two north poles, they would find that the iron ball did not tend to the central position, because that was not the place in which the magnetic force was the greatest. At that place there was no magnetic force, for the one pole com- pletely neutralised the action of the other. The greatest force would be a little way out, and that, according to Faraday's observa- X891.] The Faraday Centenary, 467 tions, systematised and expressed in the form of mathematical law by Sir Wm. Thomson, was where the ball would go. [This was illustrated by experiment.] The next discovery of Faraday to which he proposed to call attention was one of immense significance from a scientific point of view, the consequences of which were not even yet fully understood or developed. He referred to the magnetisation of a ray of light, or what was called in more usual parlance the rotation of the plane of polarisation under the action of magnetic force. It would be hope- less to attempt to explain all the preliminaries of the experiment to those who had not given some attention to those subjects before, and he could only attempt it in general terms. It would be known to most of them that the vibrations which constituted light were executed in a direction perpendicular to that of the ray of light. By experiment he showed that the polarisation which was suitable to pass the first obstacle was not suitable to pass the second, but if by means of any mechanism they were able after the light had passed the first obstacle, to turn round the vibration, they would then give it an opportunity of passing the second obstacle. That was what was involved in Faraday's discovery. [Experiment.] As he had said, the full significance of the experiment was not yet realised. A large step towards realising it, however, was contained in the observation of Sir Wm. Thomson, that the rotation of the plane of polarisation proved that something in the nature of rotation must be going on within the medium when subjected to the magnetising force, but the precise nature of the rotation was a matter for further speculation, and perhaps might not be known for some time to come. When first considering what to bring before them he thought, perhaps, he might include some of Faraday's acoustical experiments, which were of great interest, though they did not attract so much attention as his fundamental electrical discoveries. He would only allude to one point which, as far as he knew, had never been noticed, but which Faraday recorded in his acoustical papers. " If during a strong steady wind, a smooth flat sandy shore, with enough water on it, either from the receding tide or from the shingle above, to cover it thoroughly, but not to form waves, be observed in a place where the wind is not broken by pits or stones, stationary undulations will be seen over the whole of the wet surface These are not waves of the ordinary kind, they are (and this is the remarkable point) accurately parallel to the course of the wind." When he first read that statement, many years ago, he was a little doubtful as to whether to accept the apparent meaning of Faraday's words. He knew of no suggestion of an explanation of the possibility of waves of that kind being generated under the action of the wind, and it was, therefore, with some curiosity that two or three years ago, at a French watering-place, he went out at low tide, on a suitable day when there was a good breeze blowing, to see if he could observe anything of 468 The Faraday Centenary. [June 17, the waves described by Faraday. For some time he failed absolutely to observe the phenomenon, but after a while he was perfectly well able to recognise it. He mentioned that as an example of Faraday's extraordinary powers of observation, and even now he doubted whether anybody but himself and Faraday had ever seen that pheno- menon. Many matters of minor theoretic interest were dealt with by Faraday, and reprinted by him in his collected works. He was reminded of one the other day by a lamentable accident which occurred owing to the breaking of a paraffin lamp. Faraday called attention to the fact, though he did not suppose he was the first to notice it, that by a preliminary preparation of the lungs by a number of deep inspirations and expirations, it was possible so to aerate the blood as to allow of holding the breath for a much longer period than without such a preparation would be possible. He remembered some years ago trying the experiment, and running up from the drawing-room to the nursery of a large house without drawing any breath. That was obviously of immense importance, as Faraday pointed out, in the case of danger from suffocation by fire, and he thought that possibly the accident to which he alluded might have been spared had the knowledge of the fact to which Faraday drew attention been more generally diffused. The question had often been discussed as to what would have been the effect upon Faraday's career of discovery had he been subjected in early life to mathematical training. The first thing that occurred to him about that, after reading Faraday's works, was that one would not wish him to be anything different from what he was. If the question must be discussed, he supposed they would have to admit that he would have been saved much wasted labour, and would have been better en rapport with his scientific contemporaries if he had had elementary mathematical instruction. But mathematical train- ing and mathematical capacity were two different things, and it did not at all follow that Faraday had not a mathematical mind. Indeed, some of the highest authorities had held (and there could be no higher authority on the subject than Maxwell) that his mind was essentially mathematical in its qualities, although they must admit it was not developed in a mathematical direction. With these words of Maxwell he would conclude : — " The way in which Faraday made use of his idea of lines of force in co-ordinating the phenomena of electric induction shows him to have been a mathematician of high order, and one from whom the mathematicians of the future may derive valuable and fertile methods." Sir William Thomson, in moving a vote of thanks to Lord Eayleigh for his lecture, said that the Eoyal Institution was during the last part of Faraday's life, and during the whole of his scientific career, his home. The splendid results of Faraday's labours con- tributed in no small degree to the scientific glory of the 19th century, and helped to make it one of the most prolific periods in 1891.] The Faraday Centenary. 469 the world's Listory. Faraday was throughout animated solely by the love of knowledge. He freely gave his discoveries to mankind, and left it to others to turn them to practical and profitable account. Sir George Stokes, in seconding the motion, said that he had had the honour of a personal acquaintance with Faraday, whose single-minded devotion to knowledge for its own sake was beyond all praise. The vote of thanks was cordially passed. Lord Rayleigh, in acknowledgment, said that it had been a great honour and a great responsibility which had been placed upon him. He remembered with gratitude the instruction which he had derived at Cambridge from Sir Gabriel Stokes, and felt deeply in- debted to Sir William Thomson for all that he had learnt from his writings and his conversation. Sir Frederick Bramwell read the following letter from Dr. Tyndall :— Hind Head House, Haslemere, June 16, 1891. Dear Sir Frederick Bramwell, As Faraday recedes from me in time, he becomes to me more ■ind more beautiful. Anything, therefore, calculated to do honour to his memory must command my entire sympathy. But the utmost liberty I can now allow myself is to be shifted from my bed to a couch and wheeled to a position near the window, fiom which I can see the bloom of the gorse and the brown of the heather. Thus, considerations affecting the body only present an insuper- able barrier to my going to London on Wednesday. Yours very truly, John Tyndall Sir Frederick Bramwell read a list of the names of th# honorary members elected on May 4, 1891, in commemoration of the Centenary of Faraday ; and reported that the following letters had been received from them. Paris, 18 Mai 1891. Monsieur, J'ai re^u I'invitation que vous voulez bien m'adresser a assister au Cen^enaire de Faraday et I'annonce de mon election comme mem- bre honoraire de I'lustitution Royale. Je vous prie de remercier le Conseil de I'honneur qu'il me fait. Je serais tres heureux d'entendre les lectures de Lord Rayleigh et du Professeur Dewar, et tres desireux de concourir a rendre hommage a la memoire de I'illustre Faraday. Je I'ai connu a Londres, lorsqu'il a bien voulu assister a une lecture que j'y ai donnee, il y a un quart de siecle, a " Royal Institution,'* et me temoigner sa sympathie. Mais je ne puis m'engager a venir cette annee, avant que la date exacte de la reuniou Vol. XIII. (No. 85 ) 2 i 470 The Faraday Centenary. [June 17, soit fixee, etant moi-meme assujetti a de nombreux devoirs comme Senateur et comme Secretaire Perpetuel de I'Academie des Sciences. Veuillez, monsieur, agreer I'assurance de ma consideration la plus distinguee. M. Berthelot. 