1 m ••:,■■: NOTICES OF THE PROCEEDINGS AT THE MEETINGS OF THE MEMBERS OF THE ftoyal tetttutton of #reat Britain, WITH ABSTRACTS OF THE DISCOURSES DELIVERED AT THE EVENING MEETINGS. VOLUME XIV. 1893—1895. LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED, STAMFORD STREET AXD CHARING CROSS, 189G. patron. HER MOST GRACIOUS MAJESTY QUEEN VICTOBIA. Utie^Patron an* ^onorarn Member. 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 Cuichton-Browne, M.D. LL.D. F.R.S. — V.P. Honorary Secretary — Sir Frederick Bramwell, Bart. D.C.L. LL.D. F.R.S. M.Inst. C.E.-F.P. Managers. 1895-96. Sir Fredk. Abel, Bt. K.C.B. D.C.L. LL.D. F.R.S.— V.P. Captain W. de W. Abncy, C.B. D.C.L. F.R.S. The Right Hon. Lord Amherst, F.S.A. William Anderson, Esq. D.C.L. F.B B. Sir Benjamin Baker, K.C.M.G. LL.D. F.R.S. John Birkett, Esq. F.R.C.S. William Crookes, Esq. F.R.S.— V.P. Edward Frankland, Esq. D.C.L. LL.D. F.R.S.— V.P. Charles Hawksley, Esq. M. Inst. C.E. John Hopkinson, Esq. M.A. D.Sc. F.R.S. Alfred B. Kempe, Esq. M.A. F.R.S. George Matthey, Esq. F.R.S —V.P. The Right Hon. The Marquis of Salisbury, K.G. D.C.L. LL.D. F.R.S. — V.P. Basil Woodd Smith, Esq., F.R.A.S. F.S.A.— V.P. Joseph Wilson Swan, Esq. M.A. F.R.S. Visitors. John Wolfe Barry, 1805-96. Esq. C.B. F.R.S. M. Inst. C.E. Charles Edward Beevor, M.D. F.R.C.P. Arthur Carpmael, Esq. Carl Haag, Esq. R.W.S. Victor Horsley, Esq. M.B. F.R.S. F.R.C.S. Hugh Leonard, Esq. M. Inst. C.E. Sir Joseph Lister, Bart. M.D. D.C.L. LL.D. Pres. R.S. Lachlan Mackintosh Rate, Esq. Alfred Gordon Salamon, Esq. F, Felix Semon, M.D. F.R.C.P. Henry Virtue Tebbs, Esq. Silvanus P. Thompson, Esq. F.R.S. John Westlake, Esq.Q.C. LL.D. His Honour Judge Frederick Meadow,-, White, Q.C. Sir William II. White, K.C.B. LL.D. F.R.S. M.A. .C.S. D.Sc. professors. Professor of Natural Philosophy— -The Right Hon. Lord Rayleigii, M.A. D.C.L. LL.D. F.R.S. &c. Fullerian Professor of Chemistry — James Dewar, Esq. M.A. LL.D. F.R.S. &c. Fullerian Prof essor of Physiology — Charles Stewart, Esq. M.R.C.S. F.R.S. Honorary Librarian — Mr. Benjamin Vincent. Keeper of the Library and Assistant Secretary — Mr. Henry Young. Assistant in the Library — Mr. Herbert C. Fyfe. Assistants in the Laboratories— Mr. R. N. Lennox, F.C.S. Mr. J. W. Heath, F.C.S. and Mr. G. Gordon. CONTENTS. 1893. PAGE Jan. 20. — Professor Dewar — Liquid Atmospheric Air .. 1 „ 27. — Francis Galton, Esq. — The Just-Perceptible Difference .. .. .. .. .. 13 Feb. 3. — Alexander Siemens, Esq. — Theory and Practice in Electrical Science (with Experimental Illustra- tions) .. .. .. .. .. .. 27 6.— General Monthly Meeting 40 „ 10. — Professor Charles Stewart — Some Associated Organisms (no Abstract) .. .. .. .. 43 „ 17. — Professor A. H. Church — Turacin, a remarkable Animal Pigment containing Copper .. .. 44 ,, 24. — Edward Hopkinson, Esq. — Electrical Railways .. 50 March 3. — George Simonds, Esq. — Sculpture, considered apart from Archaeology .. .. .. .. 58 „ 6.— General Monthly Meeting G3 „ 10. — Sir Herbert Maxwell, Bart. — Early Myth and Late Romance (no Abstract) », .. .. 66 „ 17. — William James Russell, Esq.— Ancient Egyptian Pigments .. .. .. .. .. .. 67 40144 IV CONTENTS. 1893. vm;e March 24. — The Right Hon. Lord Rayleigh — Interference Bands and their Applications .. .. .. 72 April 10.— General Monthly Meeting .. .. „ .. 78 ,, 14. — Sir William H. Flower — Seals .. .. .. 81 „ 21. — Professor A. B. W. Kennedy — Possible and Im- possible Economies in the Utilisation of Energy 82 „ 28. — Professor Francis Gotch — The Transmission of a Nervous Impulse .. .. .. .. 94 May 1.— Annual Meeting .. .. .. .. .. 96 „ 5. — Shelford Bid well, Esq.— Fogs, Clouds, and Lightning .. .. .. .. .. .. 97 }j 8.— General Monthly Meeting .. .. .. ..108 „ 12. — The Right Hon. Lord Kelvin — Isoperimetrical Problems .. .. .. .. .. .. Ill „ 19. — Alfred Austin, Esq. — Poetry and Pessimism (no Abstract) .. .. 119 ?} 26. — Herbert Beerbohm Tree, Esq. — The Imaginative Faculty in its relation to the Drama .. .. 120 June 2. — Professor Osborne Reynolds — Study of Fluid Motion by means of Coloured Bands .. .. 129 5.— General Monthly Meeting 139 J5 9.— Professor T. E. Thorpe — The Recent Solar Eclipse 142 July 3, -General Monthly Meeting 150 Nov. 6.— General Monthly Meeting 153 Dec. 4.— General Monthly Meeting ,158 „ 15. — Special General Meeting — Decease of Dr. Tyndall, Honorary Professor of Natural Philosophy .. 1G1 CONTENTS. 1894. PAGE Jan. 19. — Professor Dewar — Scientific Uses of Liquid Air 393 „ 26.— Alfred Perceval Graves, Esq.— Old Irish Song 169 Feb. 2. — T. J. Cobden-Sanderson, Esq. — Bookbinding, its Processes and Ideal .. .. .. .. 178 „ 5. — General Monthly Meeting .. .. .. .. 185 „ 9.— Professor W. F. R. Weldon — Fortuitous Varia- tion in Animals (no Abstract) .. .. .. 188 „ 16. — Professor Nichol — Bacon's Key to Nature .. 189 „ 23. — Professor Silvanus P. Thompson — Transforma- tions of Electric Currents (no Abstract) .. .. 202 March 2. — Professor John G. McKendrick — The Theory of the Cochlea and Inner Ear (no Abstract) .. 202 „ 5.— General Monthly Meeting 203 „ 9. — William H. White, Esq. —The Making of a Modern Fleet 207 „ 16. — The Eight Hon. Lord Rayleigh — The Scientific Work of Tyndall 216 April 2.— General Monthly Meeting 225 „ 6. — Professor Victor Horsley — Destructive Effects of Projectiles .. ,. .. .. .. 228 „ 13. — Professor J. J. Thomson— Electric Discharge through Gases .. .. .. .. ..239 „ 20.— John G. Garson, M.D.— Early British Paces .. 248 „ 27. — Professor H. Marshall Ward — Action of Light on Bacteria and Fungi .. .. .. .. 259 May 1.— Annual Meeting 281 „ 4. — Professor Charles Stewart— Sound Production of the Lower Animals (no Abstract) .. .. 281 VI CONTENTS. 1S94. TAGE May 7.— General Monthly Meeting 282 11.— The Rev. S. Baring-Gould— English Folk Song 286 „ 18. — Professor A. M. Worthington — The Splash of . a Drop and Allied Phenomena .. .. .. 289 ,, 25. — Sir Howard Grtjbb — The Development of the Astronomical Telescope .. .. .. .. 304 June 1.— Professor Oliver Lodge — The Work of Hertz .. 321 „ 4. — General Monthly Meeting .. .. .. .. 350 „ 8. — C. Vernon Boys, Esq. — The Newtonian Constant of Gravitation .. .. .. .. .. 353 July 2.— General Monthly Meeting 378 Nov. 5.— General Monthly Meeting 383 Dec. 3.— General Monthly Meeting .. .. .. .. 388 1895. Jan. 18. — Professor Dewar— Phosphorescence and Photo- graphic Action at the Temperature of Boiling Liquid Air .. .. .. .. .. 6G5 „ 25. — Sir Colin Scott-Moncrieff — The Nile .. .. 405 Feb. 1. — Henry Irving, Esq. — Acting: an Art .. .. 419 M 4.— General Monthly Meeting 429 „ 8. — G. Sims Woodhead, M.D. — The Antitoxic Serum Treatment of Diphtheria .. .. .. .. 433 „ 15. — Clinton T. Dent, Esq. — Mountaineering.. .. 451 „ 22. — Professor A. Schuster — Atmospheric Electricity 4G0 March 1. — The Kev. Canon Ainger — The Children's Books of a Hundred Years Ago (no Abstract) .. .. 47 G „ 4.— General Monthly Meeting .. 477 CONTENTS. ' Vll 1895. PAGE March 8. — Professor A. W. Rucker— The Physical Work of von Hclmholtz .. .. .. .. .. 481 „ 15. — Professor Roberts-Austen — The Rarer Metals and their Alloys .. .. .. .. .. 497 „ 22. — Sir Wemyss Reid — Emily Bronte (no Abstract) .. 521 ,, 29. — Professor H. E. Armstrong— The Structure of the Sugars and their Artificial Production (jio Abstract) .. 521 April 1.— General Monthly Meeting 521 „ 5. — The Right Hon. Lord Rayleigh — Argon.. .. 524 „ 26. — John Hopeinson, Esq. — The Effects of Electric Currents in Iron on its Magnetisation .. .. 539 May 1. — Annual Meeting .. .. .. .. .. 553 „ 3. — Veterinary-Captain Frederick Smith — The Structure and Function of the Horse's Foot ... 554 „ 6. — General Monthly Meeting .. ., .. .. 5G4 „ 10. — The Hon. G. N. Curzon — A Recent Journey in Afghanistan .. .. ., .. .. 568 „ 17.— Professor Walter Raleigh — Robert Louis Stevenson .. .. .. .. .. .. 580 „ 25. — J. Viriamu Jones, Esq. — The Absolute Measure- ment of Electrical Resistance .. .. .. 601 „ 31. — The Earl of Rosse — The Radiant Heat from the Moon during the progress of an Eclipse .. 622 June 7. — Professor Alfred Cornu — Phenomenes Physiques des Hautes Regions de 1' Atmosphere .. .. 638 „ 10.— General Monthly Meeting 649 July 1. — General Monthly Meeting .. .. .. .. 652 Nov. 4. — General Monthly Meeting ... .. .. .. 655 Dec. 2. — General Monthly Meeting .. .. .. .. 661 Index to Volume XIV. f 671 PLATES. TAGE The Splash of a Drop, Scries I. to XIV. .. .. 289, 293-303 Photographs taken with the Capetown Astrographic Telescope 312, 313 Apparatus and Vessels used in the Production and Storage of Liquid Air 396,398,400 i&ogai Institution of ffireat WEEKLY EVENING MEETING, Friday, January 20, 1893. Sir Frederick Bramwell, Bart. D.C.L. LL.D. F.R.S. Honorary Secretary and Vice-President, in the Chair. Professor Dewar, M.A. LL.D. F.R.S. M.B.L Liquid Atmospheric Air. The prosecution of research at temperatures approaching the zero of absolute temperature is attended with difficulties and dangers of no ordinary kind. Having no recorded experience to guide us in conducting such investigations, the best instruments and methods of working have to be discovered. The necessity of devising some new kind of vessel for storing and manipulating exceedingly volatile fluids like liquid oxygen and liquid air, became apparent when the optical properties of the bodies came under examination. The liquids, being in active ebullition, were in a condition which rendered optical measurements impossible. All attempts at improvement on the principle of using a succession of surrounding glass vessels, the annular space between such vessels having the cool current of the vapour coming from the boiling liquid led through them, proved a failure. Apart altogether from the rapid ebullition interfering with experimental work, the fact that it took place involved a great additional cost in the conduct of experiments on the properties of matter under such exceptional conditions of temperature. While suffering great anxiety on the question of expenditure, the Goldsmiths' Company came forward with the handsome contribution of 1000/. to continue the work with improved apparatus. Personally, I desire to express my grateful thanks to the Goldsmiths' Company for tendering such encouragement and support. On careful consideration it became apparent that the proper way of attacking the problem was to conduct a series of experiments on the relative amounts of heat conveyed to boiling liquid gases ; firstly, by means of the convective transference of heat by the gas particles, and, secondly, by radiation from surrounding bodies. The early experiments of Dulong and Petit on the laws of radiation had proved the very important part played by the gas particles sur- rounding a body in dissipating heat otherwise than by pure radiation. In the year 1873 I used a highly-exhausted vessel in calorimetric experiments " On the Physical Constants of Hydrogenium " (Trans. Vol. XIV. (No. 87.) b Professor Dewar [Jan. 20, Koy. Soc. Ed., vol. xxvii.) and the subsequent investigations of Crookes, and especially of Bottomley, having confirmed the great importance to be attached to the gas particles in the gain or loss of heat, it naturally occurred to me that the use of high vacua surround- ing the vessels containing liquid gases would be advantageous. In order to arrive at definite data, some means of conducting com- parative experiments between the amount of convective and radiant heat at such low temperatures had to be devised. The apparatus shown in Fig. 1 measures the relative volumes of gas distilled in a given time under definite conditions, so that the measure of the gas distilled is proportional to the amount of heat conveyed to the liquid. The experiments are made in the following way : the distilling vessel to the right consists of two concentric spherical chambers, the space between being highly exhausted by a mercurial air-pump. The inner sphere is filled with liquid ethylene, oxygen, Fig. 1. or air, and the whole apparatus immersed in water maintained at a constant temperature. Distillation begins immediately and continues at a constant rate provided the liquid in the bulb is maintained at the same level. This is not possible, but a sufficient uniformity is attained by making the observations during the evaporation of the first fourth of the contents. Having measured the volume of gas produced per minute when the sphere is surrounded with a high vacuum, the vessel is taken out of the water, the end nipped off, air allowed to enter, and then again closed. In this condition the inner sphere is filled up again with the liquid and the above experiment repeated. The following results were obtained, using ethylene and oxygen respectively : Liquid Oxygen, Vacuum . . . . 170 cc. per minute. » » Air 840 „ „ „ Ethylene, Vacuum .. 56 „ „ » Air 250 „ These results prove that under the same conditions a high vacuum 1893.] on Liquid Atmospheric Air. 3 diminishes the rate of evaporation to one-fifth part of what it is when the substance is surrounded with air at atmospheric pressure, or, in other words, liquid oxygen or ethylene lasts five times longer when surrounded with a vacuous space. The next step was to construct a series of glass vessels sur- rounded by a vacuous space, suitable for various experiments, and such are represented in Fig. 2. In vessels of this kind, if the vacuum is very high, no ice appears on the surface of the outer vessel, even although the walls of the vacuous space are within half an inch of each other, and the liquid oxygen or air evaporates almost solely from the surface, no bubbles of gas being given off throughout the mass of the liquid. So far the convective transference of heat has been stopped by the use of a high vacuum, but if the inner vessel is coated with a bright deposit of silver, then the radiation is Fig. 2. diminished also, with the result that the rate of evaporation is further reduced to more than a half. In such vessels liquid oxygen or liquid air can be kept for hours, and the economy and ease of manipulation greatly improved. The arrangements represented in Fig. 2 may be employed to study the law of radiation at low temperatures. All that is necessary for the purpose is to immerse the outer vessel in liquids maintained at different temperatures. The following preliminary results have been obtained, using oxygen, which boils at — 180° C, in the inner sphere : — Temperature. Radiation. -115°C 60 cc. - 78° C 120 „ + 6°C 300 „ + 65° 0 600 „ These results show that radiation (along with such convective transference as remains) grows approximately at the rate of the cube b 2 4 Professor Dewar [Jan. 20, of the absolute temperature. Many further experiments must, however, be made before the real law of radiation at low temperatures can be strictly defined. To produce exceedingly high vacua in vessels used for such pur- poses as the collection and storage of liquid air, a mercurial vacuum made in the following manner has been found highly satisfactory. Take, as an illustration, a glass vessel shaped like Fig. 3, and after placing in it a quantity of mercury and connecting the pipe H with a good working air-pump, place in an oil or air-bath heated above 200° C, and distil off a good quantity of the mercury. While the distillation is taking place the tube is sealed off at the point A, and the bulb instantly removed from the heated bath to such an extent as to allow condensation to take place in the small chamber marked B W in the figure. As the air-pump can maintain a vacuum of ten millimetres, no difficulty arises in sealing the glass tube during the continuance of the distillation. In somo cases the mercury in the vessel has been heated up to near its boiling point in air, and then the air-pump started, causing thereby an almost explosive burst of mercurial vapour which very effectually carries Fig. 3. all the air out of the vessel. After cooling, the vessel is removed from the bath, and the excess of mercury brought into tho small bulb B W, care having been taken to remove any small globules of mercury, which adhere with great tenacity to the surface of the glass, by heating K while the part B W is kept cool. In this way the vessel K is filled with nothing but mercurial vapour, the pressure of which depends solely on the temperature of the liquid mercury contained in the small enlargement, and as this can, if necessary, be cooled to —190° C. by immersing it in liquid air, we have the means of creating in K a vacuum of inconceivable tenuity. It is sufficient for the production of very good vacua to cool the mercury in B W to — 80° C. (using solid carbonic acid as the cooling agent), and while in this condition to seal off the bulb containing all the condensed mercury, so that K is left full of saturated vapour at — 80° C. When very high exhaustions are required it is better not to seal off the mercury bulb, as the glass is apt to give off some kind of vapour. A similar mode of proceeding is adopted when other shaped vessels have to be highly exhausted, and no difficulty has arisen in operating with vessels having the capacity of more than a litre. The perfection of the vacuum, assuming that nothing remains but molecules of mercury in the form of vapour, depends upon the tem- perature to which the subsidiary bulb is cooled. The well-known law which expresses approximately the relation between temperature and pressure in the case of saturated vapours, must be assumed to be applicable to mercury vapour at temperatures where direct measure- ment becomes impossible. Having calculated the constants of a 1893.] on Liquid Atmospheric Air. 5 vapour pressure formula from observed data at high temperatures, it is easy to arrive at a value of the vapour pressure for any- assumed lower temperature. Such a formula as the following, log. P = 15-1151 - 2-2931, log. T ^— , where P is pressure in millimetres of mercury and T is the absolute temperature, agrees well with the experimental results. This formula gives the vaponr pressure at 0° C. as 0-000 18 mill., and at - 80° C. as 0-000,000,003 mill., or respectively, about the sixth and the four hundred thousandth of a millionth of an atmosphere. Such a high vacuum could never be reached by the use of any form of mercurial air-pump. The electric discharge in such vacua produces intense phosphorescence of the glass, giving thereby a continuous spectrum, which makes the detection of the mercury lines difficult. Consider for a moment the proofs that could be adduced that mercury vapour, even below a millionth of an atmosphere pressure, can behave like an ordinary saturated vapour. The most character- istic property of a space filled with any saturated vapour is that cooling to a lower temperature causes partial condensation of the vapour in the form of liquid or solid. The amount of vapour in a mercurial vacuum at the ordinary temperature would weigh about the tenth of a milligram in the volume of a litre, and to see such an amount of the metal it would require to be concentrated on a small area in the form of a fine metallic film. Experiment has shown that the fifth of a milligram of gold may be made to cover one square centimetre of surface, so that a minute quantity of metal can be observed if properly deposited. This can be easily achieved in such mercurial vacua by cooling a small portion of the surface of the glass to the temperature of — 180° C. by the applica- tion of a pad of cotton wool saturated with liquid oxygen. In an instant the vapour of mercury deposits in the form of a brilliant mirror, which, on the temperature rising, becomes subdivided into a mass of exceedingly minute spheres of liquid. A repetition of the cooling does not bring down a new mirror, provided the first area is maintained cool, but if the vessel contains excess of liquid mercury any number of mirrors of mercury may be deposited in succession. Mercury is thus proved to distil at the ordinary temperature when the vapour pressure is under the millionth of an atmosphere. Further, it is easy to prove in this way that the cooling of the liquid mercury in "such a subsidiary vessel (which has been de- scribed as a temporary part of the vacuum vessel) greatly improves the vacuum. For this purpose it is sufficient to cool the said vessel with some solid carbonic acid, and then to try and reproduce a mirror of mercury in the way previously described. No mercury mirror can be formed so long as the cold bath is maintained. If a piece of blotting paper, cut into any desired shape, be moistened with water, and then applied to the surface of one of the vacuum vessels Professor Dewar [Jan. 20, containing excess of liquid mercury, the local reduction of tempera- ture produced by the evaporation soon causes a rough image of the paper to appear in the form of minute globules of condensed mercury. Such experiments support the view that the laws of saturated vapours are maintained at very low pressures. In Fig. 4 specimens of the old and new vessels for collecting and manipulating liquid gases are shown. In each of the old forms it Fig. 4. will be noted that a mass of phosphoric anhydride placed in the lower portion is required to absorb traces of water, otherwise the vessels are useless for optical observations. The vacuum receivers get over this difficulty. The perfection of the vacuum in different vessels, all treated m the same way, differs very much, and after use they almost invariably deteriorate. The relative rates of evaporation of liquid oxygen under the same conditions in different vessels is the best test of the vacuum. In many of the large vessels used for the storage of liquid gases, it 1893.] on Liquid Atmospheric Air. Fig 5. is convenient and more effective to cause the deposition of a mercury mirror over the surface of the inner vessel (by leaving a little liquid mercury in the lower part of the double-shaped flask), instead of silvering as previously described. Under such conditions the mer- cury instantly distils and forms a brilliant mirror all over the surface of the inner vessel. The fact that mercury has a very high refrac- tive index and is a bad conductor of heat are factors of importance in retarding the conveyance of heat. After the mercury mirror has been formed any further increase in the thickness of the film can be prevented, and at the same time the vacuum improved by freezing the excess of liquid mercury in the lower part of the vessel. The vacuum vessels described equally retard the loss as well as the gain of heat, and are admirably adapted for all kinds of calorimetric observations. The future use of these vessels in thermal observations will add greatly to the accuracy and ease of conducting investiga- tions. The double spherical form of vacuum vessel is excellent for showing that the elevation or depression of a given volume of air a few feet causes an increase or diminution of volume, due to the small change of atmospheric pressure. The volume of air in the inner sphere is guarded from any sudden change of temperature by the surrounding highly vacuous space. This is only one of the many uses to which such receivers can be put. In making vacua, many other substances have been examined along with mercury, but they have not given equally satisfactory results. Sulphur would occur to any one as a substance that might replace mercury, seeing the density in the form of vapour, and also the latent heat of vaporisation, are nearly identical ; and it has the further advantage of being a solid at ordinary temperatures. The sulphur vacua have, however, so far not been an improvement, chiefly because traces of organic matter are decomposed by the sulphur, giving sulphuretted hydrogen and sul- phurous acid, gases which are dissolved by and remain in the sulphur. When the surface of such a sulphur vacuum is cooled with liquid oxygen in the manner previously described, a faint crys- talline deposit occurs, only it takes a much longer time to appear than in the case of the mercury vacuum. If a similar vessel is boiled out, using phosphorus as the volatile substance, the application of liquid oxygen to the surface causes instant deposition. Thus it can be proved sulphur and phosphorus distil at ordinary temperatures just like mercury. An investigation as to the electric conductivity of metals, alloys, and carbon at low temperatures has been undertaken in 8 Professor Deivar [Jan. 20, conjunction with my friend, Professor J. A. Fleming, D.Sc, F.E.S. The experiments are made by means of a resistance coil shown in Fig. 5, consisting of a piece of notched mica coiled with the fine wire to be tested, and of stout insulated copper-rod connections. The coil and connection are immersed in liquid oxygen contained in a vacuum test-tube, and the temperature of —200° C. can be reached by exhausting the oxygen by means of a powerful air- pump. The results point to the conclusion that absolutely pure Fig. 6. ZO + TEMPERATURE — Electrical Resistance of Metals at Low Temperature. metals seem to have no resistance near the zero of temperature as indicated by the above curves (Fig. 6) obtained by experiment. With alloys there is little change in resistance, as indicated in the curves (Fig. 7). The conductivity of carbon decreases with low temperatures, and increases with high ones. At the tempera- ture of the electric arc, carbon appears to have no resistance. The optical constants of liquid oxygen, ethylene, and nitrous oxide have been so far determined, and in this matter my colleague, Professor Liveing, has been associated with me in the conduct of this work. The results obtained are given in the following table, 1893.] on Liquid Atmospheric Air. and tend to confirm the Law of Gladstone as being applicable to such substances : — Refractive Indices of Liquid Gases. Oxygen Ethylene .. Nitrous Oxide Index. 1-2236 13632 13305 Law of Gladstone Ref. Constant. . .. 1-989 . . .. 0-626 . . .. 0-263 ., D = Constant, Eef. Molecular. , 6-364 , 17-528 , 11-587 Fig. 7. + TEMP£RATUR£ — Electrical Resistance of Alloys at Low Temperatures. The determination of the refractive index of liquid oxygen, at its boiling-point of — 182° C, presented more difficulty than would have been anticipated. The necessity for enclosing the vessel containing the liquid in an outer case to prevent the deposit of a layer of hoar-frost which would scatter all the rays falling on it, rendered manipulation difficult ; and hollow prisms with cemented sides cracked with the extreme cold. It was only after repeated attempts, involving the expenditure of a whole litre of liquid oxygen on each experiment, that we succeeded in getting an approxi- mate measure of the refractive index for the D line of sodium. 10 Professor Deicar [Jan. 20, Fig. 8. -' The mean of several observations gave the minimum deviation with a prism of 59° 15' to be 15° 11' 30", and thence p = 1-2236. The density of liquid oxygen at its boiling-point of —182° C. is 1*124, and this gives for the refraction-constant, ^— = 1*989, and for the refraction-equivalent 3*182. This corresponds closely with the refraction-equivalent deduced by Landolt from the refractive indices of a number of organic compounds. Also it differs little from the refraction-equivalent for gaseous oxygen, which is 3*0316. This is quite consistent with the supposition that the molecules of oxygen in the liquid state are the same as in the gaseous. 2 I If we take the formula , .. , ON , for the refraction-constant we find the value of it for liquid oxygen to be -1265, and the corresponding refraction-equivalent 2*024. These are exactly the means of the values found by Mascart and Lorenz for gaseous oxygen. The inherent difficulties of manipulation, and the fact that the sides of the hollow prism invariably became coated with a solid deposit, which obscured the image of the source of light, have hitherto prevented our determining the refractive indices for rays other than D. The optical projection of vacuum vessels having the shape of a double test-tube are very suitable for lecture illustration. As the critical point of oxygen is some thirty degrees higher than nitrogen it is easier to liquefy, and, consequently, becomes the most convenient substance to use for the production of temperatures about — 200° C. Liquid nitrogen, carbonic oxide, or air can conveniently be made at the ordinary atmospheric pressure, provided they are brought into a vessel cooled by liquid oxygen boiling under the pressure of about half an inch of mercury. A simple arrangement for this purpose is shown in Fig. 8. The inner tube contains the liquid oxygen under exhaustion, surrounded by a vacuum vessel, the interior space between the inner tube and the vacuum vessel being connected with a receiver containing the gas which is to be liquefied. If the object is to collect liquid air, the inner air space is left quite open, no precautions being needed to free the air from carbonic acid or moisture, because under the conditions such substances are solids, and only cause a slight opalescence in the liquid, which drops con- tinuously from the end of the inner tube and accumulates in the vacuum vessel. If the air supply is forced to bubble through a little strong sulphuric acid, the rate of condensation and the rela- tive volume of gas and liquid can be observed. Liquid air boils at the temperature of - 190° C, giving off substantially pure nitrogen. 1893.] on Liquid Atmospheric Air. 11 As the nitrogen boils 10° C. lower than oxygen, after a time the liquid alters its composition and boiling point, finally becoming pure oxygen. During the evaporation the liquid air changes very remarkably in colour, passing from a very faint blue to a much deeper shade. The changes can be traced best by the marked increase in the width of the absorption bands of liquid oxygen. If air, collected in the above manner in a vacuum vessel, is isolated from a rapid heat supply by immersing the vessel in liquid oxygen, and then a powerful air-pump brought to act upon it, after a time it passes into the condition of a clear, transparent, solid ice. Nitrogen solidifies, under such conditions, into a white mass of crystals, but all attempts to solidify oxygen by its own evaporation have failed. Such liquids as air and oxygen, we should anticipate, would be especially transparent to heat radiation, seeing they are very diathermic substances in their gaseous state. The thermal transparency of liquid oxygen can be shown by passing the radiation from the electric arc, as shown in the diagram, through a spherical Fig. 9. vacuum vessel filled with clear filtered liquid, thereby concentrating the rays at a focus and igniting a piece of black paper held there. In this experiment the oxygen lens has a temperature of — 180° C, yet it does not prevent the concentrated radiation reaching a red heat at the focus. At such low temperatures as boiling oxygen and air all chemical action ceases. If some liquid oxygen is cooled to — 200° C, and a glowing piece of wood inserted into the vessel above the liquid, it refuses to burst into flame, because of the low pressure of the vapour. An interesting experiment may be made by immersing an electric pile, composed of carbon and sodium, into liquid oxygen, when almost immediately the electric current ceases. The gaseous oxygen coming from the liquid must be exceedingly pure and dry, and as it has been alleged two chemical substances require the presence of a third one in order that they may combine, it was interesting to ascertain if a substance like sulphur would continue to burn after ignition in such an atmosphere. Sulphur placed in a small platinum vessel that had just been heated to redness, was raised to the boiling point, and in the act of combustion lowered into a vacuum vessel containing liquid oxygen. The com- 12 Professor Dewar on Liquid Atmospheric Air. [Jan. 20, bustion continued active, and for a time could be maintained in the middle of the liquid oxygen. This result suggests that oxygen and sulphur can enter into combination in a perfectly dry condition. Some notion of the temperature of liquid air is given by running on to the surface some absolute alcohol, which, after rolling about in the spheroidal state, suddenly solidifies into a hard transparent ice, which rattles on the sides of the vacuum test-tube like a marble. On lifting the solid alcohol out by means of a looped wire the appli- cation of the flame of a Bunsen burner will not ignite it. After a time the solid melts and falls from the looped wire like a thick syrup. It is not the question of the change of state in matter, however interesting, that in our day has special attractions for the chemist, but the means of studying the properties of matter generally under the conditions of such exceptionally low temperatures as are the con- comitants of the transition in the case of substances like oxygen and nitrogen. The work of investigation in this field proceeds slowly but surely, and one need not despair (unless on the grounds of expense) in the future of adding further data to our knowledge of the pro- perties of matter near the zero of absolute temperature. At the commencement of the lecture reference was made to the dangers and difficulties of this kind of research, and it becomes a pleasant duty to acknowledge the great services rendered by my assistants. But for the persistency and determination of Mr. Lennox, coupled with his marked engineering ability, the work would not have made such progress, and he has been ably supported by Mr. Heath. [J. D.] 1893.] Mr. Francis Galton on The Just-Perceptible Difference. 