L . £ . 1. THE LONDON, EDINBURGH, and DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. CONDUCTED BY SIR DAVID BREWSTER, K.H. LL.D. F.R.S.L.&E. &c. RICHARD TAYLOR, F.L.S. G.S. Astr.S. Nat.Il.Mosc. &c RICHARD PHILLIPS, F.R.S.L.&E. F.G.S. &c SIR ROBERT KANE, M.D. M.R.I.A. " Nee aranearum sane textus ideo melior quia ex se fila gignunt, nee noster vilior quia ex alienis libamus ut apes." Just. Lips. Folk. lib. i. cap. 1 . Not. VOL. XXVIII. NEW AND UNITED SERIES OF THE PHILOSOPHICAL MAGAZINE, ANNALS OF PHILOSOPHY, AND JOURNAL OF SCIENCE. JANUARY— JUNE, 1846. LONDON: RICHARD AND JOHN E. TAYLOR, RED LION COURT, FLEET STREET, Printers and Publishers to the University of London; SOLD BY LONGMAN, BROWN, GREEN, AND LONGMANS ; CADELLJ SIMPKIN, MARSHALL AND CO.; S. HIGHLEY ; WHITTAKER AND CO.; AND SHERWOOD, GILBERT, AND PIPER, LONDON : BY ADAM AND CHARLES BLACK, AND THOMAS CLARK, EDINBURGH; SMITH AND SON, GLASGOW; HODGES AND SMITH, DUBLIN: AND G. W. M. REYNOLDS, PARIS. " Meditationis est perscrutari occulta,- contemplationis est admirari perspicua Admiratio generat qua3stionem, quaBStio investigationem, investhjatio inventionem." — Huso de S. Victore. CONTENTS OF VOL. XXVIII. (THIRD SERIES.) NUMBER CLXXXIV.— JANUARY, 1846. , Page Mr. R. Hunt on the Influence of Magnetism on Molecular Ar- rangement (with a Plate) 1 Mr. R. W. Fox on certain Pseudomorphous Crystals of Quartz 5 Prof. J. R. Young on the General Expression for the Sum of an Infinite Geometrical Series 10 Drs. T. Tilley and D. Maclagan on the Conversion of Cane- sugar into a substance isomeric with Cellulose and Inuline . 12 Mr. G. G. Stokes's Remarks on Professor Challis's Theoretical Explanation of the Aberration of Light 15 Lieut.-Col. P. Yorke on the Solubility of Oxide of Lead in Pure Water , 17 The Rev. B. Bronwin's Equations for the Determination of the Motion of a Disturbed Planet by means of M. Hansen's Al- tered Time 20 Lieut.-Col. Sabine on some Points in the Meteorology of Bom- bay (with a Plate) 24 Mr. T. Taylor on some New Species of Animal Concretions . . 36 Mr. C. B. Cayley's Inquiries in the Elements of Phonetics . . 47 Mr. A. Smith on Fresnel's Theory of Double Refraction .... 48 Mr. J. D. Dana on the Origin of the constituent and adventi- tious Minerals of Trap and the allied Rocks 49 Mr. G. B. Jerrard's Reflections on the Resolution of Algebraic Equations of the Fifth Degree 63 Proceedings of the Royal Society 64 Action of Nitric Acid on Wax 66 Dry Distillation of Wax 67 Analysis of Phosphate of Alumina, by M. A. Delesse 68 A New Planet 69 Notice of an Aurora Borealis seen at Manchester 70 Meteorological Observations for November 1845 .. 71 Meteorological Observations made by Mr. Thompson at the Garden of the Horticultural Society at Chiswick, near London ; by Mr. Veall at Boston ; by the Rev. W. Dunbar at Applegarth Manse, Dumfries-shire ; and by the Rev. C. Clouston at Sandwick Manse, Orkney 72 NUMBER CLXXXV.— FEBRUARY. Mr. H. Collen on the Application of the Photographic Camera to Meteorological Registration (with a Plate) 73 a 2 IV CONTENTS OF VOL. XXVIII. — THIRD SERIES. Page Mr. G. G. Stokes on Fresnel's Theory of the Aberration of Light 76 Mr. E. Wilson's Observations on the Development and Growth of the Epidermis 82 The Rev. J. Challis on the Aberration of Light, in Reply to Mr. Stokes 90 Dr. A. Waller's Observations on certain Molecular Actions of Crystalline Particles, &c. ; and on the Cause of the Fixation of Mercurial Vapours in the Daguerreotype Process (with a Plate) 94 Note to Mr. Hennessy's Paper on the Connexion between the Rotation of the Earth and the Geological Changes of its Sur- face 106 The Rev. W. V. Harcourt's Letter to Henry Lord Brougham, F.R.S. &c, containing Remarks on certain Statements in his Lives of Black, Watt, and Cavendish 106 Mr. J. Cockle on a Proposition relating to the Theory of Equa- tions 132 Mr. R. Moon on Fresnel's Theory of Double Refraction .... 134 Mr. R. Moon's Reply to some Remarks contained in Prof. Young's recent paper '* On the Evaluation of the Sums of Neutral Series " 136 Jesuiticus's Remarks on a Paper by Mr. Moon on Fresnel's Theory of Double Refraction 144 The Editor's Observations on the subject of the preceding Com- munications , 146 Proceedings of the Royal Society 147 Analysis of a Substance occurring with Disthene, by M. A. De- lesse .... 150 Hydrated Silicate of Magnesia, by M. A. Delesse 152 Analysis of the Elie Pyrope or Garnet, by Prof. Connell. 152 Analysis of Meteoric Iron from Burlington, Ostego County, New York, by Mr. C. H. Rockwell 154 Preparation of Chloro-acetic Acid 154 Composition of Phosphate of Ammonia and Magnesia 155 Composition of Common Phosphate of Soda 155 On several New Series of Double Oxalates, by M. Rees Heece 156 Reaction for the Discovery of Sulphurous Acid, by M. Heintz. . 157 Analysis of the Molares of a Fossil Rhinoceros 158 Experiments on the Yolk of Eggs, by M. Gobley 158 Meteorological Observations for December 1845 159 Table 160 NUMBER CLXXXVI.— MARCH. M. C. Langberg on the Determination of the Temperature and Conducting Power of Solid Bodies 161 CONTENTS OF VOL. XXVIII. THIRD'SERIES. V Page Mr. T. Hopkins on the Causes of the Semi-diurnal Fluctua- tions of the Barometer 166 The Rev. J, Challis on the Principles to he applied in explaining the Aberration of Light 176 Prof. J. W. Draper on the Cause of the Circulation of the Blood 178 Mr. J. Cockle on the Existence of Finite Algebraic Solutions of the general Equations of the Fifth, Sixth, and Higher Degrees 190 Mr. T. Taylor on some New Species of Animal Concretions. . 192 Lieut.-Col. Sabine on the Winter Storms of the United States 200 Mr. R. C. Taylor on the Anthracite and Bituminous Coal-Fields in China 204 Prof. C. F. Schcenbein on the Conversion of the solid Ferrocya- nide of Potassium into the Sesqui-ferrocyanide 211 Prof. C. F. Schcenbein on the Decomposition of the Yellow and Red Ferrocyanides of Potassium by Solar Light 211 Prof. Potter's Reference to former Contributions to the Phi- losophical Magazine, on Physical Optics 212 Prof. J. R. Young on Differentiation as applied to Periodic Series : with a few Remarks in Reply to Mr. Moon 213 Mr. Moon in Reply to Jesuiticus 215 Proceedings of the Royal Society 219 Royal Astronomical Society 223 Experiments on the Spots on the Sun, by Prof. Henry 230 Method of Purifying Oxide of Uranium from Nickel, Cobalt and Zinc, by Prof. Wohler 232 On some New Double Haloid Salts, by M. Poggiale 232 On the Volatile Acids of Cheese, by MM. Iljenko and Laskowski 234 On the Double Salts of the Magnesian Group 235 Preparation of Hypophosphites 236 Biela's Comet 238 Meteorological Observations for January 1846 239 Table 240 NUMBER CLXXXVII.— APRIL. Mr. W. Brown, Jun., on the Oscillations of the Barometer, with particular reference to the Meteorological Phenomena of November 1842 (with Six Plates) 241 Prof. De Morgan on the Derivation of the Word Theodolite. . 287 Mr. T. Graham's Reply to the Observations of M. Pierre, on the Proportion of Water in the Magnesian Sulphates and Double Sulphates 289 M. F. Donny on the Cohesion of Liquids and their Adhesion to Solid Bodies 291 VI CONTENTS OF VOL. XXVIII.— THIRD SERIES. Page Dr. Faraday's Experimental Researches in Electricity. — Nine- teenth Series. On the Magnetization of Light and the Illu- mination of Magnetic Lines of Force 294 Lieut. -Col. Sabine on the Cause of remarkably Mild Winters which occasionally occur in England 317 M. Pouillet's Observations on the Recent Researches of Prof. Faraday 324 Mr. G. G. Stokes on the Aberration of Light 335 Analysis of Diaspore from Siberia, by M. A. Damour. ....... 336 On Boracic ^Ether 337 Action of Boracic Acid on Pyroxylic Spirit 339 On a Simple Method of Protecting from Lightning, Buildings with Metallic Roofs, by Prof. Henry 340 Observations on Capillarity, by Prof. Henry 34 1 Obituary 343 Meteorological Observations for February 184G 343 Table 344 NUMBER CLXXXVIIL— MAY. Dr. Faraday's Thoughts on Ray-vibrations 345 Mr. J. E. Teschemacher on the Wax of the Chama;rops .... 350 Mr. J. Middleton's Analysis of a Cobalt Ore found in Western India 352 Mr. H. E. Strickland on the Structural Relations of Organized Beings 354 Mr. W. J. Henwood's Abstract of Meteorological Observations made during the year 1845 at Gongo Soco, in the interior of Brazil 364 Dr. R. D. Thomson on Pegmine and Pyropine, animal sub- stances allied to Albumen 368 The Rev. B. Bronwin on certain Definite Multiple Integrals . . 373 Mr. W. R. Birt on the Storm-Paths of the Eastern Portion of the North American Continent 379 Prof. De Morgan on the first introduction of the words Tangent and Secant 382 Dr. J. Lhotsky's Complete Collection of Kepler's Works 387 The Rev. J. Challis on the Aberration of Light, in Reply to Mr. Stokes 393 Mr. J. Cockle on the Finite Solution of Equations 395 Dr. Faraday's Experimental Researches in Electricity. — Twen- tieth Series. On new Magnetic Actions, and on the Mag- netic Condition of all Matter 396 Prof. Louyet's Description of a new Mercurial Trough 406 Proceedings of the Royal Society. 408 CONTENTS OF VOL. XXVIII. — THIRD SERIES. Vll Page Note by Mr. T. Hopkins on his Paper on the Semi-diurnal Fluc- tuations of the Barometer 41 G On some new Compounds of Perchloride of Tin, by M. Lewy. . 416 Analysis of two species of Epiphytes, or Air Plants, by John Thomson, A.M 420 Analysis of Ceradia furcata Resin, by Robert D. Thomson, M.D. 422 Meteorological Observations for March 1846 423 Table 424 NUMBER CLXXXIX.-JUNE. Dr. D. P. Gardner's Researches on the Functions of Plants, with a view of showing that they obey the Physical Laws of Diffusion in the Absorption and Evolution of Gases by their Leaves and Roots 425 Dr. C. F. Schcenbein on the relation of Ozone to Hyponitric Acid 432 Mr. T. Graham on the Composition of the Fire-Damp of the Newcastle Coal Mines « 437 Dr. J. Stenhouse's Observations on the Resin of the Xanthorcea hastilis, or Yellow Gum-resin of New Holland 440 Mr. H. Sloggett on the Constitution of Matter 443 Messrs. Scoresby and Joule's Experiments and Observations on the Mechanical Powers of Electro-Magnetism, Steam, and Horses 448 Dr. Faraday's Experimental Researches in Electricity. — Twen- tieth Series. — Action of Magnets on Metals generally (con- cluded) 455 The Astronomer Royal on the Equations applying to Light under the action of Magnetism 469 The Rev. W. V. Harcourt's Letter to Henry Lord Brougham, F.R.S. &c, containing Remarks on certain Statements in his Lives of Black, Watt and Cavendish 478 NUMBER CXC— SUPPLEMENT TO VOL. XXVIII. The Rev. W. V. Harcourt's Letter to Henry Lord Brougham, F.R.S. &c, containing Remarks on certain Statements in his Lives of Black, Watt, and Cavendish (concluded) 505 Prof. Owen's Observations on Mr. Strickland's Article on the Structural Relations of Organized Beings 525 Prof. Marignac's Observations on Messrs. Lyon Playfair and Joule's Memoir on Atomic Volume and Specific Gravity . . 527 Vlll CONTENTS OF VOL. XXVIII. — THIRD SERIES. Page The Astronomer Royal's Remarks on Dr. Faraday's Paper on Ray-vibrations 532 Mr. R. Mallet's Explanation of the Vorticose Movement, as- sumed to accompany Earthquakes 537 Prof. E. Wartmann on the Causes to which Musical Sounds produced in Metals by discontinuous Electric Currents are attributable 544 Mr. E. F. Teschemacher's Account of various Substances found in the Guano Deposits and in their Vicinity 546 Dr. Gregory's Notes on the Preparation of Alloxan 550 On Chloroazotic Acid 555 Notices of New Localities of Rare Minerals, and Reasons for uniting several supposed Distinct Species, by Francis Alger. 557 Notice on certain Impurities in Commercial Sulphate of Copper, by Mr. S. Piesse 565 On a New Eudiometric Process, by Prof. Graham 566 Equivalent of Chlorine 566 On Hippuric Acid, Benzoic Acid, and the Sugar of Gelatine. . 567 Comparative Analyses of Oriental Jade and Tremolite, by M. Damour 568 Meteorological Observations for April 1846 569 Table 570 Index 571 PLATES. I. Illustrative of Lieut.-Col. Sabine's paper on the Meteorology of Bombay. II. Illustrative of Mr. Hunt's paper on the Influence of Magnetism on Molecular Arrangement. III. Illustrative of Dr. Waller's paper on the Molecular Actions of Cry- stalline Particles. — Mr. Collen's paper on the Application of Photo- graphy to Meteorological Registration. IV. V. VI. Illustrative of Mr. Brown's paper on the Meteorological Phaeno- VII. f mena of November 1842. VIII. IX. Errata and Addenda. Page 190, Note **, between " 3." and "p." add vol. xxvii. ... 391, for Salis deliquio read Solis. , for Bontschii read Bartschii. ... 393, for Sagincnsibus read Saganeniibus. . &rr°* THE yLoyj. LONDON, EDINBURGH and DUBLIN §i$kttl$\ PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. H [THIRD SERIES.] JANUARY 1816. I. The Influence of Magnetism on Molecular Arrangement. By Robert Hunt, Keeper of Mining Records, Museum of (Economic Geology. [With a Plate.] p" ■ To Richard Phillips, Esq., F.R.S. Dear Sir, AVING been engaged some time since in investigating the influences of bodies on each other in the dark, the results of which investigations were published under the title of "Thermography," I then observed many peculiar effects which led me to believe that magnetic electricity had some in- fluence in determining the arrangements of molecules. From that time until a few days since, the subject has rested with me without any further research. Having however put the subject to the test of experimental examination, I am induced, the results being of great interest, to transmit to you an ac- count of my experiments. In doing this, I shall, for the pre- sent, confine myself strictly to a description of the arrange- ments used and the results obtained, reserving any theoretical views for some future period, when by a greater number and variety of experiments it appears probable some general law of action may be satisfactorily deduced. 1. I placed a concentrated solution of nitrate of silver in a test-tube, against the poles of a permanent horse-shoe magnet, having another tube containing a similar solution not in con- tact with it. The crystallization commenced first in the tube connected with the magnet, immediately at the point opposite the upper surface of the metal (Plate II. fig. 1) ; a large tabular crystal shot off from this point towards the bottom of the glass, dividing the lower portion of the fluid in two parts. Other crystals sprung off from different points above and be- Phil. Mag. S. 3. Vol. 28. No. 184. Jan. 1846. B 2 Mr. R. Hunt on the Influence of Magnetism low this crystalline plate, but all of them arranged themselves at angles inclining towards the magnet; no crystallization taking place in the upper stratum of the fluid. In the other tube, crystals formed irregularly throughout the fluid, but in no part were the crystals so dense as in the tube which I sup- pose to be under the influence of magnetism. 2. With a view of determining if the cooling influence of the metal had anything to do with the crystalline arrangement, portions "of the same solution of nitrate of silver were put into glass capsules. One of these was placed against the poles of the magnet, and the other in contact with a mass of brass of the same weight. In the first, crystallization commenced op- posite the north pole of the magnet, and proceeded slowly in regular lines to crystallize over every part ; all these lines have a tendency towards the poles of the magnet. In the capsule in contact with the brass, crystallization commenced at a point furthest from the metal, and even when the fluid had become quite cold, nearly one quarter of it, which was nearest the mass of metal, remained quite free from any crystalline forma- tion. 3. To exhibit this in a more striking manner, a capsule was placed between the mass of brass and the magnet, in con- tact with each, as shown in fig. 2 ; the solution of nitrate of silver in this case, not being so concentrated as that previ- ously used, the arrangement was allowed to remain at rest for some hours. It was then found that crystallization had taken place only over one portion of the fluid, and that immediately in connexion with the north pole of the magnet, except three long crystals which sprung from the fluid opposite the south pole, and were directed towards those springing from the north pole. This experiment was repeated four times, and, except when the solution was so concentrated as to crystallize almost immediately, the same result was obtained. 4. The phenomenon of molecular disposition under mag- netic influence is pleasingly seen by a modification of the ar- rangement described. The two glass capsules with their so- lutions are placed on a plate of glass blackened on its under surface, one glass being put in contact with the brass and the other with the magnet. Their images are to be observed in the black mirror on which they rest, the light falling upon them at an angle of about 25°. As the fluids cool, the cir- culating currents coloured by their refracting powers are seen in the mirror. In the image of the capsule in contact with the brass, no regularity of circulatory movement is observable; but in that under magnetic influence, a series of perfectly re- gular curved lines proceed from the circumference to the on Molecular Arrangement. 3 centre; ami these are crossed by small streamers springing laterally from these primary curves, presenting an appearance similar to that shown in fig. 3. These curves are constantly varying in position, but they uniformly preserve the utmost regularity. 5. The magnet was suspended from a tripod, and two steel needles attached to its poles; these needles were made to dip into a solution of nitrate of silver in a watch-glass. As the pellicle formed over the surface, it arranged itself in a series of curved lines, as represented in fig. 4, which are strikingly similar to those produced by sprinkling iron-filing on stretched paper placed over a magnet. That these curves are due to magnetic influence there can be no doubt, as no such effect could be produced by any cooling influence, inde- pendent of magnetic excitation. 6. A similar arrangement was allowed to remain in action for twelve hours. At the end of this time crystallization had taken place in every part of the fluid, but there was an evi- dent tendency to a curvilinear arrangement of the crystals. Around the wire depending from the north pole of the mag- net, some revived silver had made its appearance : no such change was discovered at the south pole. 7. Wires similarly suspended were dipped into a solution of sulphate of iron. Crystallization commenced around the wire at the north pole, but after a few hours crystals had formed around both of the wires, but in the greatest quantity around the north pole wire. On removing them from the so- lution, the crystals were found to present an arrangement si- milar to that represented in fig. 5, showing obviously a ten- dency to arrange themselves along lines of magnetic direc- tion. 8. A solution of protonitrate of mercury was placed under similar circumstances; crystallization commenced at the wire suspended from the north pole, and proceeded rapidly to a line midway between the two wires; one-half of the fluid being crystallized and the other remaining fluid. At length a few crystals formed around the wire hanging from the south pole, which all took a direction towards the opposite arrangement of crystals. 9. With a more dilute solution, the crystallization of the ni- trate of mercury took place only around the wire at the north pole, and immediately at the central point between the two wires, from which small needle-shaped crystals radiated to- waids either pole. 10. A plate of glass, with an edge of clay, forming a shal- low trough, was placed upon the poles of an electro-magnet, B2 4. On ike Influence of Magnetism on Molecular Arrangement. capable of supporting fifty pounds when connected with a single galvanic pair excited by water acidulated with sulphu- ric acid. On pouring a warm and tolerably strong solution of nitrate of mercury into the trough, there was immediately formed over the surface a series of beautifully regular curves from pole to pole, as shown in fig. 6, which also represents the arrangement. 11. A similar glass trough, filled with a moderately strong solution of the nitrate of mercury, was supported on the poles of the same electro-magnet, connected with a small battery of a more permanent, but less powerful arrangement, and all was allowed to remain at rest until crystallization had taken place. The result was similar to that already described (9.), but much more strikingly shown. The order of arrangement taken by the crystals is shown in Plate II. fig. 7. 12. A plate of copper with an edging of wax was placed on the electro-magnet in the same manner as the glass plate; over it a very weak solution of nitrate of silver was quickly poured; the plate immediately blackened from the decompo- sition of the silver salt by the copper. In about a minute the finely divided silver arranged itself into curves, as represented in fig. 8, which were after a few minutes again destroyed. By using a sheet of chemically-pure copper, obtained by electro- type deposit, I found a permanent impression of these curves could be obtained, owing to the oxidation of the copper along the spaces, which the finely divided silver, when distributed in curve-lines, did not cover. 13. A plate of hard copper, such as is used by engravers, was placed in precisely the same circumstances, and covered with a tolerably strong solution of nitrate of silver. It was left in contact with the electro-magnet for a night. On wash- ing off the deposit of silver which covered it, it was found that the acid of the silver salt had bitten deeply into the plate over an oval space around the poles, leaving a small space between them quite bright. The copper over this etched space was covered with an immense number of minute holes; and be- yond this the oxidation of the surface had proceeded in curved lines, as represented in fig. 9. We thus have perma- nent evidence of the influence of magnetic force in determi- ning chemical action. 14. Into one of the glass troughs before named, placed on the electro-magnet, a weak solution of nitrate of silver was poured, and into this an equally weak solution of sulphate of iron. In about five minutes precipitation of silver commenced ; this precipitate arranged itself over the glass in curves pro- ceeding from and around the poles in the same manner as it Mr. R. W. Fox on Pseudomorphous Crystals of Quart z. 5 distributed itself over the copper plate. In a short time, pre- cipitation increasing, two curious curved spaces were formed by the fine deposit, proceeding from one pole towards the other in opposite directions, increasing in width as they pro- ceeded, until they were abruptly checked at a little distance from the poles towards which they were directed ; these spaces being very distinct from the first formed curved lines. Fig. 10 represents this very interesting arrangement. These experiments are sufficient to show that magnetism exerts a powerful influence on molecular arrangements, and that it regulates the direction of crystalline formations. I hope to be enabled to pursue this interesting inquiry still further ; it has most important bearings on many of the great phaenomena of nature, and I am therefore anxious thus early in my inquiry to call attention to the singular and conclusive results which I have obtained. I have the pleasure of remaining, Dear Sir, yours truly, 6 Craig's Court, Dec. 10, 1845. Robert Hunt. II. On certain Pseudomorphous Crystals of Quartz. By Robert Were Fox, Esq.* I SUBMIT to the Society's notice some specimens of quartz, with pseudomorphous octahedral crystals of the same substance, which appear to me to possess a sort of hi- storical interest, or at least to indicate that a succession of changes must have occurred in the condition of the mineral vein from which they were taken. They were found b}' S. Peters (dealer in minerals) in one of the heaps of vein stones, at the Consolidated Mines, and I understand were broken from a copper vein in " killas" at the depth of. about 160 fathoms below the surface. He observed that many of the crystals contained water, and he secured some of it for me, by carefully breaking some of them. This he did mostly in my presence, and we had considerable difficulty in collecting even very small portions of the liquid in different phials. Two of these por- tions were nearly tasteless, or saline in a very slight degree, as far as I could judge from a single drop of each. In both common salt was detected, and nothing else in one of the por- tions; but the other, when evaporated, left minute needle- formed crystals, which I was prevented by an accident from examining. The third portion of water was much more in * Read at a meeting of the Cornwall Polytechnic Society, on the 8th of October, 1845, and communicated by the Author. 6 Mr. R. W. Fox on Pseudomorphous Crystals of Quartz, quantity than both the others — nearly a tea-spoonful, and ob- tained from only one crystal. It was very acrid to the taste, and gave very copious precipitates when tested by muriate of barytes and hydrocyanate of potash, showing the presence of much sulphuric acid and iron. Oxalate of ammonia and ni- trate of silver, indicated, moreover, the presence of lime and muriatic acid. The saline matter in this water (mostly sul- phate of iron) was equal to one-tenth of its weight; and if it contained any common salt, of which I am not positive, the proportion was very small indeed. Litmus paper showed an excess of acid, the nature of which was not ascertained. Many of the pseudomorphous crystals are more than an inch in diameter, and are partly or entirely filled with cry- stalline quartz, whilst others are empty, or partly filled with more or less numerous fragments of disintegrated fluor. I counted nearly a hundred of such fragments taken from one of the crystals or cavities, exclusive of many other very small pieces. All the fragments are corroded, and indicate, by their rounded edges and indented surfaces, the action of a solvent which penetrated most readily between the planes of cleavage*. Besides this disintegrated fluor, perfect octahedrons of fluor occur in the same specimens; but they were rather more im- bedded in the quartz and more protected from injury than the others. Water was found alone in some of the pseudomor- phous crystals or cavities, and in others it was found with fragments of fluor, or with crystalline quartz. The most perfect pseudomorphous octahedrons occur within large cavities of quartz. Some of the latter are more than two inches in diameter, having the same form, and their sides generally parallel to those of the former. The quartz specimens to which the crystals are attached, present, when broken, the appearance of fortification agate, having lines parallel to their structure of transparent and milk-white quartz, differing in thickness ; these seem to indi- cate that the siliceous matter had been deposited at intervals of greater or less duration, or at least under different circum- stances. After a time an entire change of conditions appa- rently occurred in the vein, and octahedral crystals of fluor were formed on the quartz ; then silex was deposited either in a compact form, or in minute crystals, and coated the cry- stals of fluor; afterwards fluor again appeared, forming octa- hedrons over the others, and mostly with sides and angles par- allel to them. These processes appear from some of the * When crystals of alum were kept for a time in water, the planes of cleavage were first acted on, and fragments were separated from the crystals resembling those of the disintegrated fluor. Mr. R. W. Fox on Pseudomorphous Crystals of Quartz. 7 crystals to have been again repeated : then came a coat of silex over the fluor, or judging from the lines, many coats of it, forming a thick crust, having a surface of small quartz crystals. Some specimens were found at the same time with one or more layers of quartz between two or more portions of fluor, which tend to confirm these views. I think it may be inferred, from the well-defined and smooth impressions which the octahedrons of fluor have left in the quartz, and the general parallelism of the sides and angles of the outer cavities to those of the smaller pseudomorphous crystals inclosed in them*, that the inner and outer crystals of fluor were perfect and uninjured until after the whole se- ries of them were coated with quartz. At some subsequent period then it would appear that other changes occurred in the vein, and that the solution or destruction of the fluor com- menced. Some of the cavities which were found to contain water only, as well as those which contained water together with disintegrated fluor, have the appearance of having been so hermetically sealed, that it is difficult to understand how the liquid solvent could have obtained access to the fluor and abstracted it from its case. It cannot be supposed that the pressure of the column of water above it, although equal to more than half a ton on some of the larger crystals, could alone have produced the effects ; for not only must the solvent have been continually admitted through the crusts of the quartz, but the salts resulting from the solution of the fluor must, at the same time, have passed through thSm in the op- posite direction, — a sort of endosmose and exosmose must have existed, as I conceive, to produce the phaenomena ; whilst in other instances, the thick envelopes of quartz were impervious and protected the fluor from injury. The salts resulting from the solution of the fluor must have been soluble, although this condition seems to present some difficulties under the circum- stances of the case ; and doubtless the destruction of the fluor was very slowly effected in many instances, and in others it was begun, but never completed. The differences in the saline contents of the water obtained from some of the crystals is an- other circumstance of some interest, indicating the existence of different conditions in the vein when the water was last ad- mitted into the respective crystals. The phaenomena exhibited by these minerals cannot, I con- * How are such coincidences to be accounted for? Are we to assume that jwlarising forces have determined the arrangement ? In many instances the layers of quartz which were interposed between the crystals are very thin, imperfect, and pervious to water; but in others they are not so, and some of the inner crystals now contain water. 8 Mr. It. W. Fox on Pseudomorphous Crystals of Quartz. ceive, be accounted for but by supposing the water existing in the fissures of the earth to have been changed by circulation from time to time, and to have been charged with different ingredients at different periods. I have on former occasions alluded to various causes which would produce circulation in the subterranean waters, such as the opening or closing of any portions of fissures ; the ascent of warm and the descent of cooler currents of water, in conse- quence of the differences in their specific gravities; or in some instances by the pressure of the sea- water acting on the fresh*. Nearly two years ago I stated in this room my views in refer- ence to the operation of this latter cause on land springs, and at the same time I attempted to show the possibility, not to say probability, of steam existing in fissures below the water at a very great depth. I may perhaps be permitted to refer again to this subject, because it appears to me to be one of some interest. I then took it for granted that the tempera- ture of the earth increases in some proportion to the increase of depth below its surface, and that if the ratio be taken at 1° Fahr. for every forty-eight feet, as found in our deep mines, and if Le Roche's data for calculating the elastic force and density of steam be adopted, the forces of steam and of water pressure would balance each other at rather more than nine miles deep, each being equal to the pressure of more than 1400 atmospheres. The density of the steam would there be about one-fourth that of water at 60° Fahr., and its tempera- ture above 1050° Fahr. But the temperature may probably not increase so rapidly as this at great depths, and the equi- librium in the pressures of the column of water and of steam may occur much further below the surface, where the density of steam under an augmented pressure of water would, of course, be still greater. However this may be, it would seem that, under any probable circumstances in regard to the ratio of increase in the earth's temperature, the increase in the pressure of the lengthened column of water would not keep pace with the rapidly increasing tendency of the water in de- scending into more heated parts of the earth to expand into steam, the elasticity of which at very high temperatures, when confined and in contact with water, is greatly augmented by very small increments of sensible heat. No water could long remain unchanged into steam below the line of division between them, and there the steam would * Columns of sea and spring water, about five feet high, balanced against each other in a U-shaped tube, more than a year ago, still remain un- mixed, showing nearly the same difference of level as at first (exceeding an inch). Mr. It. W. Fox on Pseudomorphous Crystals q/Quaais.r-9 be denser than at any deeper station, for it would be continu- ally diminishing in density in descending further, from the augmentation of the temperature of the earth, because the ex- panding influence of the increasing heat would much exceed the condensing influence of the extended column of steam, added to that of the nearly constant column of water. The line of demarcation between the water and steam would, doubtless, conform in some degree to the inequalities of the surface. It may be difficult at first to conceive the steam ca- pable of supporting the water, or rather of existing perma- nently under it; but this difficulty will, I think, be obviated by the consideration, that the points of contact may be, for the most part, in very narrow fissures, or mere cracks in the rocks; and that the water being greatly heated, may be much less than four times the density of the steam in immediate contact with it. A continual struggle would, no doubt, exist between the water and steam under such circumstances, so that in many places they would alternately encroach beyond the line of demarcation ; but as the checks on both would increase in proportion to the extent of their encroachments from the di- minution of the temperature above and its augmentation below, such encroachments would probably not be very extensive, or of long duration under ordinary circumstances. Supposed temporary encroachment of the water on the limits of the steam to occur at one point, the steam would probably en- croach on the water at another at the same time, and then, inactions taking place, the effects would be reversed. Thus, assuming what indeed would appear to follow from admitted data as necessary consequences, steam would not only exist below the water, but such oscillations would tend to give mo- tion and activity to the water in the neighbouring fissures, causing it to circulate in the earth more or less freely and ex- tensively according to circumstances. In volcanic districts, where the heat may be great at comparatively small depths, analogous phaenomena sometimes occur at the surface, which are probably caused by the action and reaction of steam and water. Amongst these may be included the intermitting Geyser springs in Iceland, as well as some of the mud volca- noes found in Sicily, and in Asia, and America. It seems probable that earthquakes may be produced by the action of highly elastic vapour rapidly generated at great depths, in consequence perhaps of copious and sudden in- fluxes of water into intensely heated parts of the earth; and their lines of direction are doubtless influenced by those of the fissures or veins of the districts in which they occur. But these are phasnomena of comparatively rare occurrence, and 10 Prof. J. R. Young on the General Expression it is no wonder that they should be so, when we consider how vastly greater must be the force required to uplift the' rocky crust of the earth and wrench it asunder, than that which will support a column of water equal to the thickness of that crust. Since the foregoing paper was read, I have rather hastily examined some other portions of water taken from different pseudomorphous crystals. One of those portions contained muriatic and sulphuric acids, iron, a trace of lime, and of common salt. Acid was a little in excess, and some peroxide of iron was left in the cavity from which the water was taken. In another the same acids were detected and some iron. In the third portion there seemed to be nothing besides a little common salt. In many of the octahedral cavities, oxide of iron was found, and sometimes iron pyrites or copper pyrites adhering to the sides; these were apparently deposited from some of the water which had entered the crystals in some in- stances, but in others they were evidently imbedded in the fluor, and, adhering to the deposit of quartz, were not dissolved with the former. Earthy carbonate of iron occurs in some cavities mixed with very minute crystals of quartz; and I have one pseudomor- phous quartz crystal which is filled with fragments of fluor, intermixed with translucent fragments of carbonate of iron and earthy carbonate of iron, all curiously cemented together into one mass ; the iron ore being rather in excess. I have also some hollow pseudomorphous crystals of quartz formed originally on carbonate of iron, which appear to be water-tight, and yet the latter substance has, like the fluor, been abstracted. III. On the General Expression for the Sum of an Lifinite Geometrical Series. By J. 11. Young, Professor of Mathe- matics in Belfast College*. ^I^HE general expression for the sum 4 1— x + x* — xz + xA — &c. is 1 xc of the infinite series S = l+x t+jr which reduces to — — when # is a proper fraction, either po- * Communicated by the Author. for the Sum of an Infinite Geometrical Series. 11 sitive or negative, on account of the evanescence of #*". It is usual to consider the infinite exponent in this expression as invariable throughout all the changes of x within the limits 0 and 1 ; although it is known that for any fixed exponent short of infinite, however great it may be, the expression into which it enters becomes more and more considerable as x ad- vances from 0 towards 1 ; and notwithstanding the additional fact, that when this exponent is actually infinite, the expres- sion referred to becomes ultimately equal to — . But it is evident — due weight being given to the circum- stances here mentioned — that this assumption, as to the inva- riability of the infinite exponent, is unwarrantable and erro- neous ; and that the exponent must follow some law of varia- tion exactly fitted to counteract and neutralize the tendency which, as x approaches to 1, the expression a'00" would other- wise have to depart from zero, and ultimately to become — . If x, at any stage of its approach to 1 , be generally repre- sented by 1 — -r j then the law of variation alluded to will be expressed by go " = k go ' : that is, the exponent must vary as k. For it is a remarkable fact that, commencing with the ex- ponent 4* and proceeding onwards to infinity, we shall inva- riably have ©'-»-. (D---. (!)--. (?)'=-. /16801\16802_ /25684^25685_ (y lX V16802/ -'3,,,'-V25685/ -'3-» '" V1" / And since ('3 ...)co/ is necessarily zero, and no power short of infinite can give zero, it follows that in order that / i \«" ( I — r- ) may be uniformly zero, and that all tendency to depart from zero may be counteracted, oo " must be k go ' ; so that the strictly accurate form for S is •3... s = >+0-i) -0-t)' which is equal to — when k is infinite. And in this manner is the formula, employed in my paper (p. 363, last vol.), esta- blished. 12 Drs. Tilley and Maclagan on the Conversion of Cane-sugar In the same way that it has now been proved thatT 1 — j- ) is always equal to * 3 ... , whatever be k, above 3, may it be further shown that (l+-r-) is always equal to 2* ... ; and / 1 \Aoo/ [ # t thence that \l+-j-) is necessarily infinite when k is : so that it is indisputably true that the extreme of the convergent cases of the above series S, usually written in the form 1 — 1 + 1—1+1 — 14- &c. is — , and that the extreme of the divergent cases, usually written in the same form, is really infinite, as stated in my former paper; which last conclusion could never have been anticipated from the theory hitherto prevalent. The views now developed are only the continuation and completion of those exhibited in my paper on Series submitted to the British Association in June 1845. If I have been anticipated in any of these views, which are doubtless calculated to produce a reform in the existing theory, I hope to be informed of the circumstance through the medium of this Journal. I have only further to add, that when an expression for the conver- gent cases of a series is found — as it often may be by aid of the differential theorem — then the general equivalent of the series may afterwards be ascertained by developing this ex- pression sufficiently far to unfold to us the general form of the remainder. The expression for the convergent cases of the general series, discussed at page 439 of the last volume, may in this manner be determined ; and the development of this expression by common division, as there proposed, furnishes the formula by which that expression must be corrected, in order that the algebraical equivalent of the series may be ex- hibited in its utmost generality. Belfast, November 21, 1845. IV. On the Conversion of Cane-sugar into a substance isomeric •with Cellulose and lnuline. By Thomas Tilley, Esq., Ph.D., and Douglas Maclagan, M.D., F.R.S. Edin.