9, Rue de Grenelle, Paris, le 20 Mai 1891. Monsieur le Secretaire Honoraire, Je vous prie de vouloir bien presenter mes vifs remerciments aux Membres du Conseil de I'lnstitution Koyale pour I'bonneur que m'a fait I'assemblee generale en m'elisant membre honoraire. Je ferai mon possible pour me rendre a Londres afin d'assister aux seances oii Lord Eayleigh et le Professeur Dewar rappelleront quelques-uns des admirables travaux de Faraday et d'etre personnelle- ment " admis " a I'lnstitution. Mais cela dependra naturellement de la date de ces reunions. Veuillez agreer, je vous prie, Monsieur le Secretaire Honoraire, I'expression de mes sentiments respectueux et devoues. A. CORNU. Bureau Central Me'teorologique, 176, Rue de rUniversite, Cabinet du Directeur, Paris, le 16 Mai 1891. Monsieur le Secretaire Honoraire, Je vous prie de transmettre au Conseil de I'lnstitution Royale I'expression de ma plus vive reconnaissance pour la haute distinction qu'il a bien voulu m'accorder par la nomination de " membre honO' raire." J'attache d'autant plus de prix a cette favour qu'elle a pour occa- sion la celebration du centenaire de la naissance de Faraday, I'un des plus grands hommes de bien et I'une des plus pures illustrations du monde scientifique. Je serais tres heureux si mes obligations me permettent de recevoir personnellement le diploma qui m'est destine et d'entendre celebrer la gloire de Faraday par les savants les plus autorises. Veuillez agreer, monsieur le Secretaire honoraire, I'assurance de ma haute consideration. E. Mascart. Institut Pasteur, 25, Rue Dutot, Paris, le 20 Mai 1891. Monsieur le Secretaire, J'ai re9u, avec des sentiments de vive satisfaction, la lettre par la- quelle vous m'informiez que, a I'occasion du centenaire de la naissance de Michael Faraday, I'lnstitution Royale de la Grande Bretagne m'a elu membre honoraire de cette celebre Institution. Je suis touche profondement de cette haute marque d'estime 1891.] The Faraday Centenary. 471 donnee a mes travaux et je vous prie d'etre aupres des membres de rinstitution I'interprete de mes sentiments de gratitude. Malheureusement, I'etat de ma sante ne me permettra pas de pouvoir assister aux legons qui seront faites a I'lnstitution Eoyale pour honorer la memoire de I'illustre Faraday, sous la presidence de S.A.R, le Prince de Galles, ni d'avoir Thonneur d'aller en personne recevoir le diplome qui m'est destine. Veuillez recevoir, monsieur le Secretaire, I'expression de ma haute consideration. L. Pasteur. [Translation.] Heidelberg, May 21, 1891. Dear Sir, You have been so kind as to inform me by a letter of May, 1891, that the Koyal Institution of Great Britain has nominated me as honorary member at the last general meeting. I am exceedingly grateful for such a mark of favour so kind and indulgent towards me. I beg you to thank the Royal Institution heartily for their sign of friendly sympathy. I feel how much I am esteemed by the distinction, especially as I do not conceal from myself how far from the object in view are my scientific efforts to obtain the end before me. I am very sorry that I must renounce the pleasure of being present at the Faraday festivities, my age not allowing me to undertake a long journey so far away from home. I beg to assure you of my highest respect, in which I remain, dear sir, your obedient humble servant, E. BUNSEN. Charlottenburg, Marchstrasse,^ June 4, 1891. Dear Sir, I beg to excuse that I shall not be able to come to London for the Centenary of the birth of Michael Faraday, in order to receive there the Diploma of Membership to the Royal Institution in so exceptionally honouring way, as you indicate, namely, by the hands of His Royal Highness the Prince of Wales. I was obliged to accept an election as honorary president of the Commission of Jurors at the Electric Exhibition at Frankfurt, and the first meeting of this com- mission for the constitution and organization shall take place in the same time, when I ought to come to London. Begging that you will be so kind to excuse me also before Hi& Royal Highness, I am. Sir, your obedient servant, Hermann v. Helmholtz. 2 I 2 472 The Faraday Centenary. [June 17, Berlin, 10, Dorotheen Strasse, May 24, 1891. My Dear Sir Frederick, When returning home from a short Whitsuntide excursion I found your kind letter conveying the welcome news of my having been elected an Honorary Member of the Koyal Institution of Great Britain. I hasten to express my heartfelt thanks for the rare distinction bestowed upon me. The honour of becoming associated with so renowned a corporation, conspicuous at all times, is doubled by the auspicious occasion on which it is conferred. In Faraday, I admired the incomparable experimental thinker ; I loved the noble-minded, kind-hearted man. During the twenty years I have had the good fortune of living in dear old England I did not miss a single one of his lectures. It would be difficult to say how deeply I am indebted to these and to a great many other lectures I attended at the Royal Institution, and often in my own courses when showing a highly instructive experiment, I delight in telling my students where and by whom performed I saw it for the first time. I am glad to hear that two lectures on Faraday's life work will be delivered by the eminent professors of the Institution in the theatre hallowed by his never-to-be-forgotten addresses. Unfortu- nately my duties in the University do not permit me to leave Berlin during the months of June and July, so I must forego the pleasure of hearing them. They will, however, most undoubtedly be printed. I remain, my dear Sir Frederick, with reiterated thanks, yours very sincerely, A. W. VON HOFMANN. Tutzing, Bavaria, May 19, 1891. Dear Sir, I have received the announcement of my election as Honorary Member of the Royal Institution of Great Britain. Although I feel the great honour of this election, and although I would be very proud to accept the diploma in such a glorious assembly as will be present at the Centenary of the birth of Michael Faraday, I must beg excuse for me. Our University lectures shall be re-opened next week and then be continued until the end of July, and I am bound by my office and business to stay at Berlin during this whole time. So I must beg you, dear sir, to express my hearty thanks to the Members of the Royal Institution of Great Britain, and to forward to me that diploma. Yours very sincerely, Run. ViRCHOW, M D. LL.D., F.R.S. Professor in the University of Berlin, 1891.] Tlie Faraday Centenary, 473 12, Ware Street, Cambridge, Mas«., U.S.A. Sib, I feel highly honored by my election as an Honorary Member of the Royal Institution of Great Britain, and gratefully accept the privi- leges it implies. It would give me the greatest pleasure to be able to take part in the celebration of the Centenary of the Birth of Michael Faraday, but I am at present in such poor health that an ocean voyage would be impracticable. Another year I earnestly hope I may be able to visit the " old country " once more, and shall look forward with satisfaction to be received as a member where I have often been a guest. Indeed I have very tender associations with the Royal Institution ; for it was there, as a young man on my first visit to England, that I made the acquaintance of Faraday through the intro- duction of a mutual friend. That acquaintance was to me an inspira- tion, and I look back to it as one of the most important influences in my education. I remember distinctly that after one of his lectures to a juvenile audience, when I could not restrain my enthusiasm, and expressed my admiration at his power of commanding attention, and my surprise at the simplicity of the means employed, the great master replied, " That is the whole secret of interesting these young people. I always use the simplest means, but I never leave a point not illustrated. If I mention the force of gravitation I take up a stone and let it drop." At this distance of time I cannot be sure that I quote his exact language, but the illustration and the lesson I could not forget ; and to this lesson more than to any one thing I owe whatever success I have had as a teacher of physical science. You can then well understand how glad I should be to pay honor to the memory of Michael Faraday not only as the consummate investigator, but also as the great teacher and noble man. I have the honour to be, Sir, your obedient servant, JosiAH P. COOKB. New Haven, Conn., U.S.A., May 28, 1891. Sir, Your communication announcing the high honor conferred on me by the Royal Institution in electing me Honorary Member on the occasion of the Faraday Centenary was received early this week. It is a special pleasure to have my name associated with those of the Members of the Royal Institution in whose laboratory Faraday, one of the greatest of philosophers, carried on a large part of his work, and to have it thus honored in connection with the Centenary of the birth of the illustrious Faraday. I regret to have to say that the state of my health will not permit of my visiting London to attend the proposed lectures of Lord Rayleigh and Professor Dewar. I have the honour to be your obedient servant. Jambs D. Dana. 474 The Faraday Centenary, [June 17, New Haven, Conn., U.S.A., May 25, 1891. My Dear Sir, Your note has been received informing me that T have been elected an Honorary Member of the Royal Institution of Great Britain. Please express to the Managers of the Institution my high appreciation of the distinguished honor which has been conferred on me. I regret that my engagements are not likely to permit me to be present at the interesting