13 WEEKLY EVENING MEETING, Friday, January 27, 1893. David Edward Hughes, Esq. F.R.S. Vice-President, in the Chair. Francis Galton, Esq. F.P.S. M.B.L TJie Just- Perceptible Difference. We seem to ourselves to belong to two worlds, which are governed by entirely different laws; the world of feeling and the world of matter — the psychical and the physical — whose mutual relations are the subject of the science of Psycho-physics, in which the just-per- ceptible difference plays a large part. It will be explained in the first of the two principal divisions of this lecture that the study of just-perceptible differences leads us not only up to, but beyond, the frontier of the mysterious region of mental operations which are not vivid enough to rise above the threshold of consciousness. It will there be shown how important a part is commonly played by the imagination in producing faint sensations, and how its power on those occasions admits of actual measurement. The last part of the lecture will deal with the limits of the power of optical discrimination, as shown by the smallest number of adjacent dots that suffice to give the appearance of a continuous line, and the feasibility will be explained of transmitting very beautiful outline drawings of a minute size, and larger and rougher plans, maps, and designs of all kinds, by means of telegraphy. Material objects are measurable by external standards, about which it is sufficient to say that when we speak of a pound, a yard, or an hour, we use terms whose meanings are defined and understood in the same sense by all physicists. The feelings, on the other hand, cannot be measured by external standards, so we are driven to use internal ones, and to adopt a scale of sensation formed by units of just-perceptible differences, rising in the arithmetical order of 1, 2, 3, &c, and by their side a scale of measurements of the stimuli that provoked them. The attempts of those who first experimentalised in Psycho-physics were mainly directed to ascertain the relation between the increase of stimulus and the corresponding increment of sensation. Their net result has been to confirm, within moderate limits, the trustworthiness of Weber's law, namely, that each successive incre- ment of sensation is caused by the same percentage increment of the previous stimulus. The rate at which a stimulus must be increased in order to give a 14 Mr. Francis Galton [Jan. 27, just-perceptible increment of sensation, has been taken at the average of 1 per cent, for light, 6 per cent, for muscular effort, 33 per cent, for sound and warmth ; also 33 per cent, for pressure upon most parts of the body, and as high as 16 per cent, upon the finger tips. But these values must not be trusted too far; they cease to be exact towards the two ends of the scale. A mechanical arrangement clearly illustrates the consequences of Weber's law. It includes an axle to which is fixed a wheel, a part of a logarithmic spiral, and an index hand. This portion of the machine is carefully balanced, so that it will remain steady in any position in which it is set, while a small force is sufficient to cause it to turn ; behind all is a card with equal graduations upon it, over which the index travels. A string, with a scale pan at one end and a counterpoise at the other, is wrapped round the wheel. A string fastened to the axle passes over the logarithmic arm, and a ball is fastened to its free end. The varying weights put in the scale pan will now represent varying amounts of stimulus, and the graduations to which the index points, represent the corresponding variations of sensation. I exhibit a diagrammatic model of the apparatus, much too rough to give exact indications, but still sufficient for rough explanatory purposes. Owing to the obvious properties of a spiral, the more the axle to which it is fixed is rotated in the direction of its concave side, the further does the point at which the string is hanging travel away from the axis, and the leverage exerted by the weight of the ball will increase. Whatever be the weight in the scale pan, there is within the working range of the apparatus some position of the beam at which that weight will be counterbalanced by the ball. The pro- perty of the logarithmic spiral is that equal degrees of rotation correspond to equal percentage increments of leverage. Hence, when percentage increments of weight are successively placed in the scale pan, the index attached to the beam will successively travel over equal divisions of the scale, in accordance with Weber's formula. The progressive increase in the effective length of the logarithmic arm is small at first, but is seen soon to augment rapidly, and then to become extravagant. We thus gain a vivid insight through this piece of mechanism into the enormous increase of stimulus, when it is already large, that is required to produce a fresh increment of sensation, and how soon the time must arrive when the organ of sense, like the machine, will break down under the strain rather than admit of being goaded farther. The result of all this is, that although the senses may perceive very small stimuli, and can endure very large ones without suffering damage, the number of units in the scale of sensation is comparatively small. The hugest increase of good fortune will not make a man who is already well off many degrees happier than before; the utmost torture that can be applied to him will not give much greater 1893.] on The Just-Perceptible Difference. 15 pain than lie has already sometimes suffered. The experience of a life that we call uneventful usually includes a large share of the utmost possible range of human pleasures and human pains. Thus the physiological law which is expressed by Weber's formula is a great leveller, by preventing the diversities of fortune from creating by any means so great a diversity in human happiness. The least-perceptible difference varies considerably in different persons, delicacy of perception being a usual criterion of superiority of nature. The sense of pain is curiously blunt in idiots. It varies also in the same person with his health, and extraordinarily so in hysteria and hypnotism, at which times sensitivity is sometimes almost absent, and at other times exceptionally acute. It is somewhat affected by drugs. Thus Dr. Lauder Brunton writes concerning strychnine, that when taken in small doses for a long time, the im- pressions are felt more keenly and are of longer duration. The sense of touch is rendered more acute; the field of vision is increased, distant objects are more distinct, and the sense of hearing is sharpened. (Pharmacology, 1885, p. 888.) Other drugs or intoxicants may yet be discovered and legitimately used to heighten the sensitivity, or indeed any other faculty during a brief period, in order to perform that which could not otherwise be performed at all, at the cheap price of a subsequent period of fatigue. Measure of the Imagination. — The first perceptible sensation is seldom due to a solitary stimulus. Internal causes of stimulation are in continual activity, whose effects are usually too faint to be per- ceived by themselves, but they may combine with minute external stimuli, and so produce a sensation which neither of them could have done singly. I desire now to draw attention to another concurring cause which has hitherto been unduly overlooked, or only partially allowed for under the titles of Expectation and Attention. I mean the Imagination, believing that it should be frankly recognised as a frequent factor in the production of a just-perceptible sensation. Let us reflect for a moment on the frequency with which the imagination produces effects that actually overpass the threshold of consciousness, and give rise to what is indistinguishable from, and mistaken for, a real sensation. Every one has observed instances of it in his own person and in those of others. Illustrations are almost needless; I may, however, mention one as a reminder ; it was current in my boyhood, and the incident probably took place not many yards from where I now stand. Sir Humphry Davy had recently discovered the metal potassium, and showed specimens of it to the greedy gaze of a philosophical friend as it lay immersed in a dish of alcohol to shield it from the air, explaining its chemical claim to be considered a metal. All the known metals at that time were of such high specific gravity that weight was commonly considered to be a peculiar characteristic of metals ; potassium, however, is lighter than water. The philosopher not being aware of this, but convinced as to its metallic nature by the reasoning of Sir Humphry, fished a piece out 16 Mr. Francis Galton [Jan. 27, of the alcohol, and, weighing it awhile between his finger and thumb, said seriously, as in further confirmation, " How heavy it is ! " In childhood the imagination is peculiarly vivid, and notoriously leads to mistakes, but the discipline of after life is steadily directed to checking its vagaries and to establishing a clear distinction between fancy and fact. Nevertheless, the force of the imagination may endure with extraordinary power and even be cherished by persons of poetic temperament, on which point the experiences of our two latest Poets-Laureate, Wordsworth and Tennyson, are extremely instructive. Wordsworth's famous " Ode to Immortality " contains three lines which long puzzled his readers. They occur after his grand description of the glorious imagery of childhood, and the " perpetual benediction " of its memories, when he suddenly breaks off into — " Not for these I raise The song of thanks and praise, But for those obstinate questionings Of sense and outward things, Fallings from us, vanishings," &c. Why, it was asked, should any sane person be " obstinately " disposed to question the testimony of his senses, and be peculiarly thankful that he had the power to do so ? What was meant by the " fallings off and vanishings," for which he raises his " song of thanks and praise " ? The explanation is now to be found in a note by Wordsworth himself, prefixed to the ode in Knight's edition. Words- worth there writes, " I was often unable to think of external things as having external existence, and I communed with all I saw as something not apart from, but inherent in, my own immaterial nature. Many times while going to school have I grasped at a wall or tree to recall myself from this abyss of idealism to the reality. At that time I was afraid of such processes. In later times I have deplored, as we all have reason to do, a subjugation of an opposite character, and have rejoiced over the remembrances, as is expressed in the lines 1 Obstinate questionings,' &c." * He then gives those I have just quoted. It is a remarkable coincidence that a closely similar idea is found in the verses of the successor of Wordsworth, namely, the great poet whose recent loss is mourned by all English-speaking nations, and that a closely similar explanation exists with respect to them. For in Lord Tennyson's " Holy Grail " the aged Sir Percivale, then a monk, recounts to a brother monk the following wrords of King Arthur : — " Let visions of the night or of the day Come, as they will; and many a time they come Until this earth he walks on seems not earth, This light that strikes his eyeball is not light, The ah- that smites his forehead is not air, But vision," &c. * Knight's edition of Wordsworth, vol. iv. p. 47. 1893.] on The Just- Perceptible Difference. 17 Sir Percivale concludes just as Wordsworth's admirers formerly had done : " I knew not all he meant." Now, in the Nineteenth Century of the present month Mr. Knowles, in his article entitled " Aspects of Tennyson," mentions a conversa- tional incident curiously parallel to Wordsworth's own remarks about himself : — " He [Tennyson] said to me one day, * Sometimes as I sit alone in this great room I get carried away, out of sense and body, and rapt into mere existence, till the accidental touch or movement of one of my own fingers is like a great shock and blow, and brings the body back with a terrible start.' " Considering how often the imagination is sufficiently intense to mimic a real sensation, a vastly greater number of cases must exist in which it excites the physiological centres in too feeble a degree for their response to reach to the level of consciousness. So that if the imagination has been anyhow set into motion, it shall, as a rule, originate what may be termed incomplete sensations, and whenever one of these concurs with a real sensation of the same kind, it would swell its volume. This supposition admits of being submitted to experiment by comparing the amount of stimulus required to produce a just-per- ceptible sensation, under the two conditions of the imagination being either excited or passive. Several conditions have to be observed in designing suitable experiments. The imagined sensation and the real sensation must be of the same quality ; an expected scream and an actual groan could not reinforce one another. Again, the place where the ima^e is localised in the theatre of the imagination must be the same as it is in the real sensation. This condition requires to be more carefully regarded in respect to the visual imagination than to that of th© other senses, because the theatre of the visual imagination is described by most persons, though not by all, as internal, whereas the theatre of actual vision is external. The important part played by points of reference in visual illusions is to be explained by the aid they afford in compelling the imaginary figures to externalise themselves, super- imposing them on fragments of a reality. Then the visualisation and the actual vision fuse together in some parts, and supplement each other elsewhere. The theatre of audition is by no means so purely external as that of sight. Certain persuasive tones of voice sink deeply, as it were, into the mind, and even simulate our own original sentiments. The power of localising external sounds, which is almost absent in those who are deaf with one ear, is very imperfect generally, otherwise the illusions of the ventriloquist would be impossible. There was an account in the newspapers a few weeks ago of an Austrian lady of rank who purchased a parrot at a high price, as being able to repeat the Paternoster in seven different languages. She took the bird home, but it was mute. At last it was discovered that the apparent performances of the parrot had been due to the ventriloquism of the Vol. XTV (No. 87.) o 18 Mr. Francis Galton [Jan. 27 dealer. An analogous trick upon the sight could not be performed by a conjuror. Thus he could never make his audience believe that the floor of the room was the ceiling. As regards the other senses, the theatre of the imagination coin- cides fairly well with that of the sensations. It is so with taste and smell, also with touch, in so far that an imagined impression or pain is always located in some particular part of the body, then if it be localised in the same place as a real pain it must coalesce with it. Finally, it is of high importance to success in experiments on Imagination that the object and its associated imagery should be so habitually connected that a critical attitude of the mind shall not easily separate them. Suppose an apparatus arranged to associate the waxing and waning of a light with the rising and falling of a sound, holding means in reserve for privately modifying the illumi- nation at the will of the experimenter, in order that the waxing and waning may be lessened, abolished, or even reversed. It is quite possible that a person who had no idea of the purport of the experi- ment might be deceived, and be led by his imagination to declare that the light still waxed and waned in unison with the sound after its ups and downs had been reduced to zero. But if the subject of the experiment suspected its object, he would be thrown into a critical mood ; his mind would stiffen itself, as it were, and he would be difficult to deceive. Having made these preliminary remarks, I will mention one only of some experiments I have made and am making from time to time, to measure the force of my own imagination. It happens that although most persons train themselves from childhood upwards to distinguish imagination from fact, there is at least one instance in which we do the exact reverse, namely, in respect to the auditory presentation of the words that are perused by the eye. It would be otherwise impossible to realise the sonorous flow of the passages, whether in prose or poetry, that are read only with the eyes. We all of us value and cultivate this form of auditory imagination, and it commonly grows into a well-developed faculty. I infer that when we are listening to the words of a reader while our eyes are simultane- ously perusing a copy of the book from which he is reading, that the effects of the auditory imagination concur with the actual sound, and produce a stronger impression than the latter alone would be able to make. I have very frequently experimented on myself with success, with the view of analysing this concurrent impression into its constituents, being aided thereto by two helpful conditions, the one is a degree of deafness which prevents me when sitting on a seat in the middle rows from following memoirs that are read in tones suitable to the audience at large ; and the other is the accident of belonging to societies in which unrevised copies of the memoirs that are about to be read, usually in a monotonous voice, are obtainable, in order to be perused simultaneously by the eye. Now it sometimes happens that 1893.] on The Just-Perceptible Difference. 19 portions of these papers, however valuable they may be in themselves, do not interest me, in which case it has been a never-flagging source of diversion to compare my capabilities of following the reader when I am using my eyes, and when I am not. The result depends some- what on the quality of the voice ; if it be a familiar tone I can imagine what is coming much more accurately than otherwise. It depends much on the phraseology, familiar words being vividly re- presented. Something also depends on the mood at the time, for imagination is powerfully affected by all forms of emotion. The result is that I frequently find myself in a position in which I hear every word distinctly so long as they accord with those I am perusing, but whenever a word is changed, although the change is perceived, the new word is not recognised. Then, should I raise my eyes from the copy, nothing whatever of the reading can be under- stood, the overtones by which words are distinguished being too faint to be heard. As a rule, I estimate that I have to approach the reader by about a quarter of the previous distance, before I can distinguish his words by the ear alone. Accepting this rough estimate for the purposes of present calculation, it follows that the potency of my hearing alone is to that of my hearing plus imagina- tion as the loudness of the same overtones heard at 3 and at 4 units of distance respectively ; that is as about 32 to 42, or as 9 to 16. Consequently the potency of my auditory imagination is to that of a just-perceptible sound as 16 — 9 to 16, or as 7 units to 16. So the effect of the imagination in this case reaches nearly half-way to the level of consciousness. If it were a little more than twice as strong it would be able by itself to produce an effect indistinguishable from a real sound. Two copies of the same newspaper afford easily accessible materials for making this experiment, a few words having been altered here and there in the coj>y to be read from. I will conclude this portion of my remarks by suggesting that some of my audience should repeat these experiments on themselves. If they do so, I should be grateful if they would communicate to me their results. Optical Continuity. — Keenness of sight is measured by the angular distance apart of two dots when they can only just be distinguished as two, and do not become confused together. It is usually reckoned that the normal eye is just able or just unable to distinguish points that lie one minute of a degree asunder. Now, one minute of a degree is the angle subtended by two points, separated by the 300th part of an inch, when they are viewed at the ordinary reading distance of one foot from the eye. If, then, a row of fine dots touching one another, each as small as a bead of one 300th part of an inch in diameter, be arranged on the page of a book, they would appear, to the ordinary reader to be an almost invisibly fine and continuous line. If the dots be replaced by short cross strokes, the line would look broader, but its apparent continuity would not be affected. It is im- c 2 20 Mr. Francis Gallon [Jan. 27, possible to draw any line that shall commend itself to the eye as possessing more regularity than the image of a succession of dots or cross strokes, 300 to the inch, when viewed at the distance of a foot. Every design, however delicate, that can be drawn with a line of uniform thickness by the best machine or the most consummate artist, admits of being mimicked by the coarsest chain, when it is viewed at such a distance that the angular length of each of its links shall not exceed one minute of a degree. One of the apparently smoothest outlines in nature is that of the horizon of the sea during ordinary weather, although it is formed by waves. The slopes of debris down the sides of distant mountains appear to sweep in beautifully smooth curves, but on reaching those mountains and climbing up the debris, the path may be exceedingly rough. The members of an audience sit at such various distances from the lecture table and screen that it is not possible to illustrate as well as is desirable the stages through which a row of dots appears to run into a continuous line, as the angular distance between the dots is lessened. I have, however, hung up chains and rows of beads of various degrees of coarseness. Some of these will appear as pure lines to all the audience ; others, whose coarseness of structure is obvious to those who sit nearest, will seem to be pure lines when viewed from the farthest seats. Although 300 dots to the inch are required to give the idea of perfect continuity at the distance of one foot, it will shortly be seen that a much smaller number suffices to suggest it. The cyclostyle, which is an instrument used for multiple writing, makes about 140 dots to the inch. The style has a minute spur- wheel or roller, instead of a point ; the writing is made on stencil paper, whose surface is covered with a brittle glaze. This is per- forated by the teeth of the spur-w7heel wherever they press against it. The half perforated sheet is then laid on writing paper, and an inked roller is worked over the glaze. The ink passes through the per- forations and soaks through them on to the paper below ; consequently the impression consists entirely of short and irregular cross bars or dots. I exhibit on the screen a circular letter summoning a committee, that was written by the cyclostyle. The writing seems beautifully regular when the circular is photographically reduced ; when it ia. enlarged, the discontinuity of the strokes becomes conspicuous. Thus, I have enlarged the word the six times ; the dots can then be easily seen and counted. There are 42 of them in the long stroke of the letter h. The appearance of the work done by the cyclostyle would be greatly improved if a fault in its mechanism could be removed, which causes it to run with very unequal freedom in different directions. It leaves an ugly, jagged mark wherever the direction of a line changes suddenly. A much coarser representation of continuous lines is given by 1893.] on The Just-Perceptible Difference. 21 embroidery and tapestry, and coarser still by those obsolete school samplers which our ancestresses worked in their girlhood, with an average of about sixteen stitched dots to each letter. Perhaps the coarsest lettering, or rather figuring, that is ever practically em- ployed is used in perforating the books of railway coupons so familiar to travellers. Ten or eleven holes are used for each figure. A good test of the degree of approximation with which a cyclostyle making 140 perforations to the inch is able to simulate continuous lines, is to use it for drawing outline portraits. I asked the clerk who wrote the circular just exhibited to draw me a few profiles of different sizes, ranging from the smallest scale on which the cyclostyle could produce recognisable features, up to the scale at which it acted fairly well. I submit some specimens of the result. The largest is a portrait of ltj inches in height, by which facial characteristics are fairly well conveyed ; somewhat better than by the rude prints that appear occasionally in the daily papers. It is formed by 366 dots. A medium size is £ inch high and contains 177 dots, and would be tolerable if it were not for the jagged strokes already spoken of. The smallest sizes are ^ inch high and contain about 90 dots ; they are barely passable, on account of the jagged flaws, even for the rudest portraiture. I made experiments under fairer conditions than those of the cyclostyle, to learn how many dots, discs, or rings per inch were really needed to produce a satisfactory drawing, and also to discover how far the centres of the dots or discs might deviate from a strictly smooth curve without ceasing to produce the effect of a flowing line. It must be recollected that the eye can perceive nothing finer than a minute blur of one 300th part of an inch in angular diameter. If we represent a succession of such blurs by a chain of larger discs, it will be easily recognised that a small want of exactitude in the alignments of the successive discs must be unimportant. If one of them is pushed upwards a trifle and another downwards, so large a part of their respective areas still remains in line, that when the several discs become of only just perceptible magnitude, the projecting portion will be wholly invisible. When the discs are so large as to be plainly perceptible, the alignment has to be proportionately more exact. After a few trials it seemed that if the bearing of the centre of each disc from that of its predecessor which touched it, was correctlv given to the nearest of the 16 principal points of the compass, N., NNE., NE., &c, it was fairly sufficient. Consequently a simple record of the successive bearings of each of a series of small equidistant steps is enough to define a curve. The briefest way of writing down these bearings is to assign a separate letter of the alphabet to each of them, a for north (the top of the paper counting as north), 6 for north-north-east, c for north- east, and so on in order up to p. This makes e represent east, i south, and m west. To test the efficiency of the plan, I enlarged one of the cylostyle 22 Mr. Francis Gallon [Jan. 27, profiles, and making a small protractor with a piece of tracing paper, rapidly laid down a series of equidistant points on the above principle, noting at the same time the bearing of each from its predecessor. I thereby obtained a formula for the profile, consisting of 271 letters. Then I put aside the drawing, and set to work to reproduce it solely from the formula. I exhibit the result ; it is fairly successful. Emboldened by this first trial, I made a more ambitious attempt, by dealing with the profile of a Greek girl copied from a gem. I was very desirous of learning how far the pure outline of the original admitted of being mimicked in this rough way. The result is here ; a ring has been painted round each dot in order to make its position clearly seen, without obliterating it. The repro- duction has been photographically reduced to various different sizes. That which contains only fifty dots to the inch, which is consequently six times as coarse as the theoretical 300 to an inch, is a very creditable production. Many persons to whom this portrait has been shown, failed to notice the difference between it and an ordinary woodcut. The medium size, and much more the smallest size, would deceive anybody who viewed them at the distance of one foot. The protractor used in making them was a square card with a piece cut 1893.] on The Just-Perceptible Difference. 23 out of its middle, over which transparent tracing paper was pasted. A small hole of about J of an inch in diameter was punched out of the centre of the tracing paper ; sixteen minute holes just large enough to allow the entry of the sharp point of a hard lead-pencil were perforated through the tracing paper in a circle round the centre of the hole at a radius of ^ inch. They corresponded to the sixteen princi- pal points of the compass, and had their appropriate letters written by their sides. The outline to be formulated was fixed to a drawing- board, with a T rule laid across it as a guide to the eye in keeping the protractor always parallel to itself. The centre of the small hole was then brought over the beginning of the outline, and a dot was made with the pencil through the perforation nearest to the further course of the outline, and this became the next point of departure. While moving the protractor from the old point to the new one it was stopped on the way, in order that the letter for the bearing might be written through the central hole. These were afterwards copied on a separate piece of paper. A clear distinction must be made between the proposed plan and that of recording the angle made by each step from the preceding one. In the latter case, any error of bearing would falsify the direction of all that followed, like a bend in a wire. The difficulties of dealing with detached portions of the drawing, such as the eye, were easily surmounted by employing two of the spare letters, R and S, to indicate brackets, and other spare letters to indicate points of reference. The bearings included between an R and an S were taken to signify directive dots, not to be inked in. The points of reference indicated by other letters are those to which the previous bearing leads, and from which the next bearing departs. Here is the formula whence the eye was drawn. It includes a very small part of the profile of the brow, and the directive dots leading thence to the eye. The letters should be read from the left to the right, across the vertical lines. They are broken into groups of five, merely for avoiding confusion and for the convenience of after reference. The part of the Profile that includes U &c. iiiilU jiihi &c. &c. The Eye. URkkk kklll mSVap ponmn mmimm mlmlm UmZZ VnTnn mnmmm nmimlm mmnZZ Tjjjj jjkkc chinmn mnun onooZ Letters used as Symbols. R....S = (....)• Z=end. U, V, T are points of reference. By succeeding in so severe a test case as this Greek outline, it 24 Mr. Francis Gallon [Jan. 27, may be justly inferred that rougher designs can be easily dealt with in the same way. At first sight it may seem to be a silly waste of time and trouble to translate a drawing into a formula, and then, working backwards, to retranslate the formula into a reproduction of the original drawing, but further reflection shows that the process may be of much practical utility. Let us bear two facts in mind, the one is that a very large quantity of telegraphic information is daily published in the papers, anticipating the post by many days or weeks. The other is that pictorial illustrations of current events, of a rude kind, but acceptable to the reader, appear from time to time in the daily papers. We may be sure that the quantity of telegraphic intelligence will steadily increase, and that the art of newspaper illustration will improve and be more resorted to. Important local events frequently occur in far- off regions, of which no description can give an exact idea without the help of pictorial illustration ; some catastrophe, or site of a battle, or an exploration, or it may be some design or even some portrait. There is therefore reason to expect a demand for such drawings as these by telegraph, if their expense does not render it impracticable to have them. Let us then go into details of expense, on the basis of the present tariff from America to this country, of one shilling per word, 5 figures counting as one word, cypher letters not being sent at a corresponding rate. It requires two figures to per- form each of the operations described above, which were performed by a single letter. So a formula for 5 dots would require 10 figures, which is the telegraphic equivalent of 2 words ; therefore the cost for every 5 dots telegraphed from the United States would be 2 shillings, or 21. for every 100 dots or other indications. In the Greek outline there is a total of 400 indications, including those for directive dots, and for points of reference. The transmis- sion of these to us from the United States would cost 81. I exhibit a map of England made with 248 dots, as a specimen of the amount of work in plans, which could be effected at the cost of 5Z. It is easy to arrange counters into various patterns or parts of patterns, learning thereby the real power of the process. The expense of pictorial telegraphs to foreign countries would be large in itself, but not large relatively to the present great expenditure by newspapers on tele- graphic information, so the process might be expected to be employed whenever it was of obvious utility. The risk is small of errors of importance arising from mistakes in telegraphy. I inquired into the experience of the Meteorological Office, whose numerous weather telegrams are wholly conveyed by numerical signals. Of the 20,625 figures that were telegraphed this year to the office from continental stations, only 49 seem to have been erroneous, that is two and a third per thousand. At this rate the 800 figures needed to telegraph the Greek profile would have been liable to two mistakes. A mistake in a figure would have exactly the same effect on the outline as a rent in the paper on which 1893.] on Tie Just-Perceptible Difference. 