* WHEN the juice of beetroot undergoes fermentation at temperatures varying from 30° to 40° C, the cane- sugar which it contains is at first converted into sugar of grapes, and after some time into mannite, lactic acid and a * Communicated by the Chemical Society; having been read April 21, 1845. into a substance isomeric with Cellulose and Inuline. 13 gummy substance, having a composition identical with that of gum-arabic. This is remarkable, inasmuch as it affords an instance of what may be called a retrograde chemical action, the sugar being converted into dextrine, — a change similar to that which occurs in fruits when they lose their sweetness, and assume that condition commonly called " sleepy." The conversion of cellulose into dextrine and sugar seems to be a process of continual occurrence and great importance in the vegetable ceconomy, but we are not aware of any example of the reverse of this action, except those instances mentioned above ; in the former of which sugar is converted by fermen- tation into a body having all the properties and composition of gum ; in the latter, the sugar being changed into cellulose*. We therefore consider the observation we are about to describe to be possessed of some interest, as affording another case of a similar retrograde action. It has been observed that the effervescing drinks known as lemonade, gingerade, &c, made by forcing carbonic acid gas into solutions of sugar variously flavoured with tartaric acid and essential oils, in certain cases lose their fluidity, and assume a thick, slimy consistence. When the bottles containing these thickened liquids are opened, the expansion of the carbonic acid expels their con- tents with difficulty, owing to their extreme tenacity. In- stances of this change are of continual occurrence, all the manufacturers of whom we have inquired having observed it when the bottles had been kept for some time. Various opi- nions have been expressed by them as to the cause of the con- version, but it seems to occur invariably when the liquor is kept long enough. We are indebted to Mr. Baildon of this city (Edinburgh) for an opportunity of examining a sample of gingerade, in which this thickening had occurred. This liquid is made by sweetening an infusion of ginger-roots with cane- sugar, and flavouring it with oil of lemons and tartaric acid ; this is then placed in bottles, and carbonic acid forced by pres- sure into the fluid. Another manufacturer uses the following ingredients in the preparation of effervescing lemonade: — 2 ounces of honey, 4 pounds of sugar, 2 ounces of citric acid, 2 drachms of oil of lemons and I| ounce of bicarbonate of soda. According to the opinion of this manufacturer, the change occurs chiefly in winter, when the liquid is exposed to cold, and he thinks that the addition of a double proportion of honey tends to prevent it. To separate the substance to which the viscidity was owing, the contents of a bottle were digested with six or seven parts of alcohol, under the action of which the gummy matter consolidated, and when dried became so hard * See Mulder's All. Phys. Chem., p. 243 ct seq. 14 On a peculiar Metamorphosis of Cane-sugar. as to be pulverizable. After being powdered, it%as again digested and washed with alcohol until nothing more was dis- solved. When dried at 100° C. it had the appearance of a semi-transparent horny substance, and was sufficiently elastic to render pulverization difficult. The alcohol contained in solution a quantity of sugar of a brownish colour, quite un- crystallizable, and rendered sour by the presence of the acid used in the manufacture. The gummy substance treated with cold water slowly reas- sumes its original appearance. When treated with a large quantity of boiling water it forms a mucilage, which filters with difficulty. Iodine produces no effect on the solution. Subjected to Trommer's test for dextrine, sugar and gum, this did not indicate the presence of any of these substances. With nitric acid it produces oxalic acid. It gives a precipi- tate with diacetate of lead. It contains, after having been washed with alcohol, a small quantity of ashes, amounting to 1*37 per cent. It was analysed in the usual manner. I. 0*746 of substance gave, with oxide of copper and chlo- rate of potash, 4-070 HO and 1-1735 C02 = 0*04727 H and 0-32448 C. II. 0-1525 of substance gave 0*092 HO and 0-232 C02 = 0-010222 H and 0-06474 C. These numbers, allowance being made of the ashes, give the following proportions : — I. II. Atoms. Calculated. Carbon . . 43-80 43-31 24 43-71 Hydrogen 6-14 6-80 21 6-25 Oxygen . . 50-06 49-89 21 50-04 From this it would appear that this gummy substance is isomeric with cellulose and inuline*. This substance, which has a composition similar to cellu- lose and inuline, is evidently formed from the cane-sugar in the lemonade, as all" its other constituents exist in too small quantity to admit the idea of their having been its origin. * Cellulose, Payen. Endine. From turnip. Fromberg. Carbon . 43-40 Carbon . 43-95 Hydrogen 6-12 Hydrogen 6-13 Oxygen . 50-38a Oxygen . 49-66b Inuline. Parnell. From Dahlia root. Payen. Carbon . 43-95 Carbon . 44-19 Hydrogen 6-30 Hydrogen 6-17 Oxygen . 49*75c Oxygen . 49*64d " Ann. des Sc. Nat., 1840, p. 73. Bot. b Mulder, Op. cit., p. 203. c Phil. Mag., vol. xvii. p. 126. d Op. cit., p. 91. Mr. G. G. Stokes on the Aberration of Light. 15 2 affcms sugar . . . . C 24< H 22 O 22 1 ... water .... H Q I ... gummy substance C 24 H 21 0 21 This substance is formed then from 2 atoms of sugar by the abstraction of 1 atom of water. As a solution of the gummy substance gave a compound with lead, we endeavoured to obtain by its aid its atomic weight. 0*260 of the precipitate gave of lead and oxide of lead quantities equal to 0*316 oxide of lead, which, when al- lowance is made for ashes, is equal to 55*8 per cent, of oxide of lead. We had not enough of the salt to enable us to make the combustion, but have calculated the formula from the quantity of lead. Atoms. Calculated Carbon . 19*31 24 1834-4 = 18-7 Hydrogen 2-76 21 260-0 = 2-7 Oxygen . 22-11 21 2100-0 = 21-4 PbO . . 55-80 found 4 5578-0 = 57*1 From 55*8 per cent, oxide of lead the atomic weight found is 4400-0. The calculated one is 4198*4. We had imagined that this curious change in sugar might have been the effect of organization, but our friend Mr. John Goodsir was kind enough to examine the substance, and in- formed us that he could discover no trace of organization. V. Remarks on Professor Challis's Theoretical Explanation of the Aberration of Light. By G. G. Stokes, M.A., Fel- low of Pembroke College, Cambridge*. r|^HERE are a few points connected with Prof. Challis's JL paper on the Aberration of Light, published in the num- ber of this Magazine for November 1845, respecting which I wish to offer a few remarks. In the first place I perfectly agree with Prof. Chailis, that the explanation of aberration is really independent of the manner in which light may pass through the eye; but I can- not agree with him that it is necessary to suppose that we see a star in its true place, and that it is the wire of the telescope with which it is observed that is affected by aberration. The following mode of viewing the subject, due to Boscovich, will perhaps put the matter in a clearer point of view. If we wish to determine the real or apparent direction of an object, we may, theoretically speaking, adopt the following plan: — Let two small circular holes be so adjusted that the * Communicated by the Author. 16 Mr. G. G. Stokes on the Aberration of Light. light from the object which passes through the centr%of the one shall also pass through the centre of the other. The line join- ing the centres of the holes will then determine the direction of the object. Now this is, in principle, just what is done in the case of an astronomical instrument, only, the fixed points are replaced by the optical centre of the object-glass of the telescope with which the object is viewed, and by the wire to which it is referred. When the image of a star is bisected by the wire, we define the apparent direction of the star to be that of the line joining the optical centre, of the object-glass with the bisecting wire. Whether it is the wire or the star which is seen out of its true place, is a question with which we have no concern. The answer which we shall be disposed to give to it depends on the theory of aberration which we adopt. According to the theory of aberration which I ex- plained in the July number of this Magazine, the answer would of course be, that it is the wire which is seen in its true place. The principal thing, however, to which I object in Prof. Challis's paper, is the reasoning by which he establishes his equation (5.). In the figure, a b is a very small portion of a wave of light, which in the small time t would be pro- pagated to c d if the a'ther from a to b were moving with the velocity of the aether at b, whjle, in consequence of the difference in the velocity of the aether at a and b, the disturbance at a is propa- gated to e. Now Prof. Challis takes cae for the angle through which the normal to the wave's front is displaced as the wave passes from a b to e d. But a c is only the direction in space along which the disturbance at a is propagated, a direction which has no immediate relation to the normal to the wave, inasmuch as it differs from it by an angle which is of the order of the aberration, the very order of quantities that we are considering. In fact, according to the reasoning in my paper, to which Prof. Challis does not appear to object, I found that the law of aberration does not result from supposing the waves of light to be carried by the moving aether, so long as its motion is taken arbitrary ; and in order to explain aberration, I was compelled to suppose udx + vdy + xvdz to be an exact differential, at least when the square of the aberration is neglected. It is evidently immaterial whether we make the construc- tion that Prof. Challis has given, or suppose ef to be the po- sition into which the wave a b would come at the end of the Col. Yorke on the Solubility of the Oxide of Lead. 17 time t, in consequence of the velocity of propagation combined with the velocity of the aether at a, and suppose thatyis brought to d in consequence of the difference of velocity of the aether at a and b. It is easy to show that df is equal and parallel io c c, so that, according to this construction, the nor- mal to the wave ought to be displaced by the motion of the aether through the angle /6d from /"ft to db, which is just the contrary direction to that given by Prof. Challis's construc- tion. Prof. Challis seems to think that the undulatory theory of light cannot be maintained unless it can be shown that the law of aberration ought to be the actual law, whatever may be the motion of the aether. But it is surely sufficient to show that a conceivable kind of motion exists which would lead to the observed law of aberration, provided we have no reason for regarding that sort of motion as improbable. Now even were I to allow that udx + vdy+ wdz cannot, in the case of ordinary fluids, be an exact differential unless the motion is rectilinear, that would not be a fatal objection. For the equa- tions of motion of fluids commonly employed are formed on the hypothesis that the mutual action of two elements of the fluid is normal to the surface which separates them, whereas one of the most remarkable properties of the aether with which we are acquainted, is the great tangential force which it is ca- pable of exerting, in consequence of which the transversal vibrations which constitute light are propagated with such an immense velocity. VI. On the Solubility of Oxide of Lead in Pure Water. By Lieut.-Col. Philip Yorke*. T N the Philosophical Magazine for August 1834, I published ■*■ a paper on the action of water and air on lead. Some of the principal results contained in it were confirmed by Bons- dorff in two papers ; he found that 7000 parts of pure water free from access of carbonic acid dissolved one of oxide of lead ; my experiments gave y^^th to ^^th. Since that time two papers have appeared on the same subject, one by Dr. Christisonf, and one by Mr. R. Phillips, Jun.J The last- named chemist considers that the oxide of lead is not dis- solved, but merely mechanically suspended in the water, be- cause the liquid is deprived of the lead by passing it through * Communicated by the Chemical Society ; having been read May 17, 1845. t Transactions of the Royal Society of Edinburgh. X Chemical Gazette for Jan. 1, 1845. Phil. Mag. S. 3. Vol. 28. No. 184.. Jan. 184-6. C 18 Col. Yorke on the Solubility of the Oxide of Lead. a paper filter. It is to this opinion that I propose to direct attention in the present notice. The fact that the aqueous solution of oxide of lead would not pass through a filter was noticed by me in the paper al- ready referred to ; but as the action of tests on the liquid was just what one observes with solutions; as no time allowed for subsidence made any difference in these appearances ; as the liquid deposited crystals of oxide of lead not only on the lead but on other bodies ; as when decomposed by the voltaic bat- tery it gave metallic lead at the negative pole, and peroxide at the positive; I did not consider that the stoppage of the oxide of lead by the filter was any proof of its not being dis- solved. There still, however, remains this question to be an- swered,— In what way does the paper act in retaining the ox- ide? and I think that the following experiments afford an answer to the question. I placed some clean rods of lead in bottles of distilled water loosely stoppered ; in this way, after removing the rods of lead, I obtained a clear liquid, which, when tested by sulphuretted hydrogen, gave a deep brown colour. On passing this liquid through a double filter, which had been previously washed with hot distilled water, it appeared to be very nearly deprived of lead: when two or three fluid ounces had passed through, the filters were removed, washed, then immersed in a solution of sulphuretted hydrogen, again washed and dried. Some torn fragments of the filters were then mounted in Canada balsam for examination by the microscope. On examination with powers of from 1 50 to 400, the fibres of the flax com- posing the paper were seen to be browned, and in many in- stances it could be distinctly observed that the colouring sub- stance occupied the interior of the tubular fibre. Now, it is stated by Mr. Crum, in the Philosophical Magazine for April 1844, that cotton wool possesses the power of abstracting the oxide of lead from its solution in lime-water, and that this property is made available in the processes for dyeing cotton with the chromates. I found that on filtering a solution of oxide of lead in lime water through a triple filter, that whereas the original solution gave a deep black when tested by sul- phuretted hydrogen, the filtered liquid gave but a pale brown ; and it required that the unfiltered liquid should be diluted with thirty times its volume of water to produce the same test as the filtered. I then tried the effect of mere immersion of the paper in the aqueous solutions before used. A bit of filtering-paper ten inches by two inches was boiled in distilled water and then put into an ounce phial filled with the aqueous solution ; after Col. Yorke on the Solubility of the Oxide of Lead. 19 remaining six hours the liquid was poured off and tested: it gave a pale brown, and it required that the liquid which had not been in contact with the paper should be diluted with ten times its volume of water to produce the same tint. This ex- periment was repeated with a stronger solution of oxide of lead in water, the water was poured off at the end of four hours; it then gave a pale brown, and it required that the original liquid should be diluted with four times its bulk of water to produce the same tint. A fresh portion of the same solution was then poured on the same paper and left for a night; then, on testing, the liquid gave a brown tint, barely perceptible, and it required that the original liquid should be diluted with from fifteen to twenty times its volume of water to produce the same. From these experiments it is clear that the effect in ques- tion is dependent on a power possessed by the paper in com- mon with several other porous bodies and organised fibres, of separating certain substances from their solutions, a power sufficiently well known, though little understood*. In consi- dering this view of the subject in the present instance, there is a circumstance of some practical importance which it would appear ought to follow, viz. that after the fibres of the paper had been saturated with the oxide of lead, then this substance should pass through in solution. To ascertain whether this was the case I made the following experiments. I obtained a strong aqueous solution of oxide of lead by immersing slips of clean lead in about three quarts of distilled water, contained in a two-necked bottle, through which oxygen gas was passed and maintained in contact with, under a slight pressure. In this manner I procured a solution which when quite clear yielded 7jootn or* ignited oxide of lead. A filter of paper rather less than 2 o~otn °f an mcn thick and four inches in diameter was prepared and washed ; then, by fitting into one of the two necks of the bottle a siphon with equal legs, so as- to resemble Gay-Lussac's apparatus for washing filters (except that I used a contrivance to prevent the necessity of the air supplied to the bottle from bubbling through the solution), I was enabled to allow the filtration to go on with consider- able regularity for many hours. The first portion of liquid which passed through gave a pale brown when tested ; when nine fluid ounces had passed through the effect was the same as at first, and a portion [a) was reserved for future com- parison. When forty fluid ounces had passed through, the * The effective filter mentioned by Dr. Clark is formed of well-washed sand, and has been in use during twelve months without any apparent diminution of power. C2 20 Rev. B. Bronwin on the Determination of liquid, which was quite clear, gave a much darker tint with the test than any which had previously been obtained in the experiment. It gave a tint about equal to that given with the unfiltered liquid when diluted with its own volume of water; while it (/. e. the last filtered portion) required to be diluted with twice its volume of water to produce the same tint as that given by the reserved filtered portion (a). The liquid now passed through the filter very slowly; it was tested again, when eight more fluid ounces had passed through, with the same result as before, except that the tint was a trifle darker. This experiment sufficiently shows that the effect contem- plated does occur, and that it would be unsafe to trust to the action of a filter to separate oxide of lead from water for an unlimited time. VII. Equations for the Determination of the Motion of a Disturbed Planet by means of M. Hansen's Altered Time. By the Rev. Brice Bronwin*. T HE theory of M. Hansen on Lunar and Planetary Per- turbations, owing to the two times r and t which it con- tains, is attended with many difficulties, and is very perplexing. His results I think are in an advantageous form ; but perhaps they might be obtained more easily by the equations given in this paper, which are referred to the plane of the orbit as if it were a fixed plane, because I have proved that so referred they are true. [See this Magazine for November 1844, and also the Cambridge Mathematical Journal, No. 24.] The equation A* , . . — = 1 + e cos (y — it) = 1 + e cos it cos v + e sin ir sin v is true for the disturbed orbit; h, e, and ir having their known variable values depending on the disturbing force. If /z0, e0, and 7r0 be the values of these quantities when the disturbing force is made to vanish, then ecosnr=e0cos7r0-f- / (cosh- de — esin7r dn), e sin it = e0 sin tt0 + / (sin n d e + e cos 7r d 7r), These values substituted in the above equation give * Communicated by the Author. the Motion of a Disturbed Planet. 21 i^_ = 1 +£0cos (u— *r0) / h dh fi r ° v w firj + cos y / (cosTrt?^— esin7r£?7r) + siny / (sinTrJtf-f ecos7r£/7r). Let the constant quantities X ana g be the same functions of a constant time t which o and r are of / ; then putting the former in place of the latter, we may put them under the sign of integration, changing t into t after the integrations are per- formed. This will change the last equation into /V , 2 Phdh p . JL.— \+e ncos(o— 7rn) / h/ cos(X— ii)de fi r v fij g J -t- J e sin (A— it) dir. But fhdh = — C-j-hdU hdt . , xdR (2hdt . x dr . . . WR de— sm(y — 7r)-v 1 cos(u — w) H — sinfy — it) )-=-, fi K dr \ pr fi /do . hdt , AR /2hdt . . . dr , .\dR dii— — cosfy — it)-^ I sin a- w] cosfy — it) I — . fie dr \ fire v fie / dv d R The coefficients of —z— are put under the above form for ay * convenience. Substituting these values, we find T=^ + ^°cos ("-*») + I^f^r Si" g d~t~"dt ' + ~d\Tt* r*dt + This value, substituted in the known equation gives Of the four quantities h0, hv eoi ev two are to be found in terms of the others, which will be arbitraries of the theory ; and the mode of determining them will be obvious after the development is effected. Putting for the latitude, i for the inclination, 3 and 0 for the longitude of the node on the plane of the orbit and on the fixed plane, we have 3 = / cos i d 0, sin = sin i sin (o — S) = sin i (cos ^ sin u — sin •& cos u), sin? cos •& = sin/0cos$0 + / (cosz'cosSd? — sin? sin 3 ^3), the Motion of a Disturbed Planet. c2$ sins" sin .&=sirw0 sin S0+ / (coszsindrfz 4- sin/cos^rf-&). Substituting these values, and changing u into A, and put- ting it under the sign of integration, we obtain sin ss sin i0 sin (u — S0) + I sin (A — d) cos i d i — / cos (A — -5) sin i d •&. ~ ,. dt dR cosidtdR But dt — r—- : ~TTi «•& = j—. -— r-r. A sin 2 a 0 # sin i d i These values being put in the above, it will become . . . . . . , /*cosidt dR . , sin$ =sm *0sin (« - S0) +J j^j ~jj sin (A - S) /cos idt dR . RN ___cos (*-*). To abridge, we may write this sin = sin i0 sin (u — $0) + Q» or sin

= sin i sin (u — • 3), dsin 6 . . , ., c?w — ; — I = sin z cos (u — 3) -7-, dt dt we change $, w, 1, and 3 into uo + ^ °> *o + & *» anc^ •&o + 1*^ * $> &c« being the parts depending on the disturbing force; and if we expand, taking account of the first power only of 8 + B8u, 8d=C84> + D8y. From these we may correct the values of i and .& or 6 by means of the corrections of

* co -h O O O O © 1-1 o : © ii \i $ £&***£ i i * i a aJ g «5 i g i g «5 »8 Sj3J=j3j3 . -J S S SJ3 SJJJ3 J .-,•„.• J J= S .§ .E .Sj3j3 "3 "3 "3 "3 "3 w 5 *3 "3 W "3 W "3 ^ "3 "3 "3 £ £ * "3 "3 ~3 * ^ P * JS "3 "3 u o o u u UUbUUUUUUU aJ «J « g «• g 4 « U «• «S | c | g » » | £ |* || »' IS B £ g J «5 | & m i £2 •U!W XBfl[ •uoj !f8 soa "!W XBW -»g *B •uojsoa jo sXbq 22 -|«H|e» -»; --I --, -Cl-H -|« TfT^^TtT^lr5r^Tt^•^■^0 — ONV© •^fTflO ONCM r-i T*Tf^rr^ioio^Tj,''*'ri<'^,''3,^i,coco-'i,-'3,'**co'«tf''* —In -|ei -lei -^» -^» -ci -(« —lei —lei -Id -lei -Id -(ei --n»Of)0»'OMO>oio Tf Tf CO CM CO'*UOTj<'3<-<3i'3«COCOCOCOT''3,CO-*J'-'3'CO-io wio --»- • onon — t^^o — oc^»ci-<-iHio oov©i>aooN©-ooioe ^oo ^'O«i0iOU0inu0''*'^,''3,iOlO»OlOiO'O (sooiocicfOio\oo(sw't<«5(«)c^iot<)-i(s»TfaiOHMMOorj ?l9'r^'P?9'?''P'?'f5'??,0P97,^9l!,l^'^?0PlP7?'o ^w^ip^-jroooaicco— T'lpotCTi^r^ovM'^'c) •** o -^i* © O © ONONONONONONONONONONONONONONONOOOOOO ONONOnOnONONONONON COC005«(S(M(N(N(NCICNClCNCOCO(Nrfl^<»«roO<^«^eN^r~ON«coip<^Olip C0 00C0roCNC^O)C^C^C^rNCon« uo oo co co on uo r-ON ON ON ON ON CM CM CM CM >-(M roi'i/MOr»XONO -M fi^iOior>00ONO - oo ono ^^^^.^^^rtrtp-OtCICMCMCMCMCMOlCMCMCO « o « ® the LONDON, EDINBURGH and DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. [THIRD SERIES.] FEBllUAE'Y 1846. 1 XVI. On the Application of the Photographic Camera to Me- teorological Registration. By Henry Collen, Esq.* [With a Plate.] N April 1844, Mr. Ronalds applied to me for the purpose of obtaining some photographic representations of figures, forming " a sort of pictorial register of atmospheric electri- city " upon glass plates coated with Canada balsam, which figures had been executed at the Kew Observatory by means of his electrograph, described in the Fourteenth Report of the British Association. The desired result was quickly obtained by the usual photogenic process, and also by the camera; the latter being found however, as was to be expected, the greatly superior mode. Several other impressions were afterwards made from figures on coated metallic plates, some of which were shown attached to Mr. Ronalds' s report to the meeting at York. The sharpness and delicacy of the positive impres- sions thus obtained gave rise to some experiments, made by us conjointly, for the purpose of applying the photographic camera to the registration of Volta's electrometer, the ther- mometer, and the siphon barometer. The projection of sha- dows on photographic paper, which, by the way, had been already proposed and tried by several persons, was at once objected to by Mr. Ronalds, whose knowledge of the delicacy required in observing and registering the various instruments at the Observatory, made him fully aware of the necessity of obtaining as perfect definition as the best optical arrange- ment would produce; an excellent compound lens, made and kindly lent to us by Mr. Ross, was therefore used, and has been employed on each of the instruments, i. c. the electro- * Communicated by the Author. Phil. Mag. S. 3. Vol. 28. No. 185. Feb. 1846. G 74 Mr. H. Collen on the Application of Photography. meter, the barometer, and the thermometer, and a series of experimental observations permanently registered at Kew. The accompanying figure (Plate III. fig. 1) is part of a day's registration of the effect of atmospheric electricity on Volta's electrometer ; the gradual decline of daylight is shown, and also the continuation of the registration, by artificial light; without the use of the latter, it is obvious that the ap- plication of photography to these purposes would be very in- complete, if not wholly useless ; and it may perhaps, in some cases, be advisable to make its use constant. The various intensities of light from a clouded sky frequently give rise (of course) to variations in depth of tint on the paper, which thus becomes an approximation to Sir John Herschel's actinograph ; and-it may be here worth while to remark, that sometimes, when with such a sky these intensities of action on the paper are augmented, the electricity of serene weather ma- nifests a tendency to increase also; this fact may be compared with the almost invariable tendency of the sun's light and heat, in a clear sky, to diminish the tension of those electrometers which receive their charges by absorption. The calotype process is that which is used, being, of all those upon paper, the most sensitive, which quality is highly essential during the use of artificial light; it is very advan- tageously employed for these purposes, instead of the Da- guerreotype, on account of its cheapness, and also on account of the facility with which representations can be obtained of any required length. In the apparatus at present constructed, the paper is moved by a clock at the rate of one inch per hour, and is cut into pieces nine inches long; but for constant use they should be twelve inches long, so that by the introduction of two pieces during twenty-four hours, a continuous register of the effects would be preserved without further attention than the appli- cation of the artificial light (if not used constantly) at the de- cline of daylight; at present an Argand lamp is used, which, of course, requires some attention, but where available, a common gas-light would be greatly preferable; this however is not the case at the Kew Observatory, and for this reason only, the experiments have not been continued during the night. The construction of the apparatus is very simple, although many tedious experiments have been made to produce the re- sult; it consists essentially of the following arrangement: — The instrument to be registered is placed so as to be between the light and a lens of considerable aperture, with very short focus, and flat field of sufficient extent for the purpose ; and Mr. H. Collen on the Application of Photography. 75 the paper is placed so as to be in the exact focus for obtaining an image of the same size as, or larger than, the object. When the electrometer is the instrument to be registered, the figures of the extreme ends only of the straws are allowed to fall upon the paper, an opake diaphragm pierced with a slit, the curve of which is part of a circle of which the length of the straws is the radius, being placed very near the paper. In the registration of the thermometer or barometer, the difficulty arising from the refraction of light by the glass tube was proposed to be met in two ways, the first of which, the one adopted, consists in the use of a diaphragm with a straight slit, which can be opened from, or contracted towards, its exact centre by a very simple arrangement, and is placed in front of the mercury, i. e. on the side next to the light, so as to regu- late the quantity admitted; this regulation has also the effect of preserving the necessary sharpness of figure, which too much light tends to injure. The second method proposed, which has not yet been tried, consists in the employment of a piece of glass tube, the bore of which is a trifle larger than the outside of the tube of the instrument; this, having two opposite surfaces ground flat and polished, and being long enough to include the range of va- riation, is cemented on to the tube of the instrument with Ca- nada balsam, and would render it easy (by making all but a central slit opake) to get rid of the partial illumination of the column of mercury on the side which is required, for a good impression on the paper, to be quite dark. The surface of the mercury in the barometer sustains a blackened pith- ball of the same diameter as the bore of the tube, but freely sliding therein; it is proposed however to make a float of platinum foil with a sharp edge, which will probably be found to be more advantageous. The thermometer used is mercurial, with a broad flat bore. The wet- bulb, hair hygrometer, &c, as well as every other instrument which by its action affords a distinct sign, may obviously be registered in the same manner. Several minor points of difficulty remain still to be over- come, but it is hoped that enough has been done to justify the expectation that the photographic camera may become a really useful and convenient instrument in the hands of the exact meteorologist. The electrical experiments were made by means of a small conductor, insulated for the occasion ; Mr. Ronalds not feeling either authorised, or disposed, to interrupt the course of obser- vations carried on by means of the ordinary high conductor, until the proposed mode of registration is quite matured. G2 [ 76 ] XVII. On Fresnel's Theory of the Aberration of Light. By G. G. Stokes, M.A.t Fellow of Pembroke College, Cam- bridge*. ^^HE theory of the aberration of light, and of the absence of any influence of the motion of the earth on the laws of refraction, &c, given by Fresnel in the ninth volume of the Annales de Chimie, p. 57, is really very remarkable. If we suppose the diminished velocity of propagation of light within refracting media to arise solely from the greater density of the aether within them, the elastic force being the same as without, the density which it is necessary to suppose the aether within a medium of refractive index jx. to have is ju.2, the density in vacuum being taken for unity. Fresnel supposes that the earth passes through the aether without disturbing it, the aether penetrating the earth quite freely. He supposes that a refracting medium moving- with the earth carries with it a quantity of aether, of density pr — 1-, which constitutes the ex- cess of density of the aether within it over the density of the aether in vacuum. He supposes that light is propagated through this aether, of which part is moving with the earth, and part is at rest in space, as it would be if the whole were moving with the velocity of the centre of gravity of any por- tion of it, that is, with a velocity ( 1 % )v, v being the velo- city of^he earth. It may be observed however that the result would be the same if we supposed the whole of the aether within the earth to move together, the aether entering the earth in front, and being immediately condensed, and issuing from it behind, where it is immediately rarefied, undergoing likewise sudden condensation or rarefaction in passing from one refracting medium to another. On this supposition, the evident condition that a mass v of the aether must pass in a unit of time across a plane of area unity, drawn anywhere within the earth in a direction perpendicular to that of the earth's motion, gives ( 1 ^ ) v f°r l'ie velocity of the aether within a refracting medium. As this idea is rather simpler than Fresnel's, I shall adopt it in considering his theory. Also, instead of considering the earth as in motion and the aether outside it as at rest, it will be simpler to conceive a ve- locity equal and opposite to that of the earth impressed both on the earth and on the aether. On this supposition the earth will be at rest; the aether outside it will be moving with a ve- locity v, and the aether in a refracting medium with a velocity * Communicated by the Author. On Fresnel's Theory of the Aberration of Light. 77 -tt. in a direction contrary to that of the earth's real motion. P On account of the smallness of the coefficient of aberration, we may also neglect the square of the. ratio of the earth's ve- locity to that of light ; and if we resolve the earth's velocity in different directions, we may consider the effect of each resolved part separately. In the nintfi volume of the Comptes Rendus of the Academy of Sciences, p. 774, there is a short notice of a memoir by M. Babinet, giving an account of an experiment which seemed to present a difficulty in its explanation. M. Babinet found that when two pieces of glass of equal thickness were placed across two streams of light which interfered and exhibited fringes, in such a manner that one piece was traversed by the light in the direction of the earth's motion, and the other in the contrary direction, the fringes were not in the least displaced. This result, as M. Babinet asserts, is contrary to the theory of aber- ration contained in a memoir read by him before the Aca- demy in 1829, as well as to the other received theories on the subject. I have not been able to meet with this memoir, but it is easy to show that the result of M. Babinet's experiment is in perfect accordance with Fresnel's theory. Let T be the thickness of one of the glass plates, V the ve- locity of propagation of light in vacuum, supposing the aether at rest. Then — would be the velocity with which light would P traverse the glass if the aether were at rest ; but the aether v moving with a velocity —# the light traverses the glass with a P V v velocity — + — , and therefore in a time But if the glass were away, the light, travelling with a velo- city V + v, would pass over the space T in the time T + (V±v) = ±(l+%). T Hence the retardation, expressed in time, =((/.— 1 ) ^, the same as if the earth were at rest. But in this case no effect would be produced on the fringes, and therefore none will be produced in the actual case. I shall now show that, according to Fresnel's theory, the laws of reflexion and refraction in singly refracting media are 78 Mr. G. G. Stokes on Fresnel's uninfluenced by the motion of the earth. The method which I employ will, I hope, be found simpler than Fresnel's ; besides it applies easily to the most general case. Fresnel has not given the calculation for reflexion, but has merely stated the result; and with respect to refraction, he has only considered the case in which the course of the light within the refracting medium is in the direction of the earth's motion. This might still leave some doubt on the mind, as to whether the result would be the same in the most general case. If the aether were at rest, the direction of light would be that of a normal to the surfaces of the waves. When the motion of the aether is considered, it is most convenient to de- fine the direction of light to be that of the line along which the same portion of a wave moves relatively to the earth. For this is in all cases the direction which is ultimately observed with a telescope furnished with cross wires. Hence, if A is any point in a wave of light, and if we draw A B normal to the wave, and proportional to V or — , according as the light is passing through vacuum or through a refracting medium, and if we draw B C in the direction of the motion of the aether, and proportional to v or -|, and join A C, this line will give the direction of the ray. Of course, we might equally have drawn A D equal and parallel to B C and in the opposite di- rection, when D B would have given the direction of the ray. Let a plane P be drawn perpendicular to the reflecting or refracting surface and to the waves of incident light, which in this investigation may be supposed plane. Let the velocity v of the aether in vacuum be resolved into p perpendicular to the plane P, and q in that plane; then the resolved parts of v the velocity —^ of the aether within a refracting medium will r be ^, -^. Let us first consider the effect of the velocity p. It is easy to see that, as far as regards this resolved part of the velocity of the .ether, the directions of the refracted and reflected waves will be the same as if the aether were at rest. Let BAC (fig. I) be the intersection of the refracting surface and the plane P; D A E a normal to the refracting surface; AF, AG, AH normals to the incident, reflected and refracted waves. Hence A F, A G, A H will be in the plane P, and Z GAD = FAD, ^sinHAE=sinFAD. Take AG = AF, A H = — A F. Theory of the Aberration of Light. 79 Draw Gg, Hh perpendicular to the plane P, and in the di- rection of the resolved part p of the velocity of the aether, and Fig. 1. F/in the opposite direction F/:H/cFA V and join A with /, g and h. ThenyA, Ag, Ah will be the directions of the incident, reflected and refracted rays. Draw F D, H E perpendicular to D E, and join fD, h E. Then f D F, h E H will be the inclinations of the planes f A D, h A E to the plane P. Now V tan H E h = ¥>~*V tan FD/_ Vsin F AD» -» " *-» t fr-i Vsin HAE' and sin FAD = !«, sin HAE; therefore tanFD/= tanHE^, and therefore the refracted ray A h lies in the plane of inci- denceyA D. It is easy to see that the same is true of the re- flected ray Ag. Also Z g AD =fAD; and the angles f A D, h A E are sensibly equal to F A D, H A E respectively, and we therefore have without sensible error, sinyA D = jtx. sin h A E. Hence the laws of reflexion and refraction are not sensibly affected by the velocity p. Let us now consider the effect of the velocity q. As far as depends on this velocity, the incident, reflected and refracted rays will all be in the plane P. Let A H, A K, A L be the in- tersections of the plane P with the incident, reflected and re- fracted waves. Let \J/, fyp \J/' be the inclinations of these waves to the refracting surface; let N A be the direction of the re- solved part q of the velocity of the aether, and let the angle NAC = «. The resolved part of q in a direction perpendicular to A H is <7sin (\J/ + a). Hence the wave A H travels with the velo- city V + (/sin (\\> 4 a); and consequently the line of its inter- 80 Mr. G. G. Stokes on Fresnel's section with the refracting surface travels along A B with the Fig. 2. velocity cosec \J> { V + q sin (\J/ + a) } . Observing that \ is the . . V velocity of the aether within the refracting medium, and — the velocity of propagation of light, we shall find in a similar manner that the lines of intersection of the refracting surface with the reflected and refracted waves travel along A B with velocities cosec vl>;{V + <7 sin (ty— «)}, cosec \I/ J h -^sin (vj/ + a) [_ f* r" J But since the incident, reflected and refracted waves intersect the refracting surface in the same line, we must have sin4//{V-f-<7sin(\J/ + a)} = sin^V + ^sin^— «)}}"j ftsin4/{V + ?sin(rJ/ + a)} = sinf jv + ^sin(4/ + «)j. f (A) Draw H S perpendicular to A H, ST parallel to N A, take S T : H S : : q : V, and join H T. Then H T is the direc- tion of the incident ray ; and denoting the angles of incidence, reflexion and refraction by ' = sin ce^s» measuring rGTTB& to 2jootn °^ an mch. 1. The granules, which I may distinguish by the name of primitive granules, are globular in form, homogeneous, solid, brightly illumined by transmitted light when the centre is under the focus of the microscope, but dark when viewed upon the surface, the darkness being increased whenever they are 84 Mr. E. Wilson's Observations on the congregated in clusters. These granules I conceive to be the first organic shape of the blastema of the liquor sanguinis. 