occasion of the centennial which is to be celebrated. I remain, Sir, with sincere respect, yours faithfully, J. WiLLARD Gibes. Washington, June 1, 1891. Sir, I have the honour to acknowledge receipt of the invitation with which you have honoured me, in the name of the Eoyal Institution of Great Britain, to be present at the Centenary of the birth of Faraday and receive the Diploma of honorary membership of the Institution. No ordinary engagements would be allowed to prevent my attend- ance at a celebration of such interest by an Institution whose name and organization are so intimately associated with the greatest of experimental physicists. But physical disability renders it im- prudent to undertake a journey abroad at the present time. I can therefore only assure you of my very high appreciation of the honour done me, and my extreme regret that I cannot be present in person to receive it. I am, with high respect, your most obedient servant, Simon Newcomb. University of Rome. May 22, 1891. Sir, In reply to your communication informing me of the honor just conferred on me at the General Meeting of the Royal Institution of Great Britain, I can but express my earnest thanks and assure you of the deep sympathy I feel in all that has been, or may be done, to honor the memory of Michael Faraday. "With regard to my attending the lectures I fear it will be extremely difficult, as although the University courses finish about the middle of June, they are followed immediately by a long series of examina- tions which carry us into the middle of July. I must reserve, there- fore, my acceptance, but it would give me great satisfaction to be present besides procuring me the pleasure of becoming personally acquainted with many colleagues whom I have not the advantage of knowing. 1891.] Tlie Faraday Centenary, 475 Allow me, meanwhile, to thank the Managers and yourself for the kind intention of communicating to me the date to be fixed upon for the lectures. I have the honor to be, Sir, yours truly, Stanislas Cannizzaro. [Translation.] K. Osservatorio del CoUegio Romano, Eome, May 26, 1891. Dear Sir, I have received your esteemed letter of the present month in- forming me of the great honour that has been conferred upon me by naming me an honorary member of the Eoyal Institution of Great Britain, and inviting me to attend the scientific gathering to celebrate Faraday's Centenary. I fully appreciate the distinction, and my wish would be to attend the said gathering, but I cannot come to a determination until June, and I must know the exact date of the meeting. I must in the meanwhile ask you to kindly convey my best wishes for the Institution, and pray accept the respectful regards of your obedient servant PlETRO TaCCHINI. University, Copenhagen, May 22, 1891. Sir, Having by your letter been informed of my being elected an honorary member of the Eoyal Institution of Great Britain in occasion of the Centenary of the birth of Michael Faraday, I beg you, Sir, receive my sincere thanks for this acknowledgment of my labours and the honour thereby shown not only myself, but also my little hardly treated native country. Of course I would have much gratification in attending on your meeting in London to receive the Diploma personally, but unfortunately my health for the moment is not quite to be relied upon for making the said long journey. I have the honour to be. Sir, your obedient servant, Julius Thomsen. Upsala, June 2, 1891. Dear Sir, I have the honour to acknowledge the receipt of your estimated letter, by which you have announced to me that, in connection with the Centenary of the birth of Michael Faraday, the Eoyal Institution of Great Britain in London has conferred on me the grand honour to be elected an Honorary Member of the Institution. 476 The Faraday Centenary. [June 17, Moreover, you have kindly invited me to attend to the lecture, which is to be delivered the 17th June at the very place where the celebrated explorer of physical truths has worked. Unhappily for me I cannot see any possibility for my going to London this summer, and therefore I allow me to beg you to be my interpreter before the Royal Institution and express my most humble thanks for the great honour the Royal Institution has bestowed on me. At last I permit me to express my warmest felicitations for the prosperity of the Royal Institution, and hope that the Institution in the future may be able to continue her noble work to support many such heros of science as the celebrated Michael Faraday, whose epoch- making discoveries, deep thoughts and ingenious presentiments now fructify the scientific labours everywhere and in the greatest manner contribute not only to the successful progress of science, but also to the happiness and welfare of the whole humanity. I am, Sir, your most obedient servant, Rob. Thalen, Prof, at the University in TJpsala, St. Petersburg, May 14/26, 1891. Most honoured Sir, In answer to your information of my being elected Member of the Royal Institution of Great Britain in connection with the Centenary of the birth of Faraday, I can only express my heartfelt thanks for the honour of being admitted to the circle of the highly esteemed, universally renowned English men of science. The engagements and duties, which I took on me, make it impossible for me to leave Russia and come personally amongst you at the ejid of June or in July. These are the reasons why I must beg you, most honoured Sir, to be so kind to transmit my sincere and profound gratitude to the Members of the Royal Institution, and my welcome to the memory of Michael Faraday as from one who is a devoted admirer of his glorious name. I have the honour to be, Sir, your obedient servant, D. Mendeleeff. Geneve, 10 Mai 1891. Monsieur, J'ai rhonneur de vous accuser reception de la lettre par laquelle vous m'annoncez que I'lnstitution Royale de Londres a daigne me conferer le titre de membre honoraire et je vous prie de vouloir bien me servir d'interprete aupres de vos savants collegues pour leur exprimer ma reconnaissance pour une aussi honorable distinction. Mais je regrette que mon age et ma eante ne me permettent pas 1891.] llie Faraday Centenary. 477 d'aller a Londres assister a I'assemblee oil doit etre celebre le cen- tenaire de I'illustre pliysicien Michael Faraday. Veuillez agreer, Monsieur, I'assurance de ma consideration la plus distinguee. Charles Marignac, Professeur honoraire d V Universite de Geneve. Amsterdam, May 16, 1891. Sir, I have the honour of accusing the receipt of your missive con- taining the communication that the Royal Institution of Great Britain. has conferred upon me the honorary membership, Let me express the high satisfaction I feel, that the Institution, which at all times has taken the lead in the domain of science, has done me the honour of associating my name with herself. That this takes place at a moment that you remember your august compatriot, makes it particularly agreeable to me. It is with sentiments of profound gratitude that I accept the honour, and I take the liberty of asking you to be so kind as to bring my thanks into the Institution. If my health, which lately has somewhat sufiered, permits it, I will be present in London to be admitted to the Institution. I have the honour to be, Sir, your obedient servant, J. D. VAN DER WaALS. Bruxelles, le 15 Juin 1891. Monsieur le Secretaire Honoraire, J'ai compte jusqu'au dernier moment de pouvoir me rendre a Londres pour assister a la Seance, Juin 17, de I'lnstitution Royale de la Grande Bretagne, remercier ses membres de I'honneur qu'ils m'ont fait, et de recevoir des mains de S.A. Royale le Prince de Galles le diplome de membre honoraire de I'lnstitution ; mais I'etat d'affaiblisse- ment resultant de mon grand age (78 ans) m'empeche absolument d'entreprendre le voyage. Je suis done oblige de vous prier d'excuser mon absence, de remercier en mon nom les membres de I'lnstitution Eoyale de I'insigne honneur qu'ils m'ont fait et de me faire parvenir par la voie de I'ambassade de Belgique a Londres et au besoin par la poste, le diplome de membre honoraire. Veuillez agreer. Monsieur le Secretaire honoraire, avec mes plus vifs remerciements, I'hommage de mes sentiments de haute et res- pectueuse consideration. J. S. Stas. Sir Frederick Bramwell also reported that the following con- gratulations had been received from Russia : — 478 The Faraday Centenary, [June 17, [Telegram.] The Imperial University of St. Petersburg heartily congratulates the Royal Institution of Great Britain on the memorable centenary of the birthday of its illustrious member and president, the great natural philosopher, Michael Faraday. Hector of University, Nikitin. [Telegram.] Eemembering the great discoveries of Michael Faraday, the Im- perial Medical Academy of St. Petersburg begs to congratulate the Eoyal Institution of Great Britain at the celebration of the hundredth birthday of the eminent natural philosopher. President Pashutin. [Telegram.] The Imperial Technical Society of Russia begs the Royal Institution to receive on this memorable anniversary the most cordial congratulations, and the expression of a sincere admiration and a profoimd gratefulness to the genius of Faraday the creator of electrical engineering. President, Guercevanov. Secretary, Sieznivsky. [Printed.] The most distinguished member of the Eoyal Institution of Great Britain, Michael Faraday, by his continued labours enriched the science of electricity with new ideas, the development of which has justly given our century the right to call itself the age of electricity. The Russian Physico-Chemical Society at the Imperial University of St. Petersburg, begs to congratulate the Eoyal Institution of Great Britain on the hundredth anniversary of the birthday of Michael Faraday, the celebrated natural philosopher. President, Prof. Th. Petruohefsky. Secretary, N. Khamontoff. The following honorary members were introduced to H.R.H. The Prince of Wales, and received their diplomas at his hands : — Professor A. Cornu (of Paris). „ E. Mascart (of Paris). „ Pietro Tacchini (of Rome). „ J. D. Van der Waals (of Amsterdam). 