25 a similar outline had been drawn, which had not been pasted together again with perfect precision. The dislocation thereby occasioned would never exceed the thickness of the outline. The command of 100 figures from 0 to 99, instead of only 26 letters, puts 74 fresh signals at our disposal, which would enable us to use all the 32 points of the compass, instead of 16, and to deal with long lines and curves. I cannot enter into this now, nor into the control of the general accuracy of the picture by means of the distances between the points of triangles each formed by any three points of reference. Neither need I speak of better forms of pro- tractor. There is one on the table by which the ghost of a compass card is thrown on the drawing. It is made of a doubly refracting image of Iceland spar, which throws the so-called " extraordinary " image of the compass card on to the ordinary image of the drawing, and is easy to manipulate. All that I wish now to explain is that this peculiar application of the law of the just-perceptible difference to optical continuity gives us a new power that has practical bearings. Postscript. — A promising method for practical purposes that I have tried, is to use " sectional " paper ; that is, paper ruled into very small squares, or else coarse cloth, and either to make the drawing upon it, or else to lay transparent sectional paper or muslin over the drawing. Dots are to be made at distances not exceeding three spaces apart, along the course of the outline, at those intersections of the ruled lines (or threads) that best accord with the outline. Each dot in succession is to be considered as the central point, numbered 44 in the following 11 21 31 41 51 61 71 12 22 32 42 52 62 72 13 23 33 43 53 63 73 14 24 34 44 54 61 74 15 25 35 45 55 65 75 16 26 36 46 56 66 76 17 27 37 47 57 67 77 schedule, and the couplet of figures corresponding to the portion of the next dot is to be written with a fine-pointed pencil in the interval between the two dots. These are subsequently copied, and make the formula. By employing 4 for zero, the signs + and — are avoided ; 3 standing for —1, 2 for —2, and 1 for —3. The first figure in each couplet defines its horizontal coordinate from zero ; the second figure, its vertical one. Thus any one of 49 different points are indi- cated, corresponding to steps from zero of 0, + 13 + 2, and + o 26 Mr. F. Galton on The Just-Perceptible Difference, [Jan. 27, intervals, in either direction, horizontal or vertical. Half an hour's practice suffices to learn the numbers. The figures 0, 8, and 9 do not enter into any of the couplets in the schedule, the remaining 51 couplets in the complete series of 100 (ranging from 00 to 99), con- tain 21 cases in which 0, 8, or 9 forms the first figure only ; 21 cases in which one of them forms the second figure oniy ; and 9 cases in which both of the figures are formed by one or other of them. These latter are especially distinctive. This method has five merits — medium, short, or very short steps can be taken according to the character of the lineation at any point ; there is no trouble about orientation ; the bearings are defined without a protractor, the work can be easily revised, and the correctness of the records may be checked by comparing the sums of the successive small co-ordinates leading to a point of reference, with their total value as read off directly. A method of signalling is also in use for military purposes, in which positions are fixed by co-ordinates, afterwards to be connected by lines. [F. G.] 1893.1 Mr. Alexander Siemens on Electrical Science. 27 WEEKLY EVENING MEETING, Friday, February 3, 1893. Sir Frederick Abel, K.C.B. D.C.L. F.R.S. Vice-President, in the Chair. Alexander Siemens, Esq. M.Inst.C.E. M.B.I. Theory and Practice in Electrical Science. (With Experimental Illustrations.} When I was requested to give a Friday evening discourse at this Institution, I felt very much honoured at having an opportunity of speaking to an audience that has listened to so many illustrious men of science. At the same time I felt that instead of selecting a purely scientific subject I should be more likely to interest you if I drew your attention to some illustrations of the way in which science is applied to practice. The tendency of our century, and especially of the latter half, has been to obliterate ancient distinctions, and to break down barriers which formerly were held to be insurmountable. In this resjDect I need only remind you that at one time, in chemistry, substances were divided into acids and bases, into metals and metalloids, and that until very lately in physics, some gases were classed by themselves as being permanent, and soon. All of these distinctions have been found untenable in the light of modern research, and in a similar manner the strict divisions maintained for a long time between different branches of science have been more and more abolished, so that nowadays anybody who wishes to excel in any one branch of science ought to possess solid knowledge of the principles of all the others. One of the most important barriers broken down by the spirit of our times is that formerly held up between science and practice, and the state of mind in which a learned professor once exclaimed about his own particular branch of science : " Thank goodness, there is no practical application of it possible," is more and more forgotten. Instead of that, endeavours are now made on all sides to turn to practical account all scientific investigations. While quite admitting that it would give much cause for regret if this tendency were developed too far, so as to interfere with the pro • gress of purely scientific researches, it cannot be denied that the application of scientific principles has brought about that immense progress which is characteristic of the last half-century. A conspicu- ous example of the influence of applied science is furnished by the way the use of electricity has been introduced into our daily life, and 28 Mr. Alexander Siemens [Feb. 3, several causes have contributed to facilitate the scientific treatment of electrical problems. Not the least among these is the circumstance that at first electricity could not be produced at a cheap rate for general commercial uses. Thus it came about that telegraphy, for which weak currents are sufficient, was for a long time the only practical application, and during this period of comparative quiet a number of the most eminent scientific philosophers devoted their time to discover the characteristic features of this great power in nature, and the laws which it obeys. The consequence has been that at the time when the discovery of the dynamo-electric principle made cheap electricity a possible commodity, the laws on which electric currents act were thoroughly understood, and the development of the intro- duction of electrical appliances could take place on the firm basis of scientific knowledge. The obligations that electrical engineers owe to science they have acknowledged in a practical manner in naming the units by which electricity is measured after the learned men who created the science of electricity. The circumstance that it is possible to reproduce perfectly the exact conditions for which electrical apparatus have been designed, has much facilitated the direct application of laboratory experiments to practical problems. It is, for instance, quite feasible to take a small quantity of ore, to subject it in a laboratory to chemical and electrical treatment, and to judge from the results whether it will be possible to design works for the treatment of such ores in large quantities on the same lines. As far as electricity is concerned it is possible in such cases to predict with absolute accuracy how much energy is wanted in each case to deposit a given quantity of metal in a given time. The electrical engineer is thus enabled to arrive, in a comparatively easy and inexpensive manner, at reliable data, which in other branches of applied science have to be obtained by costly ex- periments on a large scale. One of the most striking instances of the direct application of scientific researches to practical purposes has been furnished by Dr. John Hopkinson, who explained in his lecture before the Institution of Civil Engineers in the year 1883, how he had been led by mathe- matical considerations to infer that alternate-current machines could be run in parallel, and what conditions were necessary to secure success. Ris conclusions were tried shortly afterwards at the South Foreland Lighthouse, and have proved since to be of the utmost value for central electric lighting stations on the alternate-current system. For the sake of historical accuracy I should mention, perhaps, that Dr. John Hopkinson called attention in the following year to a communication to the Royal Society by Mr. Wilde, who bad previously demonstrated the possibility of working alternators in parallel; yet the facts just related are an apt illustration of the point I desired to lay before you. While science is a safe guide for the engineer, and will warn him 1893. on Theory and Practice in Electrical Science. 29 of the mistakes and fallacies which ought to be avoided, there are sometimes other considerations which will modify to an important I bO d ;5 <§» degree conclusions based on scientific principles alone. As an example, the case of heating by electricity may be cited. The scien- 30 Mr. Alexander Siemens [Feb. 3, tific data in connection with this problem are as follows : A kilo- gram of coal burnt to best advantage will give 8080 calories. The same amount of coal consumed in a boiler will produce steam sufficient for 1 H.P. for 1 hour, and this horse-power can generate electricity at the rate of 660 watts, or about 570 calories, per hour. Assuming that in heating by burning coal, only a quarter of the theoretical effect is attained, and taking the price of coal at 20s. per ton, while the cost of a Board of Trade unit of electricity is 8d., it would appear that a farthings worth of coal will produce as much heat as 2 2d. worth of electricity. These figures apply to the conditions of life in London, where fuel is abundant and power comparatively expensive ; elsewhere, in Norway for instance, fuel may be expensive, and power, in the shape of waterfalls, cheap. Under such altered conditions electricity may with advantage be employed for heating purposes, by producing it with the aid of water-power, and utilising the heat generated by it, in special appliances. One of the most important industries of Norway is the making of horseshoe nails, for which special machines have been constructed, into which a heated rod of iron has to be fed. For this purpose the rod is passed through a charcoal fire, placed close to the nail-making machine, and a great deal of difficulty is experienced in maintaining the rod at an even and suitable temperature. The apparatus placed in front of you is designed to replace these charcoal fires, and its con- struction is shown by the diagram on the wall. The essential part of it is a hollow carbon, through which a current of electricity is sent, heating the carbon to any desired temperature. In this appa- ratus, a current of 400 amperes and 5 volts is used, equal to 2 Board of Trade units per hour, which is supplied from a transformer, the primary circuit of which is connected to the high-pressure mains of the London Electric Supply Company. A diagram of the connec- tions showrs that the two wires connected to the supply main are led to a commutator on the table, by wrhich the current can either be sent to the transformer of the heating apparatus, or to another one, which will be mentioned later on. In order to prevent loss of heat by radiation, the carbon is placed in a box filled with sand, and the necessary precautions are taken to let the current pass through the carbon only. After the carbon has become white hot, a rod of iron, in passing through it, is rapidly heated, and the temperature it attains depends on the speed at which it is fed forward. It would have been very inconvenient to bring a nail-making machine here. With your permission, I will therefore ask Mr. Williamson, who designed the apparatus, to show us how to make spiral steel springs. By the side of the nail-rod heater stands a similar apparatus for the heating of rivets, which is also illustrated by a diagram, and will be shown in action. It is obvious that such an apparatus can be used in many places 1893/ Theory and Practice in Electrical Science. 31 where a coal-fire would be dangerous, and that, considering the waste of fuel in the usual rivet-heating, it probably will be more economical in cost, especially where electric lighting plant is E3 •" 32 Mr. Alexander Siemens [Feb. 3, The ingenious way in which Mr. Crompton has utilised the heating effect of electric currents for cooking purposes has no doubt been admired by most of you at the Crystal Palace Exhibition last year ; and when we remember that these cooking utensils consume fuel only during the time they are actually in use, and that they can be put in and out of action at a moment's notice, we cannot doubt Diagram 3. Rivet-heating. that these and many other obvious advantages will facilitate their introduction in spite of the figures, as to cost, given by the scientific data. Of late the transmission of power by electricity has occupied a very prominent place in the public interest, and the project of utilising the force of the Niagara Falls at distant towns is as closely discussed as the plan of constructing long railways on which trains are to run at fabulous speeds. As you will hear a discourse on electric railways in three weeks from to-day, I will not take up your time with this branch of the subject, but will rather draw your attention to the distribution of power by electricity from a central generating station. Before entering further into this, let me remind you that the earliest magneto-electric machines were used nearly sixty years ago for the production of power. I will mention only Jacobi's electric launch of 1835 as an example ; it must, therefore, be considered altogether erroneous to ascribe the invention of the transmission of power to an accident at the Vienna Exhibition in 1873, when, it is said, an attendant placed some stray wires into the terminals of a dynamo- machine ; it began to turn, and the transmission of power was first demonstrated. As a matter of fact, Sir William Siemens once informed me that his brother Werner was led to the discovery of the dynamo-electric 1893.] on Theory and Practice in Electrical Science. 83 principle by the consideration that an electro-magnetic machine behaved like a magneto-electric machine, when a current of electricity was sent into it, viz. both turn round and give out power. It was, of course, well known that a magneto-electric machine produces a current of electricity when turned by mechanical power, and Werner concluded that an electro-magnetic machine would behave in the same manner. We all know that he was right, but I relate this circumstance only as a further proof that the generation of power by electric currents had been a well-known fact long previous to the Vienna Exhibition. Another well-known instance of transmission of power to a distance is furnished by the magneto-electric ABC telegraph instruments, where the motion at the sending end supplies the currents necessary to move the indicator at the receiving station. As an illustration of the distribution of power by electricity I will briefly describe some radical alterations that have been made at the works of Messrs. Siemens Brothers and Co. by the introduction of electric motors in the place of steam engines. The diagram on the wall shows in outline the various buildings in which work of different kinds is carried on with the help of different machines. Electric motors are supplying the power, sometimes by driving shafting to which a group of tools is connected by belting, and sometimes by being coupled direct to the moving mechanism. Each section of the works has its own meter measuring the energy that is used there, and all of them are connected by underground cables to a central station, where three sets of engines and dynamos generate the electric current for all purposes. There are two Willans and one Belliss steam engines, each of 300 I.H.P., coupled direct to the dynamos and running at a speed of 350 revolutions per minute. Eoom is left for a fourth set ; but, including some auxiliary pumps and the switchboards for controlling the dynamos and for distributing the current, the whole space occupied by 1200 horse-power measures only 32 by 42 feet. Close by are the condensers and three high-pressure boilers, which have replaced some low-pressure ones formerly used for some steam engines driving the machinery in the nearest building. The advantages that have been secured by the introduction of electric motors may be briefly stated under the following heads : — 1. Various valuable spaces formerly occupied by steam engines and boilers have been made available for the extension of workshops, and these are indicated on the diagram by shading. 2. By abolishing to a great extent the mechanical transmission of power a considerable saving is effected in motive power, which is especially noticeable at times when part only of the machinery is in use. 3. As the electric motors take only as much current as is actually required for the work they are doing, a further saving is effected and Vol. XIV. (No. 87.) d 34 Mr. Alexander Siemens [Feb. at the same time the facility with which the speed of the motors can be altered without their interfering with each other, presents a feature that is absent from mechanical transmission. a 09 m bo OB P QQQO. ni M L m\ r.iq 1893.] on Theory and Practice in Electrical Science. 86 4. The big steam engines, being compound and condensing, pro> duce a horse-power with a smaller consumption of fuel than the small high-pressure steam engines scattered throughout the works. 5. The numerous attendants of the old steam engines and boilers have mostly been transferred to other work ; only a few of them are required at the central station, and one or two men can easily look after all the electric motors used in the various parts of the works. Elsewhere, equally favourable results have been obtained by the introduction of electrical distribution of power, and in this respect I bog to refer you to a paper read before the German Institution of Civil Engineers by Mr. E. Hartmann in April of last year, and to a paper read by Mr. Castermans before the Society of Engineers in Liege in August last, in which he compares in detail various methods of transmission of power, of which the electrical one was adopted for a new small arms factory. We may, therefore, take it for granted that the advantages alluded to above have not resulted from local circumstances at Wool- wich, but that they can be realised anywhere by the adoption of the electric current for distributing power from a central station. At first sight this result appears to be of interest only to the manu- facturer, but the development of this idea may lead to far-reaching consequences when we consider that cheap power is one of the most important requisites for cheap production. You can see on the diagram that the various buildings are separated by roads, and we can easily imagine that in each of them an independent owner carries on work, so that the diagram represents part of a manufacturing town. While power was generated by steam engines, the cost of pro- ducing one horse-power varied a good deal in the different parts, and the various owners could not have obtained their power on equal terms, those possessing the largest steam engines having a distinct advantage. This inequality is done away with altogether when the power is distributed by electricity, as the current can be supplied for large or small powers at the same rate per Board of Trade unit. It is therefore clear that the establishment of central stations for the generation of electricity on a large scale will bring about the possi- bility of small works competing with large works in quite a number of trades, where cheap power is of the first consideration. Another circumstance favouring small works is the diminution of capital outlay brought about by the employment of electric motors. Not only are the motors cheaper than boilers and steam-engines of corresponding power would be, but the outlay for belting and shafts is saved, and the structure of the building need not be as substantial as is necessary where belts and shafting have to be supported by it. A commencement has already been made in this direction by the starting of electric light stations, where the owners do all in their power to encourage the use of the current in motors in order to keep the machinery at their central station more uniformly at work. The introduction of electricity as motive power will apparently 36 Mr. Alexander Siemens [Feb. 3, present a strong contrast to the effect steam has had on the develop- ment of industries for the reasons already stated ; and, in addition, there are many cases where the erection of boilers and steam engines, or even of gas engines, would be inadmissible on account of want of space or of the nuisances that are inseparable from them. Motive power will, therefore, be available in a number of instances where up to the present time no mechanical power could be used, but the work had to be done by manual labour or not at all. You may have noticed that I have confined my remarks hitherto to the case of distributing electricity over a limited area, but that I have not yet discussed the question of transmitting power to a great distance. Theoretically we have been told over and over again that the motive power of the future will be supplied by waterfalls, and that their power can be made available over large areas by means of electric currents. As a prominent example, the installation is con- stantly mentioned by which the power of a turbine at Lauffen was transmitted over a distance of 1 10 statute miles to the Frankfurt Exhibition with an efficiency of 75 per cent. No doubt this result is very gratifying from a purely scientific point of view, but, unfortu- nately, in practical life only commercially successful applications of science will have a lasting influence, and in this respect the Lauffen installation left much to be desired. On the one hand science tells us that the section of the conductor can be diminished as the pressure of electricity is increased, and it appears to be only necessary to construct apparatus for generating electricity at a sufficiently high pressure so as to reduce the cost of a long conductor to reasonable limits. On the other hand, experience shows that at these high potentials the insulation of the electric current becomes a most difficult problem, and for practical purposes difficulty means an increased outlay of money. As an illustration of the difficulties encountered in the employment of high-tension currents, I can demonstrate to you that many of the insulating materials em- ployed with success for low-pressure currents break down under the strain of high-pressure electricity. For the purpose of these experiments the current of electricity delivered by the street main at a pressure of 2400 volts is diverted to a large transformer placed on the ground-floor, and from there it is led through a twin cable to this room at a pressure which can be in- creased up to 50,000 volts. This twin cable was used in 1891 at the Frankfurt Exhibition, for conveying a current of 20,000 volts from the main Exhibition to the Exhibition on the Main, and when it was returned to the works, it was found that the insulation was as good as when it was first manufactured. A sample of it lies on the table, and by its side the sample of a concentric cable designed for a current of 2500 volts. A comparison of the two shows in a striking manner how elaborately high-tension cables have to be insulated. 1893] on Theory and Practice in Electrical Science. 37 By the first experiment I will try to show you how the space surrounding a conductor connected to a source of high-pressure elec- tricity is, so to speak, filled with electric stresses, that become visible when a vacuum tube is brought near the conductor. This experiment 38 Mr. Alexander Siemens [Feb. 3, was shown here by Nikola Tesla in connection with bis lecture on alternate currents of high frequency ; but I want to show you that high tension and low frequency produce the same effect. The next experiment was suggested by Dr. Obach, and the appa- ratus employed in it is shown in Diagram 5. A copper conductor (thickly insulated with indiarubber) is placed in a brass tube, and the annular space between them is filled with coloured water which com- municates with a vertical glass tube inserted in the centre of the horizontal brass tube. One conductor from the high-tension trans- former is connected to the insulated copper conductor, and the other to the brass tube. Under these conditions no current passes, but the electric stress heats the insulating material, which shows itself by the rise of the coloured liquid in the glass tube. Werner Siemens called attention to this phenomenon in a paper contributed to Poggendorf 's Annalen in 1857, in which he commu- nicated a series of experiments on electrostatic induction, proving, as he expressly stated, the correctness of Faraday's theory of molecular induction. Not very long ago Signor Riccnrdo Arno showed that a cylinder of insulating material, brought under the influence of a rotary field and suitably suspended, would commence to revolve, thus showing that molecular movement was set up in it. He produced this effect by means of an apparatus, a copy of which you see before you. A hollow cylinder of gutta-percha is suspended on the point of a needle, so that it can be made to turn with very little friction. Around it are placed four vertical metal strips to which the high-tension current is brought, as shown in Diagram 6. Between the two terminals of the high-tension circuit, a connection is made by an inductionless resistance in the shape of a U-tube filled with water and a condenser. Two of the metal strips opposite each other are joined to the ends of the inductionless resistance and the other two strips are connected to the condsnser. In this way there is a difference of a quarter of a phase between the two currents, and a rotating field is produced, which causes the cylinder to revolve on account of the electrical hysteresis set up. When the current is reversed the cylinder revolves in the opposite direction. This result also obtains in the case of a glass beaker which is inverted and supported by a pin- point. Wood, slate, and marble are usually reckoned to be insulating materials, but you will see that they do not offer a protracted resis- tance to a current of high potential. When the electric spark passes through marble it converts the carbonate of lime into quicklime, as can readily be shown by moistening the broken surface with phenol- phthalein, which leaves the carbonate of lime white and colours the quicklime a beautiful pink colour. Even glass is pierced ; and we must confess that at present we have no very reliable means of dealing with electricity of very high pressure. 1893.] on Theory and Practice in Electrical Science. 39 Enough has been shown, however, to prove that by utilising electricity we can extend the employment of natural forces for r/J/MM/M/S/WH/t W/MMMUMM ■■•; . ■ procuring the necessaries of life ; and our experience shows that every time this has been done in the past, the burden of manual 40 General Monthly Meeting. [Feb. 6-, labour has been lightened, and the comforts of mind and body have been made more accessible to the toiling multitude. In one word, all real and lasting progress is based on the practical application of scientific knowledge. [A. 8.] GENERAL MONTHLY MEETING, Monday, February 6, 1893. Sir James Crichton-Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Frederick Canton, Esq. M.R.C.S. William Rolle Malcolm, Esq. were elected Members of the Royal Institution. The Special Thanks of the Members were returned for the following Donations : — Mrs. Bloomfield Moore £10 Robert Wilson, Esq 50 John Bell Sedgwick, Esq 50 for carrying on investigations on Liquid Oxygen. The Managers reported, that they had reappointed Professor James Dewar, M.A. L.L.D. F.R.S. as Fullerian Professor of Chemistry. The following Resolution from the Managers was read : — HodgJcin's Trust. " Having regard to the fact that the work of the Institution is devoted to the attainment of truth, and thereby constitutes in itself an investigation of the relations and co-relations existing between man and his Creator," Resolved, " That the income of the fund be devoted to that work, and that once in seven years a sum not exceeding 100 guineas be paid to some person, to be selected by the Managers, for writing an Essay showing how the work of this Institution has during the pre- ceding period of seven years furthered the objects of the Trust." 1893.] General Monthly Meeting. 41 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 Lords of the Admiralty — Nautical Almanac for 1896. 8vo. 1892. The Governor-General of India — Geological Survey of India. Kecords, Vol. XXV. Part 4. 8vo. 1892. Tlie New Zealand Government — Statistics of the Colony of New Zealand for the year 1891. fol. 1892. Results of a Census taken in 1891. fol. 1892. Accademia del Lincei, Reale, Roma — Atti* Serie Quinta : Rendiconti. Classe di Scienze fisiche matematiche e naturali. 2U Semestre, Vol. I. Fasc. 10-12. 8vo. 1892. Rendiconti, Serie Quinta, Classe di Scienze Morali, Storiche "e Filologiche, Vol. I. Fasc. 9-10. Svo. 18D2. Academy of Natural Sciences, Philadelphia — Proceedings, 1892, Part 2. 8vo. Astronomical Society, Royal — Monthly Notices, Vol. LI II. No. 1. Svo. 1892. Bankers, Institute o/->Touraal, Vol. XIII. Part 9. Vol. XIV. Part 1. 8vo. 1892-3. Ball, Sir Robert, LL.D. F R.S. {the Author)— An Atlas of Astronomy. Svo. 1892. British Architects, Royal Institute of — Proceedings, 1892-3, Nos. 4-8. 4to. Transactions, Vol. VIII. New Series. 4to. 1892. British Astronomical Association — Journal, Vol. III. Nos. 1, 2. 8vo. 1893. Memoirs, Vol. I. Part 5 ; Vol. II. Part 1. Svo. 1893. British Museum Trustees — Catalogue of Marathi and Gujarati Books. By J. F. Blumhardt. 8vo. 1892. Boston Public Library, U.S.A. — Bulletin, New Series, Vol. III. Nos. 1-4. Svo. 1892-3. Canadian Institute — Transactions, Vol. III. Part 1. Svo. 1892. Chemical Industry, Society of — Journal, Vol. XL Nos. 11, 12. Svo. 1892. Chemical Society — Journal for Dec. 1892, Jan. 1893. Svo. Cracovie, VAcademie des Sciences — Bulletin, 1892, Nos. 9, 10. Svo. Crisp, Frank, Esq. LL.B. F.L.S. M.R.I. — Journal of the Roval Microscopical Society, 1892, Part 6. 8vo. Editors — American Journal of Science for Dec. 1892 and Jan. 1893. 8vo. Analyst for Dec. 1892 and Jan. 1893. 8vo. Athenaeum for Dec. 1892 and Jan. 1893. 4to. Author for Dec. 1892 and Jan. 1893. Brewers' Journal for Dec. 1892 and Jan. 1893. 4to. Chemical News for Dec. 1892 and Jan. 1893. 4 to. Chemist and Druggist for Dec. 1892 and Jan. 1893. Svo. Electrical Engineer for Dec. 1892 and Jan. 1893. fol. Electric Plant for Dec. 1892 and Jan. 1893. Svo. Electricity for Dec. 1892 and Jan. 1893. 8vo. Engineer for Dec. 1892 and Jan. 1893. fol. Engineering for Dec. 1892 and Jan. 1893. fol. Horological Journal for Dec. 1892 and Jan. 1893. Svo. Industries for Dec. 1892 and Jan. 1893. fol. Iron for Dec. 1892 and Jan. 1893. 4to. Iron and Coal Trades Review for Dec. 1892 and Jan. 1893. 4to. Ironmongery for Dec. 1892 and Jan. 1893. 4to. Lightning for Dec. 1892 and Jan. 1893. 8vo. Monist for Dec. 1892 and Jan. 1893. Svo. Nature for Dec. 1892 and Jan. 1893. 4to. Open Court for Dec. 1892 and Jan. 1893. 4to. Photographic Work for Dec 1892 and Jan. 1893. Svo. Surveyor for Dec. 1892 and Jan. 1893. 8vo. Telegraphic Journal for Dec. 1892 and Jan. 1893. fol. 42 General Monthly Meeting. [Feb. 6, Editors — (continued) Transport for Dec. 1892 and Jan. 1893. fol. Zoophilist for Dec. 1892 and Jan. 1893. 4to. Electrical Engineers, Institution of— Journal, No. 101. 8vo. 1893. Index, Vols. XI.-XX. 8vo. 1892. Florence, Biblioteca Nazionale Centrale — Bolletino, Nos. 167-169. 8vo. 1892. Franklin Institute— Journal, Nos. 804, 805. 8vo. 1892. Geographical Society, Royal — Supplementary Papers, Vol. III. Part 2. 8vo. 1892. Geographical Journal, Vol. I. Nos. 1, 2. 8vo. 1893. Geological Institute, Imperial, Vienna — Verhandlungen, 1892, Nos. 11-14. 8vo. Geological Society — Quarterly Journal, No. 193. Svo. 1893. Glasgow Philosophical Society — Proceedings, Vol. XXIII. 8vo. 1892. Index, Vols. I.-XX. 8vo. 1892. Harvard University — University Bulletin, Nos. 53, 54. 8vo. 1892-3. Bibliographical Contributions, Nos. 17, 32, 37, 39, 45. 8vo. 1892. Imperial Institute — Report of Progress to Nov. 1892. 8vo. 1892. Institute of Brewing— Transactions, Vol. VI. No. 2. 8vo. 1892. Johns Hopkins University — American Chemical Journal, Vol. XIV. No. 8. 8vo. 1892. Studies in Historical and Political Science, Tenth Series, No. 12 ; Eleventh Series, No. 1. 8vo. 1892-3. University Circular, No. 102. 4to. 1893. Linnean Society — Journal, No. 203. Svo. 1893. Manchester Geological Society— Transactions, Vol. XXII. Part 2. Svo. 1892. Manchester Literary and Philosophical Society — Memoirs and Proceedings, Vol. I. 8vo. 1892. Massachusetts I intitule of Technology, Boston, U.S.A. — Technological Quarterly, Vol. V. Nos. 1, 2. Svo. 1892. Mechanical Engineers, Institution of — Proceedings, 1892, No, 3. 8vo. Meteorological Office— Hourly Means for 1889. 4 to. 1892. Meteorological Society, Royal — Meteorological Record, Nos. 45, 46. Svo. 1892. Middlesex Hospital— Reports for 1891. Svo. 1892. Ministry of Public Works, Rome— Giornale del Genio Civile, 1892, Fasc 9-11. Svo. And Designi. fol. 1892. Newton, A. V. Esq. (the Author) — Patent Law and Practice. Svo. 1893. Odontological Society— Transactions, Vol. XXV. No. 2. Svo. 1893. Payne, Wm. W. Esq. and Hale, Geo. E. Esq- (the Editors) — Astronomy and Astro- Physics for Dec. 1892 and Jan. 1893. 8vo. Pharmaceutical Society of Great Britain — Journal for Dec. 1892 and Jan. 1893. 8vo. Calendar, 1893. Svo. Raffard, N. J. Esq. (the Author)— Da Locomotive Electrique a Grande Vitesse. 8vo. 1892. Richardson, B. W. M.D. F.R.S. M.R.I, (the Author}— The Asclepiad, Vol. IX. Part 4. Svo. 1892. Royal Irish Academy — Proceedings, Series III. Vol. II. No. 3. Svo. 1892. Royal Society of London — Proceedings, No. 317. Svo. 1893. Russell, The Hon. R., F.R. Met. Soc. M.R.I, (the Author)— Observations on Dew and Frost. Svo. 1892. Saxon Society of Sciences, Royal — Philologisch-Historische Classe : Berichte, 1892, Nos. 1, 2. Svo. Scottish Society of Arts, Royal— Transactions, Vol. XIII. Part 2. Svo. 1892. Selhorne Society— Nature Notes, Vol. III. Nos. 37, 38. 8vo. 1893. Sociedad Cieniifica " Antonio Alzate," Mexico — Memorias, Tomo VI. Numeros 1-4. 8vo. 1892. Societe Scientifique de Chili— Actes, Tome II. Livraison ler. 4to. 1892. Society of Architects— Proceedings, Vol. V. Nos. 3-5. Svo. 1892. Society of Arts— Journal for Dec. 1892 and Jan. 1893. 8vo. Statistical Society, Royal— Journal, Vol. LV. Part 4. 8vo. 1892. 1893.] General Monthly Meeting. 43 Surgeon-General's Office, U.S. Army — Index Catalogue of the Library, Vol. XIII. 4to. 1892. Tacchini, Professor P. Eon. Mem. R. I (the Author) — Memorie della Societa degli Spettroscopiati Italiani, Vol. XXL Disp. 11% 12. 4to. 1892. United Service Institution, Royal — Journal, Nos. 178, 179. 8vo. 1893. United States Department of Agriculture — Monthly Weather Review for Septem- ber, 1892. 4to. 1892. Publications, 1887-92. 8vo. Weather Bureau, Bulletin, Nos. 5, 6. 8vo. 1892. United States Navy — General Information Series, No. XL 8vo. 1892. Vereins zur Beforderung des Gewerbfleises in Preussen — Verhandlungen, 1892. Heft 10. 4to. 1892. Victoria Institute— Transactions, No. 102. 