2. The aggregated grannies, measuring about yotW o*n °f an inch in diameter, are minute masses, composed of four, five or six of the preceding, or as many as can be aggregated with- out leaving an unoccupied space in the centre of the mass. With an imperfect focus, these granules have the appearance of possessing a transparent globular nucleus, but this appear- ance ceases when the focus is perfect, and then the compo- nent granules are quite obvious, and the centre becomes a dark point, namely, the shadow caused by the meeting of the primitive granules. 3. The nucleated granules, measuring between ^y— th and Wootn °f an mcn m diameter, are in point of construction an " aggregated granule" with a single tier of " aggregated gra- nules" arranged around it, so as to give the entire mass a cir- cular or oval form. The central aggregated granule has now become a nucleus, and at the same time has undergone other changes which indicate its longer existence. For example, the primitive granules composing it are denser than they were originally, and they are separated from each other by a very distinct interstitial space filled with a transparent and homo- geneous matter. Sometimes this interstitial substance presses the granules asunder equally on all sides, constituting a cir- cular nucleus; but more frequently two opposite granules are more widely separated than the rest, and the nucleus receives an elongated form. The interstitial substance is most con- spicuous at the line of junction of the nucleus with the secon- dary tier of " aggregated granules," and in this situation gives a defined character to the nucleus. Close observation and a perfect focus render it quite obvious that the peripheral tier of granules are in reality aggregated, they are lighter than the shaded granules of the nucleus, and apparently softer in texture. The nucleated granules are more or less flattened in form, and present a flat surface of contact with the dermis. It is the latter circumstance that gives the facility of determining their mode of construction. 4. The cells of the deep stratum of the epidermis, measu- ring 3 o\y otn to 2 j1ootn °f an mcn ni tneu> l°ng diameter, are the most striking feature of this layer, and may be said to be its chief constituent. They originate, as is evident from their structure, in the nucleated granules previously described, and consist of a transparent layer added to the exterior of the former; or, if 1 might be permitted to describe them as they appear in their tesselated position, they are constituted by the Development and Growth of the Epidermis. 85 addition of a transparent border to the last-described nucle- ated granule. The periphery of this transparent border is bounded by a dark interstitial substance, which gives the bor- der a defined outline ; and in the latter situation I imagine a cell-membrane to exist. I am not satisfied, however, that this is the case; and the difficulty of isolating these cells, and their roughness of outline when separated, serve to prove that if a membrane be really present, it must be exceedingly thin and easily torn. Assuming therefore, from analogy rather than from demonstrative evidence, that there exists a boun- dary membrane to the bodies I am now describing, I have termed them " cells ; " the cavity of the cell I apprehend to be the "transparent border," the "nucleated granule" is the nucleus of the cell, the "aggregated granule" of the latter the nucleolus, and the entire body a "nucleolo-nucleated cell." Before quitting the structure of the "nucleolo-nucleated cell," or primitive cell of the epidermis, there is a point of much interest to be mentioned with regard to it, which is, that the "transparent border" just described is itself a tier of "aggregated granules." The nucleolus therefore is an "ag- gregated granule," the nucleus a tier (taking its flat surface) of "aggregated granules" surrounding the former, and the cell a tier of " aggregated granules " enclosing the whole. To return to the mosaic-like plane of the under surface of the epidermis, the largest of the pieces composing this plane are the nucleolo-nucleated cells. These are placed without order, some being closely pressed together, others being se- parated by moderate intervals, and here and there some sepa- rated by interspaces equal to the breadth of the cells. The interspaces, or intercellular spaces, are occupied by the "nu- cleated granules," "aggregated granules," and "primitive granules," irregularly set in a homogeneous interstitial sub- stance, which fills up all vacuities. The granules and inter- stitial substance modify the light transmitted through them variously at different foci of the microscope ; sometimes the granules look dark while the interstitial substance is light, and sometimes the reverse is the case. Such is the structure of the mosaic-like plane of the under surface of the epidermis, and so far, my observations, having reference to facts, are demonstrable and admit of being spoken to positively. The interpretation of the facts I would willingly leave to others, but feel that I am called upon to state any opinion, founded on the above observations, that 1 may have formed of the signification of these appearances. In the first place, then, I must acknowledge myself wholly divided between 86 Mr. E. Wilson's Observations on the a belief in the formation of the " aggregated granule " by the aggregation of primitive granules, the idea which prompted me to give them that name, and the formation of the aggre- gated granule by the cleavage of a primitive granule. If this question related merely to the formation of the " primary ag- gregated granule," it would be unimportant, but it has a more extended application. The outermost layer of the nucleus is composed, as I have shown, of "aggregated granules," and so also is that layer which alone forms the space in the nu- cleolo-nucleated cells. To them the hypothesis of cleavage of a simple granule would be most suitable, and this theory would explain better than any other, changes which remain to be described in the further growth of the epidermic cell. In the second place, the relation of cell and nucleus is a question on which I feel considerable doubt. The process of develop- ment appears to consist in the successive production of gra- nules, one layer of granules succeeding another, so that if the organisable principle exist in each separate granule, the or- ganisable force may be supposed to be more and more weak- ened in successive formations, until the moment arrives when it ceases entirely. Is that which I have described as a nu- cleolo-nucleated cell really a cell or still a nucleus? The only solution of the question that occurs to me is, determining the presence of a cell-membrane, in which I have not satisfactorily succeeded. Admitting the nucleolo-nucleated bodies now described to be cells in their earliest state of formation, their size is smooth to 2jootn °f an nicn m tne l°n& diameter, and that of their nu- cleus from 77(j\joth to ^jyo1'1 of an inch. In the stratum im- mediately above the deepest layer, I find cells measuring -^--th of an inch with nuclei of Tjoyth. Above these, cells measuring Ta\jotn> with nuclei varying from ¥IJ^th to ^^th, and above the latter cells measuring y^^th, with nuclei of _Ti__th. In following the layers of the epidermis upwards to the surface, cells may be observed possessing every interme- diate degree of size between the last-mentioned cell, namely 1 th and ^Anth, which is the measurement of the scales 1.5 00 , l)UO ' . which constitute the uppermost stratum of the epidermis. It must not be supposed, however, that the growth of the epi- dermic cells reaches its maximum only at the surface : I have found cells of that magnitude in the deeper strata; and there is every indication of the growth of these cells being com- pleted in the stratum immediately above the mosaic-like layer. Young cells are remarkable for the large size of the nucleus as compared with the entire bulk of the cell; and it is quite Development and Growth of the Epidermis. 87 evident also that the nuclei, up to a certain point, grow with the cells, their mode of growth appearing to be, the separa- tion of the original granules by the deposition between them of interstitial matter; and in addition, as I believe, by clea- vage of the latter and the consequent multiplication of the gra- nules. In cells measuring ^imo10 ant^ Tiiootn °^ an mcn> ' found the granular character of the nucleus to be very mani- fest. Besides growth, it is apparent that 'other changes are taking place in the nucleus ; imbibition and assimilation of or- ganisable material must necessarily be in action in order to accomplish the formation of interstitial matter; but in addi- tion to this the central granules undergo another change, by which they are altered in character and become distinguished from the rest when submitted to chemical experiment. For example, when dilute acetic acid is added to the cells measu- ring TTTroTrth of an inch and less, the entire nucleus is rendered transparent and less discernible than before; but when cells of a somewhat larger size, and consequently longer growth, are submitted to the same process, the nucleus is rendered much more distinct than it was previously. But the body which is made so conspicuous in this latter experiment is not the entire nucleus, but simply the central and older granules of the nucleus ; the younger granules retain the character of those of the young cells, they are made more transparent than they were before, and have faded from sight. I may mention also, that the nucleus brought into view by the acetic acid is more or less irregular in form, and has the appearance of being constituted by the fusion of the original granules. How much of this appearance may be real and how much the effect of the acid, I do not pretend to say, and I set no value on the ex- periment beyond the demonstration of the mere fact which it is made to illustrate. I now turn to the growth of the cells. I have remarked, in an earlier paragraph, that the formation of the young cell appears to be due to the development of a stratum of "aggre- gated granules" externally to the nucleated mass, which I have regarded as the cell-nucleus. Now nothing is more cer- tain than that the growth of the cell is due to a successive re- petition of this process, the growth of the cell-membrane being consentaneous with the development and growth of " aggre- gated granules" within it. In cells of TTj\njtn ^tjVo10 OT>an inch, the "aggregated granules" of the periphery are not easily discernible; but in cells measuring y^^th, and thence upwards to the complete size of the epidermic cell, the fact is quite evident, and is apparent even in the cell-scale. Indeed a cell, at the lull period of growth, is a kind of cell-microcosm, 88 Mr. E. Wilson's Observations on the containing in its interior secondary cells, tertiary cells, nu- cleolo-nucleated cells, nucleated granules, aggregated gra- nules, and primitive granules. It will be observed that this hypothesis of cell growth differs from that of Schwann. The theory of Schwann always ap- peared to me to be incompetent to the explanation of the growth of the large scale of epidermis and epithelium in a tissue manifestly subjected to considerable pressure. I sought in vain for the watch-glass cells, elliptical cells, and globular cells in the epidermis; but my search has been rewarded by the discovery of the above-described beautiful process of form- ation and growth. It will be seen that, according to this view of the growth of the epidermic cells, they never possess anything approaching to a globular shape, that the scales are not flattened spheres, but on the contrary always possessed a flattened form, and have increased by a peripheral growth. This mode of growth again is made manifest by the observa- tion of a vertical section of the epidermis. The most careful examination can distinguish no difference between the size of the deeper and the superficial strata of cells ; they have all the same average thickness, all the same average length, — an ap- pearance easily explained when we regard them as parent- cells containing secondary and tertiary cells of the same ave- rage size as the cells of earlier formation. It is true that the complete size of a cell is very quickly attained, and that its growth, taking place in the deepest stratum of the epidermis, could not be expected to produce any difference of character in the middle and superficial strata ; but this is not mentioned, as far as I know, by Schwann. The process of growth here described explains also the fact of the disappearance of the nucleus in the scales of epidermis. The outermost granules of the nucleus have become the nuclei or nucleoli of secondary cells, and have consequently been moved away from their original position in the performance of their office of centres of growth to secondary cells. The original nucleus, therefore, is not lost, but merely robbed of some of its component granules, which may be discovered in many parts of the epidermic scale, instead of being concen- trated in a single mass. In these scales, and particularly in epithelial scales, the central and dense part of the original nucleus is generally perceptible; in the latter it constitutes the scale nucleus; and in the epidermic scale there is always some one little mass larger than the rest, particularly if the scale have been for some time immersed in fluid, as when it is examined in the serum of a blister. In an epidermic cell, measuring Q^th of an inch in long diameter, I found several Development and Growth of the Epidermis. 89 secondary cells measuring tjW&i otners measuring jqVo10 > and in the interstices, primitive granules, aggregated granules, and nucleated cells. My observations, it will be seen, have been chiefly directed to the epidermis, and I am prevented at present from carry- ing them further, but I have no doubt that the epithelium will be found to be identical in the phaenomena of development and growth with the epidermis. I have observed the same structure in the epithelium of the mouth and fauces, and also in that of the bladder and vagina. Incomplete epithelial cells, measuring 7jyth and y^th of an inch from the fauces, pre- sented a very remarkable appearance; they had a rounded lobulated border, evidently composed of a row of secondary cells and a depressed centre, as though the action were sub- siding in the latter, while it was progressing in the circumfe- rence. Another illustration of the structure now described, I found in the cells of melanosis, and in the pigmentary cells of the choroid membrane of the eyeball. I am induced to believe that the same structure will be discovered more extensively than at present can be anticipated. The corpuscles of mela- nosis, according to my observations, are parent-cells, having an average admeasurement of To\jotn °* an mc^> containing secondary cells and nucleated and aggregated granules, as well as separate primitive granules. The " aggregated gra- nules" measured from TTtJootn to ^oVo^1 °f an inch, and the primitive granules about 2onoUtn- There is another feature in the history of development of the epidermic cell, which I regard as peculiarly interesting. This relates to an organic change taking place in the assimi- lative powers of the primitive granules, by which the latter are altered in their colour, in short, are converted into "pig- ment granules." Pigment granules appear to differ in no re- spect from the " primitive granules," excepting in that of co- lour, and perhaps also in chemical composition. They have the same globular form, the same size, and occupy the same position in the cell, being always accumulated around the nu- cleus, and dispersed less numerously through the rest of the cell. The nucleus of the cell in the epidermis of the Negro appears to consist wholly of pigment granules, while in the European there is a greater or less admixture of coloured and uncoloured granules. The central granules are generally lighter in tint than the rest, and give the idea of a colourless nucleolus, while those around the circumference are deeper coloured. Besides a difference in the depth of colour of the separate granules entering into the composition of a single Phil. Mag. S. 3, Vol. 28. No. 185. Feb. 1846. H 90 Rev. J. Challis on the Aberration of Light. cell, there is also much difference in the aggregate of the gra- nules composing particular cells. For example, intermingled with cells of a dark hue, there are others less deeply tinted, which give the tissue in which they are found a mottled ap- pearance. This fact is well-illustrated in the hair, and also in the nails, in which latter it is no uncommon thing to find an isolated streak produced by the accumulation of a number of cells containing coloured granules, in the midst of colour- less cells. When pigment granules are examined separately, they offer very little indication of the depth of colour which is pro- duced by their accumulation. I have observed some to have the hue of amber, while others scarcely exceeded the most delicate fawn. The depth of colour of the deep stratum of the epidermis in the Negro, is evidently due to the composi- tion of that layer of these granules, while the grayness of the superficial layers of the same tissue results not merely from the desiccation of these granules, but also from the fact of those subsequently produced being less strongly coloured, and also from the addition of a colourless cell-membrane. The epidermic scale of the Negro has a mottled appearance, from the numerous secondary nuclei and their attendant co- loured granules which are scattered through its texture. P.S. Since my communication of the above paper to the Royal Society, I have confirmed its truth by further observa- tions, and have ascertained that the same principle of growth is applicable to the formation of mucus and pus-corpuscles. December 1845. XIX. On the Aberration of Light, in Reply to Mr. Stokes. By the Rev. J. Challis, M.A., Plumian Professor of Astro- nomy in the University of Cambridge*. r|^HE remarks Mr. Stokes has made on my Explanation of -*- the Aberration of Light, since they have little reference to the more important parts of the communication, require from me but brief notice. I agree with all Mr. Stokes has said about the direction of vision through a telescope, but cannot perceive what it has to do with aberration. In selecting the wire of an astronomical telescope for the terrestrial object to which the direction of the celestial object is referred, I had not the least reference to vision through a telescope. It would have answered my pur- * Communicated by the Author. Rev. J. Challis on the Aberration of Light. 91 pose equally well if I had fixed upon a division of the gradua- tion of a circle used for astronomical observation. The fol- lowing method of viewing the subject will put this in a clear light:— Let apq be a circle of given radius, the centre of which coincides with the place of the spectator's eye, and partakes of the earth's motion. Let the plane of the circle pass through e1 c y, the line in which the eye moves, and through sp' e, the line in which light comes to the eye from a star. To find the point of the circle on which the light impinges by which the star is seen, take e1 e equal to the space passed over by the eye while light travels over the radius of the circle; take e' p1 equal to the radius of the circle ; draw ep parallel to e1 ' p', and join p' p. Then p is the point required; for ftp is evidently equal and parallel to e1 e. Consequently p is the point of the circle which is seen in coincidence with the star s. If the star were at 5' in the direction of the line e' eq produced, the point q on that line would be seen in coincidence with it. Now suppose the circle to be graduated, and to be used by an astronomer to measure the angle ses' ; then most certainly he would read off' the angle peq instead of the angle pi e q, be- cause to turn a given point of the circle from apparent coin- cidence with one star to apparent coincidence with the other, the circle would be moved through the angle p eq. The dif- ference between the two angles, viz. sep, is equal to the amount of aberration determined by astronomical observation. The phenomenon is thus entirely accounted for. It follows as a corollary from this reasoning, that the di- rection sp' e of the progression of light from a celestial object, H 2 92 Rev. J. Challis on the Aberration of Light. just before it enters the eye, is the true direction of the object, atmospheric refraction not being considered. It seems probable also that th's is the direction in which the object is seen ; if so, the point j» is seen out of its true place. This, however, is not ; n essential consideration. I think it important to remark, that the foregoing explana- tion of aberration rests on no hypothesis whatever, being a strict deduction from ascertained facts, without reference to any theory of light. The cause assigned for aberration is, there- fore, a vera eausa, which consequently excludes every explana- tion of a hypothetical kind, such, for instance, as that which Mr. Stokes proposed in the July number of this Magazine. Aberration being explained in this manner, it is interesting to inquire whether a proposed theory of light be consistent with this explanation. The object of such an inquiry would be to test the truth of the proposed theory. The only condi- tion the theory is required to fulfil, in addition to that of tem- poraneous transmission, is, that the light from an object tra- verse, just before it enters the eye, a straight line directed to the true position of the object. The above condition is satisfied on the theory of emission, because according to that theory light passes from the object to the eye in a straight line. In the undulatory theory, the di- rection of transmission of light is the direction of transmission through space of a given point of a wave in a given phase of vibration. Where the aether is undisturbed, this direction is normal to the front of the wave. Where the aether is in mo- tion, it is the direction resulting from the composition of the motion of propagation of the wave with the motion of trans- lation of the aether. It is easy, therefore, to determine, for a given motion of translation of the aether, the angle which the normal to the front of the wave makes with the direction of transmission of light. In the figure, let//« (not necessarily equal nor parallel to e1 e) represent the motion of the aether, p' e representing the velocity of light ; then e n is the direction of the normal to the wave that enters the eye at e. If the normal underwent no angular deviation the whole distance from the object to the eye, en would also be the direction of the object, and consequently aberration on this theory would not be accounted for. I gave Mr. Stokes the credit pi having first shown that the normal is shifted through a certain angle as the wave is propagated through the aether set in motion by the earth, and by reasoning as he has done, and supposing certain analytical conditions, which I shall speak of presently, to be satisfied, the deviation is found to be from p1 towards », exactly through the angle p1 en. Consequently op* is the di- Rev. J. Challis on the Aberration of l^ght. 93 rection of the object, and the required condition is satisfied by the undulatory theory of light. I admit the correctness of Mr. Stokes's strictures on that part of my communication to which he principally objects. Mr. Stokes's own reasoning in the July number, or the fol- lowing, may be substituted for the part objected to. The point a is carried with the velocity V— w, and the point b with the velocity V— w/, in the direction of the axis of z. As w is less than w, a is carried further than b in the small time $t, (1 IS) by (V-w)$t-(V-w')dt, that is, by (a/— w)8/, or — 8*8*. Dividing by 8#, the interval between a and b, the angular dis- d w placement of the front of the wave in the plane of z x is — 8 /, (J *153 0 2! 0 Z which is equal to -y-. -^j, since V = j- very nearly. To in- , . ... . dw du tegrate this expression, it is necessary to assume that -j— = -j- . So considering the motion in the plane z y, the integration re- quires that -r- = -r~. These conditions, which are alluded to ' dy d z above, I agreed with Mr. Stokes that it was necessary the motion of the aether should satisfy. I went a step further, and endeavoured to show that they do not restrict the motion. The reasoning for this purpose was based on hydrodynamical equations, in which the squares of the velocities were neg- lected. This may generally be done when the motion is small. But obviously all cases of motion for which ~r~. — , J dt dt and -j- vanish are to be excepted, and the instance before us may be one of this class ; for the motion must be nearly sym- metrical about the line in which the earth's centre moves, and if the earth's centre be taken for origin of co-ordinates, the velocity must be very approximately a function of co-ordi- nates independent of the time. On this account I doubt the applicability of those equations, and in the present state of our knowledge of the subject, it seems the best course simply to suppose the motion of the tether to be such as to satisfy the ... dw du , dw dv m, . . . two conditions -r- = -p- and -. — = -=—. lliere is nothing dx dz dy dz n improbable in the supposition : it saves the undulatory theory; but I must protest against its being considered necessary for the explanation of the aberration of light. Cambridge Observatory, January 8, 1846. [ «* ] XX. Observations on certain Molecular Actions of Crystalline Particles, $c ; and on the Cause of the Fixation of Mercu- rial Vapours in the Daguerreotype Process. By Augustus Waller, M.D.* [With a Plate.] HEN a piece of glass is covered with a solution con- taining the double phosphate of ammonia and magne- sia, and traces are made upon it by any hard body, it is known that they become visible shortly afterwards by the salt being precipitated upon them. Berzelius, who mentions this test in his Elements of Chemistry, states that Wollaston pro- posed to make use of this fact as a test of the presence of magnesia in solution, which has since been frequently adopted. According to Berzelius, "the cause of this property is of a mechanical nature, probably from the glass being covered with microscopic crystals, the facets of which take a different posi- tion on the traces, for some reason which is not easily ex- plained." More recently, Prof. Liebig has alluded to this subject in his Vegetable Physiology, § 157. These effects are referred by him to a state of unstable equilibrium of the various particles which compose the liquid, which is destroyed whenever a dynamical action is created sufficiently powerful to overcome the feeble attractions, or the inertia of the mole- cules in solution. He ascribes to the same cause the sudden solidification of water, which had remained liquid when below the freezing-point, upon being agitated ; the precipitation of a mixture of potash and tartaric acid ; also the detonation of fulminating powder from the contact of any solid body. Neither of these eminent observers mentions having submitted these traces to microscopic examination, although that is the only manner to test the hypothesis advanced by Berzelius. On the present occasion it is my intention to describe some observations I have made, in order to elucidate the influence of molecular action on the precipitation of saline bodies, si- milar to that observed in the double phosphate, and to show that a similar influence is exerted over bodies in a gaseous state and in a state of vapour, and afterwards to point out some phaenomena hitherto unexplained, such as the fixation of the mercurial vapours in the Daguerreotype for instance, which evidently depend upon a like cause. In order to obtain the double phosphate, I have generally used a solution containing about ten grains of phosphate of soda with about three of carbonate of ammonia in an ounce and a half of water. 1 have preferred this mixture, because the ingredients are more easily procured, and are less acted * Communicated by the Author. On certain Molecular Actions of Crystalline Particles, S?c. 95 upon by the atmosphere than the phosphate of ammonia. The magnesian solution was generally a few grains of sulphate of magnesia to the same quantity of water as above. A small quantity of the first mixture is poured on a piece of glass, and to this are added a few drops of the magnesia in solution; if it be allowed to remain undisturbed, in a few mi- nutes the surface of the liquid becomes covered with a thin film, and on the glass appear minute shining crystals; but if before these crystals have time to form, any solid substance, as a glass rod or an empty pen, for instance, is passed over the glass through the liquid, the course it follows becomes visible shortly after. The images which are thus formed are double, and may be termed the upper and lower images. I will first describe the upper images : — They appear on the surface of the liquid itself, when the film would otherwise have been formed. They are seen immediately after the passage of the pen through the liquid, whereas the lower ones only become apparent a few moments after. Being formed on a moveable surface, they are not perfect representations of the traces that have been made, and are changed and distorted by any movement of the liquid. When the solution of the salt is weak, they frequently disappear a few moments after their formation and are redissolved in the liquid; when the liquid is more concentrated, they likewise disappear, owing to the formation of the film on the surface. The production of these images appears to be independent of the chemical na- ture of the body used for tracing. They may be obtained in- dependently of the lower ones, by drawing a thread gently over the surface of the liquid, without its coming in contact with the surface of the glass. The lower images are formed on the surface of the glass, under the upper ones. A few seconds after the tracing has been made upon the glass, they begin to appear, and gra- dually become more distinct. The space of time which elapses before their appearance depends upon the strength of the solution. When it is strong they appear quickly, and when weak they take several minutes before they are visible. To cause the formation of any images, the tracing must al« ways be made after the mixture of the two solutions ; under no other circumstances have I been able to create them. Thus, when the tracing is made on a perfectly dry glass, or on one slightly wet, and then immediately covered with the solu- tion, no images will be created. This is likewise the case when we make traces in either the magnesian or the phosphate so- lution before their mixture together. The passage of any solid substance in the proper solution 96 Dr. A. Waller's Observations on certain on glass will cause the formation of a deposit. Wood, glass, slate, and other similar substances, all have equal power in this respect, but metallic substances are less active. Other polished surfaces may be used instead of the glass plate, and I have formed these images on quartz and agate with the same effect. The difference of crystalline texture exerts no influence, but the images seem to be with more difficulty produced on polished silver and copper than on a vitreous surface. A very slight degree of friction will excite the formation of an image, although a moderate degree of pressure is more fa- vourable. Electricity exerts no influence in the formation of these images. In one experiment, in order to diminish the friction, I adapted two fine wires of a spiral form to a battery suffi- ciently strong to decompose water freely. These wires were moved through the solution in. various directions, and the marks of the passage of the two poles became equally appa- rent without any difference on either side ; and when after- wards disconnected from the battery and used in a similar manner, they produced the same effects. It is remarkable with what fidelity the traces of lines be- come visible in this manner. Letters thus formed by a pen, are much more faithfully rendered than when written on paper with ink, and lines may be formed which are scarcely visible to the naked eye. Microscopic inspection shows this extreme exactness to a much greater degree than could have been an- ticipated; for we see a simple line become as it were decom- posed into a number of parallel lines, which represent the point of contact between the two solids (see Plate III. fig. 2). These lines are composed of very minute and confused cry- stals, of an irregular appearance and joined together. Their diameter varies from 0*02 of a millimetre to about double that size. Between these parallel lines are frequently seen others still more minute. The other crystals which become deposited by the common crystalline powers over the untouched parts of the glass, are much larger than either of these. When the point of intersection of two lines is examined under the micro- scope, we perceive the appearance represented. While cry- stalline masses are in process of formation, it is impossible to prevent the deposition of crystals on other parts of the glass; but if while these are fresh they are subjected to a sharp cur- rent of water, the irregular crystals are mostly carried away, while the images are left almost intact. It is therefore evident that the same power which causes this deposit, renders them more adherent to the surface of the glass than the other cry- Molecular Actions of Crystalline Particles, fyc. 97 stals. Another method of demonstrating the difference of their adherence, is by allowing the solution to dry on the glass, when by brushing it slightly with the feather of a pen, most of the irregular crystals are taken off and the images re- main. Other substances capable of forming a like deposit. — Chloride of platinum and nitrate of potash, mixed together, form a double chloride, with which images can be obtained with as much ease as with the double phosphate. The only differ- ence is, that the double chloride precipitates in the shape of octahedrons, &c. Solutions of tartaric acid and nitrate of potash deposit crystals of bitartrate of potash, which are capa- ble of forming upper and lower images with nearly as much facility as the double phosphate. The lower images formed by the bitartrate differ in one respect from those by the phos- phate, for shortly after their formation they appear to lose their adhesion to the glass, and the slightest agitation of the liquid causes them to be detached ; and if a sentence has been written, the curious appearance is presented of fragments of words and letters floating about in confusion. Under the microscope also they differ, fewer parallel lines are perceived, and the crystals are larger and unequal in size. Liquor po- tassse added to a solution of tartaric acid will form images exactly similar to those just mentioned. Caustic soda and tartaric acid produce the same result, but the solution must be much more concentrated. Images formed by gaseous bodies. — These traces are formed in the same manner as those which are crystalline, by passing a solid body over a piece of glass covered with a liquid con- taining a gas in solution, when they are immediately perceived by the bubbles which are deposited. On account of the spe- cific gravity of the gas, these images are not very durable, for after a short time the gas which composes them rises to the surface. As a general rule, the ingredients, whose combina- tion causes the formation of the gas, should be added together gently, and so diluted that whatever gas is formed they re- main dissolved in the liquid. I have been surprised to find how much gas n ay be in this way made to remain in solution ; and as most of them appear capable of being dissolved in this unstable manner, traces may be obtained from them all; and I have ascertained by experiment, that such is the case with carbonic, acetic and hydrochloric acids. To obtain carbonic acid, I have generally used the subcar- bonate of soda and tartaric acid. Acetate of ammonia was employed to liberate acetic acid, and hydrochloric acid was obtained from common salt and sulphuric acid. A mixture 98 Dr. A. Waller's Observations on certain capable of forming traces has the property of disengaging its gas in bubbles, whenever it is brought in contact with any dry surface ; as for instance, when a mixture of this sort formed on a slip of glass is caused to spread over a part of the surface which has not previously been wetted, bubbles of gas are im- mediately evolved on that spot, although none are perceived elsewhere. This effect is also produced with champagne, seltzer and other effervescing waters, which however have not the property of forming gaseous traces. Any surface, whether metallic or non-metallic, will be found to effect the separation of the gas from the liquid; and I have not perceived that there- was any difference from the surface being perfectly po- lished or rough. The immersion of a piece of bread in champagne to renew the effervescence, is merely an example of the contact of a fresh surface with the gas; in a short time it ceases to have this effect, but if a fresh piece is used, the effervescence is re- newed as before. The difference of effect between this and a piece of metal arises solely from the superior extent of surface presented by the cavities of the bread. The disengagement of steam from boiling water by platinum foil or any other solid substance, is likewise of the same nature. After a very short time this effect ceases, unless renewed by a fresh surface. The most natural explanation of these phaenomena, is to refer them to some molecular action of the solid on the gas, proba- bly of a mechanical nature, which lasts a very short time, when the solid acquires a "droit de domicile" in the liquid, and be- comes perfectly inert. M. Legrand, who has made most cor- rect experiments on the point of ebullition of saline solutions, remarks, that platinum possesses no power in equalizing ebul- lition after a few moments, when, according to him, all the air has been expelled from its surface ; but on the contrary, zinc and iron will act as long as they are present in the liquid, which he attributes to their power of decomposing water. Previously to showing the existence of the same action in bodies in a state of vapour or of fume, I will make a short di- gression with respect to the constitution of vapours in general. The term vapour is commonly applied to bodies in three different conditions, — 1st, that of temporary gas diffused in the atmosphere; 2nd, that of liquid particles mechanically suspended there ; 3rd, that of solid particles suspended in like manner. To the two latter, to speak more correctly, may be applied the term of fumes. The first correspond to solution in a liquid, and the other two to that of suspension in the same. As examples of the first, we have the vapours of water while in an invisible state, and those of bromine, &c. Of the Molecular Actions of Crystalline Particles, fyc. 99 second, water as in mists, fogs, &c. ; and of the third, the va- pours of arsenic and of corrosive sublimate. Bodies in either of these conditions possess the faculty of assuming a definite crystalline form on becoming solid. The properties of the gaseous vapours are so well known, that it is unnecessary to dwell upon them here. The second class, or the liquid globular vapours or fumes, which, as we have said, cause those accumulations known under the name of fogs, clouds, or mists, are those which I intend at present to examine, as they comprehend the theory of the fixation of the mercurial vapours in the Daguerreotype. It was formerly believed that vapour or mist was composed of minute spherules or globules of liquid water, and in