1891.] The Faraday Centenary. 479 The Duke of Northumberland then asked tlie meeting to express its sense of the kindness of his Royal Highness in presiding, and said he had permission to read two letters written many years ago, proving how keen was the interest taken by him in the lessons he had received from Faraday. The letters were as follows, the first being addressed to Mr. Faraday, and the second to Mrs. Faraday on the occasion of her husband's death : — "Windsor Castle, 16 January, 1856. Dear Sir, I am anxious to thank you for the advantage I have derived from attending your most interesting lectures. Their subject, I now feel, is of great importance. I hope to follow the advice you gave us of pursuing it beyond the lecture room, and I can assure you that I shall always cherish with great pleasure the recollection of having been assisted in my early studies in chemistry by so dis- tinguished a man. Believe me, dear sir, yours truly, Albert Edward. Wiesbaden, 10 September, 1867. Dear Mrs. Faraday, Although I have not the pleasure of knowing you, I cannot resist sending you a few lines to tell you how deeply grieved and distressed I am to hear of the death of your husband. Professor Faraday. Having had the great pleasure of knowing him for some years, and having heard his interesting lectures already when quite a boy, I can fully appreciate how great the loss must be, not only to you, but to the whole country at large, where his name was deeply venerated by all classes. His name will not only be remem- bered as a great and distinguished scientific man, but also as a good man, whose excellent and amiable qualities were so universally known. Pardon my trespassing so soon on your great grief, and Believe me, dear Mrs. Faraday, yours very sincerely, Albert Edward. The Duke of Northumberland continued : He thought they would all agree that that was a touching letter of condolence. His Royal Highness had now long been a patron of the Institution, and had watched its progress with interest, which he hoped would be con- tinued. He trusted that his Royal Highness would have the gratifi- cation of seeing the country prosper long under the rule of his august family, and of seeing the benefits of science resulting in the increased happiness of the people. Sir W. Grove seconded the resolution, and said he was possibly the only one in the room who had known Faraday in his prime. 480 The Faraday Centenary. [June 17, '91. He wished they had been celebrating the centenary with Faraday alive. The thanks of the meeting to his Royal Highness having been expressed by acclamation, The Trince of Wales acknowledged it as follows : — Ladies and Gentlemen, I feel that I cannot, out of courtesy to yourselves, and of the noble duke who has so kindly proposed the usual thanks, and to Sir William Grove who has given us an interesting speech, pass it by without expressing to you my warmest thanks. It is a great honour and privilege to me to preside on this most interesting and memorable occasion. I have now known this room for thirty-six years, and I agree with Sir William Grove in wishing that we were celebrating the centenary of Faraday alive, and not dead — that he was alive to spend his hundredth birthday among us. I feel every time I come into this room as if I can see him standing there at that table, where he gave his interesting lectures and experiments when I was a boy. I again tender my thanks to you, as I do to Lord Eayleigh, for the most interesting lecture he has given. There was an exhibition in the Library of memorials of Faraday kindly lent to the Institution by Miss Jane Barnard and others. June 26, '91.] The Faraday Centenary. 481 THE FARADAY CENTENARY. Friday, June 26, 1891. The Duke of Northumberland, K.G. D.C.L. LL.D. President, in the Chair. There were also present — Lord Halsbury, Sir Lyon Playfair, Sir Richard Webster, Sir Edward Fry, Sir William Thomson, Sir Joseph Lister, Sir James Crichton Browne, Lord Rayleigh, Sir Joseph Fayrer, Sir William Bowman, Sir Frederick Abel, Dr. Frankland, Professor Odling, Mr. Ludwig Mond, and Sir Frederick Bramwell. The Chemical Work of Faraday in relation to Modern Science. By Professor Dewar, M.A. F.R.S. Prof. Dewar commenced his lecture by saying that his eminent colleague had done such ample justice to the physical side of Faraday's work, that his own task would be limited to dealing with those early researches in which he developed that astounding manipu- lative power which enabled him to conduct his subsequent electrical investigations in so remarkable a manner. He proposed to give a brief sketch of the more important of the distinctive chemical labours of Faraday, and then to select one of the many veins of investigation he had opened up, and show what had resulted from its development. Faraday's chemical work might be divided into the following groups or periods : — Period of Analytic Work. Organic Research. Study of Gaseous Properties. Investigations on Steel and Glass. Determination of Electro-chemical Equivalents. Regelation. Action of Metals on Light. Work on Chemical Manipulation. Published Lectures. Having given a short resume of Faraday's progress through these Bubjects, Prof. Dewar referred to his first great work in organic research, the production of two comjDounds of chlorine and carbon, the perchloride and the protochloride, and the determination of the composition of " Julian's chloride of carbon." The original specimens prepared by Faraday were exhibited, and it was pointed out that the discoverer's analyses of these bodies were absolutely accurate, not- withstanding the difficulties attending such work at that time. His discovery of " bicarburet of hydrogen " (now widely known and largely manufactured as benzol), and a "new hydrocarbon" (now known as butylene) was then described, it being pointed out that having regard to the methods of working which Faraday had to employ, the isolation and determination of the composition of such bodies was marvellous, and was to be explained only by his wonderful manipulative skill. 482 The Faraday Centenary, [June 26, Probably Faraday's most remarkable discovery in organic chemistry was the fact that naphthalene could be dissolved by strong sulphuric acid, and that when thus dissolved the solution did not precipitate naphthalene on being treated with water. That enabled him to prove combination between sulphuric acid and a hydrocarbon. The body, which he called " sulpho-naphthalic acid," is probably the first of the sulpho-acids now so largely employed in the colour industry. Faraday's next important work was an investigation into the properties of combinations of steel with other metals, in the course of which he demonstrated the now well-recognised fact that an ad- mixture of such minute proportions as one-five-hundredth of such metals as silver, nickel, palladium, &c,, will entirely alter the character of the metal. Concurrently with this, he worked on the improvement of optical glass ; and it was observed that although the fruits of his labours in this direction lay dormant for some time, they ultimately resulted in one of his most important discoveries, namely, the rotation of the plane of polarisation in the magnetic field. The glass produced by Faraday by the fusion of oxide of lead with boracic acid was selected by him because of its superior fluidity combined with great density. (Experiments were given illustrating the peculiar physical and electrical properties of the Faraday glass.) The next research was that on the liquefaction of gases, which, although carried out by Faraday, was nevertheless done at the insti- gation of Davy. Davy had discovered a substance which proved to be a hydrate of chlorine, and which he found could be kept either in ice or in sealed tubes. Faraday had produced a quantity of this substance during the cold weather, and had made an analysis of it. Davy then suggested that it should be heated in a sealed tube, and, without saying what he really expected to take place, indicated that one of three things would happen, namely, that it would either melt, act on water, or produce liquid chlorine. The latter event happened, and opened up vast possibilities, the prosecution of which Davy left to Faraday. (Experiment on the liquefaction of chlorine given.) The necessity of obtaining tubes strong enough to stand the pressure required for the liquefaction experiments led Faraday to make investi- gations at this time into the production of bottle and other glass. Faraday next turned his attention to researches on the electro- chemical relations of bodies, crystallisation, and the action of metals on light. It was in connection with the research on crystallisation in 1856 that Faraday made his interesting discovery of the pheno- menon of regelation, by virtue of which two portions of a piece of ice, after being severed, freeze together again on being brought into contact, even when the temperature of the surrounding medium is higher than the freezing point of water. Although discovered by Faraday, it was not until comparatively recent times that the explana- tion of the phenomenon was given, and its influence on glacial motion clearly established. (Experiment on regelation shown.) 