8vo. 1892. WEEKLY EVENING MEETING, Friday, February 10, 1893. Sir James Crichton-Browne, M.D. LL.D. F.E.S. Treasurer and Vice-President, in the Chair. Professor Charles Stewart, M.R.C.S. Pres. L.S. Some Associated Organisms. [No Abstract.] U Professor A. H. Church Feb. 17, WEEKLY EVENING MEETING, Friday, February 17, 1893. William Huggins, Esq. D.C.L. LL.D. F.R.S. Vice-President, in the Chair. Professor A. H. Church, M.A. F.R.S. M.B.I. Turacin, a remarkable Animal Pigment containing Copper. The study of natural colouring matters is at once peculiarly fascinating and peculiarly difficult. The nature of the colouring matters in animals and plants, and even in some minerals (ruby, sapphire, emerald and amethyst, for example) is still, in the majority of cases, not completely fathomed. Animal pigments are generally less easily extracted and are more complex than those of plants. They appear invariably to contain nitrogen — an observation in accord with the comparative richness in that element of animal cells and their contents. Then, too, much of the coloration of animals, being due to microscopic structure, and therefore having a mechanical and not a pigmentary origin, differs essentially from the coloration of plants. Those animal colours which are primarily due to structure do, however, involve the presence of a dark pigment — brown or black — which acts at once as a foil and as an absorbent of those incident rays which are not reflected. Many spectroscopic examinations of animal pigments have been made. Except in the case of blood- and bile-pigments, very few have been submitted to exhaustive chemical study. Spectral analysis, when uncontrolled by chemical, and when the influence of the solvent employed is not taken into account, is very likely to mislead the investigator. And, unfortunately, the non-crystalline character of many animal pigments, and the difficulty of purifying them by means of the formation of salts and of separations by the use of appropriate solvents, oppose serious obstacles to elucidation. Of blood-red or haemoglobin it cannot be said that we know the centesimal composition, much less the molecular weight. Even of haamatin the empirical formula has not yet been firmly estab- lished. The group of black and brown pigments to which the various melanins belong still awaits adequate investigation. We know they contain nitrogen (8J- to 13 per cent.), and sometimes iron, but the analytical results do not warrant the suggestion of empirical formulae for them. The more nearly they appear to approach purity the freer the majority of them seem from any fixed con- stituent such as iron or other metal. It is to be regretted that Dr. Krukenberg, to whom we are indebted for much valuable work 1893.] on Turacin, a remarkable Animal Pigment. 45 on several pigments extracted from feathers, has not submitted the in- teresting substances he has described to quantitative chemical analysis. I must not, however, dwell further upon these preliminary mat- ters. I have introduced them mainly in order to indicate how little precise information has yet been gathered as to the constitution of the greater number of animal pigments, and how difficult is their study. And now let me draw your attention to a pigment which I had the good fortune to discover, and to the investigation of which I have devoted I am afraid to say how many years. It was so long ago as the year 1866 that the solubility in water of the red colouring matter in the wing-feathers of a plantain- eater was pointed out to me. [One of these feathers, freed from grease, was shown to yield its pigment to pure water.] I soon found that alkaline liquids were more effective solvents than pure water, and that the pigment could be precipitated from its solution by the addition of an acid. [The pigment was extracted from a feather by very dilute ammonia, and then precipitated by adding excess of hydrochloric acid.] The next step was to filter off the separated colouring matter, and to wash and dry it. The processes of washing and drying are tedious and cannot be shown in a lecture. But the product obtained was a solid of a dark crimson hue, non-crystalline, and having a purple semi-metallic lustre. I named it turacin (in a paper published in a now long-defunct periodical ' The Student and Intellectual Observer,' of April, 1868). The name was taken from " Touraco,'" the appellation by which the plantain-eaters are known — the most extensive genus of this family of birds being Turacus. From the striking resemblance between the colour of arterial blood and that of the red touraco feathers, I was led to compare their spectra. Two similar absorption bands were present in both cases, but their positions and intensities differed somewhat. Naturally I sought for iron in my new pigment. I burnt a portion, dissolved the ash in hydrochloric acid, and then added sodium acetate and potassium ferrocyanide. To my astonishment I got a precipitate, not of Prussian blue, but of Prussian brown. This indication of the presence of copper in turacin was confirmed by many tests, the metal itself being also obtained by electrolysis. It was obvious that the proportion of copper present in the pigment was very considerable — greatly in excess of that of the iron (less than ■ 5 per cent.) in the pig- ment of blood. Thus far two striking peculiarities of the pigment had been revealed, namely, its easy removal from the web of the feather, and the presence in it of a notable quantity of copper. Both facts remain unique in the history of animal pigments. The solubility was readily admitted on all hands, not so the presence of copper. It was suggested that it was derived from the Bunsen burner used in the incineration, or from some preservative solution applied to the bird-skins. And it was asked " How did the copper get into the feathers?" The doubters might have satisfied themselves as to 46 Professor A. E. Church [Feb. 17, copper being normally and invariably present by applying a few easy tests and by the expenditure of half-a-crown in acquiring a touraco wing. My results were, however, confirmed (in 1872) by several independent observers, including Mr. W. Crookes, Dr. Gladstone, and Mr. Greville Williams. And in 1873 Mr. Henry Bassett, at the request of the late Mr. J. J. Monteiro, pushed the inquiry somewhat further. I quote from Monteiro's ' Angola and the River Congo,' published in 1875 (vol. ii. pp. 75-77). " I purchased a large bunch of the red wing-feathers in the market at Sierra Leone, with which Mr. H. Bassett has verified Professor Church's results conclusively," &c, &c. Mr. Bassett's results were published in the Chemical News in 1873, three years after the appearance of my research in the Phil. Trans. As concentrated hydrochloric acid removes no copper from turacin, even on boiling, the metal present could not have been a mere casual impurity ; as the proportion is constant in the turacin obtained from different species of touraco, the existence of a single definite compound is indicated. The presence of traces of copper in a very large number of plants as well as of animals has been incon- testably established. And, as I pointed out in 1868, copper can be readily detected in the ash of banana fruits, the favourite food of several species of the " turacin-bearers." The feathers of a single bird contain on the average two grains of turacin, corresponding to * 14 of a grain of metallic copper ; or, putting the amount of pigment present at its highest, just one-fifth of a grain. This is not a large amount to be furnished by its food to one of these birds once annually during the season of renewal of its feathers. I am bound, however, to say that in the blood and tissues of one of these birds, which I analysed immediately after death, I could not detect more than faint traces of copper. The particular specimen examined was in full plumage ; I conclude that the copper in its food, not being then wanted, was not assimilated. Let us now look a little more closely at these curious birds them- selves. Their nearest allies are the cuckoos, with which they were formerly united by systematists. It has, however, been long con- ceded that they constitute a family of equal rank with the Cuculidae. According to the classification adopted in the Natural History Museum, the order Picariae contains eight sub-orders, the last of which, the Coccyges, consists of two families, the Cuculidae and the Musophagidae. To the same order belong the Hoopoes, the Trogons, the Wood-peckers. The plantain-eaters or Musophagidae are arranged in six genera and comprise 25 species. In three genera — Turacus, Gallirex, and Musophaga — comprising eighteen species, and following one another in zoological sequence, turacin occurs ; from three genera (seven species) — Corythaeola, Schizorhis, and Gymno- schizorhis — the pigment is absent. [The coloured illustrations to H. Schlegel's Monograph (Amsterdam, 1860) on the Musophagidae were exhibited]. The family is confined to Africa : 8 of the turacin- bearers are found in the west sub-region, 1 in the south-west, 2 in 1893.] on Turacin, a remarkable Animal Pigment. 47 the south, 2 in the south-east, 4 in the east, 2 in the central, and 2 in the north-east. It is noteworthy that, in all these sub-regions save the south-east, turacin-bearers are found along with those plantain-eaters which do not contain the pigmeut. Oddly enough two of the latter species, Schizorhis africana and S. zonura, possess white patches destitute of pigment in those parts of the feathers which in the turacin-bearers are crimson. These birds do not, I will not say cannot, decorate these bare patches with this curiously complex pigment. [Some extracts were here given from the late Mr. Monteiro's book on Angola, vol. ii. pp. 74-79, and from letters by Dr. B. Hinde. These extracts contained references to curious traits of the touracos.] Usually from 12 to 18 of the primaries or metacarpo-digitals and secondaries or cubitals amongst the wing feathers of the turacin- bearers have the crimson patches in their web. Occasionally the crimson patches are limited to six or seven of the eleven primaries. I have observed this particularly with the violet plantain-eater (Musophaga violacea). In these cases the crimson head-feathers, which also owe their colour to turacin, are few in number, as if the bird, otherwise healthy, had been unable to manufacture a sufficiency of the pigment. I may here add that the red tips of the crest feathers of Turacus meriani also contain turacin. In all the birds in which turacin occurs, this pigment is strictly confined to the red parts of the web, and is there unaccompanied by any other colouring matter. It is therefore found that if a single barb from a feather be analysed its black base and its black termina- tion possess no coj^per, while the intermediate portion gives the blue- green flash of copper when incinerated in the Buusen flame. [A parti-coloured feather was burnt in the Bunsen flame, with the result indicated.] Where it occurs, turacin is homogeneously distributed in the barbs, barbicels and crochets of the web, and is not found in granules or corpuscles. To the natural question " Does turacin occur in any other birds besides the touracos ? " a negative answer must at preseut be given. At least my search for this pigment in scores of birds more or less nearly related to the Musophagidaa has met with no success. In some of the plantain-eaters (species of Turacus and Gallirex) there is, however, a second pigment closely related to turacin. It is of a dull grass-green colour, and was named Turacoverdin by Dr. Krukenberg in 1881. I had obtained this pigment in 1868 by boiling turacin with a solution of caustic soda, and had figured its characteristic absorption band in my first paper (Phil. Trans., vol. clix. 1870, p. 630, fig. 4). My product was, however, mixed with unaltered turacin. But Dr. Krukenberg obtained what certainly seems to be the same pigment from the green feathers of Turacus corythaix, by treating them with a 2 per cent, solution of caustic soda. I find, however, that a solution of this strength 48 Professor A. H. Church [Feb. 17, dissolves, even in the cold, not only a brown pigment associated with turacoverdin, but ultimately the whole substance of the web. By using a much weaker solution of alkali (1 part to a thousand of water) a far better result is obtained. [The characteristic absorption band of turacoverdin, which lies on the less refrangible side of D, was shown ; also the absorption bands of various preparations of turacin.] I have refrained from the further investigation of turacoverdin, hoping that Dr. Krukenberg would complete his study of it. At present I can only exj>ress my opinion that it is identical with the green pigment into which turacin when moist is converted by long exposure to the air or by ebullition with soda, and which seems to be present in traces in all preparations of isolated turacin however carefully prepared. A few observations may now be introduced on the physical and chemical characters of turacin. It is a colloid of colloids. And it enjoys in a high degree one of the peculiar properties of colloids, that of retaining, when freshly precipitated, an immense proportion of water. Consequently, when its solution in ammonia is precipitated by an acid, the coagulum formed is very voluminous. [The experi- ment was shown.] One gram of turacin is capable of forming a semi-solid mass with 600 grams of water. Another character which turacin shares with many other colloids is its solubility in pure water and its insolubility in the presence of mere traces of saline matter. It would be tedious to enumerate all the observed properties of turacin, but its deportment on being heated and the action of sulphuric acid upon it demand particular attention. At 100° C, and at considerably higher temperatures, turacin suffers no change. When, however, it is heated to the boiling-point of mercury it is wholly altered. No vapours are evolved, but the substance becomes black and is no longer soluble in alkaline liquids, nor, when still more strongly heated afterwards, can it be made to yield the purple vapours which unchanged turacin gives off under the same circumstances. This peculiarity of turacin caused great difficulty in its analysis, for these purple vapours contain an organic crystalline compound in which both nitrogen and copper are present, and which resist further decomposition by heat. [Turacin was so heated as to show its purple vapours, and also the green flame with which they burn.] This production of a volatile organic com- pound of copper is perhaps comparable with the formation of nickel- and ferro-carbonyl. The action of concentrated sulphuric acid upon turacin presents some remarkable features. The pigment dissolves with a fine crimson colour, and yields a new compound, the spectrum of which presents a very close resemblance to that of hasmatoporphyrin [Turacin was dissolved in oil of vitriol : the spectrum of an ammoniacal solution of the turacoporphyrin thus produced was also shown], the product obtained by the same treatment from hasmatin : in other respects also this new derivative of turacin, which I call turacoporphyrin, reminds one 1893.] on Turacin, a remarkable Animal Pigment. 49 of hreniatoporphyrin. But, unlike this derivative of h*eroatiu, it seems to retain some of its metallic constituent. The analogy between the two bodies cannot be very close, for if they were so nearly related as might be argued from the spectral observations, hjematin ought to contain not more but less metal than is found to be present therein. The percentage composition of turacin is probably — Carbon 53 ■ 69, hydrogen 4 ■ 6, copper 7*01, nitrogen 6*96, and oxygen 27 ■ 74. These numbers correspond pretty nearly to the empirical formula, C82 H81 Cu2 N9 032. But I lay no stress upon this expression. I have before said that copper is very widely distributed in the Animal Kingdom. Dr. Giunti, of Naples, largely extended (1881) our knowledge on this point. I can hardly doubt that this metal will be found in traces in all animals. But besides turacin only one organic copper compound has been as yet recognised in animals. This is a respiratory, and not a mere decorative, pigment like turacin. Leon Fredericq discovered this substance, called haemocyanin. It has been observed in several genera of Crustacea, Arachnida, Gastropoda and Cephalopoda. I do not think it has ever been obtained in a state of purity, and I cannot accept for it the fantastic formula — C867 H1369 Cu S4 0258 — which has recently been assigned to it. On the other hand, I do not sympathise with the doubts as to its nature which F. Heim has recently formulated in the Comptes Bendus. It is noteworthy, in connection with the periodic law, that all the essential elements of animal and vegetable organic compounds have rather low atomic weights, iron, manganese and copper representing the superior limit. Perhaps natural organic compounds containing manganese will some day be isolated, but at present such bodies are limited to a few containing iron, and to two, haeinocyanin and turacin, of which copper forms an essential part. If I have not yet unravelled the whole mystery of the occurrence and properties of this strange pigment, it must be remembered that it is very rare and costly, and withal difficult to prepare in a state of assured purity. It belongs, moreover, to a class of bodies which my late master, Dr. A. W. von Hofmann, quaintly designated as " dirts" (a magnificent dirt truly !)— substances which refuse to crystallize and cannot be distilled. I have experienced likewise, during the course of this investigation, frequent reminders of another definition propounded by the same great chemist, when he described organic research as " a more or less circuitous route to the sink ! " I am very glad to have had the opportunity of sharing with an audience in this Institution the few glimpses I have caught from time to time during the progress of a tedious and still incomplete research into the nature of a pigment which presents physiological and chemical problems of high if not of unique interest. Let my last word be a word of thanks. I am indebted to several friends for aid in this investigation, and particularly to Dr. MacMunn, of Wolverhampton, the recognised expert in the spectroscopy of animal pigments. [A. H. C] Vol. XIV. (No. 87.) E 50 Mr. Edicard Hopl'iiison [Feb. 24, WEEKLY EVENING MEETING, Friday, February 24, 1893. Sir Frederick Abel, K.C.B. D.C.L. D.Sc. F.R.S. Vice-President, in the Chair. Edward Hopkinson, Esq. M.A. D.Sc. Electrical Railways. One of the most striking of the many new departures in the practical application of electrical science, which made the Paris Exhibition of 1881 memorable, was a short tramway laid down under the direction of the late Sir William Siemens, from the Palais de l'lndustrie to the Place de la Concorde, upon which a tramcar worked by an electric motor plied up and down with great regularity and success during the period of the Exhibition. Yet few of those who saw in this experiment the possibilities of a great future for a new mode of traction would have ventured to predict that within ten years' time, in the United States alone, over 5000 electric cars would be in opera- tion, travelling 50,000,000 miles annually, and carrying 250,000,000 passengers, or that electrical traction would have solved the problem of better communication in London and other large cities. Two years before the Exhibition in Paris the late Dr. Werner Siemens had exhibited at the Berlin Exhibition in 1879 an experimental electric tramway on a much smaller scale, and his firm had put down in 1881 the first permanent electric railway in the short length of line at Lichterfelde, near Berlin, which, I believe, is still at work. In the same year Dr. William Siemens undertook to work the tramway, then projected, between Portrush and Bushmills, in the North of Ireland, over six miles in length, by electric power, making use of the water- power of the Bush River for the purpose, an undertaking which I had the advantage of carrying out under his direction. It is no part of my object to-night to follow further the history of electric traction, which is so recent that it is familiar to all ; but, in alluding to these initial stages of its development, I have desired to recall that it was the foresight and energy of Dr. Werner and Dr. William Siemens, and their skill in applying scientific knowledge to the uses of daily life, which gave the first impulse to the development of the new electrical power. The problem of electric traction may be naturally considered under three heads : — (1) The production of the electrical power. (2) Its distribution along the line. (3) The reconversion of electrical into mechanical power, in the car motor or locomotive. 1893.] on Electrical 'Railways. 51 The first of these, here in England at any rate, is dependent upon the economical production of steam power, although there are essential points of difference between the conditions under which steam-power is required for electric traction purposes and for electric lighting. But in Scotland and Ireland, and in many countries abroad, there is abundant water power, now only very partially utilised. The Portrush line is worked in part by water and in part by steam-power, but for the Bessbrook and Newry Tramway (of which there is a working model on the table) water-power is exclusively used. A few experiments will show that the demand for power on the generating plant is greatest at the moment of starting the car or train, when, in addition to the power required to overcome the frictional resistances, power is also required to accelerate the velocity. Thus, if instead of a single car there are a number of trains moving on the one system, and it so happens that several are starting together, the demand made upon the generating plant may at one moment be three or four times as great as that made a few seconds after. This is shown in the diagrams which exhibit the variation of current supplied by the generators on the City and South London Railway, with eight trains running together, the readings being taken every ten seconds. The maxima rise as high as double the mean ; thus the generating plant must be capable of instantly responding to a demand double or even treble the average demand upon it. In electric lighting it is true there is not less variation between the maximum demand and the mean taken during the ordinary hours of lighting, but it is only in the event of sudden fog that the probable demand cannot be accurately gauged beforehand, and provided for by throwing more generators into action. Thus in a lighting station each generator may be kept working approximately at its full load, and therefore under conditions of maximum economy, whereas in a traction station the whole plant must be kept ready to instantaneously respond to the maximum demands which may be made upon it, and must therefore necessarily work with a low load factor, and consequently with diminished economy. So important is the influence on cost of production of the possible demand in relation to average demand, that the Corporation of Manchester, under their order for electric supply, have decided, upon the advice of their engineer, to annually charge a customer 31. per quarter for each unit per hour of maximum supply which he may require, in addition to 2d. for each unit actually consumed, i. e. for being ready to supply him with a certain amount of electrical power if required to do so, they charge an additional sum equivalent to the charge for its actual consumption for 1440 hours. In one respect water-power has an economic advantage over steam- power, because although steam engine and turbine alike work with greatly reduced efficiency at reduced loads, when the turbine gates are partially closed and the water restrained in the reservoir it is not e 2 52 Mr. Edward Hophinson [Feb. 24, subject to loss of potential energy, whereas the energy of the steam held back by valves of the engine suffers loss through radiation and condensation. At Bessbrook the turbine and generator dynamo combined yield 60 per cent, of the energy of the water as electrical energy available for work on the line, but when the load is reduced to a third of the full load the efficiency is reduced to 33 per cent. So on the City and South London line, a generator engine and dynamo will yield, when working at their full load, 78 per cent, of the indicated horse-power as useful electrical power, but at half load the efficiency falls to 65 per cent. Notwithstanding these conditions the generator station of the City and South London line is producing electrical energy at a cost of l*56d. per Board of Trade unit, which is less than the annual average cost of production of any electric station in England, with the single exception of Bradford, which has the advantage both of cheap coal and cheap labour. In output it is the largest of any Electric Generating Station in England, the total electrical energy delivered in 1892 being 1,250,000 Board of Trade units, the second on the list being the St. James and Pall Mall with 1,186,826 units. Let us pass now to the consideration of the distribution of the electric power along the line. I have equipped the three model tracks before you with three different kinds of conductors. In two of them the rails of the permanent way, which are necessarily uninsulated, are made use of for the return current. This plan, with I believe the almost single exception of the Buda-Pesth Tramway, has been universally adopted with the object of saving the cost of a return conductor ; but it is doubtful whether such an arrangement can be considered final, for it must necessarily create differences of potential in the earth, which already in some instances have had disturbing effects upon our observatories, or upon our telegraph and telephone systems. It appears to be probable in the more or less distant future that the use of the earth for the passage of large current will be prohibited by legislation ; and that it will be reserved for the more delicate and widely extended operations of telegraphy and telephony. These disturbances may of course be easily avoided by the use of an insulated conductor for the return circuit; and it may be that our legislature, looking forward to a remoter future, when electrical forces may be utilised, compared with which even those involved in our present telegraj)hs and telephones are incon- siderable, will insist upon all, — tramways, telegraphs and telephones, — using an insulated return ; a course which I venture to think would be of present benefit to these services, as well as a safeguard for the interests of the future. In the case of conductors which are in such a position that contact may be made from them to the ground through the body of a horse or some other animal coming into contact with them, there is another strong argument for an insulated return, as many animals, and notably horses, are far more sensitive to electric 1893.] on Electrical Bailways. 53 shock than man. It is not perhaps well known, but still a fact, that a shock of 250 volts is quite sufficient to kill a horse almost instan- taneously. The first model has a single overhead conductor with return by the rails ; but in place of a single fishing-rod collector or trolley to take the current from the overhead wire there are fixed on the car two rigid bars, one at each end, which slide along the under surface of the wire and make a rubbing contact against it. This system, devised by Dr. John Hopkinson, has the advantage that there is less difficulty in maintaining contact on uneven roads or on curves, and that the catenaries of the suspended wire may be hung with greater dip, and therefore with less tension. Again, the double contact obviates the frequent breaks and consequent sparking of a single trolley system. The second model shows the system adopted on the City and South London line, and more recently followed on the Liverpool Overhead line, of a conductor of channel steel, upon which collectors fixed to the locomotives make a sliding contact. The third track shows an overhead system like the first, but with an insulated return in place of return by the rails. The characteristic feature of an electric motor is that it delivers us the mechanical power we require directly in the form of a couple about an axis instead of in the form of a rectilinear force, as is the case with steam, gas, or air engines, w7hich must be reduced to a rotary form by connecting rod and crank. Thus it is possible to sweep away all intermediate gear, and to arrive at once at the simplest of all forms of a traction motor, consisting of but one pair ■ of wheels fixed on a single axle with the armature constructed directly upon it, with its magnets suspended from it and maintained in their position against the magnetic forces acting upon them by their weight. Such a locomotive is shown in the third model before you. So far as I am aware, a locomotive of such simplicity as this has never been constructed for practical work, but on the City and South London line the armatures of the motors are placed directly on the axles, and the magnets suspended partly from the axles and partly from the frame. The second model is an exact reproduction of the locomotives on the City and South London line, but with a different arrangement of motors. Here both armatures are included in the same magnetic circuit, and both magnets and armatures carried on the frame of the locomotive and not on the axles. The armatures are geared to the axles by diagonal connecting rods, the axle boxes being inclined, so that their rise and fall in the horn blocks is at right angles to the connecting rods. This design, which is due to the late Mr. Lange, of Messrs. Beyer, Peacock & Co., allows of the motor armature being placed on the floor level of the locomotive, and so more easily accessible. This model wall serve to show some of the characteristic features, as well as some of the characteristic defects, of an electric motor as 54 Mr. Edward Hopkinson [Feb. 24, such. But in order to show these clearly I may refer for a moment to the general theory of a motor. It is easily shown that in a series wound motor the couple or turning moment on the axle is a function of the current only, and independent of the speed and electro-motive force. Again, it follows from Ohm's law that the current passing through the motor multiplied by the resistance of the magnet and armature coils is equal to the difference between the electro-motive force at the terminals of the motor and the electro-motive force which would be generated by the motor, if it were working at the same speed as a generator of electricity, that is to say the difference between the electro-motive force at the terminals and what is called the " back " or " counter " electro-motive force of the motor. Hence if the terminals of the motor be coupled direct to the line at the moment of starting when the motor is still at rest, the current will be very great and its power entirely absorbed in the coils of the armature and magnets, but the turning moment will then be a maximum. The motor then begins to move, part of the power being spent in over- coming frictional resistances and part in accelerating the train. A back electro-motive force is then set up, increasing as the speed increases, and causing the current to diminish until finally a position of equilibrium is established, when the speed is such that the back electro-motive force together with the loss of potential in the coils of the motor is equal to the potential of the line. But in practice the mechanical strength of the motor, and the carrying power of its coils, as well as the limited current available from the generators, makes it necessary to introduce resistances in circuit with the motor to throttle the current and to reduce it within projDer limits. It is to this point I desire to draw attention, that in traction work when starting the motor resistances must be introduced, which, with the resistance of the motor itself, at the moment of starting, absorb the whole power of the current, reducing the efficiency of the motor to nil, and which continue to absorb a large percentage of the power, until the condition of equilibrium is established. This is the great defect in electric motors for traction work, and its importance can be shown very clearly by reference to the work done on the City and South London line. There the motors when working with their normal current have an efficiency of 90 per cent., but the actual all- round efficiency of the locomotive as a whole is 70 per cent, only, so that the loss in starting is equal to 20 per cent, of the whole power. Of course in some respects the City and South London line is exceptional in that a start is made every two or three minutes. Various devices have been suggested with a view to diminishing this waste of power in starting an electric motor, but none entirely meet the case. Thus, if the locomotive or car has two motors, these can be coupled in series at the start, and subsequently thrown into parallel, thereby doubling the tractive force with a given current, or for the same tractive force reducing the loss of power by three-fourths. When through the increase of speed of the motor the back electro- 1893.] on Electrical Railways. 