Newton's works we find evidence that such was his opinion. According to another view, first advanced I believe by De Saussure, these vapours were composed of vesicles or very minute bubbles, exactly resembling, on a small scale, the common soap-bubble. This opinion has received the assent of Fresnel and Berzelius, and at present obtains general credence. The proofs on which it is considered to be founded, are principally the observa- tions of De Saussure, who asserts that on high mountains, or in the clouds, he has been able to detect these air-vesicles with the naked eye, and has seen them burst as they came in contact with each other. Berzelius recommends the exami- nation of the vapour of water over a dark surface, such as that of ink, with a lens of a short focus. He says, that vesicles may be detected in this manner, varying in size from -^j-^-q to 2tVo^1 °f an 'nch> which occasionally burst as they touch each other. The suspension of clouds is also used as an ar- gument in favour of the vesicular theory, as it is contended that liquid spherules would descend to the ground by their specific gravity in such situations. Fresnel indeed compares the globules to small balloons, which dilate or contract, accord- ing to the temperature of the air they contain. A few days' stay at the convent of St. Bernard gave me an opportunity of repeating the observations on the clouds, as mentioned by De Saussure, which may be also made in this season on our London fogs. Globules of various sizes in these circumstances are frequently discerned by the naked eye float- ing in all directions. I have endeavoured to ascertain their vesicular structure, but have been unable to do so from direct observations. It is frequently a most difficult point, in mi- croscopic investigation, to decide upon the existence of a thin transparent membrane. It is still more so to pronounce upon the vesicular or spherular structure of globules in constant agitation ; and I believe that if minute spherules and vesicles 190 Dr. A. Waller's Observations on certain could be mixed together, we do not possess any means at pre- sent of distinguishing them. I have never been able to detect that appearance of burst- ing of the globules mentioned by De Saussure, but sometimes, when the agitation of the air is slight, two of the larger glo- bules may be seen floating towards each other, and afterwards disappear suddenly, which may be explained, if we admit that it is caused by the union of the two spherules into one, which is too heavy to remain any longer in suspension, and whose rapid deposition conceals it from the sight. There may be urged as objections to the vesicular theory, that if the pellicle become extremely thin, the vesicle would no longer be perceived any more than the apex of an air- bubble before bursting, or the central black spot of a system of Newton's coloured rings. It will be seen below that the globules of vapour possess the power of depositing themselves in a crystalline form, which requires a tranquil deposition of particles, such as could scarcely be deemed possible, if the air contained in each had to escape at the moment of its crystal- lization. I have endeavoured to fix the globules of water on glass and other substances, so as to be enabled to submit them to microscopic inspection, but from their volatile nature and other causes have not succeeded. However, it is easy to do so with almost any other volatile substance; and I have examined several in this way without detecting the slightest appearance of a vesicular structure. Mercury is deposited under the form of globular particles, with a metallic lustre whose dia- meter is 3^jotn °f a millimetre, m which I have never detected any internal cavity by the most careful examination*. Flour * In order that others who may wish to verify these results may operate in the same conditions as myself, it is proper to state that the mercurial vapours were disengaged in a hox, such as is used in the Daguerreotype pro. cess ; and after the mercury had been raised to a temperature of about 90° centigrade, it was allowed to cool. Three experiments were made in this manner: in the two first the glass plate was placed four inches above the mercury, in the other it was eight inches distant. The appearance of the globules was the same in each case ; if any difference existed in their size, those of the last experiment were rather larger. In another experiment, where a common Daguerreotype plate was substituted for one of glass, the appearance of the globules was in all respects the same. From the manner in which they are deposited, they appear to exert an influence over each other, as they are frequently found in groups of three or four, or more, Mr. Ross has stated on the part of Mr. Solly (Microscopical Society, De- cember 1843), that these globules are deposited in hexagonal groups; but with preconceived ideas no doubt it would be very easy to form such shapes, as it would be to form triangles or any other simple geometrical figure, particularly when the illusions inseparable from catoptric microscopy Molecular Actions of Crystalline Particles, Sfc. 101 of sulphur is found to consist of solid globules, several of which adhere together; when acted upon by a gentle sol- vent, their external portion is dissolved, and there remains a regular octahedron. An interesting experiment may be made on the fumes of sal-ammoniac, which appear whenever mu- riatic acid and ammonia are brought together. Two small phials, each containing one of these substances, are covered by an inverted tumbler: above the surface of the acid are seen at a short distance the fumes of the salt, which at the end of a few hours are found to have condensed into a thin snowy pellicle, completely obturating the mouth of the bottle. This partition is so delicate, that the slightest agitation will cause it to fall into the liquid. In all these cases it is found that the fumes possess the power of remaining suspended a much greater length of time than would be expected from the difference of their specific gravity with that of air, which is also the case with the fumes of other substances, and smoke in particular. This can only be accounted for by the continual state of agitation of the air, even within an enclosed space, and by the elasticity of the solid and liquid particles. In the case of solid particles this can be readily admitted, but with regard to liquid globules, there is probably some action similar to that which takes place on the impinging of solid elastic balls, which after becoming flattened rebound in virtue of their tendency to recover their original shape. The causes which act in fixing different vapours and fumes are the same as those which determine the precipitation of solid particles in solution, such as for instance, sharp points of any kind, minute filaments, and more especially the existence of a crystalline particle to act as a nucleus. Non-conducting sub- stances, as woollen cloth, the nap of a hat, the web of the spider, &c, are covered with aqueous globules when no rain has fallen, and when polished surfaces near present no such deposition. Having now shown the existence of a crystalline power in vapours, we shall proceed to prove the influence of a force which disturbs this equilibrium in the same manner as in the saline solutions above mentioned. The friction of a solid body on glass will leave traces which are invisible until breathed upon. are added to those of physiology. This tendency of the mind, of which a good account has been given by Miiller in his Elements of Physiology, is so strong, that where groups of globules are concerned, I would always advise their being mapped down under the microscopic camera lucida, and put by for some time for future inspection. I shall have occasion to advert to this subject more fully hereafter. 102 Dr. A. Waller's Observations on certain Many bodies possess this property, but the mineral steatite, or soap-stone, produces the effect better than any other I know. A considerable degree of friction may be used over the traces thus produced by steatite, without affecting the appearance of the traces when breathed upon repeatedly. The glass may even be heated considerably without affecting them. By ex- amining with the microscope the parts that have been traced upon by steatite, we are unable, any more than with the naked eye, to detect any material cause for the deposition of vapours in these places, as it probably depends upon the transparency of the mineral, which being so attenuated is unable to affect the rays of light. When the traces have been brought out by breathing upon them, they must be covered with another piece of glass, which impedes the evaporation of the water and allows them to be submitted to the microscope. The parts untouched by the steatite present the appearances that have been already mentioned. On the lines created by the mineral, the drops of water are differently disposed, their long diameters being parallel to the direction of the lines. These minute drops very much resemble the globules of gas deposited from a liquid, the only difference between the two consisting in the deviation from the globular form in the liquid traces, which evidently arises from the power which the water possesses of wetting glass. It is evident, therefore, that the secondary cause of these images is a difference in the position of the minute drops of water, reflecting the light differently from the other drops, which are irregularly disposed on the other parts of the glass. There exists another method of fixing vapours, which has been long known, and to which I believe attention was first directed by Prof. Draper. It consists in merely placing a body on a plain surface, such as that of a metallic speculum, or even of glass ; after a short time it is found that simple contact, such as this, has caused some molecular action, as the spot occupied by the object will become apparent by breathing on it in the same way as with the images of steatite. This observation is the more interesting, as it serves as a connect- ing link between the effects of mechanical power and those caused by other agents. The experiments of Mr. Hunt have shown the influence of heat in causing the fixation of vapours. An image of this sort formed on glass by the breath, when examined under the microscope, presents exactly the same ap- pearance as those formed by steatite. The same difficulty is experienced in bringing out, by mercurial vapours, the ther- mographic images on glass, as is found with the traces of Molecular Actions of Crystalline Particles^ §c. 1 03 steatite, which possess but in a very slight degree the power of fixing mercurial vapours. It appears therefore that the power which water has of wetting glass, causes it to have a greater tendency to deposit than mercury, which does not wet glass. The cause of the production of thermographic images is evidently similar to that which causes the deposition of a solid body from a solution. The fixation of the mercurial vapours in the Daguerreo- type process, which has excited so much interest, and for which so many theories have been advanced, is but another example of the force which causes the deposition of solid and gaseous particles from a liquid, and which produces so many other effects. In this case the chemical rays of light act in the same manner as mechanical action and caloric in causing a certain molecular disturbance. By the discoveries of Moser, it is shown that these rays possess the power of acting upon almost any body, in such a manner as to render it capable of fixing the particles of various vapours. Thus simple minerals, glass, &c. may be made to fix the mercurial vapour. It appears however that silver, gold, copper, &c, which form amalgams, or in other words, are capable of being wetted by mercury, possess this property in a greater degree than any other bodies which are incapable of being wetted by it; in the same way as we have seen that glass has the greatest power to fix the vapour of water. Admitting the truth of this theory of the Daguerreotype process, we are naturally led to inquire whether the same agent may not likewise cause the fixation of particles in a state of solution or of vapour, in the same manner as by simple mechanical action. After several unsatisfactory attempts, I finally succeeded in clearly proving this fact. The solution which shows the influence of light the most evidently, is that of the neutral chloride of gold. A few grains of this salt dissolved in an ounce of water, when ex- posed to the light, deposits minute crystals of a metallic ap- pearance on that side of the glass nearest the light. The action of light in causing the deposition of gaseous va- pours may be shown by placing some iodine in a bottle closed with a glass stopper. After being exposed to the sunshine for several hours, minute black crystals will appear on the side nearest the light, which will change their position according to the side of the glass exposed. Another substance which shows this action still better, is camphor, a piece of which, merely covered with a glass shade, will give rise to a crystal- line deposit, after an hour or two of exposure to light, and which presents the same phsenomena as that of iodine. By a prolonged exposure these crystals become very abundant, and 104- Dr. A. Waller's Observations on certain are very beautiful*. I have applied this property to the con- struction of an instrument for measuring the chemical rays of light. As the details respecting this would be foreign to our present subject, I will defer them to another occasion, and con- fine myself now to prove that these phamomena are indepen- dent of the deposits caused by radiation. 1st. The crystals are formed on the side exposed to the ac- tion of direct or diffused light. 2nd. They are not formed during the night, when the ra- diation from the earth is sufficient to cause the deposition of water. 3rd. Green glass, which retards photographic action, like- wise impedes this deposit. In an experiment which is now going on, a bottle of pale green common glass is exposed to the north, while another of white glass is placed in a southern aspect. The first became covered with minute crystals, in size averaging about a milli- metre, which have remained stationary for a week ; the second is covered with arborescent ramifications, which are daily in- creasing. Several familiar, but hitherto unexplained phaenomena, may in my opinion be easily accounted for by these molecular actions. The formation of hail I consider to be an instance of an action precisely similar to that which causes the deposition of the solids of gaseous and liquid particles. If we admit the in- fluence of this force on the globular vapours of water, it is not at all improbable that certain conditions may arise in nature when these vapours may be much more liable to this influence than we find them in our imperfect experiments. We have seen that a solution of sulphate of soda or water in a pure state may be brought by the abstraction of caloric to such a condition of unstable equilibrium, that the slightest perturba- ting cause will immediately reduce them to a solid form. If we admit that the globules which form the clouds are ca- pable of being placed in a similar condition, we have sufficient data to explain all the phaenomena that occur in the produc- tion of hail. Any nucleus formed within a cloud in this state, would create around it a deposition of all the neighbouring particles; and the size of the hail-stones would be dependent upon the thickness of the cloud it had to traverse. In the storm at Ordenburg, in 1825, mentioned by Dr. Eversman, pyrites was found in the centre, and had acted like a nucleus * I am informed by a friend, that this action of camphor was mentioned twenty years since by Dr. Hope in his lectures, but I am not aware of any- thing having been published upon the subject. Molecular Actions of Crystalline Particles, fyc. 105 round which the crystallization had taken place. Where the centre is not formed by a foreign body of this sort, it has fre- quently been mentioned that it consisted of an opake nucleus of a spongy nature, like congealed snow, which may be easily accounted for. The succession of concentric layers would be caused by the passage of the particles through strata of liquid globules not all at the same temperature; and the radiated structure indicates a gradual increase of crystalline action pro- ceeding from the centre. The temperature of the hail-stones, which has generally been found below the freezing-point, is a further corroboration of this view. The formation of butter is likewise in all probability an- other instance of molecular action of the same nature. It is well known that after the cream has been agitated for a cer- tain length of time, the globules suddenly coalesce, and by their union butter is produced. The sudden appearance of this product is the more remarkable, as it takes place at dif- ferent temperatures, although more quickly at some than others, and not gradually, as might have been expected, which precludes the idea of its being owing to any caloric developed by friction. The most minute observations have been unable to show any material alteration in the appearance of the fatty globules at the moment before the butter is formed. Little doubt can be entertained of its being caused by some molecular action, or engendered in the globules by the continued agita- tion they have undergone. Some of the most permanent gases likewise exhibit pheno- mena closely allied to the above, by their action on platinum and other metals. According to Dulong and Thenard, pla- tinum foil newly beaten has the property of acting at the com- mon temperature, on a mixture of hydrogen and oxygen; but after a few minutes' exposure to the air, it entirely loses that power, which may however be restored to it in a stronger degree than before by heating it in a covered crucible. If it be kept in a covered vessel, so as to exclude the air, it will retain the power without decrease for four-and-twenty hours. Platinum filings, made with an ordinary sized file, have the same property immediately after their formation, and which they retain for above an hour. It has also been observed, that a hollow ball of platinum has the power of condensing and absorbing different gases, which are generally disengaged at a temperature below the boiling-point (Pouillet, Elemens de Physique, § 131). The action of the gases on platinum in all the above cases greatly resembles that of carbonic acid on glass, except that not merely simple lines, but the whole sur- face of the metal exerts its influence, and that the gases them- selves are invisible. Phil. Mag. S. 3. Vol. 28. No. 1 85. Feb. 1 846. I [ 106 ] XXI. Note to Mr. Hennessy's Paper on the Connexion be- tween the Rotation of the Earth and the Geological Changes of its Swface*. HPHE values of Ix and K must be altered, as some incorrect *■ assumptions were made in obtaining them. This alte- ration will produce no changes in the general conclusions which have been arrived at. The method for obtaining the moment of inertia of a solid of revolution contained in equation (3.), appears to have been inapplicable to the case of the internal spheroid of the earth from the nature of the expression for p. The expression for the earth's moment of inertia, which is used for obtaining the theoretical coefficients of precession and nutation, is, however, adapted to our purpose. In this case we havefj '.=IK?)4{(M!)>v^-K*h When this value of K is substituted in (19.), that resulting for P will evidently be less than what has been already found, and it will give an amount of denudation of the earth's sur- face still more within the limits of geological observations than that which has been previously obtained. H. Hennessy. XXII. Letter to Henry Lord Brougham, F.R.S., fyc., con- taining Remarks on certain Statements in his Lives of Black, Watt and Cavendish. By the Rev. William Vernon Har- court, F.R.S. fyc. My dear Lord, |Na volume of biography which you have lately published, -*- I perceive that you have reprinted your contribution to M. Arago's historical notice of WTatt, in which the distin- guished author attempted to transfer to the subject of his eloge the credit of a celebrated chemical discovery, hitherto by the common consent of chemists attributed to Cavendish. Your personal challenge to myself would not have moved me to enter again on a question which I scarcely think open to dispute since the publication of the fac-similes of Caven- dish's original notes of that discovery, in the Transactions of the British Association for the Advancement of Science, had I not * Phil. Mag. vol. xxvii. p. 376, November 1845. f Airy's Tracts, Precession and Nutation, Art. 43. Letter to Lord Brougham. 107 observed, as it seems to me, other mistakes in this volume, on points of scientific history, which, venial as they are in one who cannot be supposed to have devoted much of his valuable time to these umbratile studies, are yet such as ought not to pass without some notice. I must begin, however, my criticisms on your historical chemistry, by repeating the grounds on which I deemed it needful to controvert the statements of M. Arago respecting the discovery of the composition of water. " The elope of Watt, delivered before the French Academy by one of its secretaries, and subjoined to the Annuaire for 1839, had just been published. It was blemished by statements which re- flect unjustly on the character of one whose memory is che- rished among us as a bright example of the union of modesty with science, of the purest love of truth with the highest facul- ties for its discovery, and the most eminent success in its at- tainment. Perceiving these statements to be founded in error, I took the earliest opportunity of rectifying them, at the meet- ing of the British Association which followed within two or three weeks after I became acquainted with them, rejoiced that I had it in my power, from the position in which, as President of that body, I had then the honour to be placed, to make the correction of the error as formal and public as its promulgation had been ; and persuaded that M. Arago, as soon as he should be full}' possessed of the facts, would con- sider it a duty which he owes both to the Academy and him- self, to retract the suspicions which he had expressed*." Those who feel that a sense of justice is a material part of the character of illustrious men and illustrious bodies, are still " waiting," not " till your fellow champion," as you express it, " shall seal your adversary's doom," but till he makes the amende honorable by withdrawing, in explicit terms, imputa- tions which since the lithographing of the Cavendish MSS. he must know to be unfounded. I am not content, my dear Lord, that you should either for your " colleague" or yourself, half retract and half retain those doubts which I perceive that you have republished in one part of your volume, whilst you disclaim them in another. " I cannot easily suppose," you say, " that M. Arago ever intended, and I know that I never myself intended, to insinuate in the slightest degree a suspicion of Mr. Cavendish having borrowed from Mr. Watt." Certainly, as regards yourself at least, no declaration can be more explicit than this. But what then, give me leave to ask, is the significance of the fol- lowing words in your now republished appendix to M. Arago's * Report of the British Association for 1839, p, 22. 12 ] 08 Rev. W. V. Harcourt on Lord Brougham's statements iloge ? " Whether or not Mr. Cavendish had heard of Mr. Watt's theory previous to drawing his conclusions, appears more doubtful : the supposition that he had so heard rests on the improbability of Sir C. Blagden and many others Jcnow- ing what Mr. Watt had done and not communicating it to Mr. Cavendish, and on the omission of any assertion in Mr. Cavendish's paper, even in the part written by Sir C. Blagden with the view of claiming priority as against M. Lavoisier, that Mr. Cavendish had drawn his conclusion before April 1783. Mr. Watt's theory was well known among the mem- bers of the Society some months before Mr. Cavendish's state- ment appears to have been reduced into writing, and eight months before it was presented to the Society. That the first letter of April 1783 was for some time, — two months as appears from the papers of Mr. Watt, — in thehandsof Sir Joseph Banks and other members of the Society during the preceding spring, is certain from the statements in the note to p. 330 ; and that Sir C. Blagden, the Secretary, should not have seen it seems impossible, for Sir Joseph Banks must have delivered it to him at the time when it was intended to be read at one of the Society's meetings (Phil. Trans, p. 330, note) ; and as the letter itself remains among the Society's records in the same volume with the paper into which the greater part of it was introduced, it must have been in the custody of Sir C. Blagden. It is equally difficult to suppose that the person who wrote the remarkable passage already referred to respect- ing Mr. Cavendish's conclusions having been communicated to M. Lavoisier, should not have vientioned to Mr. Caven- dish that Mr. Watt had drawn the same conclusion in the spring of 1783, that is, in April at the latest', for the con- clusions are identical, with the single difference that Mr. Cavendish calls dephlogisticated air water deprived of its phlogiston, and Mr. Watt says that water is composed of de- phlogisticated air and phlogiston." — (Life of Watt, pp. 396- 398.) To what does all this argument tend ? — Would it lead any one to guess that you mean to acquit Cavendish of plagiarism, or that "you have yourself," as you elsewhere affirm, " always been convinced that Mr. Watt had, unknown to Cavendish, anticipated his great discovery ? " Allowing a certain interval of time and place, I should not wonder at your having for- gotten or laid aside your doubts whether Cavendish, with the connivance of Blagden, had not purloined the conclusions of Watt ; but I have never before known an instance of so deliberate a disavowal of a suspicion contemporaneous and in juxtaposition with its no less deliberate reiteration. relative to Black, Watt, and Cavendish. 109 Your reprinting now these old doubts is the more unac- countable, not only because they consist so ill with your pro- fession of belief in the good faith of Cavendish, and are indeed a mere trifling after that point has been satisfactorily esta- blished, but because I have corrected the particular error out of which this tissue of suspicions was spun ; and you are now apprised that the Secretary of the Royal Society at that time was Mr. Maty, and not, as you persist in taking for granted, Cavendish's friend Dr. Blagden, who did not enter on the office till May 1784. " So that," as I told you in the Appendix to my address to the British Association, "he is not liable to the suspicion intimated by Lord Brougham, of having shown Watt's letter to Cavendish, nor to the reproach which M. Arago casts upon him, of not speaking the whole truth respect- ing the precise date at which Watt's opinions were made known in London." The confidence which you place, with so much simplicity, in the innocence of M. Arago's " intentions" contrasts strangely with the disposition you have shown to suspect Cavendish and Blagden : for M. Arago does not, like yourself, "just hint a fault," but retorts in good set terms on the English philoso- phers the imputation which Blagden had cast on Lavoisier, "That he had told the truth, but not the whole truth." "This is a heavy charge," says your illustrious colleague; "let us see whether all w/io took part in this affair are not liable to the same reproach;" — and then in a style of pointed irony, into the spirit of which I should have thought you apt enough to enter, he proceeds to fix the charge on all the parties con- cerned. 1 believe I have given no more than the plain mean- ing of these clever sarcasms when I said, " The Secretary of the Academy has not confined himself to taking from Caven- dish the honour of this discovery, but has in fact imputed to him the claiming a discovery which he borrowed from another; of inducing the Secretary of the Royal Society to aid in the fraud, and even causing the very Printers of the Transactions to antedate the presentation copies of his paper." The real truth is, that M. Arago having, when in England, heard but one side of the story, was persuaded of the insin- cerity of Cavendish. If he is now disabused of this persua- sion, I hope he will choose another method of withdrawing what he wrote under such an impression than that which you have framed for him in the following protest. " As a strange notion seems to pervade this paper that every thing depends on the character of Cavendish, it may be as well to repeat the following disclaimer, already very distinctly made, of all in- tention to cast the slightest doubt upon that great man's per- 1 1 0 Rev. W. V. Harcourt on Lord Brougham's statements 6" feet good faith in the whole affair, I never having supposed that he borrowed from Mr. \\ att, though M. Arago, Pro- fessor Robison and Sir H. Davy, as well as myself, have always thought that Mr. Watt had, unknown to him, antici- pated his great discovery." Of the deceased philosophers, whose names are here pressed into this service, I shall presently have occasion to speak ; but let me first venture to answer for M. Arago, that if he has " read the fac-similes" of Cavendish's notes, you will not find him at the same loss as yourself to discover the inferences of the experimental philosopher in the steps of his investigation', he will not join you in propounding, " that in all Cavendish's diaries and notes of his experiments, not an intimation occurs of the composition of water having been inferred by him earlier than Mr. Watt's paper of spring 1783." Those celebrated experiments of 1781, which pass with chemists for a model of a well-combined train of analytical and synthetical research, you imagine to have been without object or inference, till an imperfect attempt to repeat them had the good luck to be reasoned upon by Watt in 1783. You appear to think that the manner in which the great facts of experimental philosophy are ascertained is by one man's stumbling on the proofs, and another some time after hitting on the conclusion. If it be so, I believe that you would have been as capable of interpreting such experiments, once made, as James Watt himself; and could you have been at hand when Cavendish, in July 1781, completed the discovery of those facts which prove the composition of water, he need not have waited so long to learn what to infer from them : I doubt not but that you would at once have drawn the inference for him, established the theory, and become for ever memorable as the true discoverer ; you would, in your own amended phrase, " unknown to him, have anticipated his great discovert/." But I own I do not suspect your w colleague" of these pecu- liar views. Once satisfied that Cavendish spoke truth when he said that all the experiments on this subject published in his paper were made by him in the summer of 1781, he will no longer doubt to whom the discovery of this important fact is due ; once convinced that the experiments were communi- cated to Priestley, and that the attempt to repeat them was made in consequence of that communication; once aware that the repetition was abortive because made with a wrong gas, that neither the phlogiston nor the inflammable air of Priestley and Watt were convertible terms for hydrogen, and that their notions of the change of water into air and air into water had no reference to that particular gas, but first to relative to Black, Watt, and Cavendish. Ill nitrogen, and afterwards to a mixture of gases, the chief of which was carbonic oxide- -M. Arago will keep you "waiting" long before he rejoins you in the advocacy of any part of the sup- posed claims of your client, or thanks you lor classing him with yourself as still cherishing the conviction that " Mr. Watt had, unknown to Cavendish, anticipated his great disco- very." That which renders the self-devotion of this knight-errantry complete, is the singular fact that you are fighting for Watt against himself. I had formerly come to the conclusion that he never thought of claiming the discovery in the sense which you suppose, nor in any other respect than as regards the theory of the extrication of heat and light from the combining gases ; and a circumstance has lately been pointed out to me by a friend, which establishes this conclusion. The edition of Robison's Mechanical Philosophy, published by Sir D. Brewster, was revised by WTatt himself. In that revision we find him by no means indifferent to his own just fame. Writing to the Editor he says, " I have carefully per- used my late excellent friend Dr. Robison's articles, ' Steam and Steam-Engines/ in the Encyclopaedia Britamiica, and have made remarks upon them in such places, where either from the want of proper information, or from too great a reliance on the powers of his extraordinary memory at a period when it probably had been weakened by a long state of acute pain, and by the remedies to which he was obliged to have recourse, he had been led into mistakes in regard to facts, and also in some places where his deductions have appeared to me to be erroneous. Dr. R. qualifies me as ' the pupil and intimate friend of Dr. Black :' he afterwards, in his dedication to me of Dr. Black's Lectures upon Chemistry, goes the length of supposing me to have professed to owe my improvements upon the steam-engine to the instructions and information I had re- ceived from that gentleman, which was certainly a misappre- hension ; as though I always felt and acknowledged my obliga- tions to him for the information I had received from his con- versation, and particularly for the knowledge of the doctrine of latent heat, I never did nor could consider my improvements as originating in those communications. He is also mistaken in his assertion, p. 8 of the preface to the above work, that I had attended two courses of the Doctor's lectures; for unfor- tunately for me, the necessary avocations of my business pre- vented me from attending his or any other lectures at College." Mr. Watt then quotes from these lectures a passage in which Black is made to say, " My own fortunate observation of what happens in the lormation and condensation of steam, had 1 ] 2 Rev. W. V. Harcourt on Lord Brougham's statements suggested to my friend Mr. Watt his improvements in the steam-engine," and remarks, " it is very painful to me to con- trovert any assertion or opinion of my revered friend ; yet in the present case I find it necessary to say that he appears to have fallen into an error*." But in revising the article on Steam, and making remarks on those places in which Dr. Robison had been led into mis- takes, Watt makes no remark on the following very decisive passage: — "We know that in vital or atmospheric air there is not only a prodigious quantity of fire which is not in the vapour of water, but that it also contains light, or the cause of light, in a combined state. This is fully evinced by the great discovery of' Mr. Cavendish of the composition of water: there we are taught that water, and consequently its vapour, consists of air from which the light and greatest part of the fire have been sepa- rated ; and the subsequent discoveries of the celebrated Lavoi- sier show that almost all the condensable gases with which we are acquainted, consist either of airs which have lost much of their fire, and perhaps light too, or of matters in which we have no evidence of light and fire being combined in this manner." Thus you see, that jealous as Watt appears of any undue share in his own discoveries being attributed even to his " revered friend" Dr. Black, he allows " the great discovery of the composition of water" to be assigned to Cavendish without reclaiming the least participation in it for himself. These extracts entirely relieve his memory from any sus- picion of his having been a party to the erroneous statements contained either in the article 'Water' in the first edition of the Encyclopaedia Britannica^to which you have referred, or in the posthumous lectures of Black. Nor do I hold Black responsible for the fabulous history of this discovery given in the latter work. It is well known that that unambitious man left behind him no MSS. of any account, and that the Lectures published under his name were chiefly composed out of the reminis- cences of the able but incorrect Editor. Robison, on historical points, was a very inaccurate writer ; and to his inaccuracy I attribute the extraordinary string of errors on this subject which I have formerly pointed out. It is from the latter work that you seem to have taken your * I conceive Watt to mean that the facts known to him respecting the condensation of steam, independent of Black's theoretical explanation of them, were the foundation of his improvements ; and I am bound there- fore, on his own showing, to allow that M. Arago has done right in not placing the merit of Watt in the study and application of abstract philo- sophical principles, so much as in ingenuity of mechanical contrivance and the happy adaptation of well-observed facts. relative to Black, Watt, and Cavendish. 113 supposed facts; and you have in consequence entirely mis- stated the nature of Cavendish's experiments. Where, allow me to ask, do you find in his paper, or his notes, any such matter as this? "He then weighed accurately the air of both kinds, which he exposed to the stream of electricity ; and he afterwards weighed the liquid formed by the combustion : he found that the two weights corresponded with great accuracy " (Life of Cavendish, p. 433): and again, " Water equal to the weight of the two gases taken together remained as the produce of the combustion." Cavendish made no such experiments ; as you will find whenever you take the trouble to read either the documents themselves*, or my account of themf. I have already stated that this method of determining the composition of water, which is attended with great practical difficulties, was tried indeed at a later time by the French philosophers with such accuracy as it admits of, but that Cavendish, with his usual sagacity, had taken an easier and more certain road : having mastered beyond any of his cotemporaries the analysis of gases, and possessed himself of their specific properties, he was enabled to substitute the method of volume for that of weight ; he found that about two volumes of hydrogen and one of oxygen, when burnt together, entirely disappeared without loss of weight, and that pure 'water was the result. To draw from these premises the obvious conclusion, there was no need to weigh or compare the weight of the airs, and the water that lined the glass after combustion ; and he did not compare it. Lavoisier followed in his steps : and should you ever read his papers, you will find that he too in the first instance contented himself with deducing the equality of the weights as a corollary from experiments of the same kind as those of Cavendish. Had you happened to consult the second edition of the En- cyclopaedia Britannica as well as the fast, you would have found it purged both of these, and some other of Robison's historical mistakes. You would have found all that you have referred to omitted ; and in the article ' Chemistry,' compiled under the revision of friends and connections of Watt, the following ac- count substituted in its place. "In the year 1781, Mr. Caven- dish proved that water is not a simple element, but that it is composed of pure or vital air, and inflammable air." " In the mean time the French chemists were not idle ; the cele- brated Lavoisier, in conjunction with some of his philosophical friends, confirmed by the most decisive experiments the truth of Mr. Cavendish's discovery of the composition of' water, which * Phil. Trans, vol. lxxiv. Experiments on Air, by H. Cavendish, Esq. Report of the British Association for 1839, autograph notes of experiments. f Report of the British Association for 1839, pp. 35, 36. 