1891.] The Faraday Centenary. 483 Specimens, arranged and tabulated by himself, of Faraday's last research on the optical properties of gold leaf in a highly attenuated form were exhibited and described. Turning then to the special subject of the evening's discourse, the liquefaction of gases, Prof. Dewar stated that although Faraday made his first researches in this direction as early as 1823, the matter lay dormant for many years, until his interest in it was reawakened by Thilorier's discovery that solid carbonic acid could be produced in the form of a snow-like substance, boiling at — SCO., and capable of being handled. Faraday was the first to introduce this discovery into England in a lecture given at the Royal Institution on the 18th May, 1888 ; and, thereafter, by its aid, he resumed his work on the liquefaction of the various gases which had resisted his former efforts. All through the summer of 1844 he was busily employed at this work, using the low temperatures, which Thilorier's new product enabled him to obtain, combined with great pressures. (Specimens of gases thus liquefied by Faraday shown.) This important work was the subject of a Friday evening lecture given at the Royal Institution early in 1845, a full abstract of which appeared in the Times of that date, the Institution itself not having then commenced the publication of its proceedings. In the course of that address Faraday produced a small quantity of ethylene ; and he expressed the opinion that if a method could be found of producing liquid nitrous oxide in large quantities, that would be the material which would enable him to liquefy oxygen and the other gases which had hitherto resisted all his efforts. (Experiments showing the comparative boiling points of solid carbonic acid, nitrous oxide, and ethylene at ordinary pressure and under diminished pressure given.) Faraday hoped that the production of solid nitrous oxide would enable him to get temperatures as far below the boiling point of carbonic acid as the temperature of that body was below ordinary temperatures. As a matter of fact, it is impossible to reach such low temperatures by the agency of solid nitrous oxide, and such great depression of temperature was not attained until such time as liquid ethylene became available. The lecturer here showed and described a diagram of the machinery and apparatus now employed at the Royal Institu- tion for the liquefaction and solidification of gases, see Fig. 1. The method of producing liquid ethylene, and of employing it over and over again in the apparatus was described. The work done in connection with this subject since the time of Faraday, and especially the investigations of Andrews and Van der Waals, had enabled scientists of the present day to calculate exactly the temperature of the boiling point of hydrogen, the gaseous body which has in the liquid state the lowest boiling point of all the elementary substances, and which has up to the present time resisted liquefaction. The temperature of boiling hydrogen would be — 250^ C. The lowest point attained by Faraday was 110° C, and the lowest temperature yet reached was — 210° C. 484 The Faraday Centenary. [June 26, Prof. Dewar then performed the experiment of actually producing liquid oxygen, which was seen to boil quietly w^hen collected in an open vessel at a temperature of — 180° C. The colour was slightly blue, only a few particles of solid matter being visible, which Prof. Dewar explained were traces of solid carbonic acid, the elimination of which had given him considerable trouble. The lecturer further proved by actual experiment on his own hand and on a glass vessel that the liquid oxygen was in the spheroidal condition ; and also that alcohol when added to the liquid became instantly solidified. The usual test for oxygen by means of a glowing taper was also made on the vapour given off by the liquid. The form and arrangement of the apparatus employed on the lecture table is shown in Fig. 2. Prof. Dewar stated that the prosecution of the researches inaugu- rated by Faraday was enabling scientists to approach nearer and nearer to the zero of absolute temperature ; and the speculations of physicists were now directed to the probable characteristics of hydrogen and of matter in general when that condition should be attained. At such a temperature the properties of matter would in all probability be entirely changed ; the old Lucretian law would be suspended, molecular motion would probably cease, and what might be called the death of matter would ensue — as in fact the death of chemical affinity and chemical action was known to take place at the low temperatures already attainable. (Experiment proving this by the immersion of phosphorus, sodium, and potassium in liquid oxygen.) On the other hand, it was found that even at such low temperatures oxygen retained its characteristic absorption spectrum.* Further experiments were given proving the liquefaction of ozone by means of liquid oxygen — a tube of the liquid thus produced showing the characteristic deep blue colour of that substance. In conclusion, Prof. Dewar said that although great progress had been made since Faraday's time, chemists were still working dis- tinctly on the lines of his early researches ; and it seemed to him that no fitter method of celebrating the centenary of Faraday's birth could be chosen than the demonstration of the realisation of some of his own ideas. * The recently discovered magnetic property of the liquid adds a new interest to this subatance. " Eoyal Institution, 10th December, 1891. "Dear Sir William Thomson, — The following observation, which I liave just made, may interest the members of the Royal Society, and if you think it of sufficient importance you may announce it at this day's meeting. " At 3 p.m. this afternoon I placed a quantity of liquid oxygen in the state of rapid ebullition in air (and therefore at a temperature of — 18 1° C.) between the poles of the historic Faraday magnet, in a cup-shaped pitce of rock salt (which I have found is not moistened by liquid oxy^^eu, and therefore keeps it in the spheroidal state), and to my surprise I have witnessed the liquid oxygen, as soon as the magnet was stimulated, sud Ratleigh, M.A. D.C.L. LL.D. F.R.S. MM.!. Professor of Natural Philosophy, R.I. The Composition of Water. [No Abstract.] WEEKLY EVENING MEETING, Friday, January 29, 1892. Sir James Crichton-Browne, M.D. LL.D. F.R.S. Vice-President and Treasurer, in the Chair. Sir George Douglas, Bart. M.A. Tales of the Scottish Peasantry. It is only within comparatively recent years that the homely stories in the mouths of the common people have been constituted a branch of learning, and have had applied to them, as such, the methods and the terminology of science. A noteworthy gain to knowledge has, beyond a doubt, resulted from this treatment ; but, side by side with this gain to knowledge, is there not involved in the said method of treatment a loss to the stories themselves? Classified, tabulated, scientifically named, they are no longer the wild free product of Nature that we knew : — no doubt they are still very interesting — the study of them is full of instruction ; but their poetry, their brightness, the fragrance which clung about them in their native air, their native soil, is gone. So that, — with all due recognition of the value of the labours of the scientific folk-lorist, the comparative mythologist, — there yet remains room, I believe, to regard these stories from another point of view, namely, the literary, or critical one. I hope the time has not yet come when the old tales shall have entirely ceased to charm ; and I believe that there are persons in existence who would regard it as a real and personal loss could they be made to believe that the ideal hero of their childhood, as he falls in a bloody battle wounded to the death, is in reality a myth, or figure, for the setting of the sun ; and who would even feel themselves aggrieved could they Vol. XIII. (No. 86.) 