55 motive force balances the electro-motive force of the line, the speed can be increased by diminishing the magnetic field by reducing the effective coils on the magnets, but this device does not give any assistance at the lower speeds, as the magnets ought to be so wound as to be high on the characteristic curve, or nearly saturated with the normal current, and it is therefore not possible to obtain any increased intensity of field by increasing the convolutions of the magnet coils. If it were possible to use alternate current motors for traction work, the difficulty could at once be met by introducing a transformer in the circuit, and placing the motor in its secondary. The effective convolutions of the secondary circuit on the transformer could then be varied as the speed increases in such wise that the electro-motive force of the line is balanced by the back electro-motive force of the motor and the fall of potential due to the resistance of the motor coils, so avoiding all need for resistances. The City and South London line has enabled experiments to be made on the efficiency of the railway system as a whole, taking into account the loss of power in the generators, on the line, and in the motors, and in the resistances of the locomotives. The loss in the line is about 11 per cent, of the electrical power generated, and the efficiency of the locomotives as a whole is, as I have shown, 70 per cent. ; thus the electrical efficiency of the entire system is 62 per cent. The trains weigh with full load of 100 passengers about 40 tons, and the average speed between stations is 13*5 miles per hour. The cost of working, including all charges, during last half year was 7 * Id. per train mile, of which 4 * Id. represents the cost of production of the electric power, and 2 ■ 4d. the cost of utilising it on the locomotives. It is perhaps hardly a fair com- parison to compare the cost of working such a line as the South London line with the cost of steam traction on other lines, inasmuch as steam could not possibly be used in the tunnels, only 10 feet 6 inches diameter, in which this line is constructed, but the com- parison is not uninstrnctive. Take the Mersey Railway, where the gradients and nature of the traffic are similar. On the Mersey Railway the locomotives weigh about 70 tons, and the train, which is capable of carrying about 350 passengers, 150 tons. According to the published returns of the company, the cost of locomotive power is 14d per train mile, i. e. double the cost on the South London line, but for a train weighing between four and five times as much, but capable of carrying only 3 J times the number of passengers ; thus the cost of steam traction per ton mile of train is about half that per ton mile of train for electric traction. But it is not on the cost per ton mile that the success of a passenger line depends. The real basis of comparison is the cost per passenger mile, and here electric traction has great advantage over steam, as the dead weight of the electric motor is small compared with the dead weight of steam locomotives of the same power, and with electric motors the trains can be split up into smaller units, at but slightly increased cost, so 56 Mr. Edward Hopkinson [Feb. 24, permitting a more frequent service. We cannot expect, therefore that electric traction with our present knowledge will take the place of steam traction on our trunk lines ; but it has its proper function in the working of the underground lines now projected for London, Paris, Berlin, Brussels, and other large towns, and also I think on other urban lines, for example, on the Liverpool Overhead Eailway, where trains of large carrying capacity are not required, but a frequent service is essential ; and finally, also on those short lines, whether independent or branches of the great trunk lines, where water-power is available. When I undertook the construction of the Bessbrook line it was a condition that the cost of working should be less than the cost of working by steam, a condition which the first six months of working showed to be successfully fulfilled. When Messrs. Mather and Piatt undertook the construction of the electric plant for the City and South London Eailway, they guaran- teed that the cost of traction for a service of 8247 miles per week as actually run should not exceed 6 ■ 3d. per train mile, exclusive of the drivers' wages. Their anticipations have been more than realised, the actual cost being 5 -Id per train mile only. There are, however, other projects, both in America and on the Continent, for electric railways on which the special feature is to be an enormously high speed of travel, speeds of 150 and even 200 miles per hour being promised. With a steam locomotive, involving the recipro- cating motion of the piston and connecting rod, such speeds are probably unattainable, but they may be realised in the purely rotary motion of an electric motor. But at such high speeds as these the power required to overcome the air resistance is of special considera- tion. Probably up to speeds of 750 miles per hour, or even to higher limits still, the ordinary law of air resistance holds good, as the rate of disturbance is still less than the velocity of waves in air, but above these limits we leave the regions of ordinary locomotion and enter rather into the field of projectiles. Assuming, however, that the ordinary laws of air resistance do hold good, I calculate that the power required to propel an ordinary train 200 feet long at 200 miles per hour against the resistance of air alone, apart from the frictional resistances, would not be less than 1700 horse-power. Though there is nothing to prevent the construction of electric locomotives capable of developing this or even greater power, the strength of the materials at present at command will set a limit to the speeds which may be obtained. In order that the engineer may realise the imperfection of all his works, it is well for him to be constrained from time to time to con- template the amount of energy involved in his final purpose compared with the energy of the coal with which he starts. I have endea- voured to put before you to-night the losses that occur and the reasons for them, in some steps of the complex machine which constitutes an electric railway ; so in conclusion I will draw your attention to the ultimate efficiency of the machine, starting with the coal and ending 1893.] on Electrical Railways. 57 with the passenger carried through space. The diagram on the wall, starting with the familiar 12,000,000 foot-pounds, the energy of a pound of coal, shows the loss in each step, supposing it made with the most economical appliances known to the engineer, first in the boiler, then in the steam engine, generator dynamo, conductors, loco- motives, in the dead weight of the train, till finally we arrive at the energy expended on the passenger himself, which we find to be 133,000 foot-pounds, or but little more than 1 per cent, of the energy with which we started. It is true indeed that transportation is a more economical process than lighting with incandescent lamps, in which the final efficiency is about one-half per cent., but whether in lighting or in traction, when we consider that ninety-nine parts are now wasted for one part saved, we may realise that the future has greater possibilities than anything accomplished in the past. [E.H.] 58 Mr. George Simonds [March 3, WEEKLY EVENING MEETING, Friday, March 3, 1893. Sir James Crichton-Browne, M.D. LL.D. F.K.S. Treasurer and Vice-President, in the Chair. George Simonds, Esq. Sculpture, considered apart from Archseology. It was usual, Mr. Simonds remarked, for lecturers on Sculpture to deal more with Archaeology than Art ; he did not, however, intend to adopt this principle, but should treat his subject from the practical standpoint of the artist. He spoke next of the very wide range of the sculptor's art, and said that in metal-work especially a man might find himself called upon to produce a colossal statue to-day and a set of silver tea- spoons to-morrow ; after which he spoke of the two opposed prin- ciples on which all sculptors' work depends, viz., building up, as in modelling, and cutting down, as in carving, and called attention to the evil results which ensue when either of these processes is applied to a material for which it is unsuited, and gave illustrations of this point in the works of artists of the late seventeenth and of the eighteenth centuries, showing especially that some of the works of Bernini which were executed in marble were really more suitable for bronze. Faults in this direction, Mr. Simonds stated, were almost always the result of very high technical skill, which tempted the artist to consider it desirable to exhibit a tour de force. Even the Greeks themselves were not always free from this somewhat paltry ambition, as was demonstrated by the " Laocoon " aDd the " Group of the Farnese Bull." Such splendid misapplication of power was impossible in the early periods of Art, when the technical difficulties sufficed to keep the artist well within the limits prescribed by his material. The first efforts of sculpture were always purely imitative, and where the imitation was not very successful this was generally due to lack of technical skill rather than to any desire to idealise. This was illustrated by a series of examples of primitive sculpture from various parts of the world. The desire for beauty, however, as understood by the early artist, frequently induced him to exaggerate certain points in his work, often with very grotesque results. Instances were here given of early Etruscan and other sculpture, showing abnormal length of limb and muscular development. 1893. J on Sculpture, considered apart from Archseology. 59 It was a great advance in Art when it was known that harmony of proportion constituted one of the chief elements of beauty. Canons of proportion were established and sculpture became a dignified and beautiful, although, no doubt, to a large extent a conventional art, as was shown by various examples of Egyptian and Etruscan work. The Assyrians and the Greeks made the further discovery that fresh beauty was to be sought for in rhythm of action and in cor- rectness of construction, as is evidenced in the sculptures of the Temple at iEgina, in the bas-reliefs from the Palace of Korsabad, and others; the Assyrians especially excelling in the rendering of movement, their sculptures of animals, such as lions, horses, mules, &c, being of the very highest artistic merit and beauty. In all the above works the artist has relied for his effect on pro- portion, on action and correct construction. He has not concerned himself with the beauty that is to be found in texture and in the mobility of flesh. Sculpture depends on proportion, construction, action and texture for whatever it may possess of technical excellence. Conventionalism, however valuable in sculpture, is apt to become wearisome ; then comes an artist, bolder than the rest, who forsakes in some degree the ancient tradition, and who endeavours, usually with success, to return more closely to individual Nature ; others follow and seek to outstrip him in close imitation of Nature, and for this texture is the quality most in demand. An instance of this in the modern Italian school is Magni's " Beading Girl." The lecturer then went on to speak of the practice of painting statues, admitting that the Greeks used thus to treat them, but stating that it was not at present possible for us to realise what the effect must have been of a Greek temple with its brilliant colouring and polychrome sculpture ; he spoke next of modern attempts to revive the practice by the late John Gibson and others, which, how- ever, had not been successful ; although it is a common practice with sculptors to give a slight wash to marble if a warmer tone seems desirable ; and, indeed, the warm tints of old marble are often successfully imitated by the Italian dealers in forged antiques, such as are bought by wealthy collectors, and even sometimes find their way into national museums. The intention of sculpture should be, of course, to place before us a beautiful thought expressed by beautiful form ; such is, however, not always the sculptor's only desire ; he too often wishes to advertise his own cleverness and to produce work that shall fix the attention of even the most ignorant and careless observer. Thus eccentricity is made to do duty for originality, and the ignorance or neglect of all the rules of harmony of line and composition is supposed to be the triumph of genius over the trammels of conventionality. The result is often very ugly. The modern sculptor is under many disadvantages compared with 60 Mr. George Simonds [March 3, the old Greek. We no longer worship physical beauty as they did, nor can we easily get models of sufficient beauty and refinement to be of much use to us in our work. Moreover the profession of artists' model is a very hard one, requiring patience and a strong interest in the work. In ancient Greece the whole nation were both models and connoisseurs. In London there are hardly half a dozen models of either sex that can be considered properly qualified by Nature and by education for their profession ; yet London is probably not worse off than other Art centres. To the modern sculptor, then, only two courses are open ; either he must be content passively to follow the ideal types that have been handed down from ages past, in which case his work will certainly be lower in the scale of beauty than that on which his ideal is based, or he must strive to form an ideal for himself, based on a careful and loving study of the most beautiful form that he can find in living nature. In other words he must get the best model he can, and work as closely to Nature as possible, leaving out or passing lightly over such details of form as are blemishes or evidently accidental. By this means we may produce work of great beauty (though perhaps not quite equal to that achieved by the Greeks) and also possessed of the added charms of vitality and individuality. An over-great striving for these two last qualities often results, however, in a tolerance of downright ugliness. Artists, the lecturer declared, were always to be found anxious to produce whatever the public admired, and if the taste for eccentricity or ugliness prevailed, the supply would be forthcoming until nausea ensued, and then a better taste would prevail. Canova's works were instanced to show how sudden these changes in style and taste often are, and the highly realistic group of " Daedalus and Icarus " was com- pared with some of his ideal works of a few years later. The leaders in the revolt from the style of the eighteenth century were Canova, Flaxman and Thorwaldsen, and the movement finally ended with Gibson and his followers in utter conventionalism and graceful insipidity. Artists no longer try to make imitation antiques but claim the right to look at Nature for themselves ; and, while respecting the ancient tradition and teaching of classic art, do not accept these as being of universal application to their own work. Where they transgress them they do so wilfully, and to gain some adequate advantage. Fashion, it was stated, had considerable influence on Art, and was influenced by it. Thus the artists made beauty fashionable some fifteen years ago, and beautiful women, Greek tableaux and dresses were all the rage with the public ; but they soon went out of fashion again, and no one hears of professional beauties at the present day. After this there was a demand for character and individuality ; and sculptors were not slow to see that this could be secured by copying the living model with painful accuracy. Coarse knees and angular 1893.] on Sculpture, considered apart from Archseology. 61 projecting hips, ill-shaped breasts and bony backs were not spared to ns, and the critics sang their praises, and did thereby much injury to the public and to the younger artists, who forthwith adopted the gospel of ugliness. The lecturer then described some of the processes employed in the production of a work of sculpture, and compared the modern methods with those of the ancients, showing that we now enjoy technical advantages for the production of sculpture in all materials far superior to those of former ages. He explained models of various instruments used in measuring by sculptors when " pointing " their statues, as the roughing-out process is termed, including Kauer's pointing instrument, and Simonds' Iconograph for proportional point- ing, and described the uses of various tools and appliances used both for marble and for bronze-work. The principles of bronze- casting were illustrated by means of a working diagram, showing the core inside the mould, the empty space between core and mould to be occupied by the melted bronze, and the mould itself, with the various ducts for the metal, and vents to permit the free exit of air and generated gases. Yet with all our technical advantages we were yet deficient in style compared with the old masters. All styles, however, have only their day, since there is none so noble but that at some time it has been condemned and cast aside, and none so contemptible but that at some time it has been held to be the only true art. It is difficult to divest ourselves of prejudice in Art, and many a statue, as for instance, the famous " Esquiline Venus," has had a re- putation made for it by some enthusiastic newspaper correspondent who happened to be on the spot when it was discovered, and who has pronounced it to be a Greek work of the very best period. We are apt to forget that there are bad as well as able artists in all periods, and that the work of a really good man in a bad period is perhaps more valuable than a poor thing that chances to belong to the best period of Greek art. The lecturer then spoke of sculpture as architectural decoration, illustrating his remarks with examples from the Zwinger at Dresden, and the sculpture of the Marmorbad at Cassel, and expressed regret that English architects were so seldom able to induce their clients to expend sufficient money on high-class decorative sculpture, and that even our public buildings were left unbecomingly bare. This was to be ascribed to the fact that few even of the so-called " cultured " people knew anything of sculpture, and it was most common to see in the same house paintings worth thousands of pounds, and close beside them, and regarded by their owner with equal complacency, some wretched cheap bronzes that a sculptor would not give house- room to, but would surely condemn to the melting-pot. Most of the sculptural demand in England is for monumental or portrait work — most of it far from satisfactory ; the system of committees and com- 62 Mr. George Simonds, on Sculpture, &c. [Marcli 3, petitions being calculated to produce the worst results. A committee of one — who knows what he wants and applies to a capable artist for it — will always be the most satisfactory. The lecturer then spoke of the wholesale destruction of monu- mental statues that had taken place at various dates and in different countries, as, notably, in France, in 1792, and of the motives that induced man to erect and to destroy monuments ; and endeavoured to point out that although no monument is so effective as a sculptural one, yet it is by no means proved that a full-sized portrait in bronze of a man and his clothes is the most satisfactory form ; and that matters might often be improved by confining the portrait to a bust or a medallion, and allowing allegorical sculpture to complete the story. Various celebrated equestrian monuments were further shown in illustration, and the lecturer concluded by quoting the words of Professor Tyndall on the power exerted by a noble monumental work over the imagination, it being, he said, "capable of exciting a motive force within the mind which no purely material influence could generate." [G. S.] 1893.] General Monthly Meeting. 63 GENEEAL MONTHLY MEETING, Monday, March 6, 1893. Sir James Crichton-Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Harold A. Des Vceux, M.D. M.R.C.S. Alfred Spalding Harvey, Esq. B.A. Louis Makower, Esq. William Marcet, M.D. F.R.S. Alfred Mond, Esq. Mrs. F. W. Mott, Leslie Pyke, Esq. F.C.S. Lucas Ralli, Esq. Mrs. A. Ruffer, F. Walter Scott, Esq. Claude Vautin, Esq. Miss Laura A. WTebster, Rev. W. Allen Whitworth, M.A. were elected Members of the Royal Institution. The following Arrangements for the Lectures after Easter were announced : — John Macdonell, Esq. LL.D.— Three Lectures on Symbolism in Ceremonies, Customs, and Art ; on Tuesdays, April 11, 18, 25. Frofessor R. K. Douglas. — Three Lectures on Modern Society in China ; on Tuesdays, May 2, 9, 16. E. L. S. Horsburgh, Esq. M.A. — Three Lectures on Napoleon ; on Tuesdays, May 23, 30, June 6. Professor Dewar, M.A. LL.D. F.R.S. M.B.I. — Five Lectures on The Atmosphere ; on Thursdays, April 13, 20, 27, May 4, 11. R. Bowdler Sharpe, Esq. LL.D. — Four Lectures on The Geographical Distribution of Birds ; on Thursdays, May 18, 25, June 1, 8. James Swinburne, Esq. M. Inst. BE. — Three Lectures on Some Applications of Electricity to Chemistry (The Tyndall Lectures) ; on Saturdays, April 15, 22, 29. Henry Craik, Esq. C.B. LL.D. — Three Lectures on I. Johnson and Milton ; II. Johnson and Swift ; III. Johnson and Wesley ; on Saturdays, May 6, 13, 20. A. C. Mackenzie, Esq. Mus. Doc. — Three Lectures on " Falstaff." A Lyric Comedy, by Boito and Verdi ; on Saturdays, May 27, June 3, 10. The Managers reported that in accordance with the Acton Endow- ment Trust Deed they had awarded the Actonian Prize of one hundred guineas to Miss Agnes M. Clerke for her works on " Astronomy," as " illustrative of the Wisdom and Beneficence of the Almighty." 64 General Monthly Meeting. [March 6, The Special Thanks of the Members were returned to Mr. Frederick Davis for his present of a fine copy of the Spitzer Catalogue (on Japan paper), in six volumes, which was presented by him as a souvenir of the visit of H.R.H. The Prince of Wales, and as com- memorative of Professor De war's lecture on " Liquid Air," on the 22 nd of February last. The Special Thanks of the Members were returned for the follow- ing Donation to the Fund for the Promotion of Experimental Research at low temperatures : — Mrs. Wigan £10 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 — Classe di Scienze Fisiche, Materaaticbe e Naturali. Atti, Serie Quinta: Rendiconti. 1° Semestre, Vol. II. Fasc. 1, 2. 8vo. 1893. Classe di Seienze Morali Storiche, etc. : Rendiconti, Serie Quinta, Vol. I. Fasc. 12. 8vo. 1893. American Geographical Society— Bulletin, Vol. XXIV. No. 4, Part 1. 8vo. 1892. Antiquaries, Society of— Proceedings, Vol. XIV. No. 2. 8vo. 1892. Asiatic Society of Bengal— Journal, Vol. LXI. Part 1, No. 3. 8vo. 1892. Proceeding, Nos. 8, 9. 8vo. 1892. Asiatic Society of Great Britain, Royal— Journal. 1893, Part 1. 8vo. Astronomical Society, Royal— Monthly Notices, Vol. LIII. No. 3. 8vo. 1893. Bankers, Institute of— Journal, Vol. XIV. Part 2. 8vo. 1893. Boston Society of Natural History— Proceedings, Vol. XXV. Parts 3, 4. 8vo. 1892 Memoirs, Vol. IV. No. 10. 4to. 1892. British Architects, Royal Institute of— Proceedings, 1893, No. 10. 4to. British Astronomical Association— journal, Vol. III. No. 3. 8vo. 1893. Browne, T. B. Esq. (the Compiler)— The Advertiser's A.B.C. for 1893. 8vo. Burne, Sir Owen Tudor, K. C.S.I, (the Author) — Rulers of India: Clyde and Strathnairn. 8vo. 1892. Chemical Industry, Society of— Journal, Vol. XII. No. 1. 8vo. 1893. Chemical Society— Journal for February, 1893. 8vo. Cracovie, VAcademie des Sciences— Bulletin, 1893, No. 1. 8vo. Crisp, Frank, Esq. LL.B. F.L.S. M.R.I. — Journal of the Royal Microscopical Society, 1893, Part 1. 8vo. Editors— American Journal of Science for February, 1893. 8vo. Analyst for February, 1893. 8vo. Athenaeum for February, 1893. 4to. Brewers' Journal for February, 1893. 4to. Chemical News for February, 1893. 4to. Chemist and Druggist for February, 1893. 8vo. Electrical Engineer for February, 1893. fol. Electricity for February, 1893. 4to. Electric Plant for February, 1893. 4to. Engineer for February, 1893. fol. Engineering for February, 1893. fol. Engineering Review for February, 1893. 8vo. HorolngicaUournal for February, 1893. 8vo. Industries for February, 1893. fol. 1893.] General Monthly Meeting. 65 Editors —cord inued. Iron for February, 1893. 4to. Ironmongery for February, 1893. 4to. Lightning for February, 1893. 4 to. Nature for February, 1893. 4to. Open Court for February, 1893. 4to. Photographic News for February, 1893. 8vo. Photographic Work for February, 1893. 8vo. Surveyor for February, 1893. 8vo. Telegraphic Journal for February, 1893. fol. Transport for February, 1893. Zoophilist for February, 1893. 4to. Electrical Engineers, Institution of — Journal, Nos. 102, 103. 8vo. 1893. Florence, Biblioteca Nazionale Centrale — Bolletino, No. 171. 8vo. 1892. Franklin Institute — Journal, No. 806. 8vo. 1893. Frankland, Professor P. F. Ph.D. F.R S. {the Author) — Our Secret Friends and Foes. 8vo. 1893. " Friend of International Progress." Bombay, 1885-90. By Sir W. W. Hunter. 8vo. 1892. Geographical Society, Royal— Supplementary Papers, Vol. III. Part 2. 8vo. 1893. Geographical Journal, Vol. I. No. 3. 8vo. 1893. Geological Institute, Imperial, Vienna — Verhandlungen, 1892, Nos. 15, 16. 8vo. 1892. Georgofili, Reale Accademie — Atti, Quarta Serie, Vol. XV. Disp. 3a, 4a. 8vo. 1892. Harlem, Societe Hollandaise des Sciences — Archives Neerlandaises, Tome XXVI. Livraison 4, 5. 8vo. 1893. Horticultural Society, Royal— Journal, Vol. XV. Parts 2, 3. 8vo. 1893. Institute of Brewing — Transactions, Vol. VI. No. 4. 8vo. 1893. Iowa Laboratories of Natural History — Bulletin, Vol. II. No. 3. 8vo. 1893. Johns Hopkins University — American Chemical Journal, Vol. XV. No. 1. 8vo. 1893. American Journal of Philology, Vol. XII. No. 4. Vol. XIII. No. 4. 8vo. 1891-2. Studies in Historical and Political Science, Tenth Series, Nos. 4-6, 11, 12. 8vo. 1892. Keeler, James E. Esq. (the Author) — The Spectroscope of the Alleghany Observa- tory. 8vo. 1891. Lentzner, Karl, Esq. (the Author) — Various Publications. 8vo. 1885-93. Meteorological Office — Keport of Meteorological Council to E.S. 31st March, 1892. 8vo. 1893. Meteorological Observations at Stations of the Second Order for 1888. 8vo. 1892. Eeport of International Meteorological Conference at Munich, 1891. 8vo. 1893. Ministry of Public Works, Rome — Giornale del Genio Civile, 1892, Fasc. 12 and Designi. fol. 1892. North of England Institute of Mining and Mehanical Engineers — Transactions, Vol. XLI. Part 6. ; Vol. XLII. Part 1. 8vo. 1893. Numismatic Society — Chronicle and Journal, 1892, Part 4. 8vo. 1893. Odontological Society — Transactions, Vol. XXV. No. 4. 8vo. 1893. Payne, W. W. and Hale, G. E. (the Editors) — Astronomy and Astro-Physics for February, 1893. 8vo. Pharmaceutical Society of Great Britain— Journal, February, 1893. 8vo. Carl Wilhelm Scheele ; his life and work. 8vo. 1893. Religious Tract Society — La Glorieuse Rentree des Vaudois, 1689. 8vo. 1889. Rochester Academy of Science, U.S.A. — Proceedings, Vol. II. No. 1. 8vo. 1892. Royal Botanic Society of London — Quarterly Record, No. 52. 8vo. 1893. Royal Irish Academy — Transactions, Vol. XXX. Parts 3, 4. 4to. 1893. Royal Society of London — Philosophical Transactions, Vol. CLXXXIII. 4to. 1893. Proceedings, No. 318. 8vo. 1893. Vox, XIV. (No. 87). F 66 General Monthly Meeting. [March 6, Saxon Society of Sciences, Boyal — Philologisch-historischen Classe : Abhandlungen, Band XIII. No. 5. 8vo. 1893. Selborne Society— -Nature Notes, No. 39. 8vo. 1893. Sidgreaves, The Rev. W. (the Author) — Kesults of Meteorological and Magnetical Observations at Stonyhurst, 1892. 8vo. 1893. Sociedad Cientifica " Antonio Alzate" Mexico — Memorias, Tomo VI. Nos. 5, 6. 8vo. 1893. Society of Architects — Proceedings, Vol. V. Nos. 6, 7. 8vo. 1893. Society of Arts — Journal for February, 1893. 8vo. St. Bartholomew's Hospital— Beports, Vol. XXVIII. 8vo. 1892. St. Petershourg Academic Imperiales des Sciences — Me'moires, Tome XXXVIII. No. 14 ; tome XL. No. 1. 4to. 1892. Bulletin, Tome XXXV. Nos. 1, 2. 8vo. 1892. Tacchini, Prof. P. Hon. Mem. R.L — Memoire della Societa degli Spettroscopisti Italiani. Vol. XXII. Disp. 1\ 4to. 1893. United Service Institution, Royal — Journal, No. 189. 8vo. 1893. United States Department of Agriculture— -Monthly Weather Beview fur November, 1892. 4to. Vereins zur Beforderung des Gewerhfleisses in Preussen — Verhandlungen, 1893, Heft. 1. 4to. Yale University — Transactions of the Astronomical Observatory of Yale University, Vol. I. Parts 3, 4. 4to. 1893. WEEKLY EVENING MEETING, Friday, March 10, 1893. Sir Douglas Galton, K.C.B. D.C.L. LL.D. F.K.S. Vice-President, in the Chair. Sir Herbert Maxwell, Bart. M.P. Early Myth and Late Romance. (No Abstract.) 1893.] Mr. William J. Russell on Ancient Egyptian Pigments. 67 WEEKLY EVENING MEETING, Friday, March 17, 1893. William Huggins, Esq. D.C.L. LL.D. F.R.S. Vice-President, in the Chair. William J. Russell, Esq. Ph.D. F.R.S. M.B.I. Ancient Egyptian Pigments. The red pigment used by the Egyptians from the earliest times is a native oxide of iron, a hematite. Most of the large pieces found by Mr* Petrie are an oolitic haematite. One specimen, on analysis, gave 79*11 per cent, and another 81*34 per cent, of ferric oxide. The pieces to be used as pigments were no doubt carefully selected, and the samples that I have examined, mostly from Gurob and Kahun, are very good in colour. All the large pieces were of a singular shape, having one side smooth and curved ; and in all cases this side was strongly grooved with stria?, giving somewhat the appearance to the mass of its having been melted, and allowed to cool in a circular vessel. No doubt the explanation of this smooth-curved surface is, that these pieces had actually been in part used to furnish pigments, and having been rubbed with a little water in a large circular vessel, bad been ground to this shape. By experiment it was found that these pieces of the native haematite yielded, without any further addition by way of medium, a paint which could readily be applied with a brush, as it possesses remarkable adhesive properties, and it resembles exactly, in every particular, the red used in the different kinds of Egyptian paintings. In addition to these samples of the pigments, all of which are native minerals and in their natural conditions, there are other reds, finer in colour and smoother in texture, evidently a superior pigment ; these apparently have been made from carefully selected pieces of haematite, which have been ground and washed, and dried by exposure to the air. Some of these pieces are very fine in colour, and it would be difficult to match them with any native oxide of iron that is used as a pigment at the present day. There is every reason to believe that this is the earliest red pigment which was used, and it remains to this day the commonest and most important one ; it is a body unattacked by acids, unchangeable by heat, and even moisture and sunlight are unable to alter its colour. At the present time many artificial products are used to take the place of this natural pigment. Yellow pigments. — These, again, are natural products, and by far the most common yellow used by the Egyptians is a native ochre. These ochres consist of about one-quarter of their weight of oxide of iron, from 7 to 10 per cent, of water, and the rest of their substance f 2 68 Mr. William J. Bussell [March 17, is clay. When moist they have a greasy feel, and work smoothly and well with the brush. There is no evidence of these bodies having changed colour, but undoubtedly they are chemically not nearly so stable as the red form of oxide of iron. Many of the pieces of this pigment, found at Gurob and at Tel-el- Armarna, are very fine in colour. Some of the specimens of the very earliest colours of which the exact history is known, appear to be an artificial mixture of these two colours, the red and yellow, thus producing an orange colour. These samples were found on a tomb at Medum, which, according to Professor Flinders Petrie, was built by Nefermat, a high official and remarkable man at the Court of Senefru. Senefru is known to have lived in the fourth dynasty, about 4000 B.C., and to have preceded Khufu, the Cheops of the Greeks, who was the great Pyramid builder. Now, on Nefermat's tomb the characters and figures are incised and filled in with coloured pastes, which I have been able to examine, and it is of interest to know that this use of colour was a special device of Nefermat, for on his tomb it is stated that : " He marie this to his gods in his unspoilable writing." In this unspoilable writing the figures are all carefully undercut, so that the coloured pastes, so long as they held together, should not be able to drop out. All the pastes used are dull in colour, consisting entirely of natural minerals. Haematite, ochre, malachite, carbon, and plaster of Paris appear to be the materials used. Chessylite, as a blue, probably was known even at that date, but the artificial blues seem hardly at this period to have come into use ; certainly they are not found in the specimens of the Nefermat colours which I have examined. Another yellow pigment, far brighter in colour, was also often used. It is a sulphide of arsenic, orpiment ; it is a bright and powerful yellow, again a body found in nature, but a much rarer body than ochre, and consequently, probably was only used for special purposes, when a brilliant yellow was required. As far as it is known at present, this pigment did not come into use until the eighteenth dynasty. Gold might even be placed among the yellow pigments, for it was largely used, and with wonderfully good effect. Its great tenacity seems to have been fully recognised, for gold is found in very thin sheets, and laid on a yellow ground, exactly as is done at the present day. These pigments are then simply natural minerals, no doubt carefully selected, and sometimes ground and washed previous to being used ; but the blue colour which is so largely used by the Egyptians is an artificial pigment, and consequently has far more interest attached to it than those already mentioned. It is a body requiring considerable care and experience to make, and thus its manufacture enables us to some extent to judge of the knowledge and ability which its producers had of carrying on a chemical manufac- ture. No doubt the splendid blue of the mineral chessylite was first used, but certainly in the twelfth dynasty — that is, about 2500 b.c. 1893.] on Ancient Egyptian Pigments. 69 — these artificial blues were used. They are all an imperfect glass, a frit, made by heating together silica, lime, alkali, and copper ore.* The number of failures which may have occurred, and how much material may have been spoilt, cannot be known, but all the blue frit which I have examined — and it is a considerable amount, some being raw material, lumps as they came from the furnace, and the rest ground pigment — all has been, though differing in grain and quality, well and perfectly made. Now this implies that the materials have been carefully selected, prepared, and mixed, and that definite quan- tities of each were taken, this necessitating the carefully measuring or weighing of each constituent. An early application of the fun- damental law of chemistry, combination in definite proportion. The amount of copper ore added determined the colour ; with 2 to 5 per cent, they obtained a light and delicate blue ; with 25 to 30 per cent. a dark and rather purple blue ; with still more the product would be black; if the alkali was too little in amount, a non-coherent saud resulted ; if too much, a hard, stony mass is formed, quite unsuitable for a pigment. The difficulties, however, did not by any means end with the mixture of the materials. For the next process, the heating, is a delicate operation. Unfortunately up to the present time the exact form of furnace in which this operation was carried on is not known. The furnaces were probably, especially after use, very fragile structures, and have passed away. Considerable ex- perience in imitating these frits even when using modern furnaces has taught me that the operation is really a very delicate one ; the heat has to be carefully regulated and continued for a considerable length of time, a time varying with the nature of the frit being prepared ; and, further, in the rough furnaces used it must have been specially difficult to have prevented unburnt gases from coming in contact with the material ; but if they did a blackening of the frit must have taken place. However, all these difficulties were avoided, and a frit was made which exactly answered all the necessary requirements. It had, for instance, the right degree of cohesion, for many of the large pieces which have been found have, like the haematite, a smooth, curved striated surface, and on rubbing in a curved vessel with water, easily grind to powder. The powder is naturally much less adhesive than the haematite powrder, but on adding a little medium, it could at once be used, without other preparation, as a paint. Some of the pieces vary in colour in different parts. This may have * A sample of the pale-blue frit gave, on analysis, the following results : — Silica .. .. .. .. .. 