114 Rev. W. V. Harcou It on Lord Brougham's statements was now received and adopted by almost every chemist." A detailed account is then given of Cavendish's experiments ; and it is added, "these experiments were made in 1781, and they are undoubtedly conclusive of the composition of water. It would appear that Mr. Watt entertained the same ideas on this subject. When he was informed by Dr. Priestley of the result of these experiments, he observed, Let us consider what obviously happens in the deflagration of oxygen and hy- drogen gases," &c. "Thus it appears that Mr. Watt had a just view of the composition of water, and of the nature of the process by which its component parts pass to a liquid stale from that of an elastic fluid." In this account the ideas entertained by Mr. Watt obtain more notice perhaps than would have been accorded to them by anin- different historian; but the statement of the discovery is correct, as is also that of the view which Watt took of the subject, if we confine the assertion of the justness of his ideas to his appre- hension of the relation of Cavendish's discovery to certain theories of light and heat ; for of the material base of water he had certainly no just conception when he wrote the letter which is quoted above. I have shown that his views in 1783 and 1784 were founded on several suppositions: — 1st, that Priestley had converted water into atmospheric air; 2nd, that he had obtained a weight of water equal to the weight of a mixture of oxygen with the gases extricated by heat from moist charcoal', 3rd, that he had shown good reason to believe that carbon, combined in a certain proportion with oxygen, con- stitutes water. All these suppositions agreed perfectly with the opinions which Watt really expressed, that water was formed of dephlogisticated air and phlogiston ; but no one of them is consistent with the opinions attributed to him by an erroneous translation of his words, that water is formed by the combination of oxygen with hydrogen gas*. From your mention of Sir H. Davy's sentiments without a quotation, I suppose that he, like Dr. Henry, has been among the number of those on whose attention this untenable claim has been privately pressed ; all I know of Davy's opinion on the subject is from his published works, in which he has spoken, like other chemists, of the composition of water and of nitric acid as " the two grand discoveries of Mr. Cavendish." But in referring to the name of this much-honoured and regretted friend, I must take the opportunity of noticing what I think a serious error in your impressions respecting one point in his personal character. You begin your sketch of his life with these words: "Sir H.Davy being now removed beyond the reach of * See Report of the British Association for 1839, pp. 24, 25. relative to Black, Watt, and Cavendish. 115 such feelings, as he ought always to have been above their influ- ence, that may be said without offence of which he so disliked the mention; he had the honour of raising himself to the highest place among the chemical philosophers of the age, emerging by his merit alone from an obscure condition." A simple anecdote may suffice to set his feelings on this subject in a more favour- able light. When Davy was exhibiting to myself and three others the discoveries which he had then recently made rela- tive to his safety-lamp, and when those present, among whom were the Hanoverian minister and the late Lord Lonsdale, were highly admiring the beauty of his experiments, with still higher admiration I heard him reply, "Yes, 1 have some rea- son to be proud of them, for my experiments on flame were first made with a tallow candle in an apothecary's shop." In these slight sketches which you have given us of the history of men eminent in science, tnere is one other scientific subject besides the discovery of the composition of water, on which you appear to have bestowed some consideration, namely, — the first discoveries of the gases. Here Cavendish is still out of favour with you. You pluck another feather from his wing ; and having made a present of the discovery of water to Mr. Watt, dispense that of hydrogen gas to Dr. Black. "The nature of hydrogen," you say, " was perfectly known to him, and both its qualities of being inflammable, and of being so much lighter than atmospheric air ; for as early as 1766 he invented the air-balloon, showing a party of his friends the ascent of a bladder filled with inflammable air: Mr. Cavendish only more precisely ascertained its specific gravity, and showed, what Black could not have been ignorant of, that it is the same from whatever substance it is obtained*." You ought to have recollected, when again contravening the received opinion of chemists f, your own remarks on the sup- posed omission of Cavendish to state exactly the time when he had communicated to Priestley his experiments on the com- position of water. " Dans une addition de Blagden faiteavec le consentement de Cavendish, on donne aux experiences de ce dernier le date de l'ete" de 1781. On cite une communica- tion de [a] Priestley, sans en preciser I'epoque, sans parler de conclusions, sans meme dire quand ces conclusions se pre- * Life of Black, p. 383. t The received account of the discovery of hydrogen is this : — " Its com- bustible quality is described in the works of Boyle and Hales, of Boerhaave and Stahl; but it was not till the year 1766 that its properties were par- ticularly ascertained, and the difference between it and atmospheric air pointed out by Mr. Cavendish." — Encycl. Brit., Art. Chemistry, 1810. 116 Rev. W. V. Harcourt on Lord Brougham's statements sentaient a l'esprit de Cavendish. Ceci doit etre regarde comme une tres grosse omission [a most material omission*)." Nothing indeed can be more unfounded than this animadver- sion. In the passage to which you refer, the words of Caven- dish are these: — " All the foregoing experiments on the ex- plosion of inflammable air with common and dephlogisticated airs, except those which relate to the cause of the acid found in the water, were made by me in the summer of 1781, and mentioned by me to Dr. Priestley, who in consequence of it made some experiments of the same kind, as he relates in a paper printed in a preceding volume of the Transactions." Now you need only have referred to the volume of the Transactions which Cavendish quotes, to have found the " epoch" which you wanted. Priestley's paper was printed in March 1783; and therefore Cavendish's communication of his " conclusive" ex- periments was anterior to Watt's speculations in April, as well as to Lavoisier's experiments in June of the same year. But though this " most material" or in M. Arago's transla- tion, this "grosse" omission turns out to be none, you ought, I repeat it, to have remembered your own demand for pre- ciseness of dates, when you ascribed to Black a prior know- ledge of the distinguishing properties of hydrogen gas. In proof that Black knew before Cavendish that this gas is *.* so much lighter than atmospheric air" you allege, that " as early as 1766 he invented the air-balloon, showing a party of his friends the ascent of a bladder filled with inflammable air : Mr. Cavendish only more precisely ascertained its specific gravity." As early as 1766? — Are you not aware that Cavendish's paper on factitious airs was published in this year ? Is it not a " most material omission" that you have forgotten to lipre- ciser I'epoque" of Black's experiment with the balloon, so as to show whether it was before or after the publication of Caven- dish's paper ? Professor Leslie tells the story of the balloon somewhat differently from you. "The late most ingenious and accurate Mr. Cavendish, in 1766, found, by a most nice observation, this fluid to be at, least seven times lighter than atmospheric air. It therefore occurred to Dr. Black of Edin- bro', that a very thin bag filled with hydrogen gas would rise to the ceiling of a room. He provided accordingly the allan- tois of a calf, with a view of showing at a public lecture such a curious experiment before his numerous auditors; but owing to some unforeseen accident or imperfection it chanced to fail, and that celebrated Professor, whose infirm state of health and indolent temper more than once allowed the finest dis- * Historical note, Life of Watt, p. 383. relative to Black, Watt, and Cavendish. 117 coveries when almost within his reach to escape his penetra- tion, did not attempt to repeat the exhibition, or seek to pur- sue the project any further." If you are dissatisfied with Leslie's version of your anecdote, let me refer you to other authorities. In one of those articles of the Encyclopedia Britannica which are stated to have been composed or revised by Professor Miller, Dr. Muirhead, and Sir David Brewster, the circumstance is thus narrated : — " In the year 1766 Mr. Henry Cavendish ascertained the weight and other properties of this gas, determining it to be at least seven times lighter than atmospheric air. Soon after which it occurred to Dr. Black that perhaps a thin bag filled with hydrogen gas might be buoyed up by the common atmo- sphere." I hope I have now illustrated sufficiently the value of the ca- non of criticism which you have laid down for these delicate in- quiries,— that nothing is so necessary as to "preciser I'epoque." " Cavendish," you say, " only more precisely ascertained the specific gravity of inflammable air ; and showed, what Black coidd not be ignorant of, that it is the same from what- ever substance it is obtained" Now, in the first place, inflam- mable air is not the same from whatever substance it is obtained. This was the error into which Priestley fell when he attempted to repeat the experiments by which Cavendish had discovered the composition of water ; this was the error under which Watt laboured till after the publication of Cavendish's paper in 1784, and which nullified the researches of the one and the speculations of the other. But supposing you to mean "that inflammable air is the same, whether obtained from zinc or iron," why do you say that Black could not be ignorant of that? How do you think he was to know it? How did Cavendish know it? He tells you that he learnt it by having ascertained by experiment that the specific gravity of the gas from either material was the same. Had Black ascertained this ? Had he any test whatever by which he could know that these gases were the same ? But Cavendish iionly more precisely ascertained the specific gravity of inflammable air." If any person conversant in the history of pneumatic discoveries were to be asked to enume- rate the most important of the early advances in that branch of science, he would certainly name — 1st, the discovery of the weight of the air by Galileo ; 2nd, the discoveries of its law of compression, and of the factitious gases, by Boyle ; 3rd, the theory of the fixation of gases by chemical attraction, propounded by Newton ; 4th, the discovery of specific and elective affinities in one of those gases, by Black ; 5th, the 118 Rev. W. V. Harcourt on Lord Brougham's statements discovery of the difference of specific gravity in several gases, by Cavendish. You do not distribute their honours to any of these great discoverers with a severe attention to matter of fact ; but I must do you the justice to own that you preserve a principle of equity in your adjudications. You omit, it is true, to dwell upon, or even to mention, the main point of novelty in the re- searches of Black ; but then you give to Black the discoveries of Boyle and Cavendish, and make it up to Cavendish by allow- ing him a slice of the merit which belongs to Galileo. For Cavendish you say, " He carried his mathematical habits into the laboratory; and not satisfied with showing the other qualities which make it clear that these two aeriform sub- stances are each sui generis, and the same from whatever sub- stances, by whatever processes they are obtained, — not satis- fied with the mere fact that one of them is heavier, and the other much lighter than atmospheric air," (a previous ac- quaintance with all which facts you have taken care to ascribe to Dr. Black) " he inquired into the precise numerical relation of their specific gravities with one another and with common air, and Jirsl showed an example of weighing permanently elastic Jluids : unless indeed Torricelli may be said before him to have shown the relative weight of a column of air and a column of mercury, or the common pump to have long ago compared in this respect air with water. It is however sufficiently clear that neither of these experiments gave the relative measure of one air with another; nor indeed could they be said to com- pare common air with either mercury or water, although they certainly showed the relative specific gravity of the two bodies, taking air for the middle term or common measure of their weights." What a strange qualification of a still stranger assertion ! If instead of this confusion of specific gravities with equipon- derant columns, ending with the grave suggestion, that " the relative specific gravities of water and mercury " might have been taken by the intermediation of " air," you had said that philosophers have attempted, from the relative heights of the barometer at different elevations, to calculate the mean spe- cific gravity of the atmosphere*, there would have been mean- * The following quotation will show the nature of these calculations (Dan. Bernoulli Joh. Fil. Hydrodynainica, ilrgcntorati, 1738. Sect. 10. 16. p. 209) : — " Patet exinde quid censendum sit de ilia methodo qua in Anglia aliquando usos esse recenset D. Du Hamel, in Hist. Acad. Sc. Paris, ad indagandam rationem inter gravitates specificas aeris et mercurii : ob- servata nimirum altitudine mercurii in loco humiliori, turn etiam in altiori, gravitates specificas in aere et mercurio statuerunt, ut erat differentia relative to Black, Watt, and Cavendish. 1 1 9 ing at least in the qualification; but then what an assertion to hazard ! considering the great number of experiments ex- tant for the direct determination of the weight of air compared with that of water, first instituted by Galileo, and then re- peated successively by Descartes, Mersenne, Boyle, Hook, Newton, Cotes, and lastly by Hawksbee, whose determina- tion was assumed and quoted by Cavendish himself for the purpose of comparing the specific gravity of common air with those of the factitious gases, — it is a strong instance of the kind of equity for which I have given you credit, that you should have allotted to Cavendish the merit of having "Jirst showed an example of weighing permanently elastic Jluids." Even Descartes allowed that Galileo's "method of weighing altitudinum mercurii in barometro ad altitudinem inter locos observa* tionnm interceptam ; etiamsi aer ejusdem densitatis ponatur ab imo ob- servationis loco ad alterum usque, non licet tamen inde judicare de ejus gravitate specifica ratione mercurii. Quicquid ab experimento colligere licet hoc solum est: — " Consideremus scilicet integram crustam aeream terram ambientem atque inter ambo observationis loca interceptam, et erit pondusistius crusta? ad superficiem terra? ut pondus columnae mercurialis qualis in barometro descendit ad basin ejus; manifesta haec sunt ex eo quod summa basium A et B sustinent quidein summam ponderum qua? habent columnae aerea? A C et B D, neque tamen quaevis basis premitur sua? columnar pon- dere seorsim, et quod idem resectis columnis A g et B h intelligi debet de columnis gC et h D, diaphragmatis in g et h positis, incumbentibus. Igitur experimentum non tarn gravitatem specificam aeris in quo factum est indicat, quam omnis aeris terra? proximi gravitatem specificam mediam determinat ; prior admodum variabilis est, altera procul dubio constanter eadem fere permanet. " Faciamus computum gravitatis specificce istius medics aeris omnis qui terram ambit. Multis vero experimentis, quae in diversis locis parum supra mare elevatis sumpta fuerunt, id constat, elevationi 66 pedum proxime descensum respondere unius lineae in barometro. Sequitur inde quod aeris gravitas specifica media ratione mercurii sit, ut altitudo unius lineae ad altitudinem 66 pedum, i. e. ut ut 1 ad 9504, ergo posita gravitate specifica mercurii =1, erit gravitas specifica media aeris — 0*001 05. Nota- bile est profecto tantam esse hanc gravitatem mediam aeris : certus enim sum vel maxime saevienti hie locorum frigore aeris gravitatem specificam vixdum tantam esse quantam nunc exhibuimus pro statu medio omnis aeris terram ambientis : at sub aequatore multo erit minor, et omnibus recte perpensis non crediderim gravitatem mediam aeris qui inter utramque latitudinem 60 gr. continetur, ultra 0000090 excurrere; quo posito erit gravitas media aeris ab utroque polo ad 30 gradus terram cingentis, quod spatium paullo plus quam octavam totius terra? superficiei efficit partem, = 0*000210, qua? dupla est aeris hie locorum densissimi : sub ipso antem polo, pra?sertim ar.tarctico, admodum gravior erit aer, et fortasse aqua vix decies levior, cum est frigidissimus atque densissimus. " 32. Et quia aeris mediocriter densi gravitas specifica est ad gravitatem specificam mere, ut 1 ad 11000, ipsaque altitudo media mere, in barometro pro locis parum a superficie maris elevatis sit £| ped. Paris, erit altitudo aeris homogenii mediocriter densi 25666 pedum." 120 Rev. W.V. Harcourt on Lord Brougham's statements the air was not amiss*;" and the experiments of the great Italian philosopher, which laid the original foundation of all our knowledge of elastic fluids, ought not to have been en- tirely forgotten by any one who appreciates duly those capital discoveries by which the ideas of men are fixed and a new order of facts is ascertained. To Black, on the other hand, with like even-handed justice, you ascribe a knowledge of the lightness of hydrogen and the heaviness of carbonic gas, which you have no ground for sus- pecting him to have possessed. Experiments, indeed, had been made with a view of ascertaining such points, and your assertion, that "Cavendish first set the example of weighing permanently elastic gases," is so far from the truth, that the factitious gases themselves had been weighed both by Hawks- bee and Hales. Hair- weighed the " air of tartar," which consists of a mixture of carburetted hydrogen and carbonic gases in a bladder, and then filling it with common air com- pared the weights t; Hawksbee ascertained accurately the specific gravity of air that had passed through tubes filled with iron wires, and heated red in the fire, which consisted partly of carbonic acid and partly of nitrogen %. But these mixed * " Sa facon tie peser l'air n'est pas mauvaise, si tant est que la pesanteut* en soit si notable qu'on la puisse apercevoir par ce moyen; mais j'en doute." (CEuvres de Descartes, torn. vii. p. 440.) Thus Descartes wrote to Mersenne in 1638. In 1642 he repeated the experiment himself by a method far less susceptible of accuracy, and obtained a result much further from the truth, which satisfied him however, " que la poids de l'air est sensible en cette facon." {QZuvres, torn. viii. p. 567.) Dr. Whewell has taken notice (History of Mechanics, p. 66) that " in a letter of the date of 1631 he (Descartes) explains the suspension of mercury in a tube closed at the top by the pressure of the column of air reaching to the clouds." In this letter the atmosphere is compared to a pack of wool, the filaments of which are all heavy, and press on each other from the clouds to the earth, being only kept apart by the aether which plays between them, " ce qui fait un grand pesanteur" — expressions which at first sight might lead to the idea that he had anticipated the theory of the elevation of the barometric column j but it is evident from many subsequent letters of Descartes, that he had no correct conception of the statical pressure of fluids, and was therefore incapable of reasoning justly on this subject. The tube in which the mercury was suspended in the casein question, was a straight tube with- out a bason: he tried to account for the phenomenon of its suspension on his principle of circular movement in a plenum, by supposing that the mer- cury, before it could quit the tube, must effect the circle of motions re- quired to bring down from the sky a current of aether to supply the vacuum left at the top of the tube by the descent of the quicksilver ; and pre- suming the column of air which it had to lift to be as heavy as itself, he concluded that no such circular motion in the chain of matter could take place. It is possible however that this representation of the atmosphere as a heavy column may have conduced to suggest the more correct views of the subject afterwards adopted. f Veg. Status, p. 185. { Phil. Trans., No. 328, p. 199. relative to Black, Watt, and Cavendish. 121 gases approached too nearly to common air in that respect to enable the experimenters to establish a distinction. An at- tempt too had been made by Greenwood, a Professor of Mathematics at Cambridge in New England, to ascertain the specific gravity of the deleterious air in a well, which was doubtless chiefly carbonic gas ; but the method employed by him was not sufficiently delicate to show a difference of den- sity. Such was the state of knowledge, or rather ignorance, on this subject previous to the experiments of Cavendish. We have not the least reason to believe that any one had observed the different weights of the different kinds of air. Dr. Mayow* indeed about a century before had supposed his " nitro-igneous aura" to the combinations of which he ascribed the phaenomena of acidification, combustion and vi- tality, to be heavier than the residual air from which it is separated in those processes ; and this opinion, which proved to be correct, he entertained so distinctly, as to represent the specific lightness of the vitiated air, after it had served its purpose of sustaining life, as a provision of nature for freeing us from a noxious atmosphere. But he had no better ground for entertaining such an opinion than his observation of the movements of animals which he had confined in a close ves- sel, and which appeared in his experiments to seek for a less suffocating air in the lower part of the receiver, whilst they avoided the upper. Such loose surmises as these detract nothing from the great experimental discovery of Cavendish, the importance of which cannot be better expressed than in the words of an eminent chemist and chemical historian f: " It can scarcely be said that pneumatic chemistry was properly begun till Mr. Cavendish published his valuable paper on Carbonic Acid and Hydrogen Gas, in the year 1766." On the fruits of this discovery, in the hands of its author and of all succeeding chemists, and its consequences to the study of gaseous substances and their combinations, I need not dwell. It is enough to remark, that the ascertainment of this physical difference in the gases was the first conclusive proof of a 'plurality of elastic fluids. Another point of no small consequence to pneumatic che- mistry was first made out in this paper. From the earliest discovery of factitious airs, it had been observed that a consi- derable portion of several of these disappeared after they had been generated, though there had been no change of tempe- rature or pressure. The usual statement of this phenomenon * De parte aeria igneaque Spir. Nitri. f Dr. J. Thomson's Biographical Account of Priestley, Ann. Phil., vol. i. p. 91. Phil. Mag. S. 3. Vol. 28. No. 185. Feb. 1846. K 122 Rev. W. V. Harcourt on Lord Brougham's statements was, that the elasticity of the air had been destroyed. Dr. Hales, dissatisfied with so loose an explanation, accounted for the loss, which in the case of nitrous acid he first observed, after the following manner : — " When fresh air is let into the receiver, whose included air is impregnated with the fumes arising from the mixture of compound aquafortis, or spirit of nitre, and Whitstable pyrites, mentioned in the following ex- periment, then the air in the receiver turns very red and tur- bid, and much air is absorbed after several repeated admis- sions. When fresh air is thus admitted into the glasses full of sulphureous, though clear, air, a good many particles of the fresh air must needs be reduced by the sulphureous ones from an elastic to a fixed state, as in the effervescences of other liquors. Therefore the rising of the water in the glass vessel does not seem to be wholly owing to the rebating of the air's elasticity in some degree, but rather to the reduction of it from an elastic to a fixed state, which is further probable from hence, viz. that the whole quantity of air admitted at several times is equal, or nearly equal, to the quantity of sulphureous air A. Z., so that both airs are at the same time contained within the space A. Z." In this important observation, which was subsequently turned to such good account by Priestley and Cavendish, Hales gave the true theory of the loss of volume which oc- curs by the admission of common air to nitrous gas; but the variable, and apparently capricious, loss of elasticity which he remarked in other gases he could not explain. " Though a good part of the air," he says, " which rises from Jluids seems to have existed in an elastic state in those fluids, yet the air which arises from solid bodies, either by the force of fire or effervescence, does not seem to arise only from the interstices of those bodies, but principally from the most fixed parts of them. For since the airs which are raised by the same acid spirit from a vast variety of substances have very different degrees of permanency, as was shown in Exp. 10, No. 3, 4, 5, 6, and in Exp. 11, No. 6, 7, 8, 9, 10 of experiments on stones, hence it is probable that these airs do not arise from latent interstices of the dissolved stones, &c, but from the solid fixed particles of them; and since the whole of some of these newly-generated airs does in a few days lose its elasticity, it should seem hence probable, that whatever air arises from the spirit in the effervescence is not permanently elastic, or else that in the rotation of some stones it is thrown off into a more permanently elastic state than from others." The cause of this loss of volume was first explained in Ca- vendish's paper : he proved by experiment, that carbonic acid relative to Black, Watt, and Cavendish. I 23 is condensed over water, but not over mercury. You indeed tell us that Black "found this gas incondensable" but he has nowhere told us as much himself; and you might with more safety have presumed the contrary ; the true statement being, that he and his predecessors had found it condensable, and that Cavendish found the conditions under which it is not condensed. In the same spirit of liberality you take "the capital disco- very" that the air of the atmosphere is not the only air per- manently elastic, from its ancient owners, to appropriate it to Black, and expend much learned pains in setting forth the originality and importance of the "doctrine" which you ascribe to him. " The great step," you say, " was now made, that the air of the atmosphere is not the only permanently elastic body, but that others exist, having perfectly different qualities from atmospheric air, and capable of losing their elas- ticity by entering into chemical union with solid and with liquid substances, from which, being afterwards separated, they regain the elastic or aeriform state." "In order to esti- mate the importance of this discovery, and at the same time to show how entirely it attends the whole face of chemical science, and how completely the doctrine was original, we must now examine the state of science which philosophers had previously attained to. It has often been remarked, that no great disco- very was ever made at once, except perhaps that of logarithms: all have been preceded by steps which conducted the disco- verer's predecessors nearly, though not quite, to the same point. Some may perhaps think that Black's discovery of fixed air affords no second exception to this rule; for it is said that Van Helmont, who flourished at the end of the six- teenth and beginning of the seventeenth century, had observed its evolution during fermentation, and gave it the name of gas sijlvcstre, spirit from wood, remarking that it caused the phse- nomena of the Grotto del Cane near Naples; but though he, as well as others, had observed an aeriform substance to be evolved in fermentation and in effervescence, there is no rea- son for affirming that they considered it as differing from at- mospheric air, except by having absorbed or become mixed with various exhalations or impurities. Accordingly a cen- tury later than Van Helmont, Hales, who made more experi- ments upon air than any of the old chemists, adopts the com- monly received opinion, that all elastic fluids were only differ- ent combinations of the atmospheric air with various exhala- tions or impurities : and this was the universal opinion upon the subject, both of philosophers and the vulgar." "It is now fit that we see in what manner the subject was treated by K2 - 124 Rev. W.V. Harcourt on Lord Brougham's statements scientific men at the period immediately preceding Black's dis- coveries. The article f Air,' in the French Eficyclopedie, was published in 1751, and written by D'Alembert himself. It is, as might be expected, able, clear and elaborate. He assumes the substance of the atmosphere to be alone entitled to the name of air, and to be the foundation of all other permanently elastic bodies. When D'Alembert wrote this article, he gave the doctrine then universally received, that all the other kinds of air were only impure, and that this fluid alone was perma- nently elastic, all other vapours being only like steam, tempo- rarily aeriform. Once the truth was made known, that there are other gases in nature, only careful observation was re- quired to find them out*." After all this, should I venture to affirm that you have post- dated our knowledge of permanently elastic gases, other than the atmosphere, by about a hundred years, were I to suggest that in this case also the old story is the true one, and that Priestley has correctly recorded the real historical fact when he said, " Mr. Boyle, I believe, was the first who discovered that what we call fixed air, and also inflammable air, are really elastic fluids capable of being exhibited in a state unmixed with common air," were I to add that the existence of various elastic fluids was generally recognised by the philosophers of Europe, and particularly by those whom you have quoted as instances to the contrary, during the century which preceded Black's essay, as distinctly, and more distinctly, than by Black himself, — I know not what you would think of me. Neverthe- less, since this is a passage in the history of science which de- serves to be told with a strict regard to dry matter of fact, I must beg you to listen with patience to an account of it cer- tainly very different from your own. It was in December 1659 that Boyle published his " New Physico-mechanical Experiments," among which is to be found a description of two of those gases separable from fixed bodies, which he subsequently denominated factitious airs. The high interest which may be justly attached to all the circumstances of discoveries so important as this, induces me to give the details of it in the words of the author. " Contenting myself," he says, " to have mentioned our author's (Kircher's) experiment as a plausible, though not de- monstrative, proof that water may be transmuted into air, we will pass on to mention, in the third place, another experi- ment which we tried in order to the same inquiry. We took a clear glass bubble, capable of containing by guess about three ounces of water, with a neck somewhat long and wide of * Life of Black, pp. 331-36. relative to Black, Watt, and Cavendish. 125 a cylindrical form: this we filled with oil of vitriol and fair water, of each almost a like quantity, and casting in half a dozen small nails we stopped the mouth of the glass, which was top-full of liquor, with a flat piece of dia palma provided lor the purpose, that, accommodating itself to the surface of the water, the air might be exquisitely excluded ; and speedily inverting the phial, we put the neck of it into a small wide- mouthed glass that stood ready with more of the same liquor to receive it. As soon as the neck had reached the bottom of the liquor it was dipped into, there appeared at the upper part, which was before the bottom of the phial, a bubble of about the bigness of a pea, which seemed rather to consist of small and recent bubbles produced by the action of the dis- solving liquor upon the iron, than any parcel of the external air that might be suspected to have got in upon the inversion of the glass, especially since we gave time to those little par- ticles of air which were carried down with the nails into the liquor to fly up again. But whence the first bubble was pro- duced is not so material to our experiment, in regard it was so small ; for soon after we perceived the bubbles produced by the action of the menstruum upon the metal, ascending co- piously to the bubble named, and breaking, did soon exceed- ingly increase it, and by degrees depress the water lower and lower, till at length the substance contained in these bubbles possessed the whole cavity of the glass phial, and almost of its neck too, reaching much lower in the neck than the sur- face of the ambient liquor wherewith the open-mouthed glass was by this means almost replenished. And because it might be suspected that the depression of the liquor might proceed from the agitation whereinto the exhaling and imprisoned steams were put by that heat which is wont to result from the action of corrosive salt upon metals, we suffered both the phial and the open-mouthed glass to remain as they were in a window for three or four days and nights together ; but look- ing upon them several times during that while, as well as at the expiration of it, the whole cavity of the glass bubble and most of its neck seemed to be possessed by air, since by its spring it was able for so long to hinder the expelled and am- bient liquor from regaining its former place. And it was re- markable that just before we took the glass bubble out of the other glass, upon the application of a warm hand to the con- vex part of the bubble, the imprisoned substance readily di- lated itself like air, and broke through the liquor in divers bubbles succeeding one another. " Having also another time tried the like experiment with a small phial and with nails dissolyed in aquafortis, we found 126 Rev.W.V. Harcourt on Lord Brougham's statements nothing incongruous to what we have now delivered. And this circumstance was observed, that the newly-generated steams did not only possess almost all the whole cavity of the glass, but divers times without the assistance of heat of my hand did break away in large bubbles through the ambient liquor into the open air: so that the experiments with corro- sive liquors seemed manifestly to prove, though not that air may be generated out of water, yet that in general air may be generated anew. " Lastly, to the foregoing arguments from experience, we might easily subjoin the authority of Aristotle and of his fol- lowers the schools, who are known to have taught that air and water, being symbolizing elements in the quality of moist- ure, are easily transmutable into each other*', but we shall rather to the foregoing argument add this, drawn from rea- son— that if, as Leucippus, Democritus, Epicurus and others, followed by divers modern naturalists, have taught, the dif- ference of bodies proceeds but from the various magnitudes, figures, motions, and textures of the small parts they consist of (all the qualities that make them differ being deducible from thence), there appears no reason why the minute parts of water, and other bodies, may not be so agitated and connected as to deserve the name of air ; for if we allow the Cartesian hypothesis, according to which the air may consist of any terrene or aqueous corpuscles, provided they be kept swim- ming in the interfluent celestial matter, it is obvious that air may be as often generated, as terrestrial particles, minute enough to be carried up and down by the celestial matter, ascend into the atmosphere. And if we will have the air to be a congeries of little slender springs, it seems not impos- sible, though it be difficult, that the small parts of divers bo- dies may, by a lucky concourse of causes, be so connected as to constitute such little springs, since water in the plants it nourisheth is usually contrived into springy bodies, and even the bare altered position and connexion of the parts of a body may suffice to give it a spring that it had not before, as may be seen in a thin and flexible plate of silver, into which, by some strokes of a hammer, you may give a spring; and by only heating it red-hot, you may make it again as flexible as before. " These, my Lord, are some of the considerations at present occurring to my thoughts, by which it may be made probable that air may be generated anew." * This I presume is the hypothesis, doctrine, or theory which Cavendish was suspected of deriving from Watt. relative to Black, Watt, and Cavendish. 127 In a subsequent part of the same treatise, Boyle adds an account of another discovery of a similar kind. " I took," he says (exp. 42), " whole pieces of red coral, and cast them into as much spirit of vinegar as sufficed to swim about an inch over them : these substances I made use of that the ebullition upon the solution might not be too great, and that the opera- tion might last the longer." It gave but few bubbles, till the receiver under which it was placed was exhausted ; " then the menstruum appeared to boil in the glass like a seething-pot. To avoid suspicion, that these proceeded not from the action of the menstruum upon the coral, but from the sudden emer- sion of those many little parcels of air that are wont to be dispersed in liquors, we conveyed over distilled vinegar alone into the receiver^ and kept it awhile there to free it from the bubbles, which were but very small, before ever we put the coral into it. The former experiment was another time tried in another small receiver with coral grossly powdered, and the success was much alike." Of the two gases thus first obtained and separated, he ob- served some time afterwards that the one was inflammable*, * " Having provided a saline spirit, which by the uncommon way of pre" paration was made exceeding sharp and piercing, we put into a phial, ca~ pable of containing three or four ounces of water, a convenient quantity of filings of steel, which were not such as are commonly sold in shops to che- mists and apothecaries, those being usually not free enough from rust, but such as I had awhile before caused to be purposely filed off from a piece of good steel. This metalline powder being moistened in the phial with a little of the menstruum, was afterwards drenched with more, whereupon the mixture grew very hot, and belched up copious and very stinking fumes, which, whether they consisted altogether of the volatile sulphur of the Mars, or of metalline steams participating of a sulphureous nature, and joined with the saline exhalations of the menstruum, is not necessary here to be discussed. But whencesoever this stinking smoke proceeded, so in- flammable it was, that upon the approach of a lighted candle to it, it would readily enough take fire, and burn with a bluish and somewhat greenish flame at the mouth of the phial for a good while together; and that though with little light, yet with more strength than one would easily suspect. This flaming phial therefore was conveyed to a receiver, which he who ma- naged the pump affirmed that about six exsuctions would exhaust. And the receiver being well cemented on, upon the first suck the flame suddenly appeared four or five times as great as before, which 1 ascribed to this, that upon withdrawing of the air, and consequently the weakening of its pres- sure, great store of bubbles were produced in the menstruum, which break- ing, could not but supply the neck of the phial with store of inflammable steams, which as we thought took not fire without some noise. Upon the second exsuction of the air, the flame blazed out as before, and so it like- wise did upon the third exsuction ; but after that it went out, nor could we rekindle any fire by hastily removing the receiver: only we found that there remained such a disposition in the smoke to inflammability, that holding a lighted candle to it a flame was quickly rekindled." — New Ex- periments touching the Relation between Flame and Air, 1671. 128 Itev.W. V. Harcourt on Lord Brougham's statements and the other liable, in part, to lose its elasticity*; he ex- tended his experiments on the generation of " factitious airs" to a variety of materials, multiplying them to such an extent that one of Cotes's hydrostatical lectures is filled with the repetition of them; he remarked the condensability of muriatic acid gast, and the orange colour of nitrous acid gas \\ and extricated from red lead, by the burning-glass, the gas§, which Priestley afterwards ha\ ing obtained by the same method, was led by reasoning from the manner in which red lead is * " Experiment 8. — A mercurial gauge having been put into a conical glass whose bottom was covered with beaten coral, some spirit of vinegar was poured in, and then the glass stopper closing the neck exactly : on the working of the menstruum on the coral, store of bubbles were for a good while produced, which successively broke in the cavity of the vessel ; and their accession compressed the confined air in the closed leg of the gauge three divisions, which I guessed to amount to about the third part of the extent it had before; but some hours after the compression made by this newly-generated air grew manifestly fainter, and the imprisoned gauge-air drove down the mercury again, till it was depressed within one division of its first station ; so that in this operation there seemed to have been a double compressive power exercised, the one transient by the brisk agita- tion of vapours, the other durable from the aerial or springy particles either produced or extricated by the action of the spirit of vinegar on the coral." — Phil. Trans. 