2 l 490 Sir George Douglas [Jan. 29, be brought to realise that the bugbear of their baby years is common also to the aborigines of Polynesia. So powerful is the spell of early association. I suppose that most nations, whilst their life has remained primi- tive, have practised the art of story-telling ; and certainly the Scotch were no exceptions to the rule. Campbell of Isla, who wrote about thirty years ago, records that in his day the practice of story-telling still lingered in the remote western islands of Barra ; where, in the long winter nights, the people would gather in crowds to listen to those whom they considered good story-tellers. At an earlier date, but still at that time within living memory, the custom of story- telling survived at Pool-Ewe, in Eoss-shire ; where the young people were used to assemble at night to hear the old ones recite the tales which they had learned from their forefathers. Here, and at earlier dates in other parts of the country also, the demand for stories would further be supplied by pedlars, " gaberlunzie men," or pauper wandering musicians and entertainers, or by the itinerant shoemaker or tailor, — both of which last were accustomed to travel through thinly-popu- lated districts, in the pursuit of their calling, and put up for the night at farm-houses, — where, whilst plying their needles, they would entertain the company with stories. The arrival of one of these story-tellers in a hamlet was an important event. As soon as it ibecame known, there would be a rush to the house where he was lodged, and every available seat would quickly be appropriated. And then, for hours together, the story-teller would hold his audience spell-bound. During his recitals, the emotions of the reciter were occasionally very strongly excited, as were also those of his listeners, — many of whom, no doubt, firmly believed in all the extravagances narrated. And such rustic scenes as these have by no means been without their marked effect upon Scottish literature. Perhaps the most characteristic of the Highland tales are those which deal with heroes and giants. But these are generally very long, and, truth to tell, — with all the repetitions of dialogues, all the repro- ductions of what is practically the same situation, which distinguish them, — they are apt to appear to us wearisome. The shortest kind of popular tales are those which the Folk-Lore Society calls Beast Tales, — the stories, namely, which are concerned with the dumb animals. The Highlands, in particular, are rich in such stories ; and it is easy to imderstand how the common country-peojile — living so near to nature as they do — may come to have an insight into, and an appreciation of, the characters of the brute animals, and a sympathy with them in their tussle for existence, which is not attainable by those who lead a, more artificial life. Some of the fables and traits of animal life in which this knowledge and appreciative symjjathy have been embodied are decidedly naive and quaint. Nor are they without a human application. Thc class of stories which we may consider next — the Fairy Tales - — display a higher degree of fancy. And it would be a mistake 1892.] on Tales of the Scottish Peasantry. 491 to imagine that this quality of fancy is anything less than a cha- racteristic attribute of the minds of many of the Scottish peasantry. It displays itself, for instance, in its simplest form, in their nomen- clature— in the names which they have given either to natural objects, or to places which are characterised by some striking natural feature. For example : a waterfall in Dumfriesshire, where the water, after pouring dark over a declivity, dashes down in white foam among rocks, is known as The Grey Mare's Tail; twin hills in Roxburghshire, which have beautifully-rounded matched summits, have been christened Maiden's Paps. Then, the cirrus, or curl-cloud, is in rustic speech " goat's hair " ; the phenomenon of the Northern Lights, among the fishermen of Shetland, is the " Merry Dancers " ; the Pleiads are the " Twinklers " ; the constellation of Orion, with its star iota pendant as if from a girdle, is the " King's Ellwand," or yard-measure ; the noxious froth which adheres to the stalks of vege- tation at midsummer is the " witches' spittle." There is a root of poetry, I think, in this aptitude for giving names ; and, as a matter of fact, in the Lowlands of Scotland, rustic poets and rhymesters are far from uncommon. Nor are the peasantry, in their name-giving, wanting in literary allusiveness — allusiveness, that is, to the only book which has ever obtained universal currency among them. Thus, among the fishermen of the East Coast, the black mark below the gills of a codfish, or haddock, is "Peter's Thumb ; " whilst a coarse field-plant called by botanists Polygonum persicaria, which has its leaves strangely clouded and stained, as with droppings of some dark liquid, is locally known on the Borders as the " Flower that grew at the Foot of the Cross." Perhaps the deepest thinkers among a people who have their philosophers as well as their dreamers, are to be found among the hill-shepherds. And it is chiefly through the instrumentality of one of these that we can now enter the Fairyland of the Scottish peasant. James Hogg, the Ettrick Shepherd, was one of those common men, plus genius, who every now and then in the history of literature give to a whole world of floating thought, tradition, fancy, a permanent substantial form. No man in literature is his master in the weird tale. No man but Shakespeare, not even excepting Drayton, has written so well of the fairies. Hogg, was born in the Arcadia of Scotland, Ettrick Forest— where, as Scott tells us, the belief in fairies lingered longer than elsewhere — about the year 1770. As he grew up, the spirit of emulation was stirred in his breast by the example of the poet Burns. And so, as he wandered through the pastoral solitudes keeping his sheep, he carried an ink-horn slung from his neck, and taught himself to write, and so committed to paper his first poem. And as he thus wandered and mused, he tells us that he one day fell asleep upon a green hill-side, to dream the dream of Kilmeny, and to bear her image in his heart for ever after. The story of Kilmeny is that of a girl of poetic temperament, a lover of solitude, who, wandering alone at twilight, disappears in a 2 L 2 492 Sir George Douglas [Jan. 29, wild glen among the hills. She is sought for by her parents ; but no trace of her is found. Years pass, and the mystery remains unsolved. But at the close of the seventh year, in the same twilight hour in which she had vanished, Kilmeny returns to her home. She has been rapt away by fairies, with whom the intervening years have been spent. But in the midst of Fairyland, her heart still yearns tenderly to her home ; and when seven years have expired, and the fairies have no longer power to detain her against her will, she chooses to leave the life of pleasure which she leads among them to return to the common world. This is an outline of the story ; but the story is the least part of the poem. Its charm lies in its exquisitely flowing and melodious verse, in its suggestion of the twilight world and of a world of shadows — a land " where all things are forgotten," — in its wistful tenderness ; in one word, in the unique and perfect aptness of the style to the subject. So magical, indeed, are the fairy touches throughout the writings of the Ettrick Shepherd, that one might almost be tempted to dream that the experience with which tradition credits Thomas the Khymer had been shared by this rhymer of a later day. As in England, tales of fairies caught sight of on the country green, at twilight or by moonlight, of services rendered by mortals to fairies and gratefully and gracefully repaid, find a place among the fables of the Scottish peasantry. But it is by no means in such airy, gracious, and harmless if not beneficent, creations as this that the genius of the Scottish nation finds its fancy's most congenial food. That genius is, upon the whole, essentially a sombre one, — relieved, indeed, by a rough humour ; but tending most to an affinity with gloom. The malevolence, the hostility, of Nature, its permanence as contrasted with the transient character of man, its victoriousness in the never-ending battle waged against it by man, — a battle in which he fights for life, in which he gains a few trifling and temporary advan- tages, but in which he must recognise from the first that he fights against impossible odds : these are facts which a barren soil and a bleak and stormy climate have thrust forcibly upon the Scottish popular imagination, and which have impressed themselves deeply upon it. This gloomy view of Nature has tinged the superstitious beliefs of the peasantry, and through them their stories. And upon the back of this gloomy view of Nature, has come a sense — stronger perhaps than is felt by any other nation — of fate and doom, of the mystery of life and death, of the cruelty of the inevita- ble, the pain of separation, the darkness which enshrouds the whole. In this sense the Scotch are a nation of pessimists. They have found their religious vocation in Calvinism ; and the spirit which embraced Calvinism like a bride informs their mythology and their fireside tales. Their tendency to devil-worship, to the propitiation of evil spirits, is illustrated by the hideous usage of the Good-man's Croft, — a plot of ground near a village which was left untilled — set apart for, and dedicated to, the Powers of Evil, in the hope that their malignity might be appeased by the sacrifice, and that so they might 1892.] on Tales of the Scottish Peasantry. 