88-65 Soda .. .. .. .. .. .. 0-81 Copper oxide .. .. .. .. .. 2*09 Lime.. .. .. .. .. .. 7*88 Iron oxide, alumina, &c . . . . . . 0*57 10000 70 Mr. William J. Russell [March 17, arisen from imperfect mixing, or from some parts of the furnace being hotter than others. It hardly appears to be intentional, possibly- some of the dark, purplish-coloured frits were produced by accident ; large pieces of it have as yet, I believe, not been found. By means of comparatively small alterations these frits could be obtained of a green colour, One way was by introducing iron. If, for instance, the silica used was a reddish coloured sand, it gave a greenish tinge to the frit ; and frit made with some of the ordinary yellowish desert sand was found to give a frit undistinguishable from the most com- mon of the old Egyptian frits. Again, a rather strong green colour is obtained by stopping the heating process at an early stage, this green frit, simply on heating for a longer time, becoming blue. Another way in which even the strong-coloured blue frits have been con- verted into apparently green pigments is by their being coated over with a transparent but yellowish coloured varnish which has to a remarkable extent retained its transparency, but no doubt become with age more yellow, and although strongly green now, may very likely originally have been nearly colourless, and consequently the frit was then seen in its original blue colour. Even as early as the twelfth dynasty the green frits used were dull in colour, and if by chance a brighter green was required, then they used the mineral malachite. No doubt by far the most brilliant blue used at any time was selected and powdered chessylite, and even down to the twenty-first dynasty they seem to have made use generally of somewhat brilliant coloured frits ; but after that time more subdued colours appear to have been used, and even the scarabs were made of a much duller colour than formerly. All these blue frits form a perfectly unfadeable and unchangeable pigment. Neither the sun nor acids are able to destroy or alter their colour. The only other pigment to which I can refer this evening is the pink colour which, in different shades, was much used. This is again an artificial pigment, and belongs to an entirely different class from any of the foregoing ones, for it is one of vegetable origin. On simply heating it, fumes are given off and the colour is destroyed, but a large white residue remains ; this is sulphate of lime. It may here be stated that the white pigments used sometimes were carbonate of lime, but more generally sulphate of lime in form of gypsum, alabaster, &c. This substance is often very white in colour, is very slightly soluble in water, and has a singular smoothness of texture, which makes it work well under the brush ; and in addition to these qualities, it is a neutral and very stable compound, so is well fitted for the purpose to which it was applied. It w7as easily obtained, being found native in many parts of Egypt. It is also interesting to note that there is an efflorescence consisting of this substance which frequently occurs in Egypt, and is of a remarkably pure white colour ; probably this wras used as a superior white pigment. It was easy to prove then that the pink colour was gypsum stained with organic colouring matter, and to try and imitate the colour appeared 1893.] on Ancient Egyptian Pigments. 71 to be the most likely way of identifying it. Naturally, madder, which it is known has from the earliest times been used as a dye, was the vegetable colouring substance first tried, and it answered perfectly, giving under very simple treatment the exact shade of colour to the sulphate of lime which the Egyptian pigment had. Essentially the same colouring matter may have been obtained from another source, viz. Munjeet. In the case of madder it is interesting to note that the colour is not manifest in the plant — the Bubia tinctorum — for it is obtained from the root, and is even not ready formed there. In the root it exists as a glucoside, and this has to be decomposed before the colour becomes manifest. In this root there exists several colouring matters, which are known as madder-red, madder-purple, madder-orange, and madder-yellow. On breaking up the roots and steeping them in water for some length of time, the colours come out, some sooner than others, so that the tints vary. Again, changes of colour are easily obtained by the addition of very small quantities of iron, lime, alumina, &c, so that in these different ways a considerable range of colours could be obtained, but a delicate pink colour was the one probably generally made. This colour is easily obtained by simply stirring up sulphate of lime in a tolerably strong solution of madder, and adding a little lime, taking care to keep the colouring matter in excess; the colouring matter adheres firmly to the lime salt, and this settles on to the bottom of the vessel ; the liquid is then poured off and the solid matter, if necessary, dried, or mixed — probably with a little gum, and used at once without other preparation. That the colouring matter was really madder could also be tested by another method, viz. by means of spectrum analysis. Both the madder-red (alazarin) and the madder-purple (purpurin) give, when the light which they transmit is analysed by the prism, very characteristic absorption bands ; the purpurin bands are the ones most easily seen, consequently it became a point of considerable interest to ascertain whether from a specimen of this pigment, some thousands of years old, these absorption bands could be obtained. A small sample of this pink pigment was taken from a cartonage which was exhibited, and by treating it with a solution of alum, the colour was thus transferred to the liquid, and by throwing the absorption spectrum which it gave on the screen, and comparing it with the spectrum from a madder solution, it was clearly seen to be identical. [W. J. E.] 72 Lord JRayleigh [March 21, Fig. 1. WEEKLY EVENING MEETING, Friday, March 2 I, 1893. Sir Frederick Bramwell, Bart. D.C.L. LL.D. F.B.S. Honorary Secretary and Vice-President, in the Chair. The Bight Hon. Lord Bayleigh, M. A. D.C.L. LL.D. F.B.S. M.B I. Interference Bands and their Applications. (Abstract?) The formation of the interference bands, known as Newton's Bings, when two slightly curved glass plates are pressed into contact, was illustrated by an acoustical analogue. A high-pressure flame B (Fig. 1) is sensitive to sounds which reach it in the direction EB, but is insensitive to similar sounds which reach it in the nearly perpen- dicular direction AB. A is a " bird-call," giving a pure sound (inaudible) of wave-length (a) equal to about 1 cm. ; C and D are reflectors of perforated zinc. If C acts alone the flame is visibly excited by the waves reflected from it, though by far the greater part of the energy is transmitted. If D, held par- allel to C, be then brought into action, the result depends upon the interval between the two partial reflectors. The reflected sounds may co-operate, in which case the flame flares vigorously ; or they may inter- fere, so that the flame recovers, and behaves as if no sound at all were falling upon it. The first effect occurs when the reflectors are i close together, or are separated by any multiple of J J 2 . a ; the second when the interval is midway between those of the above-mentioned series, that is, when it coin- cides with an odd multiple of J y/ 2 . A. The factor aJ 2 depends upon the obliquity of the reflection. The coloured rings, as usually formed between glass plates, lose a good deal of their richness by contamination with white light reflected from the exterior surfaces. The reflection from the hindermost surface is easily got rid of by employing an opaque glass, but the reflection from the first surface is less easy to deal with. One plan, used in the lecture, depends upon the use of slightly wedge-shaped glasses (2°) 1893.] on Interference Bands and their Applications. 73 so combined that the exterior surfaces are parallel to one another, but inclined to the interior operative surfaces. In this arrangement the false light is thrown somewhat to one side, and can be stopped by a screen suitably held at the place where the image of the electric arc is formed. The formation of colour and the ultimate disappearance of the bands as the interval between the surfaces increases, depends upon the mixed character of white light. For each colour the bands are upon a scale proportional to the wave-length for that colour. If we wish to observe the bands when the interval is considerable — bands of high interference as they are called — the most natural course is to employ approximately homogeneous light, such as that afforded by a soda flame. Unfortunately, this light is hardly bright enough for projection upon a large scale. A partial escape from this difficulty is afforded by Newton's ob- servations as to what occurs when a ring system is regarded through a prism. In this case the bands upon one side may become approxi- mately achromatic, and are thus visible to a tolerably high order, in spite of the whiteness of the light. Under these circumstances there is, of course, no difficulty in obtaining sufficient illumination ; and bands formed in this way were projected upon the screen.* The bands seen when light from a soda flame falls upon nearly parallel surfaces have often been employed as a test of flatness. Two flat surfaces can be made to fit, and then the bands are few and broad, if not entirely absent ; and, however the surfaces may be presented to one another, the bands should be straight, parallel, and equi- distant. If this condition be violated, one or other of the surfaces deviates from flatness. In Fig. 2, A and B represents the glasses to be tested, and C is a lens of 2 or 3 feet focal length. Rays diverging from a soda flame at E are rendered parallel by the lens, and after reflection from the surfaces are recombined by the lens at E. To make an observation, the coincidence of the radiant point and its image must be somewhat disturbed, the one being displaced to a position a little beyond, and the other to a position a little in front of, the diagram. The eye, protected from the flame by a suitable screen, is placed at the image, and being focused upon A B, sees the field traversed by bands. The reflector D is introduced as a matter of convenience to make the line of vision horizontal. These bands may be photographed. The lens of the camera takes the place of the eye, and should be as close to the flame as possible. With suitable plates, sensitised by cyanin, the exposure required may vary from ten minutes to an hour. To get the best results, the hinder surface of A should be blackened, and the front surface of B should be thrown out of action by the superposition of a wedge-shaped * The theory is given in a paper upon " Achromatic Interference Bands," Phil. Mag. Aug. 1889. 74 Lord Haijleigli [March 24, plate of glass, the intervening space being filled with oil of turpentine or other fluid having nearly the same refraction as glass. Moreover, the light should be purified from blue rays by a trough containing solution of bichromate of potash. With these precautions the dark parts of the bands are very black, and the exposure may be prolonged much beyond what would otherwise be admissible. The lantern slides exhibited showed the elliptical rings indicative of a curvature of the same sign in both directions, the hyperbolic bands corresponding to a saddle-shaped surface, and the approximately parallel system due to the juxtaposition of two telescopic " flats," kindly lent by Mr. Common. On other plates were seen grooves due Fig. 2. to rubbing with rouge along a defined track, and depressions, some of considerable regularity, obtained by the action of diluted hydro- fluoric acid, which was allowed to stand for some minutes as a drop upon the surface of the glass. By this method it is easy to compare one flat with another, and thus, if the first be known to be free from error, to determine the errors of the second. But how are we to obtain and verify a standard ? The plan usually followed is to bring three surfaces into comparison. The fact that two surfaces can be made to fit another in all azimuths proves that they are spherical and of equal curvatures, but one convex and the other concave, the case of perfect flatness not being excluded. If A and B fit another, and also A and C, it follows that B and C must be similar. Hence, if B and C also fit one 1893.] on Interference Bands and their Applications. 75 another, all three surfaces must be flat. By an extension of this process the errors of three surfaces which are not flat can be found from a consideration of the interference bands which they present when combined in three pairs. But although the method just referred to is theoretically complete, its application in practice is extremely tedious, especially when the surfaces are not of revolution. A very simple solution of the difficulty has been found in the use of a free surface of water, which, when protected from tremors and motes, is as flat as can be desired.* In order to avoid all trace of capillary curvature it is desirable to allow a margin of about 1J inch. The surface to be tested is sup- ported horizontally at a short distance (y1^ or -^ inch) below that of the water, and the whole is carried upon a large and massive levelling stand. By the aid of screws the glass surface is brought into approxi- mate parallelism with the water. In practice the principal trouble is in the avoidance of tremors and motes. When the apparatus is set up on the floor of a cellar in the country, the tremors are sufficiently excluded, but care must be taken to protect the surface from the slightest draught. To this end the space over the water must be enclosed almost air-tight. In towns, during the hours of traffic, it would probably require great precaution to avoid the disturbing effects of tremors. In this respect it is advantageous to diminish the thickness of the layer of water ; but if the thinning be carried too far, the subsidence of the water surface to equilibrium becomes sur- Fig. 3. prisingly slow, and a doubt may be felt whether after all there may not remain some deviation from flatness due to irregularities of temperature. With the aid of the levelling screws the bands may be made as broad as the nature of the surface admits ; but it is usually better so to adjust the level that the field is traversed by five or six approximately parallel bauds. Fig. 3 represents bands actually observed from the face of a prism. That these are not straight, parallel, and equidistant is a proof that the surface deviates from flatness. The question next * The diameter would need to be 4 feet in order that the depression at the circumference, due to the general curvature of the earth, should amount to -^ A. 76 Lord Rayleigh [March 24, arising is to determine the direction of the deviation. This may be effected by observing the displacement of the bands due to a known motion of the levelling screws ; but a simpler process is open to us. It is evident that if the surface under test were to be moved down- wards parallel to itself, so as to increase the thickness of the layer of water, every band wTould move in a certain direction, viz. towards the side where the layer is thinnest. What amounts to the same, the retardation may be increased, without touching the apparatus, by so moving the eye as to diminish the obliquity of the reflection. Suppose, for example, in Fig. 3, that the movement in question causes the bands to travel downwards, as indicated by the arrow. The inference is that the surface is concave. More glass must be removed at the ends of the bands than in the middle in order to straighten them. If the object be to correct the errors by local polishing operations upon the surface, the rule is that the bands, or any parts of them, may be rubbed in the direction of the arrow. A good many surfaces have thus been operated upon ; and although a fair amount of success has been attained, further experiment is required in order to determine the best procedure. There is a tendency to leave the marginal parts behind ; so that the bands though straight over the greater part of their length, remain curved at their extremities. In some cases hydrofluoric acid has been, resorted to, but it appears to be rather difficult to control. The delicacy of the test is sufficient for every optical purpose. A deviation from straightness amounting to -jV of a band interval could hardly escape the eye, even on simple inspection. This corre- sponds to a departure from flatness of ^o 0I> a wave-length in water, or about ^ of the wave-length in air. Probably a deviation of T^ A could be made apparent. For practical purposes a layer of moderate thickness, adjusted so that the two systems of bands corresponding to the duplicity of the soda line do 'not interfere, is the most suitable. But if we wish to observe bands of high interference, not only must the thickness be increased, but certain precautions become necessary. For instance, the influence of obliquity must be considered. If this element were absolutely constant, it would entail no ill effect. But in consequence of the finite diameter of the pupil of the eye, various obliquities are mixed up together, even if attention be confined to one part of the field. When the thickness of the layer is increased, it becomes necessary to reduce the obliquity to a minimum, and further to diminish the aperture of the eye by the interposition of a suitable slit. The effect of obliquity is shown by the formula 2 t (1 — cose) = nX. The necessary parallelism of the operative surfaces may be obtained, as in the above described apparatus, by the aid of levelling. But a much simpler device may be employed, by which the experimental 1893.] on Interference Bands and their Applications. 77 difficulties are greatly reduced. If we superpose a layer of water upon a surface of mercury, the flatness and parallelism of the surfaces take care of themselves. The objection that the two surfaces would reflect very unequally may be obviated by the addition of so much dissolved colouring matter, e.g. soluble aniline blue, to the water as shall equalise the intensities of the two reflected lights. If the ad- justments are properly made, the whole field, with the exception of a margin near the sides of the containing vessel, may be brought to one degree of brightness, being in fact all included within a fraction of a band. The width of the margin, within which rings appear, is about one inch, in agreement with calculation founded upon the known values of the capillary constants. During the establishment of equilibrium after a disturbance, bands are seen due to variable thickness, and when the layer is thin, persist for a considerable time. When the thickness of the layer is increased beyond a certain point, the difficulty above discussed, depending upon obliquity, be- comes excessive, and it is advisable to change the manner of obser- vation to that adopted by Michelson. In this case the eye is focused, not, as before, upon the operative surfaces, but upon the flame, or rather upon its image at E (Fig. 2). For this purpose it is only necessary to introduce an eye-piece of low power, which with the lens C (in its second operation) may be regarded as a telescope. The bands now seen depend entirely upon obliquity according to the formula above written, and therefore take the form of circular arcs. Since the thickness of the layer is absolutely constant, there is nothing to interfere with the perfection of the bands except want of homogeneity in the light. But, as Fizeau found many years ago, the latter difficulty soon becomes serious. At a very moderate thickness it becomes necessary to reduce the supply of soda, and even with a very feeble flame a limit is soon reached. When the thickness was pushed as far as possible, the retardation, calculated from the volume of liquid and the diameter of the vessel, was found to be 50,000 wave-lengths, almost exactly the limit fixed by Fizeau. To carry the experiment farther requires still more homogeneous sources of light. It is well known that Michelson has recently observed interference with retardations previously unheard of, and with the aid of an instrument of ingenious construction has obtained most interesting information with respect to the structure of various spectral lines. A curious observation respecting the action of hydrofluoric acid upon polished glass surfaces was mentioned in conclusion. After the operation of the acid the surfaces appear to be covered with fine scratches, in a manner which at first suggested the idea that the glass had been left in a specially tender condition, and had become scratched during the subsequent wiping. But it soon appeared that the effect was a development of scratches previously existent in a latent state. Thus parallel lines ruled with a knife edge, at first invisible even in 78 General Monthly Meeting. [April 10, a favourable light, became conspicuous after treatment with acid. Perhaps the simplest way of regarding the matter is to consider the case of a furrow with perpendicular sides and a flat bottom. If the acid may be supj)osed to eat in equally in all directions, the effect will be to broaden the furrow, while the depth remains unaltered. It is possible that this method might be employed with advantage to intensify (if a photographic term may be permitted) gratings ruled upon glass for the formation of spectra. GENERAL MONTHLY MEETING, Monday, April 10, 1893. Sir James Crichton-Browne, M.D. LL.D. F.K.S. Treasurer and Vice-President, in the Chair. W. H. Broadbent, M.D. Henry C. J. Bunbury, Esq. William Flockhart, Esq. Francis Gaskell, Esq. George W. Hemming, Esq. Q.CL Colin Charles Hood, Esq. Charles Langdon-Davies, Esq, B. W. Levy, Esq. Mrs. W. Eathbone, Granville E. Eyder, Esq. Mrs. Sharpe, F. W. Watkin, Esq. M.A. F.E.A.S, 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 at low temperatures : — Alexander Siemens, Esq £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 Tlie Secretary of State for India — Archaeological Surrey of India, New Series, Vol. I. 4to. 1889. Keport on Public Instruction in Bengal, 1891-2. fol. 1892. The Lords of the Admiralty— Nautical Almanac Circular, No. 14. 8vo. 1893. 1893.] General Monthly Meeting. 79 Accademia dei Lincei, Beale, Boma—Atti, Serie Quinta : Rendiconti. Classe di Scienze fisiche matematiehe e naturali. 1° Semestre, Vol. II. Fasc. 3-5. 8vo. 1893. Rendiconti, Serie Quinta, Classe di Scienze Morali, Storiche e Filologiche, Vol. II. Fasc. 1. 8vo. 1893. Agricultural Society of England, Boyal — Journal, Third Series, Vol. II. Part 1. 8vo. 1893. American Association for Advancement of Science — Proceedings, 41st Meeting, Rochester. 8vo. 1892. Astronomical Society, Boyal — Monthly Notices, Vol. LIIL No. 4. 8vo. 1893. Bankers, Institute of— Journal, Vol. XIV. Part 3 8vo. 1893. Birmingham Philosophical Society — Proceedings, Vol. VIII. Part 1. 8vo. 1891-2. British Architects, Boyal Institute of — Proceedings, 1892-3, Nos. 11, 12. 4to. British Association for Advancement of Science — Report of Meeting at Edinburgh, 1892. 8vo. British Astronomical Association — Journal, Vols. I. II. III. No. 4. 8vo. 1890-3. Canada Geological and Natural History, Survey of — Contributions to Canadian Paleontology, Vol. I. Part 4. 8vo. 1892. Carpenter, H. S. Esq. (the Editor) — Bourne's Handy Assurance Manual. 8vo. 1893. Chemical Industry, Society of— Journal, Vol. XII. No. 2. 8vo. 1893. Chemical Society — Journal for March, 1893. 8vo. Civil Engineers, Institution of — Minutes of the Proceedings, Vol. CXI. 8vo. 1893. Dax, Societe' de Borda — Bulletin, Dix-septieme Annee, 3e-4e Triinestre. 8vo. 1892. Editors — American Journal of Science for March, 1893. 8vo. Analyst for March, 1893. 8vo. Athenseum for March, 1893. 4to. Author for March, 1893. Chemical News for March, 1893. 4to. Chemist and Druggist for March, 1893. 8vo. Electrical Engineer for March, 1893. fol. Electric Plant for March, 1893. 8vo. Engineer for March, 1893. fol. Engineering for March, 1893. fol. Horological Journal for March, 1S93. 8vo. Industries for March, 1893. fol. Iron for March, 1893. 4to. Ironmongery for March, 1893. 4to. Lightning for March, 1893. 8vo. Monist for March, 1893. 8vo. Nature for March, 1893. 4to. Open Court for March, 1893. 4to. Photographic Work for March, 1893. 8vo. Surveyor for March, 1893. 8vo. Telegraphic Journal for March, 1893. fol. Transport for March, 1893. fol. Zoophilist for March, 1893. 4to. East India Association— Journal, Vol. XXV. No. 1. 8vo. 1893, Electrical Engineers, Institution of — Journal, No. 104. 8vo. 1893. Florence Biblioteca Nazionale Centrale — Bolletino. Nos. 173, 174. 8vo. 1893. Franklin Institute — Journal, No. 807. 8vo. 1893. Geographical Society, Royal — Geographical Journal, Vol. I. No. 4. 8vo. 1893. Geological Institute, Imperial, Vienna — Verhandlungen, 1892, Nos. 17, 18; 1893, No. 1. 8vo. Institute of Brewing — Transactions, Vol. VI. No. 5. 8vo. 1893. Iron and Steel Institute— Journal, 1892, No. 2. 8vo. 1893. 80 General Monthly Meeting. | April 10, Johns Hopkins University — American Chemical Journal, Vol. XV. No. 2. 8vo. 1893. Studies in Historical and Political Science, Eleventh Series, No. 2. 8vo. 1893-4. University Circular, No. 103. 4to. 1893. Junior Engineering Society — Record of Transactions, Vol. II. 8vo. 1891-2. Manchester Geological Society — Transactions, Vol. XXII. Parts 3. 4. Svo. 1893. Manchester Literary and Philosophical Society — Memoirs and Proceedings, Vol. VII. No. 1. 8vo. 1892-3. Massachusetts Institute of Technology, Boston, U.S.A. — Technological Quarterly, Vol. V. No. 3. Svo. 1892. Meteorological Society, Royal— Quarterly Journal, No. 85. Svo. 1893. Montpellier, Acade'mie des Sciences et Lettres — Memoires, Tome XI. Fasc. 3. 4to. 1892. Payne, Wm. W. Esq. and Hale, Geo. E. Esq. (the Editors) — Astronomy and Astro- Physics for March, 1893. 8vo. Pharmaceutical Society of Great Britain — Journal for March, 1893. Svo. Chemical Papers, edited by W. R. Duustan, Vol. I. Svo. 1892. Preussische Alcademie der Wissenschaften — Sitzungsberichte, Nos. XLI.-LV. 8vo. 1892. Prince, C. Leeson, Esq. F.R.A.S. (the Author) — The Summary of a Meteorological Journal for 1892. Richards, Admiral Sir G. H. K.C.B. F.R.S. (the Conservator) — Report on the Navigation of the River Mersey, 1892. Svo. 1893. Rio de Janeiro, Observatoire Imperial de — Annuario, Anno VIII. Svo. 1S92. Le Climat de Rio de Janeiro. By L. Cruls. Svo. 1892. Royal Society of London — Proceedings, No. 319. Svo. 1893. Saxon Society of Sciences, Royal— Mathenmtisch-phvsische Classe, Berichte, 1892, Nos. 4-6. 8vo. Sidgreaves, Rev. W. F.R.A.8. {th< Author) — Spectrum of Nova Auriga?. 4to. 1893. Society Arch xologi que dn Midi de hi France — Bulletin, No. 10. Svo. 1892. Society of Architects — Proceedings, Vol. V. No. 8. Svo. 1893. Society of Arts — Journal for March, 1893. 8vo. Stamius, Hugh, Esq. F.R.IB.A. (the Author) — The Theory of Storiation in Applied Art. Svo. 1893. Tacchini, Professor P. Hon. M.R.I, (the Author) — Memorie della Societa degli Spettroscopisti, Italiani, Vol. XXII. Disp. 3a. 4to. 1893. United Service Institution, Royal — Journal, No. 181. 8vo. 1893. United States Department of Agriculture — Monthly Weather Review for December, 1892. 4to. 1893. Vereins zur Beforderung des Gewerbfleisses in Preussen — Verhandlungen, 1893. Heft 2. 4to. 1S93. 1893.1 Sir W. E. Flower on Seals. 81 WEEKLY EVENING MEETING, Friday, April 14, 1893. Sir Frederick Abel, K.C.B. D.C.L. D.So. F.R.S. Vice-President, in the Chair. Sir William H. Flower, K.C.B. D.C.L. LL.D. D.So. F.E.S. Seals. Sir William Flower began by recalling that about two years ago Lord Salisbury, while taking a comprehensive survey of the general state of international politics, remarked that there were, happily, then, no graver subjects to excite the anger and jealousy of rival nations than seals and lobsters, and it was to the study of the habits of these animals that the energies of diplomatists were mainly directed. In the present lecture it was proposed to speak only of seals, and, taking the common seal as a type, he described its general character and position in the Animal Kingdom. The lecturer then passed in review the distinctive traits and geographical distribution of the various allied species of true seals, and pointed out their economic uses and mode of capture. The next animal treated of was the walrus, and finally, the third group into which the seals are divided — the eared-seals, sea-lions, or sea-bears. These differ from the true seals in possessing small external ears, and in the power of using their hind feet in walking on land like ordinary quadrupeds. It is animals of this group which yield the beautiful fur called " sealskin " in commerce, and the lecture was illustrated by speci- mens of this fur in various stages of preparation. The wholesale destruction of fur-seals which formerly went on throughout the southern hemisphere was next spoken of, and a more detailed account given of the very remarkable habits of the species from the Behring Sea, which for many years has been the main source of supply of sealskin dresses, and the right of capture of which is now the subject of controversy between Great Britain and the United States. After giving an outline of the questions, as far as tbey related to the natural history of the animals, to be placed before the arbitrators, he concluded by saying that we can scarcely be too grateful to the statesmen of both nations for having so far agreed as to bring the whole of this difficult and complicated question before such a tribunal as that now sitting at Paris. [W. H. F.] o Vol. XIV. (No. 87.) 82 Professor Alex. B. W. Kennedy [April 21, WEEKLY EVENING MEETING, Friday, April 21, 1893. David Edward Hughes, Esq. F.E.S. Vice-President, in the Chair. Professor Alex. B. W. Kennedy, F.E.S. M.B.I. Possible and Impossible Economies in the Utilisation of Energy. The importance of the subject is not difficult to understand if you realise the enormous results — so large as to be even of national interest — which depend upon what can and what can not be done in the way of utilising energy. Economy in energy may mean wealth and prosperity to a nation ; waste in energy may mean diminished commerce and general depression. As an engineer, I am bound to take my stand at once on the firm basis that practically nothing is impossible except perpetual motion. In essence all the things which I shall have to characterise as impos- sible are really perpetual motions, or what is the same thing, attempts to get more out of something than there is in it. It is familiar to even the least mechanical in this room that there are, in Nature, vast — I dare not say inexhaustible — sources from which we can obtain energy by certain more or less familiar processes. I say " obtain " energy, using the most familiar expression, but per- haps the word is not a very happy one. We require energy to light lamps, to smelt metals, to drive factories, to pull trains, but in no case do we obtain it ready made as we draw water from a well. There is plenty of it in existence, plenty to be had, but to get it in the form in which we want it we have always to transform it from some other form to the required one. There is in every electric lighting station in this city, for instance, first a transformation of the natural energy of chemical combination into heat, then the transformation of heat energy into mechanical energy in a steam engine, then the transformation of the mechanical energy into electrical energy in the dynamo, and lastly the trans- formation of electrical energy into light, and also very largely back again into heat, in the lamp. Often the transformations are not so numerous as in this case, but they always exist to some extent, and all the possibilities and impos- sibilities of which I have to speak are practically related to some or 1893.] on Economies in the Utilisation of Energy. 83 other of these transformations. About them are three fundamental facts which I will ask you to note. 1. Every transformation of energy is accompanied by some waste of energy. 2. Every transformation occurs in absolute accordance with certain phenomena which reproduce themselves so exactly that they have come to be called physical laics. 