1675. f " May 26, 1676. — Sal-ammoniac was put into a receiver with a suffi- cient quantity of oil of vitriol. Then the air being exhausted, the salt was put into the oil, whereupon a great ebullition presently followed, and the mercury in the gauge showed a good quantity of air to be generated; but this by the same gauge soon after appeared to be destroyed again. The expe- riment was repeated, and both the production and destruction were slower than before. It was confirmed by these trials that some artificial airs may be destroyed, but why this destruction happens sometimes sooner and sometimes slower, may perhaps seem worthy of further inquiry." — 2ndcont. Phys. Mech. Expts. 1676. + « We put an ounce of such strong spirit of nitre as is above mentioned into a moderately large bolt head, furnished with a proportionable stem, over the orifice of which we strongly tied the neck of a thin bladder, out of which most part of the air had been expressed, and into which we had conveyed a small phial with a little highly rectified spirit of wine. Then this phial, that was before closed with a cork, being unstopped without taking off the bladder, a small quantity, by guess not a spoonful, of the al- cohol of wine was made to run down into the spirit of nitre, where it pre- sently produced a great commotion, and blew up the bladder as far as it would well stretch, filling also the stem and cavity of the glass with very red fumes, which presently after forced their way into the open air, in which they continued for a good while to ascend in the form of an orange- coloured smoke." — New Experiments about Explosions, 1672. § f September 4, 1678. — 1 exposed one ounce of minium in an open glass to the sunbeams, concentrated by a burning-glass, and found that it had lost three-fourths of a grain of its weight, though much of the minium had not been touched by the solar rays. May 29. — Repeated the same experiment, in a light glass phial sealed hermetically and exactly weighed, relative to Black, Watt, and Cavendish. 129 manufactured, to identify with the oxygen of the atmosphere*, just as Mayow identified with it the gas from saltpetre. In giving to the gases which he discovered the title of "factitious airs" Boyle did not confound them with common air. The extracts which I have given sufficiently show that he used the word air generically, in the sense which he assigns to it in the following passage : — M If I were to allow acids to be one principle, it should be only in some such metaphysical sense as that wherein air is said to be one body, though it consist of the associated effluviums of a multitude of corpus- cles of very different natures that agree in very little, save in their being minute enough to concur in the composition of a fluid aggregate consisting of flying partsf." It would indeed be a great mistake in the history of science, to suppose that the notion of the air being a simple element prevailed among philosophers down to the days of Black. From the time of that remarkable revolution in the scientific mind of Europe which attended the revival of the mechanico- corpuscular philosophy, when the phaenomena of nature were accounted for no longer by forms and qualities, but by the sizes and motions, the cohesions and disjunctions of the par- ticles of bodies, the atmosphere came at once to be conceived of as a miscellaneous aggregate of the molecules of a variety of heavy substances thrown into an elastic state, or floating in an active medium of a still finer and more divided consistence. " Tout corps invisible et impalpable," says Descartes, " se nomme airt a, savoir en sa plus ample signification J." " By air," says Dr. Wallis, M 1 find Mr. Hobbs would sometimes have us understand a pure aether, 'aerem ab omni terrae aquae- que effluviis purum, qualis putatur esse aether,' to which I suppose answers the materia subtilis of Descartes, and M. Hugens's 'more subtile matter* than air: on the other hand, M. Hugens here by air seems to understand that feculent mat- ter arising from those the earth's and water's effluvia, which and the loss of weight came to ^rd part of a grain. May 30. — I endea- voured to burn the same minium again, but such plenty of air was pro- duced, that the glass broke into a hundred pieces." * " At the same time that I got the air above-mentioned from mercurius calcinatus and the red precipitate, I had got the same kind from red lead or minium. In this process that part of the minium on which the focus of the lens had fallen turned yellow. The experiment with red lead con- firmed me more in my suspicion, that the mere, calcinatus must have got the property of yielding this kind of air from the atmosphere, the process by which that preparation and this of red lead is made being similar." — Priestley's Experiments on Air, vol. ii. p. 111. f Reflections on the Hypothesis of Alkali and Acidum, ch. iv. 1676. X CEuvres, torn. vii. p. 237. ISO Rev. W.V. Harcourt on Lord Brougham's statements are intermingled with this subtle matter. We mean by air the aggregate of both these, or whatever else makes up that hete- rogeneous fluid wherein we breathe, commonly called air, the purer part of which is Mr. Hobbs's air, and the feculent of it is M. Hugens's air*." It is curious to trace the fortunes of this materia subtilis, from the naked condition in which it was first ushered into notice, to the figure which it now makes in the speculations of science. Descartes was undoubtedly the first who formed the idea of a liquid medium grosser than heat, but more subtle than air, extending from the heavenly bodies to the earth, filling the aerial interstices with a continuous series of molecular globules, pervading the pores of glass, diamond, and the densest sub- stances, without interruption, and propagating, by communi- cation of impulses from one molecule to another, the move- ment, or rather the pressure without locomotion, simple and compound, which he considered as constituting lightf and colours. This was a grand conception, for which the philosophy of optics is under an obligation to the inventor greater perhaps than has been confessed. But the range of Descartes's views in physics was too limited to admit of his turning such a con- ception to its full account. He seems to have had no idea of intermittent or elastic forces, and did not even endow either • Extract of Letters from Dr. J. Wallis to the publisher, 1672, Phil. Trans. No. 91. f Dr. Whewell takes Descartes's " hypothesis concerning light " to have been, " that it consists of small particles emitted by the luminous body," and considers this as " the first form of the emission theory " (Phys. Optics, eh. x.) ; and so the theory of the Dioptrics seems to have been understood by some of Descartes's cotemporaries ; but he explains himself otherwise in his letters. " Je vous prie tie considerer que ces petits globes dont j'ai parle nesont point des corps qui exhalent et qui s'ecoulentdesastresjusques a nous ; mais que ce sont des parcelles imperceptibles de cette matiere que V. R. appelle elle-meme celeste, qui occupent tous les intervalles que les parties des corps transparents laissent entre ellcs, et qui ne sont autre- ment appuyees les unes sur les autres que le vin de cette cuve que j'ai pris pour exemple en la page 6 de ma Dioptrique, ou Ton pent voir que le vin qui est en C tend vers B, et qu'il n'empeche point pour cela que celui qui est en E ne tend vers A, et que chacune de ces parties tend a descendre vers plusienrs divers endroits, quoiqu'elle ne se puisse mouvoir que vers un 6eul en meme temps. Or j'ai souvent averti que par la lumiere je n'entendois pas tant le mouvement, que cette inclination ou propension que ces petits corps ont a se mouvoir; et que ce que je disoisdu mouvement, pour etre plus aisement entendu, se devoit rapporter a cette propension ; d'oii il est mani- feste que, selon moi, Ton ne doit entendre autre chose par les couleurs que les differentes varittes qui arrivent en ces propensions." (CEuvres, torn. vii. p. 193> "J' admire que vous alleguiez les pages 4 et 5 afin de prouver que relative to Black, Watt, and Cavendish. 131 his filaments of air, or his aethereal globules interposed between them, with attractive or repulsive powers. The genius of Hook, so comprehensive of clear physical notions, soon lent to this luminiferous aether the mechanical attribute which it needed, and added the notion of vibratory pulses, — a notion which was instantly reduced by Newton to the form most competent to account for the phenomena*, and on which Huygens founded, and Young with his illus- trious coadjutors have gone far to finish, the mathematical fabric of the undulatory theory of light, as it is now commonly received. So necessary indeed to any account of the phenomena of light and colours did the admission of such a medium appear, that Wallis, who not only rejected the use which Huygens and others proposed to make of it in explaining the extraordinary height at which mercury, purged of air, may be suspended in a tube, but denied it the properties of elasticity and weight, nevertheless did not scruple to say, " That there is in our air a body more subtle than the fumes and vapours mixed with it in our lower region is very certain : but whether that subtle body be, as Dr. Garden seems to suppose, much heavier than our common air, I much doubt, and rather think it is not, not having hitherto had any cogent experiment either to prove it heavy or elastic ; but it may, for aught I know, be void as well of weight as spring, and what is found of either in our common air may be attributed to the other mixtures in itf." le mouvement des corps lumineux ne peut passer jusques a nos yeux, qu'il n'y passe quelque chose de materiel qui sorte de ces corps ; car je ne fais en ces deux pages qu'expliquer la comparaison d'un aveugle, laquelle j'ai prin- cipalement apportee pour faire voir en quelle sorte le mouvement peut passer sans le mobile ; et je ne crois pas que vous pensiez lorsque cet aveugle touche son chien de son baton qu'il faille que ce chien passe tons le long de son baton jusque a sa main, afin qu'il en sent les mouvements. Mais afin que je vous reponds in forma, quand vous dites que le mouvement n'est jamais sans le mobile, distinguo; car il ne peut veritablement etre sans quelque corps, mais il peut bien etretransmis d'un corps en un autre, et ainsi passer des corps lumineux vers nos yeux par l'entremise d'un tiers, a savoir, comme je dis en la page 4, par l'entremise de l'air et des autres corps transparents, on comme j'explique plus distinctement en la page 6, par l'entremise d'une maticre fort subtile qui remplit les pores de ces corps et s'etend depuis les astres jusques a nous" (p. 240), * Phil. Trans., No. 88, p. 5088. An. 1672. "The most free and natural application of this hypothesis I take to be this: That the agitated parts of bodies, according to their several sizes, figures, and motions, do excite vi- brations in the aether " &c. t Phil. Trans. No. 171, p. 1002. [To be continued.] [ 132 ] XXIII. On a Proposition relating to the Theory of Equa- tions. By James Cockle, M.A., of Trinity College, Cam- bridge ; of the Middle Temple, Special Pleader*. J. 1 ET x be the root of the general equation of the wth -" degree, and y = A'xx' + A"xx" + A'"xx'" + A™ *>■";. . . (a.) also let mY be composed of symmetric functions of, and be homogeneous and of the ?«th degree with respect toy; then, if n > 2, 2Y may be reduced to the form (a'1A' + fl"1A" + S')2 + (a"2A"+i")2, . . . (b.) where b' and b" are not both zero. 2. For, let A'".rf + A" a£y = I' a* + F x*', . . . (c.) then if yr = (A! +'*)«*' + (A" +V)*f + lr, . . (d.) 1» = 0 (e.) Now 2Y is to be reduced, by means of (d.), to the form (b.), independently of A, or, what is the same thing, of A-f Z; butt tY-S(b4+ft-.U1}\ W ]m denoting a homogeneous function of the enclosed quan- tities of the mtb. degree. And, if n — 1 > 1, Pl ;.,]«_,]« »0 (g.) may be satisfied without making the l's zero. 3. Following a notation similar to that used in my last paper t, let (p, q) represent the coefficient of A^A^ in the development of tp2-sp* = zY = 0, (h.) p2 and px being respectively the coefficients of the third and second terms of the transformed equation in y ; then, if (h.) be reducible to the form (b.), we have ... + ... +#±*/ZT. b" = 0; . . . (i.) and both the values of the above expression can only vanish when b' = 0 = b". Substitute for b' and b", equate each ex- A'" pression to zero, and eliminate r— between the two ; then we have (1, 3) (2, 4) -(1,4) (2, 3) = 0, . . . . (j.) where, for instance, (l,3) = ^(«')-25SK').S(<"); . . (k.) * Communicated by the Author. •f- For the process, see par. 3 of the place which I have before cited, at the first line of p. 126 of vol. xxvii. of the Phil. Mag. S. 3. J Phil. Mag. S. 3. vol. xxvii. p. 292. Mr. Cockle on the Theory oj Equations. 133 so that, on developing, we shall have on writing x' . X" for 2 (#*') . X (#*"), &c., 0 = {t-2s) x {*' . X1V . (X" + X"') 4-X" . X'" . (x' + Xlv) -Af.X'".(x'' + Xl')-X".^.(x' + A'")} + 2f{(x' + X/").(A" + Alv)-(A' + ^v).(A" + ^)}. . (1.) Let / = 2 w, and s = « — 1, then, if n < 3, the last equation is identically true, but not in any other case. The method of the two first paragraphs, consequently, detects every case of failure; the last-mentioned instance of which is connected with the fact that, implicitly at least, every expression of the form (a.) contains in its right-hand side a term free from x which, with the above values of t and s, vanishes from 2Y. These values are those which occur in exterminating the 2nd, 3rd, and rth terms of an equation. 4. If, in the case of w = 2, t-=4t, and s=l, we reject in (g.) the solution ^ = 0, we are conducted to (^'-4')2(*f-O = 0, .... K) having multiplied by the coefficient of A'2 before commencing our operations. This agrees with what we have inferred from 5. It seems to follow from this, that biquadratics can be reduced to a binomial, and equations of the fifth degree to a trinomial form, by an expression for y consisting of four terms, determinable by one linear*, one quadratic, and one cubic equation. 6. At p. 384 of the 26th vol. of this work, I have only al- luded to the equation (3.), which, for cubics, conducts to the reducing equation ? + **(£) + ££=<>; .... (*J \f , / ft ft and to a similar one for biquadratics ; but if we discuss the equation

n = oo. 2sin2 — L 2(1 -cos 9) Prof. Young indeed " considers it an axiom, that what holds for all but the extreme case will hold for that too," but I must beg to submit that this is a matter of fact and not of opi- nion; and the fallacy of the principle in the present case I have sufficiently shown in the former part of this paper. With all due deference therefore to Prof. Young, I shall reassert, that Mr. De Morgan is in error in affirming (1.) to be the limit of the proposed series "when A = 1." Omit the words "when A = 1," and I admit the proposition. Insert those words, and the fact expressed is untrue, if it be not wholly unmeaning. Prof. Young says again, " It is easily proved that z*00 a Z*50 . 1 / e~ax o.o%xdx = 5, / e-axsmxdx=.—i — 5, (a.) Jo l+a2»/o l-fa2V/ from which it certainly follows, though the inference is denied by Mr. Moon, that in the limit, when a = 0, the true values of these integrals are 0 and 1." I do not deny the inference, that the limits of the integrals when a is diminished indefi- nitely, so long as it continues an actual magnitude, are 0 and 1 ; but I do deny that the limits of the integrals are to be found by putting a = 1 in the left-hand members of the two equations («.), that is, I deny that / co&xdx and / sin#d.r is fc I a a 3? £ aHa £ * £ > * JJJ s-j J *• „• Cj U O UUUUU Ut> yyoy'-',-'l-lycjcj*"oO •urd I •spiAisiqj a; ft .A! =1 ■a"§ °5 Ss * g:' Bt £ * fe &= at c £ £ g| *' £ £ £ £ £ £ £ I St' * 'urd —Id -to — :« — £* — 1« — fcl ^cocococococo^^co-^'3,-o c^o o © io nm^f'to o (onOMn- — ■ io oo o c^ -*t t^ o o> •<* COCOCOCM^COCOCM^CO^COCMC*^^COCO oob o> 6< o o 6> 6 6 6 o o 6i 6\ oob 6\ 6\ob o o o o o oco ooo ■ss oo^ti^onncticcodoonwnsfoo-iow'joocKN o (09 ciop«ipi>ip'HO^,fii>-- cp'oipioopr^opri'opop — cococMop>p 6< 6\ 6> 6iob ffia\o\o\o 6\ 6 6 6n 6i 6i 6> 6i do do odb b^b^&\cj*b\i0'rfuo^<-^'ijoodiO\C\Ol CMCMCMCMCMCMCMCMCMCMCOCOCOCMCMCMCMCMCMCMCMCMCMCMCOCMCMCMCMCMCM UOJSOJI O— > cm — cm -*r o ■** t^CM oio O O t>VO — On CO — # O 00 Oi loo-* co Oi r~ COU3 to m •**— t co ^tcoop 6 6 o> COCOCN CO — t^oo U0 CO 00 r^oo o G\ &> o\ M (N CM — co — (N 00 00 •** O O CO 00 O Ol— -H CIIOIO O ~t 00 00 — oo r^ O O Ot Ot Ot CO CO Ol CM * irt 0 •^fio CO 00 W5 — OO OO — jo sAvq 2Q onrfioorNaaoHtsfi^inior-Qo^o-iNo^iftior-Qoao- -rJ„_rJ-„--,rtOI(N01C)OI M. Langberg on the Determination of the. Temperature holes in the centres of which the rod passed, the battery and that part of the rod to be examined were effectually protected from the radiant heat of the boiling vessel. The support of thebattery was screwed to a sledge which could be moved along the edge of the horizontal divided board in a direction parallel with the metallic rod, by which means the relative distances of the points to be examined on the rod and their tempera- tures could be easily ascertained. In order that the battery should press with equal force each time against the rod, a spiral spring was so placed in the support of the battery as to force it upwards against the under side of the rod ; or it could be brought into contact with the rod in a direction at right angles to it. The observations were made in the following manner : — "When the rod had attained a constant temperature, which seldom occurred until about 2^ to 3 hours after the com- mencement of the experiment, the sledge bearing the battery was so placed that the upper end of the battery bore perpen- dicularly upon the under side of the rod. The spiral spring was then allowed to force the end against that part of the rod the temperature of which was to be examined : the needle of the multiplier diverged immediately. I waited generally about two minutes to allow the needle to come to rest, and having noted the divergence, removed the battery. After each observation I allowed four minutes to elapse before the battery was again placed in contact with the rod, partly that the needle of the multiplier might return to 0°, and partly that the equi- librium of temperature in the rod, which might possibly have been disturbed by its contact with the battery, might again be restored. This latter precaution was however needless, as observations made upon the same part of the rod immediately the one after the other, were found to give the same deviations in the needle as when a space of time was allowed to elapse between each observation. Thus far we have given very nearly the author's own words ; but as our space will not allow us to follow him through each experiment, we shall hei'e briefly add some of the precautions which were taken to avoid error, and then give the results to which the experiments have led. To ascertain whether the battery itself, after being for some time in contact with the rod, might by becoming warm no longer indicate with correctness the difference of temperature between the rod and the surrounding air, it was left in con- nexion with the heated rod for three quarters of an hour, but during the whole of that time the divergence of the needle of the multiplier scarcely changed. The circumstance that the needle and Conducting Power of Solid Bodies. 165 of the multiplier seldom returned to precisely the point from which it had been deflected, sometimes becoming stationary a little to the right, sometimes to the left of its original position, the cause of which deviation could not be traced, would give rise to a slight error, perhaps O'l to 02 of a degree, upon the scale of the multiplier, which had been divided in the manner recommended by Melloni. The divisions upon this scale not corresponding exactly with the temperatures they are intended to indicate, might also lead to a slight error ; and although the observations were always made with the aid of a magnifier, still it is possible that from 0*1 to 0*2 of a degree should escape observation. These three sources of error, which arose chiefly from the author's having used an imperfect instrument, added to another more important one, the effect, namely, of currents of air in the room cooling one part of the rod under examination more than another, the author calculates will not amount to more than O'^0 C. in the final result of any experiment. In fact it never actually amounted to so much. The metals used in the experiments were copper, steel, tin and lead ; they were all drawn out into cylindrical wires or thin rods, and their length was such that even in the middle of the rod no effect of the heating body Was perceptible. The copper alone, being the best conductor, was slightly affected through its whole length. The object of the experiments was not so much to determine the conducting power of the metals employed, as to submit the analytical law to the test of experiment ; the metallic sur- face of the rods was therefore not protected, and remained un- impaired in the three first metals ; the lead wire however soon became covered with a layer of oxide, which increased in thickness every time it was heated. The results at which the author arrived were principally the following: — The law of Biot, — that in a very thin, long metallic rod, one end of which is kept at a constant temperature above that of the surrounding air, after equilibrium of temperature has been established, the excess of temperature in any part of the rod above that of the surrounding air, decreases in geometrical progression as the part examined is removed by equal distances from the heated end — is not generally confirmed by the author's experiments, and is only true for most of the metals in the case of a very small excess of temperature. Among the metals examined copper was the only one for which the law held good, at least when the excess of temperature amounted to 30 C. With tin, the law no longer applied when the excess was 166 Mr. T. Hopkins on the Causes of the 4° C; with steel when it amounted to 2° or 3°; and lastly, with lead, when 1° of difference existed, it was not accurate. 2. The reason for this want of accordance between the ob- servation and the mathematical law is, that in establishing the latter the outward and inward power of conduction of bodies was considered as independent of the temperature. If these be considered as functions of the temperature, a proximate formula for the distribution of heat in the rod may be esta- blished, which would very nearly agree with my observations. 3. The conducting powers of bodies established by former philosophers with the aid of Biot's law are consequently in- correct, and can only be considered as partial approximations to the truth. 4. The constant coefficient for the conducting power with a difference of temperature equal 0, is therefore only to be de- termined in this manner ; either by using Biot's law and ob- serving the distribution of heat in the rod with very small differences of temperature, or more correctly, by ascertaining its value, as was done in the author's experiments by means of Poisson's formula. 5. That the method employed in the observations is accu- rate, and that the thermo-electrical battery will become in the hands of natural philosophers a more correct means of ascer- taining the temperature of the surfaces of bodies than any other, and may be used in cases where the common thermo- meters cannot be employed. XXXI. On the Causes of the Semi-diurnal Fluctuations of the Barometer. By Thomas Hopkins, Esq.* THAT the non-condensable gases and the aqueous vapour of the atmosphere, when it is at rest, press on the mer- cury of the barometer independently of each other, and con- stitute the general atmospheric pressure, is evident from their known laws of diffusion and independent existence while dif- fused through each other. But that the facts and reasonings, commonly adduced, rest- ing on those circumstances, together with the daily alterations of thermometic temperature, account for the two risings and the two fallings of the barometer, as is contended by some parties, cannot be admitted. In certain parts, such as Canada, of which an account has been recently given by Colonel Sabine, the influence of the causes named may be sufficient to account for a considerable * Read to the Literary and Philosophical Society of Manchester, Dec. 30, 1845, and communicated by the Author. Semi-diurnal Fluctuations oftlie Barometer. 167 portion of the semi-diurnal movements of the barometer which occur in that country; but these causes are not sufficient to produce the diurnal fluctuations in other places, such as Bom- bay, Calcutta and La Guayra. And there can be little doubt that the real causes, whatever they may be, which give rise to the double undulations in these tropical parts, produce them in places where they are less extensive, although the opera- tion of the causes in the latter places may be weaker and more difficult to trace. I have shown in my " Atmospheric Changes" that there is no reason to believe that the daily warming of the atmo- spheric gases by the direct influence of the sun produces any appreciable alteration in their pressure on the mercury of the barometer, as the effect of that warming on the whole column in the locality is so small, as to prevent much disturbance of atmospheric pressure; yet great influence has been attributed to solar heating near the surface in producing the semi-diurnal fluctuations that take place. Colonel Sabine, in his Report on the Meteorology of Toronto at the meeting of the British Association in 1844, gives an explanation of the daily oscillations. He says, " As the temperatureof the day increases, the earth becomes warmed and imparts heat to the air in contact with it, and causes it to ascend. The column of air over the place of observation thus warmed rises, and a portion of it diffuses itself in the higher regions of the atmosphere, where the temperature at the surface is less. Hence the statical pressure of the column is diminished. On the other hand, as the temperature falls, the column contracts, and receives in its turn a portion of air which passes over in the higher regions from spaces where a higher temperature prevails; and thus the statical pressure is augmented." In the Athenaeum of July 5, 1845, the Colonel is repre- sented as having said at the then recent meeting of the British Association, that in Dr. Buist's Meteorological Report from Bombay, " the explanations thereby afforded of the diurnal variations of the gaseous pressure at Bombay, which, although at first sight more complex than at the stations of Toronto, Prague or Greenwich, he conceives to be equally traceable to variations of temperatures." Colonel Sabine therefore, after having examined Dr. Buist's meteorological registers, retains the opinion that the semi-diurnal alterations of the gaseous pressure are produced by alterations of temperature, as that temperature is shown by the thermometer. As I propose to examine this theory and to compare it with another, it will be convenient to designate the two by distinct 168 Mr. T. Hopkins on the Causes of the names. I shall therefore call the Colonel's " the temperature theory" and the other, " the condensation theory" Both of these rest on alterations of temperature ; but the former de- pends on the temperature found by thermometric measure- ment near the earth's surface, and the latter on the temperature which must be produced by condensation of vapour in a higher part of the atmosphere, of which we have no direct measure. The semi-diurnal fluctuations of the barometer are the greatest within the tropics ; and as details of those at Bombay have not yet been published, we will proceed to examine ac- counts furnished by Kaemtz in his valuable work on Meteo- rology. In page 248 of that work we have the following tables of the hourly heights of the barometer: — Table I. Mean height of the barometer expressed in millimetres for all hours, and in different places. Places .... Gt. Ocean. Curaana. La Guayra. Calcutta. Padua. Halle. Abo. Peters- burg. Latitude . . 0°0' 10° 23' N. 10° 36' n. 22° 35' N. 45° 24' N. 54°29'n. 60° 57' n. 59° 66' n. Observers . Horner. Humboldt. Boussin- gault. Balfour. Ciminello. Kaemtz. Hall- stroem. Kupffer. Noon 75235 756-57 759-41 759-61 75702 753-29 759-31 759-47 1 751-87 755-99 758-91 759-22 756-85 75311 759-29 2 751-55 755-47 758-41 758-39 756-67 752-99 759-27 759-38 3 75115 75514 758-12 758-12 75654 752-89 759-25 4 75102 754-96 758-05 757-91 756-47 752-84 759-25 759-32 5 751-31 75514 758-10 757-93 756-46 752-86 759-27 6 751-71 755-41 758-40 75801 756-50 752-91 759-29 759-31 7 751-93 755-81 758-90 75802 756-63 753-02 759-34 8 752-35 756-21 759-19 758-54 756-79 753 14 759-39 759-32 9 752-74 756-59 759-69 759-24 756-92 753-24 759-44 10 752-85 756-87 759-93 759-33 75702 753-31 759-47 759-36 11 752-86 75715 759-98 759-09 757-02 753-29 759-47 Midnight 752-47 756-86 759-64 758.80 75701 753-23 759-41 759-35 13 752-20 756-53 759-34 758-62 756-90 753-14 759-33 14 751-77 756-21 75905 758-57 756-84 75305 759-24 759-32 15 751-63 755-89 758-81 758-49 756-78 752-99 75914 16 751-32 755-66 758-68 758-47 756-74 752-99 759-07 759-32 17 751-65 755-79 758-85 758-44 756-75 753-34 75903 18 751-95 756-18 759-32 758-68 756-79 75312 75904 759-39 19 752-84 758-58 759-94 75916 756-89 753-24 759-08 20 752-95 756-98 760-50 759-88 75701 753-37 75915 759-49 21 75316 757-31 759-63 76011 757-08 753-44 759-21 22 75315 757-32 760-50 759-19 75714 753-46 759-29 759-51 23 752-80 75701 759-99 75909 75707 753-40 759-32 From an examination of this table, it will be seen that the fluctuations are the greatest within the tropics, and they diminish, though not invariably, with the increase of latitude. Semi-diurnal Fluctuations of the Barometer. 169 The first column exhibits the fluctuations at the equator in the great ocean. The range extends beyond two millimetres, and the descent from 9 in the morning till 4 in the afternoon gives the whole extent of the range. The two next columns show the alterations at Cumana and La Guayra, both above 1 0° north latitude, and the ranges are nearly equal to that at the equator. The fourth column shows the changes at Calcutta to be nearly as great as in the preceding places, but both this and the La Guayra columns exhibit singular irregularities in the earlier parts of the mid-day descents. In the Padua column, 45° north, the fluctuation is much reduced in the extent of its range, but retains the same general character. In Halle, in latitude 54°, the alterations do not differ ma- terially from those at Padua. The changes are very small in Abo and Petersburg, and in the former place the second rise attains a greater height than the first. To these it is desirable that we should add the following table (p. 170) of the height of the dry- and wet-bulb thermo- meters, and the difference between the two, — with the dew- point and the height of the barometer at Plymouth for three years, as furnished by Mr. S. Harris, and published in the Ninth Report of the British Association (p. 167). In all these places the temperature shows only a single fluctuation, such as is seen in the table of the thermometer at Plymouth, namely one rise generally from about 5 a.m. to 1 or 2 p.m., and one fall from that time until 5 the following morning. Now, if the temperature of the atmosphere, as marked by the thermometer, caused the diurnal fluctuations in the way supposed, we ought to have in all these places one undulation in the twenty-four hours instead of two, — the rise of temperature causing a decline of the barometer during the hotter part of the day, and the fall of temperature producing a rise of the barometer in the colder part. Yet Colonel Sabine himself says that at Bombay, where there is only one rise and one fall of temperature, there are two risings and two fallings of the barometer ! And these movements of the barometer take place not only when that instrument is taken as the measure of the whole pressure of the atmosphere, but also when the vapour pressure is deducted, and the mercury of the barometer is taken as the measure of the gaseous pres- sure alone. These facts are opposed to, and are irreconcile- able with, the temperature theory. 170 Mr. T. Hopkins on the Causes of the Table II. Table of the heights of the dry- and wet-bulb thermometers, and the difference between the two, together with the dew- point and height of the barometer at Plymouth for three years. Thermo- Wet-bulb Dew- Hour. meter. thermo- meter. Difference. point. Barometer. 1 A.M. 47-52 46-20 1-32 45-00 29*8017 2 4733 4603 1-30 44-75 29-7993 3 4711 45-92 119 4475 29-7944 4 47-00 45-66 1-34 44-25 29-7928 5 46-98 45-77 1-21 44-75 297928 6 47-41 4601 1-40 44-50 29-7960 7 48-44 46-83 1-61 45-25 29-8002 8 49-68 47-51 2-17 45 00 29-8032 9 51-30 48-50 2-80 45-26 29-8048 10 52-84 49-45 3-39 46-25 29-8061 11 5300 50-02 3-88 46-75 29-8045 12 54-51 50-40 414 46-75 29-8002 1 P.M. 55 83 50-55 4-28 46-75 29-7957 2 54-77 50-44 4-33 46-75 29-7922 3 54-25 50-24 401 46-75 29-7908 4 53-45 49-80 3-65 46-75 29-7895 5 52-27 49-06 3*21 46-25 29-7938 6 51-24 4S-46 2-78 4600 29-7970 7 50-28 47-90 2-38 45-75 29-8019 8 49-44 47-51 1-93 45-75 29-8061 9 48-83 4717 1-66 45-60 29-8094 10 48-48 46-93 1-55 45-60 29-8099 11 4810 46-66 1-44 45 00 29-8092 12 47-80 46-43 1-37 45-00 29-8065 Mean . i . 50-32 47-89 2-43 45-60 29-7999 As however the aqueous vapour of the atmosphere presses on the mercury of the barometer separately and independently, it has been attempted to be shown that the variable pressure of the vapour arising from difference in the quantity in the atmosphere at different periods of the day, combined with change of the gaseous pressure resulting from alteration of surface temperature, and that the two causes acting together produced the double undulation of the barometer; to this view therefore we will direct our attention. The temperature near the surface of the earth at Plymouth, as well as at the other places, rises from about 5 in the morning till about 2 in the afternoon ; and when the wet bulb, as well as the dry thermometer, is used, as it was at Plymouth, it is seen that the temperature of the latter rises more than that of the former, or of the dew-point, and eva- poration must consequently become progressively more active; Semi-diurnal Fluctuations of the Barometer. 171 there must therefore be successively more water evaporated and thrown into the atmosphere to be added to its weight. And according to the temperature theory, this water, now converted into vapour, must, up to say 10 o'clock, press with sufficient force on the mercury to counteract the lightening influence of the rising temperature, as during that time the barometer rises. From 10 until 1 o'clock, as the temperature rises still higher, as compared with the wet-bulb thermometer and the dew-point, evaporation must go on increasing, and the in- crease of vapour pressure ought to continue; but it appears from the table not to do so, as the mercury of the barometer falls instead of continuing to rise; we have therefore to try to ascertain what can be the cause of this fall, while additional vapour is passing into the atmosphere. Those who advance the temperature theory, say that the fall of the barometer is caused by the increasing temperature of the atmosphere produced by the action of the sun on the surface of the earth, and the air near to it; and they must main- tain that this increase is sufficient, not only to lighten the atmo- sphere enough to cause the fall of the barometer, but also in ad- dition to counteract the influence of the increased vapour pres- sure. Now at Plymouth the temperature rises from 5 to 10 a.m. nearly 6°, and may be supposed to lighten the atmosphere to a certain extent; at the same time evaporation throws vapour into the atmosphere. We are, however, required to suppose that the vapour produces so much greater effect by pressing on the mercury, than the heating of the atmosphere does in reducing atmospheric pressure, that the whole pressure be- comes greater and the mercury rises. But after 10 o'clock the temperature continues to rise, but in a smaller degree, say nearly 3°, and vapour must be more abundantly thrown into the air, as is shown by the extent to which the wet-bulb ther- mometer is kept down ; yet the barometer, instead of conti- nuing to rise, suddenly turns and falls, and continues falling from 10 to 1 o'clock, the time of the highest temperature ! So that according to this theory, from 5 to 10 o'clock, the sun heats the air nearly 6° and produces some vapour; and the two influences acting together cause the barometer to rise, but from 10 to 1 the sun heats the air about 3°, and must throw much additional vapour into the atmosphere; and then these two influences still acting together cause the barometer to fall ! This is attributing opposite effects to the same causes, and must be presumed to be erroneous. But let us examine the valuable Plymouth tables a little more minutely. The first column gives the temperature as 172 Mr. T. Hopkins on the Causes of the shown by the ordinary thermometer ; the second, the tempe- rature of the wet-bulb thermometer, as kept down by the cool- ing influence of evaporation ; and the third gives the differ- ence between the two first. Now as this difference arises from the extent of the evaporation, the numbers of the difference may be taken to express the force and amount of evaporation, and to indicate the additional vapour that is discharged into the atmosphere. This force or amount at 5 o'clock in the morning is lc,21, from which time it increases to 30,39 at 10 o'clock. So that during this time, five hours, the increase in the force of evaporation is 20,18; and this in the temperature theory must be held to be sufficient to overcome the lightening effect of a rise of 5°*86 of temperature, and also to raise the mercury of the barometer to the full extent of the morning rise ! After this time, from 10 to 1 o'clock, the temperature rises further from 52°-84 to 55°'83 or 2°*99 ; and during the same period the force of evaporation increases 1°'89, that is, from 3°"39 to 40,28. Thus we are required to believe, that from 5 to 10 in the morning, 20,18 of evaporation overcame the lightening influence of 5°'S6 of temperature, and in addi- tion raised the mercury of the barometer; and from 10 to 1 in the day, 10,89 of evaporation not only failed to overcome the lightening effect of 20,99 of temperature, but allowed this relatively small amount of temperature to produce the further result of a fall of the mercury of the barometer. Or put in a tabular form, say that from 5 to 10 o'clock, 5°*86 of temperature and 2°-]8 of evaporation caused a rise. 10 to 1 o'clock, 2°-99 of temperature and l°-89 of evaporation caused a fall ! That is, where temperature, the influence which lightens the atmosphere, is relatively great and should cause a fall, the mercury of the barometer rises; and where the influence of temperature is relatively small and should cause the vapour to produce a rise, the mercury falls ! This must be erro- neous. In the same place, at Plymouth, from 1 o'clock until 4 p.m., as may be seen in the table, the temperature falls ; and as far as that temperature acted the atmosphere would of course be- come heavier. At the same time evaporation shows vapour is passing into the atmosphere; it ought therefore to follow that the barometer should rise, and considerably too, through the operation at the same time of both the causes which are supposed to contribute to the production of a rise. But the barometer does not rise ; on the contrary, it falls, and conti- nues falling until 4 o'clock. These facts and reasonings prove that neither the daily variations of surface temperature, nor the different amounts of vapour pressure, nor both taken to- Semi-diurnal Fluctuations of the Barometer. 