493 be induced to spare the crops on the surrounding fields. Of the state of superstitious dread in which some Scotchmen passed their lives, Mrs. Grant of Laggan gives a curious illustration when she tells us that in the Highlands of her day, to boast, or to congratulate a friend, was to rashly court retribution ; to praise a child upon the nurse's arm was to incur suspicion of wishing to bring down ill upon its head. Holding these beliefs, it is not to be wondered at if, in their stories, the Scotch are the past-masters of the weird. And, as a matter of fact, their very nursery-tales — many of them — would appear to have been conceived with a view to educating, for some strange purpose or other, the passions of horror and of sorrow in the child to whom they are told. Such rhymes, for instance, as " The Tempted Lady," and " The Strange Visitor," are uncanny to a degree. In the former, the Evil One himself appears, in specious guise. The Strange Visitor is Death. The nursery ballad of " The Croodin Doo "* is as full of combined piteousness and sinister suggestion of underhand wickedness as any little tragedy of its length could well be. The suggestion is that of a man's childless lawful wife bearing a bitter grudge against his child borne by another woman. The babe returns from a day's outing, and is questioned by his slighted mother as to where he has been and what he has done. But he is tired, and cries out to be put to bed. The jealous woman, however, persists in her interrogatory, in the course of which she asks him what he had for dinner. He replies that he dined off " a little four-footed fish." (The eft, or newt, is, like the toad, in the common superstition, venomous). " And what was done with the bones of this singular fish ? " asks the woman. They were given to the lap-dog. And what did the dog do? After eating them, he "shot out his feet and died." There, with admirable art, the ballad ends. Its effect is immensely heightened by a burthen, or refrain, in which, at the close of every verse, the child, with wearisome iteration and with child-like importunity, cries out to his mother to " make his bed soon." This ballad of child- life is queer fare to set before a child. Stoddart, the tourist, long ago remarked the contrast between the fairies of the English popular mythology and those of the Scotch ; and certainly the delicate, joyous, tricksy, race of moonlight revellers whom we meet in Shakespeare are scarcely to be recognised as be- longing to the same family with the soul-less, man-stealing, creatures of the Scottish peasant's fancy. The effect exercised upon popular superstition by the ruling passion of Calvinistic religion is one of the most striking things in Scottish folk-lore. The belief in fairies, for example, did not cease to exist. It was not even universally discoun- tenanced by the Church ; for we find recorded instances of Ministers of the Gospel combining with their parishioners to take measures for the restitution of infants which the fairies had changed at nurse, or for the recovery of women who had been spirited away. And certainly * A term of affection applied to a child. 494 Sir George Douglas [Jan. 29, two of the most curious pieces of composition known to me are, a pamphlet on the Second Sight written by a Minister of Tiree, and an article on the Fairies written by a Minister of Aberfoyle, — both in the Seventeenth Century. Both writers were firm believers in the superstitions upon which they wrote ; and in both cases the gross ignorance and darkness of the writer's mind is only equalled by the authoritative weight and pedantry of his style. The fairies, however, and that rough, grotesque, humoursome, but good-natured figure, the Brownie, occupy but a small space in the popular mythology in comparison with such shapes of awe, of terror, or of ill-omen, as the ghosts, " more real than living men," which the Highland Ezekiel saw borne past him on the wind in Morven, or as the witch, the wraith, the " warning," the water-kelpie, the man or woman who has the second-sight. The characteristic rough humour of the Scotch peasant, as it affects the creations of the fancy, embodies itself almost exclusively in the Brownie. The Brownie was a wild, half -human, creature, whose custom it was to devote himself to domestic service in a particular family. But he worked from perfectly disinterested motives ; and so strained was his sense of self-respect that, on the slightest attempt to recompense his services, he would disappear for ever. The Brown Man of the Moors is another of these twilight, or half-seen, creations ; but he is not of a domestic character. Wanderers upon lonely moors might, on rare occasions, catch a glimpse of him lurking in a hollow, — a short, squat, powerful figure, earth-coloured, or of the tint of the surrounding ling. " Shellycoat " dwelt in the waters. His coat was hung with shells, which clattered as he moved ; and his delight was in mischief, — such as, for instance, like Will-o'-the-Wisp, in leading travellers astray. " Nuckelavee," the Sea-Devil of the Orkney Islanders, a more formidable phantom, seems to be shaped like a man above and like a horse below ; and his peculiar horror lies in the fact that, being skinless, his raw red flesh is exposed to view. Then there is the Eiver Horse, a supernatural being supposed to feed, in the shape of a horse, on the shores of Loch Lochy, and when dis- turbed to plunge into its waters. The Eiver Bull it is who emerges from the lake to visit the cow-pastures; and cow-herds pretend that they can distinguish the calves of which he is the sire. But a more awe-inspiring water-spirit than any of these was the Kelpie ; whose appearances were generally timed cither to give warning of death by cbowning, or to lure men to a watery grave ; and who illustrates the feeling — as I have already observed, so insistent throughout Scottish mythology — of the inveterate hostility of Nature. The elements are oui- enemies, and wage an internecine war. Perhaps the most valuable element in the peasant-tales, con- sidered from the poetic standpoint, is the human element. The juxta-position of the supernatural brings out in extraordinary strength certain traits of the human. For instance : the strangest, the most startling, and to us the most incomprehensible, of all the Scotch 1892.] on Tales of the Scottish Peasantry. 495 superstitions is that which prescribed a belief in the periodical return of the dead to their former homes — not as night-walking spectres encountered only by those who were alone and in the dark — but as social beings, come back to join the family circle and share in its festivities, — in short, in the old phrase, come back " to dine and dance with the living." How anything so incredible should ever have come to be believed, we may well be at a loss to understand. Yet believed it seems to have been. There are two of the old ballads which are concerned with the belief, and they are two of the finest which have come down to us. The fragment entitled "The Wife of Usher's Well " tells how a thriving country-woman made provision for her three sons by sending them to sea. But they have not been long away from her, when she hears that they have perished in a storm. Then, in the madness of her grief, she puts up a blasphemous prayer to Heaven, — praying that the conflict of wind and wave may never cease until her sons come home to her in their likeness as she knew them of old. Her prayer is heard ; and answered. When the long dark nights of Martinmas come round, the sons return to their home. In outward seeming they are unchanged ; but the hats they wear, as we are told, are of a birk, or birch-tree, which is not of earthly growth. Rising to a height of simple, unconscious, tragic irony, the ballad goes on to detail the preparations which are made by the mother to fete the home-coming of her sons. In a fever of happiness, she issues her orders to her maids. The fatted calf is slain ; and a brief hour of joy goes by. Then, as it grows late, the young men betake themselves to rest. The mother has prepared their bed with her own hands. But the dawn draws near — the period of their Bojourn is almost up. The cock crows. They recognise the signal which binds them under penalty to return whence they came, and with a few touching words of leave-taking they depart as they had come. In this case the superstition of the return of the dead to their homes, to visit their friends, is complicated with the idea of punishment for a rash utter- ance or impious prayer. But in " The Clerk's Twa Sons of Oxen- ford " — the other ballad which deals with the same theme — in which the home-coming of the dead is timed at Christmas, the fundamental idea appears in its simplest form. These two tales are perhaps the wildest in the whole range of Scottish popular story ; but, wild as they are, they contain, I think, a distinct and deep human significance. It will be observed that, in either case, the return of the dead to their homes is fixed at a season of relaxation and festivity. At such seasons the thoughts of the working-people, being set free from their daily occupations, are at liberty to wander ; and it is a fact that the annual recurrence of such landmarks in time, with their familiar accom- paniment of usages and ceremonies, brings bygone years before the mind with a peculiai* clearness — or, at least, brings them before the minds of people who lead simple monotonous lives with few events to mark them. Nothing is commoner at such seasons than to hear the country-people refer to the friends whom they have lost since that time last year, dwelling upon particular acts of theirs, and upon 496 Sir George Douglas [Jan. 29, their ways and characters generally. Well, from this peculiar vividness of mental realisation, it is, for a bold and poetic imagi- nation, but a single step to conjure up the actual bodily presence of the departed. Hence may have arisen these wild stories ; and hence, no doubt, arose the