3. All the quantities which can appear in every transformation are as exactly measurable and have been as exactly measured as could be the temperature of this room, or the breadth of Albemarle Street. As to the first point, I use the expression " waste " rather than " loss " because the energy cannot well be said to be lost. The amount of energy wasted in a transformation is measured by noting what is called the efficiency of the transformation, which is usually expressed as a percentage. A transformation with only one per cent, loss, for example, would be said to have an efficiency of 99 per cent., and so on. Perpetual motions are simply transformations of 100 per cent, efficiency. In spite of the great and admitted imperfection of our knowledge of the physical universe, I think it is not impossible to arrive at some understanding as to how far the knowledge which we have can be held to be final, and how far or in what directions it is provisional. I mean, of course, so far as affects our particular object of saying what is, and what is not, possible in one special direction. It seems perhaps contradictory, but I think it is true, that our superstructure in physical knowledge is much more solid than our foundation. Our knowledge of the ultimate constitution of matter, and particularly of the ultimate constitution of " not-matter," cannot be said to be accurate as yet. But higher up in the scale matters are different, and it is as well that we should remember that there are physico-chemical facts and numbers that are just as fully established, although they refer to phenomena which we cannot entirely follow, as are the figures of the Nautical Almanac. Let me take the combustion of coal as an example with the external phenomena of which we are all familiar. Chemists have analysed the coal and know of what it consists ; so much carbon, so much hydrogen, so much oxygen ; they have measured for us that its elements in the combustion enter into various combinations, so that they can tell us exactly the maximum amount of heat energy which can be given out by the burning of a given weight of coal. Yet I have often enough met people who were quite convinced that they possessed the secret by which an amount of heat equal to double this quantity could somehow be obtained. The finality of our knowledge in this respect is quite independent of our ignorance of the ultimate nature of the coal or of the combustion. I have taken the phenomena of combustion as among those with which every one is fairly familiar. Let us deal with it for a few g 2 84 Professor Alex. B. W. Kennedy [April 21, Fig. 1. R ADIATI ON minutes further in special illustration of my subject. Fig. 1 shows fairly accurately how far we have got in working at the efficiency of this kind of transformation. We start with a given amount of potential energy, knowTn within very narrow limits, represented for us by a pound of coal with a sufficient weight of circumambient atmo- sphere. Let us represent this known amount of energy, as in the figure, by 100 per cent. What becomes of all this if the coal be burnt in the furnace, say, of an ordinary boiler, and if we endeavour to utilise this combustion energy in the conversion of water into steam ? On the left hand of my diagram you may see what often enough happens in every-day careless working ; on the right hand you may see what happens in thoroughly good work- ing with real care, but without any special apparatus. You will see that the amount of heat taken up by the steam varies from 50 to 80 per cent, of the whole heat ; that a small amount, from 5 per cent, down to nothing, is lost in imperfect com- bustion, that is, in the formation of carbonic oxide ; that a very much larger amount goes up the chimney, having been expended in heating the waste gases ; and that finally another large amount is purely wasted, being lost in radiation and otherwise. Now I ask you to notice particularly two things, first, looking at the right hand of the diagram, how much there is still possible. The efficiency of the pro- cess is about 80 per cent. The remaining 20 per cent, is all that can be saved. Of this some portion must go in heating the chimney gases. It is the price paid for the draught of the chimney. We must also lose something by radiation ; that is inevitable. We cannot look, therefore, to any very astound- ing increase of economy in boiler work over the best that has been clone. Secondly, I ask you to notice what an enormous amount is * The blocks illustrating this abstract have been kindly lent by the Editor of the Electrician. 40- 30- 20 10- STEAM 1893.] on Economies in the Utilisation of Energy. 85 possible on the left-hand side of the diagram which is impossible on the right — inrpossible, that is, because it has already been attained. Half of our possibilities — indeed, far more than half our possibilities — are of improving up to the best ; it is infinitely harder to improve up from the best. When any one tells us that he has invented something, or some method, by which one ton of coal goes as far as two, we may know for certain one of two things ; either he has made a mistake (which is possible enough) or else his standard of comparison has been unfor- tunately chosen. Hundreds of thousands of pounds have been thrown away on elaborate schemes which, at best, could do no more than bring bad and careless practice up to a level passed every day in places where care and common sense have been expended on the same matter. Plenty of room exists for raising the general average efficiency of boiler work ; for, if the average working all over the country were brought up to the standard of the best, there would, probably, be one-third less coal used every year than is now actually burnt. The process which we have discussed is, perhaps, really rather to be called a transference than a transformation ; at any rate, it falls into the category of transformation whose theoretical maximum efficiency is 100 per cent., or, allowing for absolutely inevitable losses, perhaps 90 per cent. But with many processes with which we have to do, unfortunately, our maximum theoretical efficiency is only 25 per cent., and instead of attaining 80 per cent, even of this we are often happy enough with half as much. In the very great majority of instances the mechanical energy which we utilise is originally obtained from the heat of combustion, transferred to some liquid or gaseous body, and by it made to cause certain parts in a machine to move, and to do mechanical work for us. Now the actual cycle of physical process, isothermal, adiabatic, isodynamic or what not, which the steam or air or gas may go through is often a very complicated one, sometimes so complicated that it is a matter of considerable difficulty to say beforehand exactly what the maximum theoretical efficiency is. We always, however, know two things about it : first, that it is always far less than 100 per cent. ; second, that it cannot exceed — and in all practical cases must fall considerably short of — a certain known limiting value much less than 100 per cent. This limiting value is the very familiar one T — T which is written — 7p — -• Here Tx stands for the highest tempera- 1 ture, measured above absolute zero, at which the working fluid receives heat. T2 stands for the lowest temperature at which the fluid parts with its heat. The difference between the two temperatures, T1 - T2, is the working difference of temperature. The value of the ratio which I have just given is always much less than unity, and must always be so. In the case of a modern steam engine its value is 86 Professor Alex. B. W. Kennedy [April 21 Fig. 2. often about 30 per cent., in the case of a gas engine from 60 to 65 per cent. In any actually possible steam engine the actual process differs so much from the ideal that not more than 20 or 25 per cent, (out of the 30 per cent, just mentioned) could be attained even if the process were carried out perfectly. But there are very great difficulties in the way of carrying out even this imperfect process at all completely, and so it comes about that, in the final results, only from 5 to perhaps 15 per cent, of the whole heat of the steam is ever turned into work, sometimes a little more, more often a little less. In Fig. 2 I have represented by 100 per cent., not the whole heat given to the steam, but that fraction of it (25 or 30 per cent.) which it is physically conceivable that any actual engine should turn into work. The space between a and b shows the losses due to the fact that the engine works in a cycle far inferior to the best possible cycle. The space between b and c shows the further losses which do actually occur in fact, the area under c being all that is utilised. What possibilities are there of increasing the theoretical maximum efficiency of an engine ? The whole matter depends upon whether we can increase the value of the fraction T - T — ^= — -. We can do this obviously by either making T] higher or T2 lower, or both. It is not difficult to see how this matter comes out practically. In all heat engines some fluid or other is used as a vehicle for the transformation of heat into work. It may be coal gas or producer gas, steam, air alone, or air mixed with the products of com- bustion, or even ether or ammonia. With steam we work between the temperatures of, say, 60° or 400° F., or thereabouts. Quite at the other end of the scale come engines worked by gas of different kinds, where combustion actually takes place inside the engine and nt)t in a furnace, and where the highest temperature may, perhaps, be 1893.] on Economies in the Utilisation of Energy. 87 70- 60 as great as 2000° F. Hot air occupies an intermediate position. With ether or ammonia the temperatures are all very much lower. From onr present point of view it is necessary to remember that all these divers working fluids work under the same physical laws and limitations. How, then, do they stand in reference to this problem of economy ? First of all, the mere nature of no one gives it any thermo-dynamic advantage over the others. The fact that steam can be liquefied in a condenser is a great convenience to us, but does not make it, per se, one whit worse or better than air, which can- FIG< 3, not be liquefied — at least % in a condenser. The man- 10<> ner in which the choice of fluid affects the value of the 90 maximum possible thermo- dynamic efficiency is indi- cated in Fig. 3. With gas, 80- the highest temperature is the temperature of com- bustion ; the theoretical maximum efficiency is on this account already ex- tremely high. With air, the temperature is only in- directly derived from the temperature of combustion, and the maximum efficiency 40 is smaller, although it is still high. With steam (apart from super-heating) 30 the temperature is depen- dent upon, and limited by, considerations of pressure, and consequently of safety. With ammonia it is simi- larly limited ; but the en- gine lies much further down the scale, both as to Tx and as to T2. From Fig. 3 we may gather that with gas engines the theoretical efficiency is already so high that we need hardly trouble ourselves about attempting to raise it. With gas, in fact, and to a smaller extent with air, the possibility of improvement lies in bringing the actual up to the theoretical process, and not in attempting to raise the efficiency of the latter. With steam, however, it is different. We want much to raise the theoretical limit of efficiency. But here we 50- 20 10- CAS Al R STEAM AMMONIA 88 Professor Alex. B. W. Kennedy [April 21, are dealing with a material which is liquid at ordinary temperatures and pressures, so that in its working condition it is a vapour and not a gas, and its temperature cannot be raised without at the same time raising its pressure. Considerations of safety and strength of our materials become here very important, but even if we left them out of account altogether, and raised the value of the maximum working pressure of steam engines from its present limit of 10 atmospheres to 20 atmospheres — that is, 100 per cent. — we should have increased the theoretical maximum efficiency only about 10 per cent., a quantity hardly worth considering in such a case. No doubt the direction in which to seek for improvement is in that of what is called super-heating the steam, or raising its tempera- ture after it has been formed — converting the vapour into gas without increasing its pressure. Theoretically this can be done to any extent, and I have no doubt that within the next coming years it will be very largely done. It is no new idea, although it is only recently that the use of mineral lubricants in engines has made it thoroughly practicable. The losses between b and c in Fig. 2 are due to many causes, but chiefly to two. The first of these is that the steam is thrown away at too high a pressure — i.e. that it is not expanded sufficiently far in the cylinder. Mechanically this is remediable at once, but only at the cost of making the engine unduly large and costly for its work. This cause of loss is, therefore, likely to remain. The second is one about which there has been much con- troversy both here and abroad, but which, thanks to the work of such men as Willans and Cotterill and Donkin, is now much cleared up. It is simply this — that as the fresh hot steam is always admitted to a cylinder which has just been emptied of steam having a much lower temperature, a cylinder, moreover, which is made of excellently conducting material, a very large proportion of that steam is at once converted into water on entrance, so that for every cubic foot of steam which leaves the boiler and passes along the pipes perhaps only two-thirds, or even half or less, does work in the cylinder as steam ; the rest passes through the engine as water. It is sometimes partially re-evaporated, but never in such fashion or at such time as to be of much real service in doing work. Here truly is a field for economy, and one with very great possibilities. I have talked long about steam engines. The subject is tempting, at least tempting to me, and, after all, steam is still the working fluid par excellence. But I must not forget that my subject has many branches, and must look at some of the others. The future of gas engines is one which has great possibilities ; we have seen that they represent, in fact, the highest existing theoretical maximum efficiency. Up to a certain point their progress was asto- nishingly rapid ; at present, for a few years, they have more or less stood still, although the number of them has continually multiplied. Just now there are signs that the manufacturers — just possibly it 1893; on Economies in the Utilisation of Energy. 89 may have something to do with the pressure of severe competition — are going to do their best to move forward a little, to make larger and faster running machines, and, in fact, to make an effort to pene- trate further into the country where the steam engine has for so long held undisputed sway. About this we must not concern ourselves here, however. The maximum theoretical efficiency of a gas engine is about 80 per cent., or nearly three times as great as in a steam engine. It is obvious that this figure is so high that we need hardly attempt to raise it, especially as we are so far from actually realising it as yet. In Fig. 4 the theoretical maximum efficiency is taken as 100 per cent., in the same way as in Fig. 2, and the line b shows how much of this is actually turned into work, the area above b representing the lost energy. The greatest cause of loss, that above the line c, is represented by the heat taken from the water surrounding the cylinder. The fact is that we are trying to obtain incom- patible results. To reach the high efficiency we make the initial tem- perature very high. But, then, any such temperature would melt up our machines altogether, if the metal were only allowed to reach it. We have, therefore, to adopt the some- what barbarous expedient of con- tinually keeping the metal cool by a current of water passing through a jacket. This water must of neces- sity pick up all the heat which can get through the metal and carry it away to waste. Although, therefore, our theoretical maximum efficiency is so much greater than that of a steam engine, our actual efficiency is not nearly so great (comparing the lines c in Fig. 2 and b in Fig. 4). Notwithstanding this, the actual energy utilised per thermal unit of combustion heat in a gas engine is very considerably greater than in a steam engine. Undoubtedly, very great possibilities for increased economies exist here. I have reserved to the end some discussion of possibilities and 90 Professor Alex. B. W. Kennedy [April 21, impossibilities in connection with some complete industrial processes. Let us take first the generation and distribution of electricity, a matter which is of such keen interest now to so many of us, whether from the point of view of economy in production or economy in our quarter's bills ! The various stages of Fig. 5 tell a tale which, perhaps, may interest you. They represent the gradually degenerative process by which the chemical energy of combustion is converted into electric light. To the left hand of the diagram is represented the boiler process, and the various transformations are represented from left to right, until the lamps are arrived at on the right hand of the figure. Similar letters are used in each section of the figure for similar quantities of energy. In each section the losses of the section before are written off, and the heat actually carried forward is called 100 per cent. K represents the losses in the boiler, which is assumed to have an efficiency of 80 per cent. H represents waste mainly due to condensation in steam pipes, and also to the driving of pumps, and other such losses inevitable in a central station. The third section represents the whole heat which has been received by that portion of the steam which actually found its way to the main engines, and of this, G is the part unavoidably lost from thermo- dynamic limitations. In Section IV. the heat actually received by the engine is called 100 per cent. Of this, the area F is wasted, and the remainder turned into work. Section V. shows the whole heat turned into work by the engine as 100 per cent., of which the area E represents the energy necessary to drive the engine itself, which, therefore, never reaches the dynamo. In Section VI. the energy received by the dynamo is taken as 100 per cent., and the area D represents the dynamo losses, which are wonderfully small. The energy — now in the form of electrical energy — which leaves the terminals of the dynamo, is represented by 100 per cent, in Section VII. Of this, a certain proportion, sometimes small, sometimes large, but here represented by C, is expended in mains, transformers, or batteries, and never reaches the lamps. Finally, at the right- hand side of the figure we get the energy received by the lamps as 100 per cent., out of which only the small, almost insignificant quantity A is turned into light, the huge remainder B being once more converted into heat. If the size of the area A in Section I. be looked at, it will be seen what an insignificant quantity of the whole heat of combustion is actually and finally turned into its intended purpose. The result savours a little of the ludicrous. Let us go back and review its possibilities. The losses K, I need not deal further with. H represents losses about which we engineers feel very sore, and which sometimes try our temper and our patience greatly, and which are particularly persistent and hard to get rid of. G and F, I have already dealt with. E and D do not look very promising as fields for radical improvement. There are few things 1893." on Economies in the Utilisation of Energy. 91 I think more creditable of modern engineers than the smallness of the losses represented by D. I do not think that the distribution losses G are likely to be reduced to any very sensational extent below the figure at which I have put them. We frequently hear of their almost neg- ligible magnitude, but whenever they get really measured, the sum of a number of things which separately are supposed to be so minute appears to be anything but neg- ligible. No doubt the 15 per cent, loss will be gradually driven back to 10 per cent. ; but it will be hard work, and will come about only by degrees and by care and pains in detail, not by any new system of dis- tribution or by any strik- ing invention. But truly in our last stage we have got one in which improvement is needed and in which we all hope that enormous improvement is possible. Moreover, here it can no longer be said that im- provement is a matter of detail and of common sense only. On the con- trary, here is a case where we know beforehand that we may any day be sur- prised by a discovery, on the part of one of the many men who are Fig. 5. 92 Professor Alex. B. W. Kennedy [April 21, devoting time and thought to the matter, which may even enable us to multiply many fold the amount of light which we can obtain from a given quantity of energy. There is yet another direction in which possible economy is to be looked for, a very fascinating one, and by no means an un- promising one. Look for a moment again at Fig. 5. Except only the process at the lamp itself, all the transformations have fair economy, so good that one sees at once that no radical defect exists in them. But cannot some of these be done away with altogether ? It is the number of them that tells, and brings down the final result. If an ordinary gas engine be substituted for a steam engine we cut out one transformation altogether. The boiler losses disappear, or rather, such corresponding losses as exist occur in the gasworks. At the same time we substitute the higher efficiency of the gas engine for the lower of the steam engine, which may be a very important matter. It is practically equivalent to cutting G out altogether. Of another kind is the possibility at present much talked of, the substitution namely, not only of a gas engine for a steam engine, but at the same time also of a gas producer for a boiler, so that the motor fluid should be producer gas made on the premises and not steam or coal gas from public mains. There seems no doubt that the combination, although it does not much reduce the number of transformations, gives under certain conditions a very high economy of fuel indeed. I do not think the evidence before us is as yet suffi- cient, although I hope it shortly will be, to enable us to say how far under ordinary working conditions the actual combined efficiency of the whole plant will be distinctly greater than that of existing systems. [The lecturer dealt with the question of the utilisation of dust- bin refuse, of the economic efficiency of electric tramways and of compressed air transmission, illustrating these by diagrams. He discussed also the effect of "load factor" on economic problems. He then concluded as follows : — ] To sum up the whole matter in the way of possibilities and impossibilities, there does not seem to be anything very startling before us in the way of possible economies, except in the two direc- tions of efficiency of lamps as light producers, and of bringing up gas engines to their theoretical maximum. In other respects matters are running along lines which I have endeavoured to indicate, and along which they will doubtless develop more or less rapidly, but always less and less rapidly as they get nearer their limiting effi- ciency. There is no one point in w7hich we have not some measure- ments which enable us to set bounds to the possibility of improvement along any known lines, and thus we have means for gauging the value of the pretensions made by each new method, or scheme, or 1893.] on Economies in the Utilisation of Energy. 93 invention, as it appears — not merely guessing at it, but actually estimating its possible value numerically. For those of us who are not born to be inventive geniuses there is always the consoling thought that the difference between good engineering and bad engineering in economy, with the very same materials, is very much greater than the difference between good engineering and any probable improvements upon it. And meantime, we find our hands sufficiently full in trying to keep up to the best existing standards, pending the time when Messieurs the discoverers show us how to get on a little further. [A. B. W. K.] 94 Mr. Francis Gotch [April 28, WEEKLY EVENING MEETING, Friday, April 28, 1893. Sin James Crichton-Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. Francis Gotch, Esq. M.A. F.E.S. The Transmission of a Nervous Impulse. The lecturer opened with a short account of the present state of our knowledge as to the anatomical structures of nerve-fibres. He then described and repeated the experiments of Helmholtz, made 50 years ago, with the object of ascertaining the rate at which a nervous impulse was conducted along a nerve-fibre. These experi- ments form the basis of our more exact knowledge as to that capacity for transmission which is the peculiar vital function of nerves. The essential feature in the process is the power which each in- dividual part of the living nerve-fibre possesses of awakening in response to a sudden change in its physical environment, this property being expressed by the term " excitability " ; in the transmission of the nervous impulse each successive individual part awakens in consequence of the subtle changes present in its aroused neighbours. The awakening thus travels along the nerve as a flame along a fuse. The power of transmitting a change, and the power of initiating such change in response to a stimulus, in other words, conduction and excitability, are thus brought into correlation. The lecturer then proceeded to demonstrate and describe experi- ments carried out by Mr. J. S. Macdonald and himself, in the Physiological Laboratory of University College, Liverpool, upon this subject, these experiments having been made in order to ascer- tain how far these two properties, (a) of responding to an external stimulus, (b) of transmitting the nerve impulse started by such a stimulus, could be considered as identical. In order to ascertain this, an agent was used to modify, on the one hand, the capacity of the nerve to be aroused by physical agencies, and on the other, its power of transmitting an impulse when aroused. The agent employed was a localised alteration in temperature, and experiments were described and demonstrated which showed that whereas cooling to 5° C. tended to block the transmission, such cooling, far from rendering the nerve less responsive to external stimuli, made it more readily affected by the stimulating influence of a large number of physical agencies. Such agencies were shown to be (1) galvanic currents, (2) condenser discharges, (3) mechanical 1893.] on The Transmission of a Nervous Impulse. 95 blows, (4) chemical reagents. To all these the nerve responded better when cooled, though it transmitted the nerve impulse pro- duced by such response with greater difficulty. To one agent only did the nerve respond less readily when under the influence of localised cold ; this was the induced electrical current. It thus appears necessary to reconstruct our view of the nature of the process during nerve transmission, for the two events in the nerve, the response to external stimuli and the power to transmit such response, are affected in a diametrically opposed manner by such a simple change as alteration in the nerve's temperature. The favourable influence of localised cold on the response of excitable tissues to external stimulation was further displayed by description and demonstration of the effects produced when muscles, and not nerves, were the objects of experiment. In all cases cold favoured the capacity of the muscle to reply to the stimulus. Finally, the lecturer brought forward some observations which appeared to show that in addition the transmitting power of a nerve is largely affected by the nature of the agent which started the nerve impulse. We have found it possible to arouse a nerve by a galvanic current in two ways : (1) so that localised cooling of a portion of the conducting path will favour the passage of the impulse (the normal condition), and (2) so that the same localised cooling will block the impulse. It would thus seem that nervous impulses, when started on their journey along nerves, bear throughout that journey some impress of the agent which started them, and hence, that the im- pulses which are initiated by even slightly different physical agencies, and are then transmitted along nerve-fibres, differ from one another as regards the character of some fundamental quality. Professor Gotch concluded that these and other recent observa- tions gave experimental proof that the property of transmission possessed by nerves is correlated, not merely with that of excitability, but largely with the source, and thus the nature of the impulse, so that the unknown molecular changes which form the living basis of such transmission in any one nerve-fibre are not the same for all impulses, but change with the source of each. [F. G.] 96 Annual Meeting. [May 1, ANNUAL MEETING, Monday, May 1, 1893. Sir James Crichton-Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. The Annual Report of the Committee of Visitors for the year 1892, testifying to the continued prosperity and efficient management of the Institution, was read and adopted. The Real and Funded Property now amounts to above 104,000Z. entirely derived from the Contributions and Donations of the Members and of others appreciating the value of the work of the Institution. Sixty- three new Members were elected in 1892. Sixty- three Lectures and Twenty Evening Discourses were delivered in 1892. The Books and Pamphlets presented in 1892 amounted to about 238 volumes, making, with 530 volumes (including Periodicals bound) purchased by the Managers, a total of 768 volumes added to the Library in the year- 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.R.S. Secretary— Sir Frederick Bramwell, Bart. D.C.L. LL.D. F.R.S. M. Inst. C.E. Managers. Captain W. deW. Abney, C.B. E.E. D.C.L. F.R.S. Shelford Bidwell, Esq. M.A. F.R.S. John Birkett, Esq. F.R.C.S. Joseph Brown, Esq. C.B. Q.C. Sir Douglas Galton, K.C.B. D.C.L. LL.D. F.R.S. David Edward Hughes, Esq. F.R.S. Alfred Bray Kempe, Esq. M.A. F.R.S. George Matthey, Esq. F.R.S. Hugo Miiller, Esq. Ph.D. F.R.S. The Right Hon. Earl Percy, F.S.A. William Chandler Roberts-Austen, Esq. C.B. F.R.S. Sir David Salomons, Bart. M.A. F.R.A.S. F.C.S. Alexander Siemens, Esq. M. Inst. C.E. Basil Woodd Smith, Esq. F.R.A.S. F.S.A. Sir Richard Webster, M.P. Q.C. LL.D. Visitors. Charles Edward Beevor, M.D. F.R.C.P. Henry Arthur Blyth, Esq. Francis Woodhouse Braine, Esq. F.R.C.S. John Tomlinson Brunner, Esq. M.P. Michael Carteighe, Esq. F.C.S. Rookes Evelyn Crompton, Esq. M. Inst. C.E. James Farmer, Esq. J.P. Robert Hannah, Esq. Donald William Charles Hood, M.D. F.R.C.P. Raphael Meldola, Esq. F.R.S. Lachlan Mackintosh Rate, Esq. M.A. Boverton Redwood, Esq. F.C.S. John Callander Ross, Esq. John Bell Sedgwick, Esq. J.P. F.R.G.S. George Andrew Spottiswoode, Esq. 1893.] Mr. Shelf ord Bidwell on Fog, Clouds and Lightning. 97 WEEKLY EVENING MEETING, Friday, May 5, 1893. Sir Frederick Bramwell, Bart. D.C.L. LL.D. F.R.S. Honorary Secretary and Vice-President, in the Chair. Shelford Bidwell, Esq. M.A. LL.B. F.R.S. M.B.I. Fogs, Clouds and Lightning. The air, as every one knows, is composed almost entirely of the two gases, oxygen and nitrogen. It also contains small quantities of other substances, of which the chief are carbonic acid gas and water vapour, and it is the latter of these constituents, water vapour, or " steam " as it is sometimes called, that will principally concern us this evening. The quantity of invisible water vapour which the air can at any time take up depends upon the temperature ; the higher the tem- perature of the air the more water it can contain. The proportion, however, never exceeds a few grains' weight of water to a cubic foot of air. Air at any temperature, containing as much water as it can possibly hold, is said to be " saturated," while the temperature at which air containing a certain proportion of water becomes saturated is called the " dew point." The water vapour contained in the atmosphere plays a very im- portant part in many natural phenomena. Among other things, it is the origin of clouds and of fogs. If a body of air containing water in the form of invisible vapour is quickly cooled to a temperature below its dew point, a portion of the vapour becomes condensed into a number of minute liquid particles of water, forming a visible mist, which, when it is suspended in the upper regions of the air, is called a cloud, and when it rests upon the surface of the earth is only too familiarly known as a fog. The cooling of water-laden air may be brought about in various ways, resulting in the formation of clouds of several distinct char- acters. [Photographic examples of cumulus, stratus and cirrus clouds were exhibited upon the screen.] For experimental purposes a small body of air may be most conveniently cooled by allowing it to expand. I have here a flask of air which can be connected with the partially exhausted receiver of an air-pump. Inside the flask is an electrical thermometer or thermo-junction, the indications of which can be rendered evident to all present by the movement of a spot of light upon a scale attached to the wall. A deflection of the Vol. XIV. (No. 87.) h 98 Mr. Shelford Bidivell [May 5, spot of light to the left indicates cold, to the right, heat. When the stop-cock is opened so that a portion of the air escapes from the flask into the air-pump receiver, you see at once a violent movement of the spot of light to the left, showing that the expansion of the air is accompanied by a fall of temperature. If more air from the room is allowed to enter the flask, the spot moves in the opposite direction. The large glass globe, upon which the beam from the electric lantern is now directed, contains ordinary air, kept in a state of saturation, or nearly so, by the presence of a little water. You will observe that although heavily laden with water vapour the air is perfectly transparent. If, now, we turn a tap and so connect the globe with the exhausted receiver, the air expands and becomes colder ; the space inside the globe is no longer able to hold the same quantity of water as before in the form of vapour, and the excess is precipitated as very finely divided liquid water — water dust it may be called — which fills the globe and is perfectly visible as a cloud or mist. In a few minutes the cloud disappears, partly, no doubt, because some of the particles of water have fallen to the bottom of the vessel, but chiefly because the air becomes in time warmed up to its original temperature (that of the room), and the suspended water is converted back again into invisible vapour. Now let us repeat the experiment, and before the cloud has time to disperse let us admit some fresh air from outside ; the cloud, as you see, vanishes in an instant. The compression of the air raises the temperature above the dew point, and the small floating particles of water are transformed into invisible vapour. I once more rarefy the air, and admit a fresh supply while holding the flame of a spirit-lamp near the orifice of the inlet pipe, so that some of the burnt air is carried into the interior of the globe. When the air is again expanded a cloud is formed which is, as you observe, far more dense than the others were. It appears on examination that the increased density of this cloud is not due to the condensa- tion of a greater quantity of water. Little, if any, more water is precipitated than before. But the water particles are now much more numerous, their increased number being compensated for by dimin- ished size. Within certain limits, the greater the number of particles into which a given quantity of water is condensed, the greater will be the apparent thickness of the mist produced. A few large drops will not impede and scatter light to the same extent as a great number of small ones, though the actual quantity of condensed water may be the same in each case. Then comes the question, why should the burnt air from the flame so greatly increase the number of the condensed drops ? An answer, though perhaps not quite a complete one, is furnished by some remarkable experiments made by M. Coulier, a French pro- fessor, nearly twenty years ago. He believed his experiments pointed to the conclusion that water vapour would not condense at all, even at temperatures far below the clew point, unless there were 1893.] on Fog, Clouds and Lightning. 