173 gether, are adequate to the production of the fall of the baro- meter from 10 to 4 o'clock in the day. And if we proceed with our inquiries into the next period of six hours, that is, from 4 to 10 p.m., we meet with facts that do not harmonize with the temperature theory. During the whole of this time, it is true the temperature falls and the barometer rises: but the vapour pressure must have dimi- nished according to the temperature theory, as the dew-point, the measure of vapour pressure, falls ; and the lowering of the dew-point after 4 o'clock showed that vapour was then con- densing in the lower part of the atmosphere. So that here it becomes necessary to suppose that the atmosphere cools enough, not only to raise the barometer to the full extent of its daily range, but also to counteract the reduction which takes place at the same time in the vapour pressure. Again, from 10 at night, although the atmosphere continued to cool, the barometer did not continue to rise, but once more fell, which fall is attributed to a diminution of vapour pressure. Thus from 4 to 10 in the afternoon and evening, cooling the atmo- sphere is represented as more powerful than reduction of va- pour pressure ; and from 10 in the evening to 4 in the morn- ing, reduction of vapour pressure is supposed to be more pow- erful than cooling the atmosphere. The two forces, we are required to believe, do not merely neutralize each other, but each in its turn exercises a paramount influence, and for the time determines an absolute rise or a fall of the barometer; and this we are called upon to admit without any satisfactory or even plausible evidence being adduced to prove it. What has been here advanced applies with the greatest force to the semi-diurnal fluctuations in atmospheric pressure which take place within the tropics. Aqueous vapour exists in the atmosphere in larger proportions in that part of the world than it does in higher latitudes ; and it is to the daily condensation of that vapour in the atmosphere, and its subse- quent evaporation there, that we are really to attribute the great deviation of the movements of atmospheric pressure from the daily march of temperature. If no vapour existed in the atmosphere, the alteration of pressure would be very little, and it would be the reverse of temperature. As the atmo- sphere became warmer, the pressure would be less ; as it be- came colder, the pressure would be more. And the hourly variation in the quantities of vapour actually found in the at- mosphere which arises from alteration of surface temperature, only introduces another element of pressure into the inquiry, which is simple in its character, — the vapour increasing or diminishing with an increase or diminution of temperature. 1 74 Mr. T. Hopkins on the Causes of the If the two were equal while acting in opposite directions, they would balance each other. But the separate action of these two causes cannot produce such a double undulation of the mercury of the barometer as that which occurs daily in the tropical regions and at Plymouth. The double undulation which takes place may be thus ac- counted for. When the sun acts with force on the surface of the earth in the morning, it heats that surface, and the air near it; increases evaporation of moisture from wet surfaces, and sends forth vapour, which presses on the mercury of the barometer and causes it to rise. The lower part of the at- mosphere being heated also rises at the same time, probably in separate vertical streams, until it reaches a height where its expansion and consequent cooling is sufficient to condense a part of the vapour which it contains. A cloud is then formed, and the heat which has been evolved in the condensation of the vapour makes the cloud lighter than the adjoining air. The vapour in the upper pari of the air being thus removed by conversion into water, no longer presses as vapour, or with the same force on that below; and the lower vapour consequently rises more freely to the height of the cloud. Both the air and vapour are also (speaking in popular lan- guage) drawn up by the ascending cloud, and fresh air flows in from adjoining low levels, forming what in some parts is called the sea breeze. Cloud more or less thick is now formed, more heat is liberated, and a larger mass of air heated, which being forced upwards expands and makes the whole atmospheric column lighter, and reduces the pressure on the surface below. Under ordinary circumstances this process proceeds while the sun acts with considerable power on the surface of the earth, which is generally from 10 a.m. to 4 p.m., when day-cloud ceases to form. In this way, from 10 in the morning till 4 in the afternoon, the barometer is caused to fall, through the condensation of vapour in the upper part of the atmosphere making the column of air warmer and lighter. But now as vapour no longer ascends, cloud ceases to form, but that cloud which had been formed remains suspended in the air, where it begins to cool from the influence of evapora- tion of the particles of water that form the cloud. When it cools sufficiently, it becomes heavier and sinks, and additional air flows towards and over it, increasing the weight of the whole column in the locality and causing the barometer to rise. By 10 the heavy air produced by cloud evaporation has partly descended and diffused itself on the surface of the earth, forming what is called the land breeze; and during the same time the cold of the surface condenses some of the va- Semi-diurnal Fluctuations of the Barometer. 175 pour into dew, when the atmosphere becomes somewhat lighter up to about 4 or 5 in the morning. As we proceed from the equator towards higher latitudes, we find less vapour in the atmosphere, and its influence on atmospheric pressure is less marked. At Padua the fall of the barometer from 10 to 4 in the day is not much more than one-fourth the extent that it is at the equator, and at St. Petersburg it is very small. In situations where there is not sufficient vapour in the atmosphere to form any daily cloud, it is to be presumed that if a barometrical registration were to be made, there would be no double movement exhibited showing a fall from 10 a.m. to 4- p.m., and a rise from 4 to 10 p.m., because there would be no condensation and warm- ing to produce the former, nor evaporation and cooling to cause the latter. The heating effects of condensing vapours may however be traced even in comparatively dry latitudes, such as that of Toronto, as shown in Col. Sabine's report to the British As- sociation in 1844. There was no fall of the barometer at that place from 4 to 10 in the morning, although the temperature had risen from 39°'20 to 46°*35, above 7°; but in the middle of the day, from 1 0 to 4, with an increase of temperature from 460,35 to 50o,55, being only 4°'20, the gaseous as well as the general atmospheric pressure was materially reduced ! not- withstanding that the increase in the quantity of vapour du- ring this time must have been as great as it was in the pre- ceding period ; and if this increased quantity had remained in the atmosphere, its pressure must have been added to that which previously existed. We are then obliged to suppose that the reduction of the pressure which took place imme- diately after 10 o'clock, arose from a cause which came into operation at that time; and that cause it is contended can be found only in the heating of the atmosphere by the conden- sation of vapour. The great defect of the temperature theory is, that it fails to account for the fall of the barometer from 10 a.m. to 4 p.m., and its subsequent rise from 4 to 10 p.m., though this is the oscillation for which we have particularly to account; whilst the theory here maintained points out the cause of these, as well as the other diurnal, and also of the casual movements of the barometer. We are therefore at liberty to conclude that the semi-diurnal fluctuations of the barometer can be accounted for only on the condensation theory. [ H6 ] XXXII. On the Principles to be applied in explaining the Aberration of Light. By the Rev. J. Challis, M.A., Plu- mian Professor of Astronomy in the University of Cam- bridge*. THE aberration of light having been brought before the notice of the readers of this Journal by several recent communications, I am unwilling to let the subject drop with- out saying a few more words respecting the principles to be applied in the explanation of the phenomenon, which possibly may appear, after all that has been said, to be involved in un- certainty. I propose to answer the question, Is the aberration of light to be attributed to known causes, or must we, to ex- plain it, have recourse to hypothesis ? The first attempts to explain aberration referred it to the combined effect of the motion of the earth and the tempora- neous transmission of light, and accordingly proceeded on the principle of attributing it to known causes. It must, however, be admitted that every attempt to show how the observed effect resulted from these causes, what was the particular modus operandi, v/as unsatisfactory. Some idea appropriate to the subject was still wanting. This idea I consider that I have succeeded in supplying. I have argued, as had not been argued before, that because the direction of a celestial object is necessarily referred to the direction of a terrestrial object, light from the one as well as light from the other must be taken account of in considering the question of aberration. It is self-evident, that if at any instant two objects appear in the same direction, whatever course the light from the more distant may have taken before it reaches the nearer, it subse- quently pursues a common course with light from the latter, and the two portions of light enter the eye at the given instant simultaneously. The direction in which the light comes is therefore judged to be the same as the direction at that instant of the nearer object from the eye. But during the interval the light takes to pass from the nearer or terrestrial object to the eye, this object is carried by the earth's motion away from the direction of the progression of light, and the two directions, at the time they are judged to be coincident, are in reality separated by a certain angle. This angle is aberration. I may refer to my communication in the February Number for a proof, which I venture to say is as cogent as any proof in the elements of geometry, that according to the principles just stated, an astronomical instrument employed to measure the earth's way, as it is called, would measure a smaller angle. * Communicated by the Author. Rev. J. Challis on the Aberration of Light. 177 The difference, or aberration, is readily calculated from know- ing by observations of the eclipses of Jupiter's satellites, the ratio of the earth's velocity to the velocity of light. Being so calculated the amount is found to be the same as the amount of aberration independently determined by astronomical observa- tion. It follows from this accordance, not only that the aber- ration of light is entirely accounted for on these principles, but also, as a corollary, that the direction of the progression of light from a star, as it enters the eye, is the true direction of the star. Whether it be the star, or the terrestrial object to which it is referred, that is seen in its true place, is a curious question, not readily answered, and not in the least degree ne- cessary to be answered in the present inquiry. Sufficient reasons have now, I think, been adduced for coming to the conclusion, that the question I proposed to consider must receive the following categorical answer: — The aberration of light is entirely due to known causes, viz. the motion of the earth and the temporaneous transmission of light, and does not require for its explanation any hypothesis whatever. What then becomes of the theories which have been framed to account for aberration on the hypothesis of certain motions of the aethereal medium ? As explanations of aberration they can be of no value, it being an acknowledged principle in phi- losophy, that an hypothesis is not to be sought for to explain what may be explained by known causes. All that is left for the theorist to do, supposing, as it appears necessary to sup- pose, that the aether is in some way put in motion by the motion of the earth, is to show that no aberration results from such motion, the whole being attributable to the earth's mo- tion. This problem I have considered in my two former communications, not because it was necessary to do so to complete the explanation of aberration, but with the view of removing an objection that might be raised against the undu- latory theory of light. By taking account both of the light from the star and the light from the terrestrial object to which the star's direction is referred, I found that no aberration would result from the motion of the tether, provided it satis- fied certain not improbable analytical conditions. A different conclusion would be arrived at by the same reasoning, if the light from the star, as is commonly done in treating of aber- ration, were alone considered. With these remarks I dismiss the subject of aberration, having attained the object I had in view in taking it up, if I have succeeded in extricating the explanation of the phaeno- menon from hypothesis and conjecture, and placing it on its true basis. Cambridge Observatory, Feb. 17, 1846. Phil. Mag. S. 3. Vol. 28. No. 18C. March 184.6. O [ 1*78 ] XXXIII. On the Cause of the Circulation of the Blood. By John William Draper, M.D., Professor of Chemistry in the University qf New York, \ MONO physiological problems there is none of greater ■*■*- interest, or of more importance in its relations to the well-being of man, than that which proposes to determine the true cause of the circulation of the blood, and the various other liquids which pass from one portion of living systems to another. Unquestionably one of the most important disco- veries ever made by any physician was that of the route of the circulation by Harvey. The clearness with which he and his successors developed that doctrine not only fully established his views, but gave rise to a serious error which is scarcely removed in our times. That error relates to the action of the heart. These earlier writers regarded the circulation of the blood as a hydraulic phasnomenon, supposing that the heart simulated exactly the action of a pumping machine. It is now on all hands con- ceded that this organ discharges a very subsidiary duty. The whole vegetable creation, in which circulatory movements of liquids are actively carried on without any such central me- chanism of impulsion ; the numberless existing acardiac beings belonging to the animal world ; the accomplishment of the systemic circulation of fishes without a heart; and the occur- rence in the highest tribes, as in man, of special circulations which are isolated from the greater one, have all served to demonstrate to physiologists that they must look to other principles for the cause of these remarkable movements. When we reflect how large a portion of the human family is destroyed by diseases dependent on derangements of the circulation, and to how great an extent the practice of medi- cine, as a scientific pursuit, must depend on just views of this important function, a natural philosopher can scarcely be more profitably employed than in attempting a solution of this pro- blem. I am persuaded that the phenomenon may be accounted for upon physical principles in a satisfactory manner ; that we can co-ordinate together, and arrange as examples of one common law, the various forms of circulatory movements, whether they occur among vegetables or animals, among in- sects, or fishes, or mammals ; and that the facts which we meet in derangements of these motions, or their cessation, as in fainting, coughing, and the different forms of disease, or such as take place after hanging, the inhalation of protoxide of nitrogen, or alcoholic drunkenness, or in that most remark- Prof. Draper on the Circulation of the Blood. 179 able of all results, the restoration from death by drowning ; in all these and many other such cases we can give the most felicitous explanation. The principal facts which I design here to establish are, — First. The systemic circulation is due to the de-oxidation of arterial blood. Secondly. The pulmonary circulation is due to the oxida- tion of venous blood. And, in conclusion, I shall offer some explanatory remarks on the phenomena of the coagulation of the blood, Several physiologists have already made an approach to the doctrine which will be developed in this memoir. Among well-informed writers it is conceded that we must look to the relations between the blood and the tissues for the true cause of the circulation. Thus Dr. Alison attributes the effect to a " series of vital attractions and repulsions," created by the operations to which the blood in the capillaries is subservient, an idea which Dr. Carpenter has rendered more explicit, by suggesting that these forces may not be "essentially different from those which are witnessed in Physics and Chemistry " (Carpenter's Human Physiology, vol. ii. p. 417). But these views do not communicate a definite idea of the true mecha- nism of the motion, nor do they exhibit that phenomenon as clearly connected with well-known chemical changes occur- ring in living systems. Should it appear, as I shall endeavour to prove, that the circulation is a necessary result of the al- ternate oxidation and deoxidation of the blood, we exchange at once a loose and ill-defined conception for a precise and definite fact. It will be perceived that I speak of the oxidation and de- oxidation of the blood as the great facts to be regarded, and leave out of consideration the spontaneous changes which that fluid itself undergoes; those minor effects which it impresses on the tissues, and those which they reciprocally impress on it. For the blood experiences in the systemic circulation an incessant change, discharging a double function. Its plasma serves for nutrition, its discs tor the production of heat. But whilst the final function of the plasma and discs is different, there is an intimate relationship between them. It is from the plasma that the discs arise, and at its expense they grow. Moreover, the tissues themselves, in their metamorphoses, impress changes on the blood ; the cells of which they are composed have an ephemeral existence, they dissolve, and the circulating fluid removes their remains and forms new ones in their stead. I doubt very much whether animals obtain ready-formed O 2 180 Prof. Draper on the Cause of the fibrine from the vegetable world. During the incubation of an egg we see this substance arising from albumen, and the analogy is probably continued in higher forms of existence. Neither is it by any means certain that fibrine exists in a state of solution in the blood. But, as we shall presently see, the probabilities are that it coagulates as it is produced by the metamorphosis of the blood, that metamorphosis being ori- ginally due to the act of respiration. Under an accelerated respiration, the discs oxidize with corresponding rapidity and the amount of fibrine increases; but if the supply of oxygen be limited, there is a restraint on the change of the discs, and the amount of fibrine declines. The ultimate products of these metamorphoses include of course all the results of the intervening stages, and those ul- timate products are chiefly water, ammonia and carbonic acid. We are justified therefore in these physiological discussions in looking at the whole process as one of oxidation, and neglect- ing intermediate metamorphoses we regard only the final ac- tion, and that action is the transmutation of oxygen into car- bonic acid, of hydrogen into water, of nitrogen into ammonia. Explanation of the General Physical Principle. — If, in a vessel containing some water, a tube of small diameter be placed, the water immediately rises to a certain point in the tube and remains suspended. Let the tube be now broken off below that point, and re- placed in the cup of water; the liquid rises as before, but though it reaches the broken extremity it does not overflow. A capillary tube may raise water to its highest termination, but a continuous current cannot take place through it. Now, suppose a rapid evaporation of the liquid to ensue from the broken extremity of the tube, as fast as the removal of one portion is accomplished others will rise through the tube, and in the course of time the vessel will be emptied. By evaporation from the upper extremity a continuous cur- rent is established ; a spirit-lamp, with its cap removed, is an example of this fact. Or, if the liquid which has risen to the upper end of the tube be of a combustible nature, oil for example, and be there set on fire, as the process of combustion goes on a current will be established in the tube, as in a common oil-lamp in the act of burning. The principle which I wish to draw from these well-known facts is, that though ordinary capillary attraction cannot de- termine a continuous flow of a liquid through a tube, there are very many causes which may tend to produce that re- sult. Circulation of the Blood. 181 Let a, b, c be a capillary tube filled with a certain liquid, between which and the tube there are at dif- ferent points affinities differing in intensity. Suppose at a the affinity between the liquid and the tube is intense, that it becomes feebler and feebler towards b, and at c has ceased altogether. Under these cir- cumstances there will be a continuous flow through the tube from a to c. To make this quite plain, let us imagine the tube a c to be formed of combustible matter of any kind, and at the point a an oxidizing liquid enters it. The liquid, as it passes along the tube, exerts its oxidizing agency, which at the expense of the tube is gradually satisfied. In successive portions of such a tube the affinity is constantly declining. It is greatest at a, diminishes as it passes along, and ceases altogether at c. Under these circumstances there will be a constant flow along the tube. A tube with an included liquid which is thus incessantly varying in its relations will give rise to a continuous move- ment. At the point of entrance, the liquid, powerfully at- tracted by the tube, rises with energy; but the chemical changes that set in, satisfying and neutralizing that attraction, to use a common expression, it loses its hold on the tube as it goes, and new quantities, arriving behind, continuously press out those which are before them. These various results may be expressed in the following general terms. If a given liquid occupies a capillary tube, or a porous or parenchymatous structure, and has for that tube or structure at different points affinities which are constantly diminishing, movement will ensue in a direction from the point of greater to the point of less affinity. Or thus : If a given liquid occupies a capillary tube, or a porous or parenchymatous structure, and whilst in that tube or structure changes happen to it, which tend continually to diminish its attraction for the surface with which it is in contact, move- ment will ensue in a direction from the changing to the changed fluid. Application of this 'principle to the Circulation of the Blood. — Let us now apply these principles to some of the circula- tions which take place in the human system, and select for that purpose the four leading forms, the systemic, the pul- monary, the portal and the placental circulation. The Systemic Circulation. — The arterial blood, which moves along the various aortic branches, contains oxygen 182 Prof. Draper on the Cause of the which has been obtained in its passage over the air-cells of the lungs, an oxidation which is indicated by its bright crim- son tint. On reaching its final distribution in the tissues, it effects their oxidation, producing heat ; and as it loses its oxygen, and receives the metamorphosed products of the tis- sues, it takes on the blue colour characteristic of venous blood. If now we contrast the relations of arterial and venous blood to the tissues, it is obvious that the former, from the fact that it can oxidize them, must have an intense affinity for them ; but the latter, as it is the result of that action after all affinities have been satisfied, must have an attraction which is correspondingly less. Arterial blood has therefore a high affinity for the tissues ; venous blood little or none. But the change from arterial to venous blood takes place in the manner I have just indi- cated ; and therefore, upon the first of the foregoing general rules, motion will take place, and in a direction from the arte- rial to the venous side. By the deoxidizing action of the tissues upon the blood, that liquid ought upon these principles to move from the arteries into the veins, in the systemic circulation. The systemic cir- culation is therefore due to the deoxidation of arterial blood. The Pulmonary Circulation. — In this circulation ve- nous blood presents itself on the sides of the air-cells of the lungs, not to carbonaceous or hydrogenous atoms, but to oxygen gas, which being the more absorbable of the consti- tuents of the air, is taken up and held in solution by the moist walls of those cells. Absorption of that oxygen takes place, and arterialization is the result. The blood from being blue turns crimson. What now are the relations between venous and arterial blood and oxygen gas ? For that gas venous blood has a high affinity, as is shown by its active absorption ; but this affinity is satisfied and has ceased in the case of arterial blood. The change from venous to arterial blood, which takes place on the air-cells which are charged with oxygen gas, ought upon these general principles to be accompanied by movement in a direction from the venous to the arterial side. The pulmonary circulation is due to the oxidation of venous blood, and ought to be in a direction from the venous to the arterial side. These considerations therefore explain the cause of the flow in opposite directions in the systemic and the pulmonic circulation ; in the former the direction is from the arterial to the venous side, in the latter from the venous to the arterial. It arises from the opposite chemical reactions Circulation of the Blood. 183 which are taking effect in the system and in the lungs ; in the former, as respects the blood, it is a de-oxidation, in the latter an oxidation. The Portal Circulation. — Two systems of forces con- spire to drive the portal blood out of the liver into the as- cending cava. 1st. The blood which is coming along the capillary portal veins, and that which is receding by the hepatic veins, com- pared together as to their affinities for the structure of the liver, have obviously this relation — the portal blood is acted upon by the liver, and there are separated from it the constituents of the bile ; the affinities which have been at work in produ- cing this result have all been satisfied, and the residual blood over which the liver can exert no action constitutes that which passes into the hepatic veins. Between the portal blood and the structure of the liver there is an energetic affinity, be- trayed by the circumstance that a chemical decomposition takes place, and bile is separated ; and that change completed, the residue, which is no longer acted upon, forms the venous blood of the hepatic veins. In the same manner, therefore, that in the systemic circulation arterial blood in its passage along the capillaries becomes deoxidized, in consequence of an affinity between its elements and those of the structures with which it is brought in contact, and drives the inert ve- nous blood before it, so too, in the portal circulation, in con- sequence of the chemical affinities and reactions which obtain between the portal blood and the substance of the liver, affi- nities and reactions which are expressed by the separation of the bile, that blood drives before it the inert blood of the he- patic veins. 2nd. The blood of the hepatic artery, after serving for the occonomic purposes of the liver, is thrown into the portal plexus. Hence arises a second force. The pressure of the arterial blood in the hepatic capillaries upon this is sufficient not only to impel it into the capillaries of the portal veins, but also to give it a pressure in a direction towards the hepatic veins ; for any pressure which arises between the arterial blood of the hepatic, and its corresponding venous blood, must give rise to motion towards the hepatic veins, no regurgitation can take place backward through the portal vein upon the blooa arriving from the chylopoietic viscera, because along that channel there is a pressure in the opposite direction, arising from the arterial blood of the aortic branches. The pressure therefore arising from the relations of the hepatic arterial blood conspires with that arising from the portal blood, and both to- gether join in giving rise to motion towards the ascending cava. 184 Prof. Draper on the Cause of the The Placental Circulation. — The umbilical arteries carry in their spiral courses, as they twist round the umbilical vein, the effete blood of the foetus, and distribute it by their ramifications to the placenta. In that organ it is brought in relation with the arterial blood of the mother, which oxidizes it, becoming by that act deoxidized itself. The foetal blood now returns along the ramifications of the umbilical vein, and finally is discharged from the placenta by that single trunk. That this is truly a change similar to that which is accom- plished in the adult lungs, is shown by the circumstance that the blood of the umbilical arteries becomes brighter on its passage into the umbilical vein. As the venous blood of the foetus is thus oxidized by the ar- terial blood of the mother, movement must of necessity ensue in it, on the same principle that it ensues in the adult lung, and must take place in the same direction, that is to say, from the venous to the arterial side. The fcetal circulation offers a very close resemblance to the circulation of fishes, and is merely a refined variety of that type. The true difference is that in fcetal life the condition of immobility is observed. In fishes the venous blood is brought to the gills, and subjected in their fibrillary tufts to the oxidizing agency of the air dissolved in the surrounding water. In these organs it therefore becomes arterialized, and is pushed into the pulmonary veins. These empty directly into the aorta, no systemic heart intervening, and the mecha- nical impulse received by the blood during its oxidation is found sufficient to carry on the aortic circulation : the heart therefore may be and is dispensed with. A fish, by sponta- neously changing its position, or by the mechanical establish- ment of currents in the surrounding medium, can obtain new surfaces of water for the oxidation of its blood ; but for the motionless fcetal mammalian a higher mechanism is required, a mechanism which can bring the oxidizing-maternal-arterial blood in relation with the branchial or placental vessels. It is true an intricate apparatus consisting of five different classes of vessels is the result, but the play of that apparatus is pre- cisely the same as in the simpler contrivance of fishes. Of the Mechanical Force with which these Motions are ac- complished.— The force by which these motions are established is not alone in the proper direction, but also of sufficient in- tensity. Some years ago I made experiments with a view of establishing this point. Some of them are inserted in the Phil. Mag. for Oct. 1838. I found that water, under such circumstances as are here considered, would pass through a piece of peritoneum, though resisted by a pressure of nearly Circulation of the Blood. 185 two atmospheres ; and the same facts were observed even in the case of gases. Thus sulphurous acid gas would pass through a piece of India rubber against a pressure of seven and one-third atmospheres; carbonic acid against a pressure of ten atmospheres; and sulphuretted hydrogen, though re- sisted by more than twenty-four atmospheres. Explanatory Remarks on the Coagulation of the Blood. — When blood recently drawn is kept in a vessel for a space of time it spontaneously separates into two well-defined portions, the one liquid and the other a soft solid — the serum and the clot. Physicians generally regard this as due to the death of the blood. Whilst it is in the system it is under the influence of the vital force; but when removed it spontaneously undergoes the change in question, and, unable to keep its primitive con- dition, coagulates and dies. Accordingly this partial solidifi- cation of the blood is looked upon as a mysterious phenome- non, and though from time to time many experiments have been made and explanations offered, that which refers it to the presence or absence of the vital principle appears to be most generally received. But it is very doubtful whether any such special power as a vital force exists. In the instance under consideration I cannot comprehend how a loss of vitality in the blood can in any manner elucidate or indeed have anything to do with the fact of its coagulation. It appears to me that what occurs to the blood when drawn is precisely the same as that which occurs to it continually when in the system. If its fibrine coagulates in the receiving cup, it tends equally so to do in the peripheral circulation. I can see no difference in the two cases. And if this be true, it obviously is a fruitless affair to be seeking for an explana- tion of a difference in habitudes in and out of the system, when those differences in reality have no existence in nature. If, when blood flows into a cup, we could by any mechanism withdraw the particles of fibrine as they agglutinate together, the phsenomenon of coagulation would never be witnessed ; and this is precisely the result in the living mechanism. The fibrine, as it passes into the proper condition, is removed by a series of events which will be hereafter explained. But whether it be in those states which physiologists designate living or dead, it exhibits continually the same tendency. When we remember that the average amount of fibrine in blood scarcely exceeds one-five-hundredth part of its weight, and that this minute quantity is sufficient, by entangling the blood-discs, to furnish so voluminous a clot, we have little 186 Prof. Draper on the Cause of the difficulty in understanding the cause of the false importance which has been attached to the fact of its coagulation. When we also remember that the phenomenon is one which, far from taking effect instantaneously, requires a considerable length of time, and estimate duly the demand that is made for fibrine by the system upon the blood, we shall have no dif- ficulty in perceiving the truth of the observation which I thus wish to bring into a clear point of view, — that the tendency to coagulation in the system is as great as it is out of it, and that the true difference in the two cases is, that in the former the resulting solid is taken up and appropriated to the wants of the oeconomy; in the latter it remains undisposed of, and, entangling the blood-discs in its meshes, produces a volumi- nous and therefore deceptive clot. It is with this matter of the coagulation of blood precisely as it was formerly with putrefaction. Many of the older phy- siologists defined a living body as a mechanism having the quality of resisting external changes. After death its parts were ultimately resolved into water, ammonia, and carbonic acid. But better views on these topics are now entertained, and we know that the living body undergoes these putrefactive changes just as much as the dead, but then in it there are appointed routes by which the resulting bodies may escape; the carbonic acid through the lungs, the nitrogenized com- pounds through the kidneys, the water through both these organs and the skin. It is in this as in the coagulation of the blood, there is no difference in the chemical changes taking place, the difference consists in the disposal finally made of the resulting products. That coagulation tends to take place equally in the living system as out of it, there is abundant proof. What are all the muscular tissues which constitute by far the larger portion of the soft parts, but fibrine which has thus been separated from the blood ? And those muscular tissues every moment are wasting away, and giving origin to the metamorphosed products that we find escaping from the lungs, the kidneys, the liver ; from what source then do they repair their waste, if not from fibrine coagulated from the blood during the act of life? Every muscular fibre is a living witness against the doctrine that it is death that brings on the coagulation of the blood. That the truth of this view, which at first sight may appear indefensible, may be more clearly made out, let us consider under what circumstances the blood is placed whilst moving in the system. We have to remember that coagulation is not an instantaneous phenomenon, but one which requires a con- Circulation of the Blood. 187 siderable lapse of time. And now, assuming the doctrine which I am advancing to be true, there are very obvious rea- sons that the blood, so long as it moves in the system, has its tendency to coagulate satisfied in a very partial manner. Let us observe its course. It leaves the left ventricle of the heart, one pulse-wave succeeding another with rapidity, and is dis- tributed through all the aortic branches. It takes but a few seconds for this movement to be complete, a period far too short to allow coagulation to take place ; it now passes on through the capillaries, or moves through parenchymatous structures ; and here, even though a great delay may occur, inasmuch as the passages are so sinuous and often so minute that the discs can move but in a single file at a time, how is it likely, under such circumstances, that coagulation should ensue ? For that to take place, it is needful that there should be a free communication throughout the mass, that each par- ticle of fibrine brought into relation with those around it may exert its plastic power and join itself to them. But in the peripheral circulation it is isolated, the cells over which it is moving, or the narrow tubes through which it goes, protect it from other particles around, and on escaping into the com- mencement of the venous trunks, it is hurried in the torrent of the circulation at once to the heart. Without delay the right auricle and ventricle pass it forward to the lungs, and if any tendency to set had been exhibited during the brief mo- ment of its passage, it is again distributed upon the capillaries of the lungs, and is situated precisely as it was when in the capillaries of the peripheral system. In this manner I regard the coagulation of blood as a sim- ple mechanical result, having no connexion with life or death, or the fictitious principle of vitality. At the two extremes of the circulation, the peripheral and the pulmonary, there is a sorting process continually going on. If a man were to agi- tate a quantity of this liquid in a tube, having a contrivance at each extremity to keep the particles of fibrine as they passed apart from one another, their plastic tendency to cohere could never be satisfied, and coagulation could never ensue. And this condition of things is, to a certain extent, approximated to in the mechanism of the body. It thus appears that by the intervention of two capillary circulations, one in the lungs and the other in the system, the coagulation of blood must be greatly retarded, though the tendency to produce that result is quite as great as when the fluid is removed from the system. And with such an obvious explanation before us, why should we resort to any occult agency, or envelope the phaenomenon in mystery, when it is plainly a mechanical affair ? 188 Prof. Draper on the Cause of the Physiologists have never given a full value to the facts, that the setting of the blood requires time and a free communica- tion through all parts of the fluid mass. If it be subjected incessantly to a mechanism which divides it into portions of inconceivable tenuity, and every moment isolates each particle from all its fellows, its coagulation must be greatly restrained. It is upon the same principle that the expressed juices of car- rots and turnips deposit a fibrinary clot, as M. Liebig and others have observed. Whilst they are enveloped in the cells of those vegetables coagulation cannot take place, for each granule of fibrine is shut out from the others. What need is there to resort to a vital principle to explain for the human ceconomy a result which equally obtains in the case of those humble plants, or why with some physiologists impute to the nervous system the quality of maintaining fluidity in the blood? These vegetables have no nerves. The application of the principles here set forth furnishes a very felicitous explanation of a great number of effects which we witness, to some of which I may briefly refer. It is well known that after ordinary death, whilst the arteries are empty, the systemic veins and also the right cavities of the heart are full of venous blood. The reason is clear, although the ordi- nary theory, that the heart acts like a pumping machine, fails, as is well known, to explain it. As long as arterial blood is deoxidizing it will move to the venous side, a movement which must continue until the arteries are empty. But it may be asked, why do not the right auricle and ven- tricle relieve the veins, and by their hydraulic action in the last moments of life push the accumulating blood through the pulmonary system ? Again the reason is clear. Movement through the lungs cannot take -place except when oxidation is going on. The systemic capillaries continuing their action long after the last breath is drawn, they make the blood accumulate in the veins, and from them there is no escape. In the same way, in fainting, the blood leaving the arteries accumulates on the venous side, and as its flow is dependent on the push of the arterial blood entering the capillaries, so soon as no more enters no pressure is exerted on the venous trunks, and if a vein is opened there is no discharge, and under such circumstances hemorrhages at once stop. After ordinary death, although the systemic arteries are empty, the pulmonary artery is full. That this should be the case is indicated upon our principles, for the blood cannot pass from the terminal ramifications of the pulmonary artery into the veins except by being oxidized. Respiration having ceased oxidation cannot take place, the movement is checked, and the blood remains in the artery. Circulation of the Blood. 