fancy — a beautiful and touching one — of the dead returning to their homes at a season of festivity, " to dine and dance with the living." To sum up; — the more striking characteristics of the Scottish peasant-tales generally would appear to be : First, an ever lively and inventive fancy. Secondly, a powerful imagination. The Scottish peasant story-teller is, like Homer, evc^avrao-tWos — " qui sibi res, voces, actus, secundum verum, optime fingit," as Quintilian renders it. And this powerful imagination is apt to be gloomily affected, and at times distempered, by the natural features and conditions of the country, and by the breedings of the national mind. Thirdly, a love of humanity, coupled with a keen sense of the hardness of its lot, — manifesting itself in a poignant pathos. Of course, in a country of mixed races like Scotland, the general characteristics of the stories differ widely in the different parts of the country. In general terms, it may perhaps be said that the Highland tales display a more inexhaustibly luxuriant fancy, whilst those of the Lowlands have the more clearly defined outline and enjoy a monopoly in depth of human significance. To glance now at the effect which has been exercised upon litera- ture by these tales. The Tales of the Scottish Peasantry have enjoyed particular advantages in the fact that the rich mine which they afford has been well and admirably worked by modern Scottish writers. Indeed, from the date of Smollett's death onward, the Scottish prose belles-lettres may be said to have been largely " a growth of the soil." And the Scottish writers who have worked the field of popular tradition have not worked in the spirit of such German authors as, for instance, Musaeus, Tieck, and Fouque, — making the popular tale a mere foundation upon which to rear their own structures of philosophy and fancy, and often transforming it almost, if not quite, beyond recognition. Neither have they worked upon the lines of such a writer as Theophile Gautier, who, though he would sometimes use the popular tale as material to work upon, was guided in his choice of subject by a purely artistic instinct. The Scottish writers are, in the first place, objective ; and, in the second, national. Foremost amongst these writers is, of course, Sir Walter Scott. In comparison with his other works, his " Border Minstrelsy " has been neglected ; yet, in all probability, he produced no more highly characteristic book ; whilst, of that great literature of fiction of which he afterwards became the author, the best and most vital parts may, I think, truly be said to have their roots in the hearts of the people. And the further he departs from that source of his inspiration, the less valuable his work becomes. Although not born in the peasant class, Sir Walter knew the Scottish peasantry, in his own way, as 1892.] on Tales of the Scottish Peasantry. 497 few men have known tliem ; and lie lived on terms of friendly inti- macy with his valued Tom Purdies and others, and of close literary confidence with such men as William Laidlaw. The two writers who rank next in the group were, however, peasants born. I have already spoken of James Hogg. Allan Cunningham, born in 1784, was a son of the land-steward on the estate on which Eobert Burns occupied a farm, — a fact which no doubt had its effect in stimulating the poetic impulse that was in him. His " Traditional Tales of the English and Scottish Peasantry" is perhaps the best of the many books which he wrote, and is especially distinguished by the sweet- ness of his style, and by the picturesque traits of old-fashioned country life, and the delightful touches of fresh nature-painting in which it abounds. After Cunningham, comes Campbell of Isla, born in 1822. He was of gentle birth, but understood and sympa- thised with the peasantry. He spoke the Gaelic language, and travelling on foot through the West Highlands, was able to get the people to tell him stories, which he accurately noted down. In his collection, therefore, we get the stories as nearly as possible in the words in which they were told. Then, among lesser writers in the same class, there are, Dougal Graham, the chap-book writer, who has been called the Scottish Kabelais ; Eobert Chambers, whose fame as a publisher has somewhat obscured his well-earned fame as an author ; besides many others, some of them of merely local reputation. Literature takes the life of tradition, and then embalms the dead body. To-day the old stories, which introduce the supernatural, have ceased to be believed or told. But, in their place, there is still to be found a body of genuine peasant- tales which do not tax credulity quite too far. And it is a fact worthy of attention that, though these stories may and do deal in horrors, yet they never descend to the merely " sensational " ; being invariably raised by some touch of fancy, of character-painting, of the picturesque, into the region of poetic fiction. In conclusion, what is there in these " old wives' tales " to justify their withdrawal, even for an hour, from the limbo of forgotten things ? They have a place, though it be a very humble one, in the history of the workings of the human mind. They are the mani- festation, in one of its simplest forms, of the literary or art impulse ; and nothing that has been thus generated, and that has stood the test of time as these tales have stood it, can ever, I believe, be unworthy of our study. These simple stories were the outcome of faint stirrings in the human breast of two passions — the Love of Beauty, and the Thirst for Fame. " One touch of Nature makes the whole world kin " ; and the lapse of centuries does not prevent our entering into the feelings of the peasant story-teller. Art is not only a thing of bound volumes and of exhibitions ; and perhaps the Scottish peasant has shown as keen a sense of it — of the story-teller's art, at least — as his mental development and the conditions of his existence would admit. [G. D.] 498 General Monthly Meeting. [Feb. 1, GENERAL MONTHLY MEETING, Monday, February 1, 1892. Sir James Crichton-Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Leopold Field, Esq. F.C.S. James Macdonald Horsburgh, Esq. M.A. Sir Philip Magnus, were elected Members of the Royal Institution. The Special Thanks of the Members were returned for the following Donations ; — Sir Benjamin Baker, £50, L. M. Rate, Esq. £50, J. W. Swan, Esq. £21, Wm. Anderson, Esq. £25, for carrying on investigations on Liquid Oxygen. The Presents received since the last Meeting were laid on the table, and the thanks of the Members returned for the same, viz : — FROM Governor-General of India — Kecords, Vol. XXIV. Part 4. 8vo. 1891. The Lords of the Admiralty — Nautical Almanac for 1895. 8vo. 1891. The Secretary of State for India — The Tribes and Castes of Bengal. By H. H. Risley. Vols. I. II. Anthropometric Data. 8vo. Calcutta, 1891. Abel, Sir Frederick, K.C.B. F.R.S. M.B.I, {the ^w^/ior)— Mining Accidents and their Prevention. 8vo. New York, 1889. Accademia dei Lincei, Eeale, Roma — Atti, Serie Quarta : Rendiconti. 2° Semes- tre, Vol. VII. Fasc. 9-12. 8vo. 1891. Memorie, Vol. IX. 4to. 1891. Atti, Anno 44, Sess. IV^-VI^ 4to. 1891. Agricultural Society of England, Royal — Journal, Vol. II. Part 4. 8vo. 1891. American Geographical Society — Bulletin, Vol. XXIII. Nos. 1-3. 8vo. 1891. Astronomical Society, Royal — Monthly Notices, Vol. LII. Nos. 1-3. 8vo. 1891. Rankers, Institute o/— Journal, Vol. XII. Part 9; Vol. XIII. Part 1. 8yo. 1891-92. Basel, Naturforsehenden Gesellschaft — Verhandlungen, Band IX. Heft 2. S\o, 1891. Birmingham and Midland Institute — Report for 1891. 8vo. 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Institute of Brewing — Transactions, Vol. V. No. 2. Svo. 1891. Jablonowski'sche Gesellschaft, Leipzig — Preisschriften, Mathematisch-naturwissen- schaftlichen Section, No. XI. 4to. 1891. Johns Hopkins University — University Circulars, No. 94. 4to. 1891. American Chemical Journal, Vol. XIII. No. 8. Svo. 1891. Linnean Society — Journal, No. 196. Svo. 1891. Madrid Royal Academy of Sciences — Memorias, Tome XV. 4to. 1890-91. Manchester Geological Society — Transactions, Vol. XXI. Part 12. Svo. 1891. McClean, Frank, Esq. M.A. M.R.I, (the Author) — Comparative Photographie Spectra of the Sun and the Metals, fol. 1891. 500 General Monthly Meeting. [Feb. 1, McKendrick, Professor J. G. M.D. LL.D. F.R.S. {the Author)— A Text Book of Physiology. 2 vols. 8vo. 1888-89. Meteorological Office — Hourly Means, 1888. 8vo. 1891. Ten Years' Sunshine in the British Isles, 1881-90. 8vo. 1891. Harmonic Analysis of Hourly Observations. 4to. 1891. 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M.B.I, (the Author)— The Asclepiad, Vol. VHI. No. 32. Svo. 1891. Rio de Janeiro, Observatoire Imperiale de — Revista, Nos. 10, 11. Svo. 1891. Royal Irish Academy — Proceedings, 3rd Series, Vol. II. No. 1. Svo. 1891. Transactions, Vol. XXIX. Part 17. 4to. 1891. Royal Society of London — Catalogue of Scientific Papers, Vol. IX. ABA-GIS (1874-83). 4to. 1891. Proceedings, Nos. 303, 304. Svo. 1892. Saxon Society of Sciences, Royal — Mathematische-Physischen Classe : Abhand- lungen, Band XVIII. Nos. 1, 2. 4to. 1891. Berichte, 1891, No. 3. Svo. 1891. Philologisch-Historischen Classe: Abhandlungen, Band XIII. No. 3. Svo. 1891. Scottish Society of Arts, Royal — Transactions, Vol. XIII. Part 1. Svo. 1891. Selborne >Soc^e