99 present in the air a number of material particles to serve as nuclei around which the condensation could take place. All air, he says, contains dust; by which term he does not mean such dust as is rendered evident in this room by the light scattered along the track of the beam issuing from the electric lantern, which consists of comparatively gross lumps of matter, but particles of ultra-micro- scopical dimensions, " more tenuous than the motes seen in a sunbeam." It is upon such minute specks of matter that water vapour is condensed. Anything that increased the number of dust particles in the air increased the density of the condensation by affording a greater number of nuclei. Air in which a flame had been burnt he supposed to be very highly charged with finely-divided matter, the products of combustion, and thus rendered extraordinarily " active " in bringing about condensation. And that, according to Coulier's view, is the reason why such a dense fog was formed when air which had been contaminated by the spirit flame was admitted to our globe. On the other hand, air, even burnt air, which has been filtered through tightly packed cotton wool, is found to be perfectly inactive. No cloud or mist will form in it, however highly it may be super- saturated. Coulier explained this fact by supjDosing that the process of filtration completely removed all dust particles from the air. On the table before you is a globe containing air which has been thus treated, and which is kept saturated by a little water. When this globe is connected with the exhausted receiver, no trace of any mist is produced : the air remains perfectly clear. We will now admit a little of the ordinary air from outside, and again cool it by expansion. Quite a respectable cloud is thereupon formed in the globe. The experiments of Coulier were repeated and confirmed by Mascart. The latter also made one additional observation which may very probably turn out to be of great importance. He found that ozone, or rather, strongly ozonised air, was a very active mist producer, and that unlike ordinary air, it was not deprived of its activity by filtration. Four or five years later, ail the facts which had been noticed by Coulier, and others of an allied nature, were independently discovered by Mr. Aitken, who has devoted much time ancl study to them and made them the foundation of an entirely new branch of meteorology. Later, perhaps, we may see reason to doubt whether all the conclusions of Coulier and Aitken are quite accurate, especially as regards the action of so-called products of combustion. What has been said so far applies equally to the generation of clouds and of country fog, for a pure unadulterated fog, such as occurs in rural districts, consists simply of a cloud resting upon the surface of the earth. The fogs, however, which afflict many large towns, and London in a marked degree, appear to possess a character peculiar to themselves. They are distinguished by a well-known h 2 100 Mr. Shelford Bidwell [May 5, colour, which has sometimes been likened to that of pease soup : their density is abnormal, so is their persistence ; and they often occur when the temperature of the air is considerably above the dew point. But what renders them especially objectionable is their acrid and corrosive quality, in virtue of which they exert a highly deleterious action upon animal and vegetable life. The uncleanness of a town fog is of course due to the sooty and tarry matters with which it is charged, and which are derived from the smoke of innumerable fires. Its other and more mischievous specialities are mainly attributable to certain products of the com- bustion of sulphur, a substance which exists in relatively large proportions (from half to one per cent.) in nearly all varieties of coal. We may make a sample of London fog in the glass globe by burning a little sulphur near the orifice of the inlet pipe while air is being admitted; and in order to prevent the entrance of any solid particles of sublimed sulphur, we will filter the air through a little cotton wool. The fog formed when the air is expanded far exceeds in density any we have yet seen. The globe appears almost as if it were filled with something that could be cut with a knife. This is hardly the time or the place to discuss the possible methods by which town fogs might be abolished as such, or rendered as innocuous as those of the country. It is impossible to doubt that year by year they are increasing in virulence, and when the burden of the evil becomes too grievous to be borne, as is likely to be the case before many more winters are past, the remedy will perhaps be found in the compulsory substitution of gas for coal as the ordinary domestic fuel. Every one has noticed how dense and dark a thundercloud is. It shuts out daylight almost as if it were a solid substance, and the glimmer that penetrates it is often imbued with a lurid or copper- coloured tint. I had always found it rather difficult to believe that these peculiarities were due simply to the unusual extent and thickness of the clouds, as is commonly supposed to be the case, and it occurred to me about three years ago, that perhaps some clue to the explana- tion might be afforded by the electrification of a jet of steam. On making the experiment I found that the density and opacity of the jet were greatly increased when an electrical discharge was directed upon it, while its shadow, if cast upon a white screen by a sufficiently strong light, was of a decidedly reddish-brown tint. As a possible explanation of the effect I suggested that there might occur some action among the little particles of water of a similar nature to that observed by Lord Eayleigh in his experiments upon water jets. Perhaps you will allow me to show his fundamental experiment before further discussing the steam jet. A jet of water two or three feet long is made to issue in a nearly vertical direction from a small nozzle. At a certain distance above 1893.] on Fog, Clouds and Lightning. 101 the nozzle the continuous stream is found to break up into separate drops, which collide with one another, and again rebounding, become scattered over a considerable space. But when the jet is exposed to the influence of an electrified substance, such as a rubbed stick of sealing wax, the drops no longer rebound after collision, but coalesce, and the entire stream of water, both ascending and descending, becomes nearly continuous. Look at the shadow of the jet upon the screen and notice what a magical effect the electrified sealing wax produces. There is one other point to which I wish to direct your particular attention. If the sealing wax, or better, the knob of a charged Leyden jar, is held very close to the jet, so that the electrical influence is stronger, the separate drops do not coalesce as before, but become scattered even more widely than when no electrical influence was operating. They become similarly electrified and, in accordance with the well-known law, repel one another. We will now remove the water jet, and in its place put a little apparatus for producing a jet of steam. It consists of a half-pint tin bottle, through the cork of which passes a glass tube terminating in a nozzle. When the water in the bottle is made to boil a jet of steam issues from the nozzle, and if we observe the shadow of the steam jet upon the screen we shall see that it is of feeble intensity and of a neutral tint, unaccompanied by any trace of decided colour. A bundle of needles connected by a wire with the electrical machine is placed near the base of the jet, and when the machine is worked electricity is discharged into the steam. A very striking effect instantly follows. The cloud of condensed steam is rendered dense and dark, its shadow at the same time assuming the suggestive yellowish-brown colour. I at first believed that we had here a repetition, upon a smaller scale, of the phenomenon which occurs in the water jet. The little particles of condensed water must frequently come into collision with one another, and it seemed natural to suppose that, like Lord Kay- leigh's larger particles, they rebounded under ordinary circumstances, and coalesced when under the influence of electricity. The great majority of the small particles ordinarily formed consisted, I thought, of perhaps only a few molecules, which were dispersed in the air and again converted into vapour without ever having become visible, while the larger particles formed by their coalescence under electrical action were of such dimensions as to impede the more refrangible waves of light. Hence the brownish-yellow colour. Other explanations have been proposed. There is the molecular shock theory of the late R. Helmholtz (who, as it turned out, had studied electrified steam jets before I made my own experiments) ; I shall refer to his speculation later. And there is the dust-nucleus theory, which no doubt appears a very obvious one. Though I knew that my own hypothesis was not quite free from objection, neither of these alternative ones commended itself to me as preferable ; and so the matter rested until a few months ago, when 102 Mr. Shelford Bidwell [May 5, the steam jet phenomenon was discussed anew in a paper communicated to the Koyal Society by Mr. Aitken. Mr. Aitken said that he did not agree with my conjecture as to the nature of the effect. This led me to investigate the matter again, and to make some further experiments, the results of which have convinced me that I was clearly in error. At the same time it seems to me that the ex- planation which Mr. Aitken puts forward is little less controvertible than my own. Mr. Aitken's explanation of the phenomenon is, like mine, based upon Lord Eayleigh's work in connection with water- jets, but, unlike mine, it depends upon the experiment which shows that water particles when strongly electrified are scattered even more widely than when unelectrified. He believes, in short, that elec- trification produces the effect, not by promoting coalescence of small water particles, but by preventing such coalescence as would naturally occur in the absence of electrical influence. In the elec trified jet, he says, the particles are smaller but at the same time more numerous ; thus its apparent density is increased. The chief flaw in my hypothesis lies in the fact that the mere presence of an electrified body like a rubbed stick of sealing wax, which is quite sufficient to cause coalescence of the drops in the water jet, has no action whatever upon the condensation of the steam jet. There must be an actual discharge of electricity. But it is by no means essential, as Mr. Aitken assumes, that this discharge should be of such a nature as to electrify, positively or negatively, the particles of water in the jet. If, instead of using a single electrode, we employ two, one positive and the other negative, and let them spark into each other across the jet, dense condensation at once occurs. [Experiment.] So it does if the two discharging points are removed quite outside the jet. [Experiment.] A small induction coil giving sparks an eighth of an inch in length causes dense con- densation when the electrodes are more than an inch distant from the nozzle and on the same level. [Experiment.] In one experiment a brass tube two feet long was fixed in an inclined position with its upper end near the steam jet, and its lower end above the electrodes of the induction coil. In about three seconds after the spark was started dense condensation ensued, and it ceased about three seconds after the sparking was stopped. No test was needed, though in point of fact one wras made, to show that the steam was not electrified to a potential of a single volt by this operation. And the time required for the influence to take effect showed that whatever this influence might be it was not induction. The inference clearly is that in some way or other the action is brought about by the air in which an electrical discharge has taken place, and not directly by the electricity itself. The idea has no doubt already occurred to many of you that it is a dust effect. Minute particles of matter may be torn off the electrodes by the discbarge, and form nuclei upon which the steam may condense. The experiments of Liveing and Dewar have indeed shown that small 1893.] on Fog, Chads and Lightning. 103 particles are certainly thrown off by electrical discharge, and the idea that such particles promote condensation appears to be sup- ported by the fact that if a piece of burning material, such as touch- paper, is held near the jet so that the products of combustion can pass into it, thick condensation is produced. [Experiment.] From a recent paper by Prof. Barus, published in the ' American Meteorological Journal' for March, it appears that he also is of opinion that such condensation is in all cases due to the action of minute dust particles. Yet it is remarkable that Mr. Aitken, the high priest and chief apostle of the philosophy of dust, gives no countenance to the nucleus theory. He does not even advert to its possibility. I imagine that his experiments have led him, as mine have led me, to the conclusion that it is untenable. And this not only in the case of electrical discharge, but also in the case of burning matter. If we cause an electrical discharge to take place for some minutes inside a suitably arranged glass bottle, and then, ten or fifteen seconds after the discharge has ceased, blow the air from the bottle into the steam jet, the condensation is not in any way affected. Yet the dust could not have subsided in that time. And again, if we fill another large bottle with dense clouds of smoke by holding a bundle of burning touch-paper inside it, and almost immediately after the touch-paper is withdrawn, force out the smoke-laden air, through a nozzle, upon the jet — you can all see the black shadow of the smoke upon the screen — nothing whatever happens to the jet. Yet a mere scrap of the paper which is actually burning, though the ignited portion may not be larger than a pin's head, at once darkens the jet. Dead smoke (if I may use the term) exerts little or no influence by itself: there must be incandescent matter behind it. The question naturally arises, whether incandescent matter may not be sufficient of itself, without any smoke at all. We can test this by making a piece of platinum wire red hot and then holding it near the jet. It is seen to be quite as effective as the burning touch-paper. Yet here there can be no nuclei formed of products of combustion, for there is no combustion ; there is simply ignition or incandescence. One other point I may mention. It is stated by Barus in the paper above referred to that the fumes given off by a piece of phos- phorus constitute a most efficient cause of dense condensation. This is true if they come directly from a piece of phosphorus ; but if phosphorus fumes are collected in a bottle and then directed upon the jet, all traces of unoxidised phosphorus being first carefully removed, they are found to be absolutely inoperative. Phosphorus in air can hardly be said to be incandescent, though it is luminous in the dark ; but it appears to act in the same manner as if its temperature were high. All these facts seem to indicate that the several causes men- tioned, electrical, chemical and thermal, confer upon the air in which they act some temporary property — certainly not due to mere 104 Mr. Shelf ord Bidwell [May 5, inert dust — in virtue of which it acquires an abnormal power of promoting aqueous condensation. I thought that possibly some clue as to the nature of this property might be obtained by observing how some other gases and vapours behaved ; but though the experiments I made perhaps tend to narrow the dimensions of the mystery, I cannot say that they have completely solved it. Indeed some of the results only introduce additional perplexities. One of the most natural things to try is hydrochloric acid, which is known to have a strong affinity for water. If we heat a little of the acid solution in a test-tube, closed with a cork, through which a glass tube is passed, and direct the issuing stream of gas upon the jet, the densest condensation results. [Experiment.] The vapours of sulphuric and nitric acids also cause dense condensation, and I sup- pose both of these have an affinity for water. But so also, and in an equally powerful degree, does the vapour of acetic acid ; yet the affinity of this acid for water, as indicated by the heat evolved when the two are mixed, is very small. Ammonia gas, when dissolved in water, causes the evolution of much heat. Yet a stream of this gas directed upon the jet has no action. [Experiment.] Ozonised air, which Mascart found so effective in his experiments with the closed vessel, is quite inoperative with the steam jet. Equally so is the vapour of boiling formic acid, which I believe is chemically a much more active acid than acetic, and has a lower electrical resistance. (See Table.) Condensation of Steam Jet. Active. Air, oxygen or nitrogen, in which electrical discharge is occurring. Burning and incandescent substances. Fumes from phosphorus. Hydrochloric acid. Sulphuric acid vapour. Nitric acid vapour. Acetic acid vapour. Inactive. Air, &c, in which electrical discharge has ceased for about 10 seconds. Smoke without fire. Bottled phosphorus fumes. Ammonia. Ozone. Steam. Alcohol vapour. Formic acid vapour. Sulphurous acid. It seems that we have here a pretty little problem which might, perhaps, be solved without much difficulty by a competent chemist, 1893.] on Fog, Clouds and Lightning. 105 but which quite baffles me.* Is it possible that the condensing vapours may contain dissociated atoms ? To return to the electrical effect. There are only two kinds of chemical change that I know of which could be brought about in air by an electrical discharge. Either some of the oxygen might be con- verted into ozone, or the oxygen and nitrogen of the air might be caused to combine, forming nitric acid or some such compound. The former of these would not account for the action of the air upon the jet, because, as we have seen, ozone is inoperative ; the latter might. But if the activity of the air is due to the presence in it of a com- pound of oxygen and nitrogen, then it is clear that an electrical discharge in either nitrogen or oxygen separately would fail to render those gases active. I arranged a spark bottle, inside which an induction-coil discharge could be made to take place ; two bent tubes were passed through the cork, one reaching nearly to the bottom for the ingress of the gas to be tested, the other, a shorter one, for its egress. The open end of the egress tube was fixed near the steam jet, and first common air, then oxygen and then nitrogen were successively forced through the bottle while the coil discharge was going on. All produced dense condensation, but I thought that oxygen appeared to be a little more efficient than common air and nitrogen a little less. This last experiment points to a conclusion to which at present I see no alternative. It is that the action on the jet of an electrical discharge is due in some way or other to dissociated atoms of oxygen and nitrogen. There is nothing else left to which it can be due. So far as Robert Helmholtz's explanation coincides with this conclusion I think it must be accepted as correct. As to the precise manner in which he supposed the dissociated atoms to act upon the jet, it is more difficult to agree with him. He thought that the abnormal condensation was a consequence of the molecular shock caused by the violent recombination of the dissociated atoms in the supersaturated air of the jet, the action being analogous to that which occurs when a supersaturated solution of sulphate of soda, for example, is instantly crystallised by a mechanical shock. To me this hypothesis, ingenious as it is, seems to be more fanciful than probable, but I can only hint very diffidently at an alternative one. To many chemical processes the presence of water is favourable or even essential. Is it possible that the recombination of free atoms may be assisted by water ? And is it possible that dissociated atoms in an atmosphere of aqueous vapour may obtain the water needed for their union by condensing it from the vapour ? According to Helmholtz, flames and incandescent substances generally cause dissociation of the molecules of oxygen and nitrogen * Two chemists of the highest eminence have been good enough to consider the problem for me, but they are unable to throw any light upon it. 106 Mr. Shelford Bidwell [May 5, in the surrounding air. This, I believe, is generally admitted. I do not know whether slowly oxidising phosphorus has the same effect. If it is conceded that the atmospheric gases are dissociated by electrical discharges, and that the presence of such dissociated gases somehow brings about the dense condensation of water vapour, we Tnm ft1^ / r \ Spark Bottle. I, Ingress tube ; E, egress tube ; W, wires to induction coil ; S, spark gap. may still regard the electrified steam jet as affording an illustration of the abnormal darkness of thunder-clouds. Perhaps another source of dissociated atoms is to be found in the ozone which is generated by lightning flashes. A molecule of ozone consists of three atoms of atomic oxygen, while one of ordinary oxygen contains only two. Ozone is an unstable kind of material 1893.] on Fog, Clouds and Lightning. 107 and gradually relapses into ordinary oxygen, the process being that one atom is dropped from the three-atom molecules of ozone, these detached atoms in course of time uniting with one another to form pairs. Thus two molecules of ozone are transformed into three of oxygen. A body of ozone is therefore always attended by a number of dissociated atoms which are looking for partners. In the steam jet experiment there is not time for the dis- engagement of a sufficient number of isolated atoms from a blast of ozone to produce any sensible effect. But the case is otherwise when the vapour is confined in a closed vessel, as in Mascart's experiment, or when it occurs in the clouds, where the movement of air and vapour is comparatively slow. Ozone, it will be remembered, was found by Mascart to produce dense condensation in a closed vessel even after being filtered through cotton wool. Similar filtration seems to entirely deprive the so- called products of combustion of their active property, a fact which has been adduced as affording overwhelming evidence in favour of the dust nucleus theory. Coulier himself, however, detected a weak point in this argument. He produced a flame which could not possibly have contained any products of combustion except steam, by burning pure filtered hydrogen in filtered air ; yet this product was found to be perfectly capable of causing dense condensation, and, as in his former experiments, filtration through cotton wool deprived it of its activity. These anomalies may, I think, be to a great extent cleared up if we assume that the effect of the cotton wool depends, not upon the mere mechanical obstruction it offers to the passage of particles of matter, but upon the moisture which it certainly contains, and which may act by attracting and facilitating the reunion of dissociated atoms before they reach the air inside the vessel. According to this view ozone would remain an active condenser in spite of its fil- tration, because free atoms would continue to be given off by it after it had passed the cotton wool. The filtration experiment should be tried with perfectly dry cotton wool, which, however, will not be easily procured, and if my suggestion is right, dry wool will be found not to deprive ordinary products of combustion of their con- densing power. To sum up. I think my recent experiments show conclusively that the dense condensation of the steam jet is not due directly either to electrical action or to dust nuclei. The immediate cause is pro- bably to be found in dissociated atoms of atmospheric gases, though as to how these act we can only form a vague guess. The discourse concluded with some remarks upon atmospheric electricity, and the exhibition of lantern photographs of lightning flashes. [S.B.J 108 General Monthly Meeting. [May 8, GENERAL MONTHLY MEETING, Monday, May 8, 1893. Sir James Crichton-Browne, M.D. LL.D. F.R.S. Treasurer and Vice-President, in the Chair. The following Vice-Presidents for the ensuing year were announced : — Sir Douglas Galton, K.C.B. D.C.L. LL.D. F.R.S. David Edward Hughes, Esq. F.R.S. Hugo Miiller, Esq. Ph.D. F.R.S. The Ri^ht Hon. Earl Percy, F.S.A. Basil Woodd Smith, Esq. F.R.A.S. F.S.A. Sir Richard Webster, M.P. Q.C. LL.D. Sir James Crichton-Browne, M.D. LL.D. F.R.S. Treasurer. Sir Frederick Bramwell, Bart. D.C.L. LL.D. F.R.S. Hon. Secretary. The Earl of Leven and Melville, Mrs. S. F. Beevor, Herbert C. Newton, Esq. H. Sylvester Samuel, Esq. F.R.G.S. Thomas Wrightson, Esq. M.P. Frederick John Yarrow, Esq. were elected Members of the Royal Institution. The Honorary Secretary reported that the late Earl of Derby E.G. M.B.I, had bequeathed 2000Z. to the Royal Institution. The special thanks of the Members were returned for the following Donation to the Fund for the Promotion of Experimental Research at low temperatures : — Alfred F. Yarrow, Esq £50 Sir David Salomons, Bart. .. .. .. £50 Henry Vaughan, Esq. .. .. .. £20 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. XXVI. Part 1. 8vo. 1893. The Secretary of State for India — Great Trigonometrical Survey of India, Vols. XXVII. XXVIII. XXX. 4to. 1892. 1893.] General Monthly Meeting. 109 The Lords of the Admiralty — Greenwich Observations for 1890. 4to. 1892. Greenwich Spectroscopic and Photographic Results, 1890. 4to. 1892, The Time of Swing of the Indian Invariable Pendulums. 4to. 1891. Annals of the Cape Observatory, Vol. I. Parts 2-4. 4to. 1881-82. The New Zealand Government — Results of a Census taken in 1891. 8vo. 1893. Accademia del Lincei, Reale, Roma — Classe di Scienze Fisiche, Matematiche e Naturali. Atti, Serie Quinta: Rendiconti. 1° Semestre, Vol. II. Fasc 6. 8vo. 1893. Classe di Scienze Morali, Storiche, etc.: Rendiconti, Serie Quinta, Vol. II. Fasc. 2. 8vo. 1893. American Philosophical Society — Proceedings, No. 139. 8vo. 1892. Aristotelian Society — Proceedings, Vol. II. No. 2, Part 1. 8vo. 1893. Asiatic Society of Great Britain, Royal — Journal, 1893, Part 2. 8vo. Astronomical Society, Royal — Monthly Notices, Vol. LIII. No. 5. 8vo. 1893. Bankers, Institute of— Journal, Vol. XIV. Part 4. 8vo. 1893. Batavia Observatory — Rainfall in East Indian Archipelago, 1891. 8vo. 1892. Magnetical and Meteorological Observations, Vol. XIV. fol. 1892. Binnie, A. R. Esq. M.Inst. C.E. M.R.I, (the Author)— -Report on the Flow of the Thames. 8vo. 1892. British Architects, Royal Institute of — Proceedings, 1893, No. 14. 4to. British Astronomical Association — Journal, Vol. III. No. 5. 8vo. 1893. British Museum Trustees— Catalogue of Seals, Vol. II. 8vo. 1892. Catalogue of Indian Coins. 8vo. 1892. Catalogue of Oriental Coins, Vol. X. 8vo. 1890. Catalogue of Chinese Coins. 8vo. 1892. Ancient Greek Inscriptions, Part IV. Sec. 1. 4to. 1893. British Museum (Natural History) — Catalogue of British Echinoderms. 8vo. 1892. Illustrations of Specimens of Lepidoptera Heterocera, Part IX. 4to. 1893. Guide to Sowerby's Models of British Fungi. 8vo. 1893. Chemical Industry, Society of — Journal, Vol. XII. No. 3. 8vo. 1893. Chemical Society — Journal for May, 1893. 8vo. Clinical Society — Transactions, Supplement to Vol. XXV. 8vo. 1893. East India Association— Journal, Vol. XXV. No. 2. 8vo. 1893. Editors — American Journal of Science for April, 1893. 8vo. Analyst for April, 1893. 8vo. Athenseuni for April, 1893. 4to. Chemical News for April, 1893. 4to. Chemist and Druggist for April, 1893. 8vo. Electrical Engineer for April, 1893. fol. Electric Plant for April, 1893. 4to. Engineer for April, 1893. fol. Engineering for April, 1893. fol. Engineering Review for April, 1893. 8vo. Hcrological Journal for April, 1893. 8vo. Industries for April, 1893. fol. Iron for April, 1893. 4to. Ironmongery for April, 1893. 4to. Lightning for April, 1893. 4to. Monist for April, 1893. 8vo. Nature for April, 1893. 4to. Open Court for April, 1893. 4to. Photographic News for April, 1893. 8vo. Photographic Work for April, 1893. 8vo. Telegraphic Journal for April, 1893. fol. Transport for April, 1893. Zoophilist for April, 1893. 4to. Electrical Engineers, Institution of — Journal, No. 105. 8vo. 1893. Florence, Biblioteca Nazionale Centrale — Bolletino, Nos. 175, 176. 8vo. 1893. 110 General Monthly Meeting. [May 8, Franklin Institute— Journal, No. 808. 8vo. 1893. Geographical Society, Royal — Geographical Journal, Vol. I. No. 4. 8vo. 1893. Geographical Society of California— Bulletin, Vol. I. Part 1. 8vo. 1893. Geological Society— Journal, No. 194. 8vo. 1893. Harvard University — Bibliographical Contributions, No. 47. 8vo. 1893. Johns Hopkins University — American Chemical Journal, Vol. XV. No. 4. 8vo. 1893. University Circulars, No. 104. 4to. 1893. Keeler, James E. Esq. (the Author) — Observations on the Spectrum of j8 Lyrse. 8vo. 1893. Linnean Society — Journal, No. 154. 8vo. 1893. Manchester Geological Society— Transactions, Vol. XXII. Parts 6, 7. Svo. 1893. Massachusetts State Board of Health — Twenty-third Annual Report. Svo. 1892. Mechanical Engineers, Institution of — Proceedings, 1S92, No. 4. 8vo. Mendenhall, T. G Esq. (the Author) — Determinations of Gravity. Svo. 1892. Miller, W. J. C. Esq. (the Editor)— The Medical Register for 1893. Svo. The Dentists' Register for 1893. Svo. Ministry of Public Works, Rome — Giornale del Genio Civile, 1893, Fasc. 1, 2, and Designi. fol. 1893. Munir Bey, His Excellency — Catalogue of the Library of the late Ahmed Ve'fyk Pacha. Constantinople. 8vo. 1893. National Life-Boat Institution, Royal — Annual Report, 1S93. Svo. North of England Institute of Mining and Mechanical Engineers — Transactions, Vol. XLII. Part 2. Svo. 1893. Odontological Society— Transactions, Vol. XXV. Nos. 5, 6. Svo. 1893. Payne, W. W. and Hale, G. E. (the Editors) — Astronomy and Astro-Physics for April, 1893. 8vo. Pharmaceutical Society of Great Britain — Journal for April, 1892. 8vo. Richardson, B. W. M.D. F.R.S. M.R.I, (the Author)- -The Asclepiad, 1893, No. 1. 8vo. Roijal Society of London — Proceedings, No. 320. 8vo. 1893. Smithsonian Institution — Bureau of Ethnology : Contributions to North American Ethnology, Vol. VII. 4to. 1890. Bibliography of the Athapascan Languages. 8vo. 1892. Annual Report of the Bureau of Ethnology, 1885-86. 4to. 1891. National Museum Report, 1890. 8vo. 1891. Society of Architects— Proceedings, Vol. V. Nos. 9, 10. 8vo. 1893. Society of Arts— Journal for April, 1893. 8vo. St. Pe'tersbourg, Acade'mie Imperiale des Sciences — Memoires, Tome XL. No. 2 ; Tome XLI. No. 1. 4to. 1892-93. Bulletin, Tome XXXV. No. 3. Svo. 1893. Teyler Museum— Archives, Se'rie II. Vol. IV. Part 1. Svo. 1893. United Service Institution, Royal— Journal, No. 182. 8vo. 1893. United States Department of the Interior — Report on Mineral Industries in the U.S. at the Eleventh Census, 1890. 4to. 1892. Vei-eins zur Beforderung des Gewerbfleisses in Preussen — Verhandlungen, 1893, Heft 3, 4. 4to. Victoria Institute — Transactions, No. 103. Svo. 1893. Zoological Society of London— Proceedings, 1892, Part 4. Svo. 1893. Transactions, Vol. XIII. Part 5. 4to. 1893. Zurich Naturforschenden Gesellschaft — Vierteljahrschrift, Jahrgang XXXVII. Heft 3, 4. 8vo. 1S92. 1893.] Lord Kelvin on Isoperimetrical Problems. Ill WEEKLY EVENING MEETING, Friday, May 12, 1893. Sir Douglas Galton, K.C.B. D.C.L. LL.D. F.R.S. Vice-President, in the Chair. The Right Hon. Lord Kelvin, D.C.L. LL.D. Pres.R.S. M.B.I. Isoperimetrical Problems. Dido, b.c. 800 or 900. Horatius Codes, b.c. 508. Pappus, Book V., a.d. 390. John Bernoulli, a.d. 1700. Euler, a.d. 1744. Maupertuis (Least Action), b. 1698, d. 1759. Lagrange (Calculus of Variations), 1759. Hamilton (Actional Equations of Dynamics), 1834. Liouville, 1840 to 1860. The first isoperimetrical problem known in history was practically solved by Dido, a clever Phoenician princess, who left her Tyrian home and emigrated to North Africa, with all her property and a large retinue, because her brother Pygmalion murdered her rich uncle and husband Acerbas, and plotted to defraud her of the money which he left. On landing in a bay about the middle of the north coast of Africa she obtained a grant from Hiarbas, the native chief of the district, of as much land as she could enclose with an ox-hide. She cut the ox-hide into an exceedingly long strip, and succeeded in enclosing between it and the sea a very valuable territory* on which she built Carthage. The next isoperimetrical problem on record was three or four hundred years later, when Horatius Codes, after saving his country by defending the bridge until it was destroyed by the .Romans behind him, saved his own life and got back into Rome by swimming the Tiber under the broken bridge, and was rewarded by his grateful countrymen with a grant of as much land as he could plough round in a day. In Dido's problem the greatest value of land was to be enclosed by a line of given length. If the land is all of equal value the general solution of the problem shows that her line of ox-hide should * Called Byrsa, from /3up