189 In a paroxysm of asthma the lungs become obstructed with mucous secretions, and the rapidity of oxidation is therefore interfered with. Under such circumstances the passage of the blood is retarded, as is shown by the great dilatation of the jugular veins. Whatever therefore deranges the process of oxidation de- ranges the flow of the blood. In violent expirations, such as in coughing, the observations of Haller show that the blood moves tardily in the lungs, and in delicate persons its retar- dation is so complete that it regurgitates in the great veins. In a violent and continuous explosion of laughter, the jugular veins become excessively distended ; the right cavities of the heart having no power to push the venous blood through the pulmonary capillaries, and owing to the expulsion of air from the air-cells, the blood itself fails to effect the passage with its usual speed. In this instance it must again accumu- late in the veins. The various cases here cited depend on retarded oxidation. I might now consider the reverse of this, or where oxidation goes on too rapidly, as when protoxide of nitrogen is breathed. Owing to the great solubility of this gas in serum, and its power of supporting combustion, we should expect to find it exert that control over the circulation which is well known to be one of its peculiarities. This paper is however extended to so great a length, that here I must stop, though I have made no allusion to the movements in the lymphatics or lac- teals, or to the flow of sap in trees, or to the circulatory move- ments of the lower animals. These can all be explained upon the same principle; thus the descent of the sap follows as a necessary consequence of the decomposition of carbonic acid in the leaf. Nor have I said anything of the obvious control which certain classes of nerves have over the systemic oxida- tion. There are many facts which prove that the nervous system regulates this operation, and can either facilitate it or keep it in check. In this there is nothing extraordinary. A piece of amalgamated zinc exhibits no tendency to oxidize in acidulated water, but by the touch of si'ver or platina it is made to submit itself to the action of that medium. The act of blushing, and all local inflammations, show that changes in the relations of the nervous system control the oxidizing action of arterial blood ; but to these things I propose to re- turn on a future occasion. What is here stated is sufficient to illustrate the general principle to which I wish to draw at- tention, that the chemical changes which are impressed on these circulating fluids are the true causes of their flow. [ 190 ] XXXIV. On the Existence of Finite Algebraic Solutions of the general Equations of the Fifth, Sixth, and Higher Degrees*. By James Cockle, M.A., Cantab. ; Special Pleader-f. 7. \\T HEN y - A' xx' + A" xx" + . . + Axi.rxXi . . (n.) *V and $rm*M-.*Al * & hv and A2 having the forms of the quantities squared in (b.) J, what is the limit of n? 8. Make 3YM = /*13+j'A' + 3L" (p.) then§ j' = J?} + Ji2) + &c; (q.) but Ja2) = 0 and A", A'", disappear from j', if] J y = A!xx' + L" + Liv + Lv + ... + L» . . (r.) and I/»=A» (**"-*=. **''') (s.) So, £'' = /*23+y'A'' + l- (t.) 9. Let yr = Lf 8* + Z/» (*f - & *f ) + I, . . (u.) 1„ = 0, L = A -f /, and Z = a constant, then^f, o=y = [i1.u_1]i2t o=j"=[l1.lw_1]22k («.) 0 = liv=[l1.lra_1]3 J .*. « — 1 > 3, or 7i > 4-. . . . . . (v.) 10. Again, j' — 0 is equivalent to** y* Aiv + . -f- yxi Axi = 0-j y*A"+. + yxiAxi =0 I yfiA™ + . + yxiAxi= 0 [' ' K ' 7fAx + yfAxi = 0j j" = 0, on eliminating A2r+1, toft -y^+.+^A-^Ol viay9Aa + xy2Ax = Oj ' ' * ' K7'' liv = 0, on eliminating Avi, Ax, to J J wyi Aiv + viUy Aviii = 0 (8.) * See my presumed solution of the equation of the fifth degree, at page 125 of the last volume of this Magazine. I there used the ratios zu z2 . . . of the quantities A', A", .. to one of their number, but have here employed other ratios, or, more properly speaking, the quantities themselves. — J. C. f Communicated by the Author. J Phil. Mag., this vol., p. 132. § Ibid. S. 3. vol. xxvii.p. 126. j| Ibid. p. 293 (16.). IT Ibid. p. 126, note J, and this vol., p. 132, par. 2. ** Phil. Mag. S. 3. p. 126, line 9. ff Ibid. (/.) and (g.) XX Ibid, ifi.) Mr. Cockle on the Finite Solution of Equations. 191 1 1. Let* Liv + Lvi + . . = ;/0+/, x+ . +p\n^ xn~\ (w.) tkenf, ivSxi.L=(l+^)(//0 + ..) + . + ?„_2^-2; . (x.) and we have, in general, n quantities 1 + p, q^ . , qn~% to sa- tisfy 3 homogeneous equations 0 = j' — j" = liv, or, n quan- tities p'wP'i) .,2^n-\ lo satisfy 3 other homogeneous condi- tions (y.) and (8.), using the former n quantities to satisfy the group ((3.), non-homogeneous with respect to them; hence rc>3. ........ (y.) 12. (v.) and (y.) are not inconsistent, for, if A - l Al _ n~r + m /_ i ^"^A^- nm m and rY'n =pr — A1;jr-1?i + A2pr_2p12+ . • -^ — %-iK> (aa-) then this accented value of Y is a critical value from which 7;o» %">'•' disappear, and, since (2.) and (3.):j: are respect- ively 3Y'5 = 0,and4Y'5--i-2Y5'2 = 0, . . . (ab.) my solution would fail if n — 1 were < 4. Hence, for all cri- tical functions (y.) degenerates into (v.) ; and, after solving critical equations, we shall have quantities ^/0, q0 . . left for sa- tisfying (other) conditions whose degrees are unaffected by our previous operations. 13. However numerous might be the groups (/3.), (y,), (8.), or the relations forming those groups, it would seem that some of the A's being lost at each descending step, the limit will not be proportionally elevated. We may make 2r = (l+i>)('-%-1 + .. + ?Ll2*n-2, . . (ac.) for the A's introduced as we ascend the groups. 14. A' and A" will introduce new values of 1 +p and q into the (now to be combined) equations (2.) and (3.), or (ab.), but, as it appears to me, no new difficulty. The y's may be de- rived from the t's§, and from each other by one operation 0, and if y = © (T), then y = 0 (y), &c. ... (ad.) Grecian Chambers, Devereux Court, James Cockle, Jun. January 31, 1846. * See Sir W. R. Hamilton's " Inquiry, &c." into Mr. Jerrard's method (Sixth Report of the British Association) from [4.] p. 301 to line 9 of p. 304. f Ibid. p. 303. | Ph'l. Mag. S. 3. vol. xxvii. p. 125. § Ibid. pp. 292, S>93. L 192 ] XXXV. On some Nexv Species of Animal Concretions. By Thomas Taylor, Surgeon. [Continued from p. 46.] Resino-bezoardic Acid Calculi. T^ERY shortly after commencing the examination of the * calculi in the College collection, my attention was drawn to several concretions which possessed the easy fusibility and genei'al characters of a resin, and which were described in the MS. Catalogue as " false West Indian Bezoars," on the supposition that they were artificial compounds. The peculiar characters however of the resin of which they consisted, and their finely laminated structure, which it would be impossible to imitate, left no doubt on my mind of their being genuine bezoars, and in January 1841 I described them to the Museum Committee as consisting of a vegetable resin, derived most probably from the resinous juices of the plants on which the wild goats of the East had fed. In the same year a very interesting paper appeared in the Annalcn der Cliemie und Pharmacie, by M. Goebel, describing a new species of calculus which he had found in the Zoological Museum at Dorpat, and to which, on the supposition of its being a biliary con- cretion, he gave the name of lithofelU.iic acid. A similar cal- culus from the Pathological Museum at Gottingen was shortly after examined by Professor Wohler. The similarity in chemical characters of the concretions ex- amined by these chemists with the resinous concretions pre- viously examined by myself, rendered it certain that they were identical in composition; but as it was important to de- termine whether they were biliary calculi or simply intestinal concretions, derived from the materials of the food, I repeated at some length my experiments, but without coming to any other conclusion than that formerly expressed. The reasons which have induced me therefore to place the calculi among the intestinal calculi in the College Catalogue are as follows. In the first place, the greater number of them contain, as the subjoined analysis will show, a small quantity of a soft viscid resin, resembling a vegetable balsam. Secondly. They resemble all other concretions formed in the intestines, by having a foreign body, as a piece of wood or a seed, for their nucleus. Thirdly. They frequently attain a very large size, quite inconsistent with the notion of their being biliary concretions, or having been contained in the gall-bladder. There is one specimen in the Museum which measures three inches and a half in length, and the same in its greatest breadth. This On some New Species of Animal Concretions. 193 calculus is of a rude triangular figure; it has evidently been accompanied by other calculi, as both of its extremities possess the smooth depressed surfaces found in concretions which have been in contact with others. Another specimen, of an oval figure, is four inches in length by three in breadth. Against the notion that these concretions may have been formed from the natural or the altered constituents of the bile concreting around foreign bodies in the intestines, it may be remarked that we have no other instance of a biliary calculus being so formed*. The large biliary concretions which are sometimes passed pei- anum by the human subject, have un- doubtedly received no increase in bulk while in the intestine, but have made their way into the intestine either through an ulcerated opening or through the dilated biliary duct, which is capable of undergoing dilatation to a much greater extent than is generally imagined. The circumstance of the Oriental Bezoar being composed of a vegetable acid, as I have shown in a former paper, toge- ther with the assertion of most Oriental travellers, that the resinous concretions are found in the stomach of the animal (not a very likely spot for a biliary calculus), adds consider- able weight in favour of their vegetable origin. It is however right to state that I have not been able to detect the presence of resino-bezoardic acid in several of the known resins. Our acquaintance with these substances is however so limited that it would require a very extended series of experiments to de- termine this question in the negative. In its chemical rela- tions, resino-bezoardic acid closely resembles the pimaric acid of M. Laurent, which that excellent chemist has recently shown to be the natural acid of the fir. This fact, coupled with the circumstance that the calculi are not very uncommon, and that vast forests of pines abound in the regions inhabited D)' tne goats, render it not improbable that this resin is derived from some of the fir tribe. As the term lithqfellinic acid gives therefore an erroneous idea of the origin of these concretions, T 1 1 • I have ventured to substitute that of resino-bezoardic acid, which does not differ materially from that of "resine animale bezoardique" given to them by Fourcroy. This name will also serve to identify the circumstances under which it was first discovered, should its natural source be hereafter ascertained. * Ambergris perhaps forms an exception to this statement. This sub- stance is found in the intestines of the Spermaceti Whale, or floating on the sea. In the Catalogue I have placed it among intestinal concretions, al- though T have pointed out at the same time that it is a biliary product; its principal constituent, ambreine, bearing the same relation to the bile of the Whale as cholesterine does to that of Man. Phil. Mas;. S. 3. Vol. 28. No. 186. March 1 846. P 194.' Mr. T. Taylor oil so?ne Resino-bezoardic acid calculi are usually of an oval figure. Their external surface is smooth and polished, and has gene- rally a greenish yellow, green, or a light brown colour. They are made up of thin concentric layers, which are frequently of a deeper tint than the exterior. In the centre of the cal- culus some foreign body is invariably found which forms the nucleus. These calculi are exceedingly brittle ; the fracture is conchoidal, and has a resinous lustre. They vary con- siderably in size, but are usually larger than the ellagic acid species. One specimen in the Museum measures nearly ten inches in circumference, They melt like resin in the flame of a candle, and when more highly heated, give off white va- pours, which have an aromatic odour, catch fire, burn with a brilliant flame, and leave behind a small shining carbonaceous ash. Resino-bezoardic acid calculi readily dissolve in alcohol, with the exception of a small quantity of flocculent matter. The alcoholic solution varies in colour in different calculi, but is usually of a red or greenish-red tint. The solution gradu- ally deposits small crystals, which, when examined by the microscope, are seen to consist of low six-sided prisms with flattened extremities. When the alcoholic solution is mixed with water the resin is thrown down. The precipitate appears under the microscope in the form of small crystalline tufts. Digested in solution of potass these calculi readily dissolve, the solution is of a brownish green colour, and when neutral- ized by an acid, a thick curdy precipitate is produced, which by agitation adheres together, and while warm may be kneaded between the fingers or drawn into threads like cobbler's-wax. The viscidity of this precipitate is owing to another resinous matter which the calculi contain ; for the pure resino-bezoardic acid similarly treated forms an amorphous precipitate which cannot be made to adhere together. They dissolve in solu- tions of ammonia and its carbonate. In concentrated sulphuric acid they also dissolve. The solution is of a red colour, and is rendered turbid by the addition of water. The precipitate is not crystalline, like that from its solution in alcohol, but consists of minute transparent yellow particles. Nitric acid acts with energy upon these calculi, nitrous acid is evolved, and a light red solution is formed, which quickly becomes yellow. Analysis. About 400 grains were reduced to a fine powder, mixed with distilled water, and subjected to distillation in a glass retort until about two ounces had passed over. The distilled New Species of Animal Concretions. 1 95 liquid was quite transparent, and possessed the peculiar aro- matic odour of the calculus, but no volatile oil could be de- tected. The powder was separated from the rest of the water by filtration, and dried at 200° Fahr. It was dissolved in twelve ounces of boiling alcohol. The solution was of a bright red colour when viewed by transmitted light, and had a greenish tinge by reflected light; with the exception of a small quantity of flocculent matter it was quite transparent. In order to separate the insoluble matter, the liquid while still hot was filtered, and the matter on the filter washed with a fresh portion of alcohol and dried. This matter was of a dirty brown colour, with a shade of green. It was when quite dry rather soft, so as to admit of being moulded between the fin- gers. When heated on platina foil it did not fuse, but soft- ened, caught fire, and burnt briskly, emitting at the same time the odour of heated Indian rubber. It was insoluble in water, either hot or cold. v That this substance was not caoutchouc, was shown by its not being dissolved or softened when acted upon by absolute aether or oil of turpentine. A solution of caustic potass ex- tracted some of its colour, but did not appear to dissolve it. The exact nature of this matter I am unable to decide ; its vegetable nature is rendered probable by the total want of any animal odour while burning. It amounted to about two per cent. The filtered alcoholic solution became slightly turbid on cooling; after standing a short time small crystals were de- posited, and a crystalline crust formed upon its surface. Some of the crystals when examined by the microscope had the form of very regular six-sided plates, and others that of six-sided prisms. When a drop of the liquid was allowed to evaporate on a glass plate, and the residue examined by the microscope, crystals were formed, whose figure was not very distinct, but appeared to be that of a six-sided prism lying on its side; occasionally a six-sided plate was also visible. The liquid was put into a retort, and about two-thirds of its bulk distilled over. It was transparent while hot, but on cooling deposited an abundant crop of small crystals. These crystals had the form of three-sided plates ; when carefully fused upon a slip of glass, they were converted into six-sided plates. The crystals obtained at different times were purified by being repeatedly crystallized from their alcoholic solution, which removed nearly the whole of their colouring matter. They possessed all the characters of the lithofellinic acid of Professor Goebel, and constituted the bulk of the calculus. P2 196 Mr. T. Taylor on some The mother-liquor was mixed with water, when a precipitate separated which by agitation was converted into a viscid tur- pentine-looking substance that adhered to the sides of the glass. When a drop of the mother-liquor was evaporated on a glass plate, very few crystals could be detected, but a great number of thick, viscid oily-like drops : by heating the glass vapours arose, and a hard uncrystalline resin was left. When the alcoholic solution of the crystals was mingled with water, a crystalline precipitate was thrown down, which beneath the microscope appeared in the form of small irregularly-shaped prisms, arranged in stellate groups. This difference in the character of the two precipitates appeared to indicate that the mother-liquor contained either a volatile oil or some soft resin in addition to the crystalline resin previously described. To determine this question the whole was placed in a retort, and submitted to distillation ; the spirit came over quite free from any essential oil, merely retaining the peculiar odour of the calculus: the last portions smelt much stronger, and were slightly turbid. The precipitate had melted and formed a deep red oil, which adhered to the sides of the retort; when cold it was soft and ductile between the fingers. It was readily soluble in solutions of potass and ammonia, the solutions were rendered milky by the addition of an acid, but no pre- cipitate fell. The milky liquor when examined by the micro- scope gave the appearance of oily globules. The soft resin remaining in the retort was now divided into two portions; to the one solution of ammonia was added, and to the other aether. The ammoniacal solution was perfectly clear and of a bright red tint ; it was neutralized by muriatic acid, a viscid preci- pitate separated, which was collected together, washed, broken into fragments, and put into a glass tube together with aether. It only partially dissolved, and after standing some days six- sided prisms were found adhering to the tube, the aethereal solution was evaporated, and a resinous matter more fusible than the former was left. That portion of the soft resin which had been digested with cold aether did not entirely dissolve, but left some cry- stals of resinous matter undissolved ; the aethereal solution was evaporated, and the residue, which was quite similar to that which had been previously treated with ammonia, was mixed with it and both dissolved in alcohol, sp. gr. 0'84;0. The tincture was set aside for some weeks ; only a small quantity of crystalline matter was deposited, together with a little soft resin ; it was therefore distilled, and the residue again treated with absolute aether, in which, with the excep- New Species of Animal Concretions. 197 tion of a very small quantity of resin, it entirely dissolved. On distilling off the aether a semi-fluid viscid balsam of a dark-red colour was left, which did not solidify at the tempe- rature of the air, and acquired a pellicle on its surface by ex- posure to air. When heated a portion of it was volatilized, giving off at the same time the odour of melted caoutchouc. It readily caught fire and burnt brightly ; its combustion was unaccompanied by the slightest trace of the odour given out by animal matter. It readily dissolved in caustic potass, and the addition of an acid threw it down unchanged: it possessed a biting acrid taste, felt particularly about the fauces ; by ex- posure to the air it became a hard resin. When submitted to distillation in a small tube retort, no oil passed over until the resin had acquired a temperature at which it began to decompose, when an empyreumatic oil came over : the quantity submitted to distillation was, how- ever, too small to render the experiment quite satisfactory. The only conclusions that can be drawn from this analysis are, that the principal constituent of the calculus is a vege- table resin, which is characterized by crystallizing in the form of six-sided prisms; that it is accompanied by a small quantity of a soft resin, probably containing volatile oil ; that in ad- dition to these it contains some other substances, as colouring and extractive matter, the precise nature of which it is impos- sible to determine, but which are doubtless also of vegetable origin. M. Goebel detected in the concretion examined by him a small quantity of the colouring matter of the bile. In no one of the concretions examined was I able to satisfy myself of the presence of that substance. It is probably therefore only an accidental constituent. Its presence is however no proof of their biliary origin, since the colouring matter and other con- stituents of the bile are frequently found in hair-balls and other concretions known to be formed in the intestine. Resino-bezoardic acid,when freed from the other substances with which it is mixed in the calculus, possesses the following properties : — It slowly dissolves in cold alcohol, more rapidly in hot; according to Goebel, one part of resino-bezoardic acid requires 29"4 of alcohol to dissolve it at 68° of Fahren- heit and 6*5 of boiling alcohol ; in cold aether it is very spa- ringly soluble, 444< parts being required, but only 47 when boiling. Its alcoholic solution has an acid reaction, and the resin is slowly deposited from it in the form of short six-sided prisms. The crystals are exceedingly small ; they have ge- nerally a yellow tint, but may be obtained quite colourless by previously digesting the alcoholic solution with animal char- 198 Mr. T. Taylor on some coal : they are hard, brittle, and easily reduced to powder, in- odorous, and have a bitter resinous taste ; their summits are generally quite flat, but are sometimes bevelled at their edges. Three-sided prisms are occasionally deposited, which appa- rently result from an extension of each alternate face of the six-sided prism. The crystallized acid fuses at 4-01° Fahrenheit, and when not heated beyond that temperature becomes on cooling an opake crystalline mass. If the fused acid be heated only a few degrees above 401° Fahrenheit, it forms when cold a trans- parent glass, without the slightest trace of crystalline struc- ture : when alcohol is poured over the fused mass a number of minute cracks are suddenly formed, which possess consider- able regularity. If a thin layer of alcohol is allowed to re- main over it, the whole is quickly converted into an aggre- gated mass of regular crystals. The most remarkable circum- stance is that the melting-point of the vitreous or amorphous resino-bezoardic acid is nearly 180° lower than that of the crystallized acid, Prof. Wbhler having determined that the crystallized acid melts at 400° Fahrenheit, while the amor- phous fuses at a temperature between 220° and 230° Fahren- heit. In this respect resino-bezoardic acid resembles sugar, sulphur, amygdaline and silvic acid ; all of which bodies have two distinct fusing-points, according as they are either in a crystalline or amorphous state : this property Wohler believes to be possessed by all dimorphous bodies. The above fact may be readily observed in the following manner, which serves as a very characteristic test of resino-bezoardic acid. Let a few grains of the powdered resin be strewed over a thin slip of glass and held over the flame of a candle until a portion only of the resin is melted : if the edges of the semi- fused portion be examined by the microscope groups of very regu- lar six-sided plates are seen ; the perfectly fused portion is glassy and devoid of crystalline structure. This test does not always succeed with the raw calculus, owing to the foreign sub- stances which it contains. When heated beyond its melting- point this acid gives off* white vapours, which have an aro- matic odour ; it finally catches fire and burns like resinous bodies in general. Resino-bezoardic acid is insoluble in water and muriatic acid. It is thrown down from its alcoholic solution by water as a white precipitate, which under the microscope appears in the form of small prismatic crystals arranged in stellate groups. It is readily soluble in a solution of potass, soda, ammonia, and carbonate of ammonia, and is precipitated on the addi- tion of an acid. The precipitate at first forms a dense white New Species of Animal Concretions. 199 coagulum, but shortly becomes pulverulent ; when examined by the microscope it is not crystallized, but consists of minute transparent amorphous particles. It melts at 220° Fahren- heit, and is evidently the amorphous state of the acid. When the potass solution is evaporated a transparent gummy mass is left, which is insoluble in solution of potass, but dissolves in pure water. When the potass solution is concentrated by boiling, the compound of the resin and alkali separates from the liquid and swims on its surface ; when cold it forms a hard yellowish mass like resin, which dissolves in aether, alcohol and water. When the ammoniacal solution of this acid is evaporated, the resin separates unaltered. Nitric acid decomposes this acid ; nitric oxide gas is evolved, and a beautiful red solution formed, which quickly becomes yellow. Concentrated sulphuric acid dissolves the resino-bezoardic acid : the resin is precipitated unaltered on the addition of water in the amorphous state. 3'777 grs. of the crystallized acid, which had been rendered perfectly colourless by digestion with animal charcoal, when dried at 180° Fahr. in a current of dry air and burnt with chromate of lead, gave 3*64 water and 9*793 carbonic acid. This result agrees with the analyses of Messrs. Ettling and Will and Professor Wohler, who found — Ettling and Will. Wohler. T. Taylor. i ' 1 i * > Carbon . 71-19 70-80 70*83 71'09 70-71 Hydrogen 10-85 10-78 10'60 10'71 Oxygen . 17'96 18-42 18-57 18*58 100-00 100*00* 100-OOf 100-00 Messrs. Ettling and Will, who have analysed some of its salts, regard the formula of the crystallized acid as C42 H74 07 -f HO, while Professor Wohler represents it as C40 H70 07 + HO. Resino-bezoardic concretions were first examined by Four- croy and Vauquelin. Their account is very slight and im- perfect, but is accompanied by a very accurate drawing of a fragment of one of them. Fourcroy states, without mention- ing his authority, that they are taken from some unknown species of Asiatic or African animals, and believes them to be formed from the resinous juices of the plants on which these animals fed. In the College Catalogue I have described them as being the true Occidental Bezoar. Subsequent consideration how- * Ann. der Chem. und JPharm., xxxix. 242. f Poggendorff's Ann. der Phys. und Chem., liv. 259. 200 Lieut.- Col. Sabine on the Winter Storms ever inclines me to believe that the true Occidental Bezoar con- sisted of diphosphate of lime, and that these concretions, which Kaempfer states were termed in Persia Lapis Bezoar Occiden- talis, on account of their similarity to the concretions brought from South America, were so called from their exterior pos- sessing the same smooth polished exterior as the diphosphate of lime concretions. The concretions described by Kaempfer under the name of Coagulum JZesinosum Bezoarticum, are evi- dently identical with resino-bezoardic acid calculi ; for he says that the Swedish ambassador, on his departure from Ispahan, purchased some specimens, which, when thrown upon burning coals, melted and gave out an aromatic odour like that of co- lophony or olibanum. In the work of Clusius there is a figure of the occidental bezoar which is quite characteristic of this calculus, and Monardes asserts that they were taken from the wild goats of Persia. It is not however probable that any particular species of concretion was confined exclusively to the animals of one or the other hemisphere, since the resinous and bitter juices from which the concretions are formed exist in the plants of both divisions of the globe. [To be continued.] XXXVI. On the Winter Storms of the United States. By Lieut.-Colonel Sabine. To the Editors of the Philosophical Magazine and Journal. Gentlemen, "VTOUR meteorological readers, and especially those who -*- take an interest in the law of storms, will, I am sure, be glad to have their attention drawn to a second memoir by Professor Loomis of New York, on the phaenomena of the great storms which are experienced in the United States du- ring the winter months. In this memoir (Art. IV. of vol. ix. of the Transactions of the American Philosophical Society) two storms are investigated, one of which occurred about the 3rd of February, 1842, and the other about the 15th of the same month of the same year. The method of investigation is the same which Professor Loomis adopted in his account of the great storm of December 20th, 1836, viz. the assemblage in one view of the atmospherical circumstances simultaneously observed over the whole extent of the United States, both during the continuance of the storm and for one or two pre- ceding days. It is by this path that we may confidently hope to attain to a knowledge of the causes which produce these great atmospherical derangements j and, thanks to the spirit of the United States. 201 of co-operative labour which distinguishes the present time, we have every prospect of seeing this path successfully pur- sued. Although the memoir itself is not very long, the illus- trations which accompany it are many, and its republication in this country without them would not convey the full amount of instruction to be derived from the text and plates conjointly. Memoirs of this description scarcely admit of an abstract; there are however certain circumstances which present them- selves in so striking a manner as common to the three storms above mentioned, as to induce the belief that they may be viewed as the characteristics of a particular class of storms which occur in the United States in the winter months of every year. The circumstances alluded to may admit of a brief notice in the light of a first generalization ; and it may have the additional advantage of attracting the attention of some of your readers to the original memoir in the Transac- tions of the American Philosophical Society. We may picture to ourselves, in the first instance, a nor- mal state of the atmosphere over the United States, in the departure from which we may trace the successive phases of derangement which constitute the storm. In this normal state the wind is from the west, or a few degrees south of west, in the lower as well as in the upper current, with the thermometer and barometer at or near their respective mean heights for the time and place : the whole body of the air from the surface of the earth to its upper limit, is proceeding harmoniously in the one direction, and having blown across the greater part of the continent of America before it reaches the middle states of the union, it is extremely dry, and the at- mosphere perfectly clear. The interruption to this normal state, which in the order of time appears first to present itself, is a change in the direc- tion of the lower stratum of the air, which becomes southerly in the countries situated in the north of the Gulf of Mexico, and south-easterly in the south-eastern states. The change in the direction of the lower stratum of air is speedily followed, or perhaps it should rather be said is accompanied, by cloud, and by a rise of temperature, which progressively increase, the one in extent and the other in intensity, attended by a falling barometer. The cloud condenses into rain or snow, the area of which progressively extends till but a compara- tively small margin of cloud remains without precipitation. The thermometer continues to rise, the barometer to fall, and the rain or snow to descend, until the instant when the ab- normal winds from the south and east give place to a more violent rush of air from the west and north-west, by which 202 Lieut.-Col. Sabine on the Winter Storms the phenomena of the storm are swept onwards, and trans- ferred successively from the middle to the eastern states, and thence to the sea, with a velocity which in different instances has been noted to vary from about twenty to thirty-six statute miles an hour. The maximum of the thermometer and mini- mum of the barometer coincide generally (and with great exactness in the eastern states) with the change of the wind, the derangement of the temperature being so great as 20° and even occasionally 30° above its normal state. The description thus given was written after reading the second memoir, and was consequently drawn principally from the phaenomena of the two storms of 1842, with only a ge- neral recollection of the similarity of the circumstances of the storm of December 1836, described in Mr. Loomis's pre- vious memoir, which I had not looked into for some months. On its reperusal since, I find a condensed view of the facts of that storm at once so graphical, and by its accordance with the description drawn from the two other storms exemplifying so well their common character, that I am induced to insert it. " The principal characteristics were as follows : — After a cold and clear interval with barometer high, the wind com- menced blowing from the south. The barometer fell rapidly, the thermometer rose, rain descended in abundance. The wind veered suddenly to the north-west, and blew with great violence : the rain is succeeded by hail or snow, which con- tinues but a short time; the barometer rises rapidly; the thermometer sinks as rapidly. These changes are not expe- rienced everywhere simultaneously, but progressively from west to east." Such then are the phaenomena, and such the order of their occurrence, in a class of storms which in the winter season, and in the localities referred to, are of frequent occurrence ; that which has been described as the normal state of the at- mosphere, and that which has been described as the interrup- tion to it, appearing to follow each other in repeated succes- sion. The facts being thus before us, it is for meteorologists to consider of their explanation. When it is remembered that the temperature of the sur- face water of the Gulf of Mexico which washes the southern shores of the United States is considerably higher than the ordinary temperature of the surface water of the ocean in the same parallel ; and that the gulf-stream which coasts the south-eastern states conveys heated water into parallels where its relative difference from the ordinary ocean-temperature is even greater than in the Gulf of Mexico, we should be pre- pared to expect that the abnormal southerly and south- of the United States. 203 easterly winds should be extremely humid as well as warm ; whilst the normal westerly wind, which has crossed the rocky mountains as well as a wide extent of continent, must be ex- tremely dry as well as cold. Now the warm and moist air being once conveyed to the previously cold and dry localities where the storm appears to originate, the subsequent order and succession of the phenomena are sufficiently intelligible. The fact of which it seems most difficult to render an expla- nation, and to which therefore attention may be profitably directed, is that of the apparent tendency of the south and south-easterly winds to insinuate themselves in the lower stratum of the air, and to prevail over the regular and normal west wind, whenever the latter has moderated after its tem- porary violence. The phenomenon is confined to the lower stratum of the air, as the direction of the upper clouds is pre- served steadily from the west. Mr. Loomis suggests in ex- planation that the momentum which the westerly wind ac- quires at its period of violence causes it to overblow itself, and produces a reaction, each storm having thus, as he con- ceives, a direct tendency to produce its successor. Is it not possible that the elastic force of the vapour rising over the heated surface of the ocean to the south and south-east of the United States, and making its way to the dry interior of the continent, may have a tendency to impede and counteract the current of air proceeding from an opposite direction ? It is not inconsistent with the notion of the independence of air and vapour when at rest, that when in motion either should affect the other. It is I believe a common opinion that air in motion carries vapour with it ; the supposition here made is the counterpart of this. I remember to have heard that at New- foundland,— where the north-west (the prevailing) wind is par- ticularly cold and dry, and where the surface of the sea to the south-east is of unusually high temperature for the latitude, owing to the gulf-stream, the sea fog, as it is called, — fre- quently makes its way from seaward against the wind ; and that the wind then gradually dies away and is succeeded by a gentle breeze from the opposite or sea quarter. But whatever may be the fate of conjectures which may be hazarded before the true explanation of the phenomena shall be arrived at and generally accepted, the very clear and lucid manner in which Mr. Loomis has arranged and combined the facts which he has collected together, and the ability and true philosophical spirit in which he has discussed them, call for our grateful acknowledgements, and cannot fail to operate as a stimulus to the co-operators in theUnited States to persevere in their meteorological observations. Mr. Loomis has ex- 204 Mr. R. C. Taylor on the Anthracite pressed an earnest wish that the co-operation should be ex- tended towards the north into the countries occupied by the Hudson's Bay Company ; and it cannot fail to be seen, on reading his memoir, how much observations in that quarter are wanted for the elucidation of questions which arise. We may hope that his wishes in this respect will not be disappointed. Believe me, sincerely yours, Woolwich, February 12th, 1846. Edward SABINE. XXXVII. On the Anthracite and Bituminous Coal-Fields in China. By Richard Cowling Taylor, F.G.S.* WE have seen the recent announcement of the sailing, from hence, of a vessel containing 308 tons of Pennsyl- vania anthracite, destined for Hong-Kong in China. Some very natural speculations have arisen from this circumstance, as to the probability of that remote country furnishing a market for American anthracite. As no details accompany the state- ment alluded to, we are not in possession of any material facts whereby an estimate can be formed of the probable success of the undertaking, in a commercial sense ; and we are not sure but the coal may have been employed for convenience merely, as ballast. In the East Indies various depots of European coal have been established, for the service of the British government steamers. This fuel, for the most part, it is understood, con- sists of the anthracitous and partially bituminous coals of South Wales, of course obtained at great expense. It appears that 5000 tons of English coal, at a freightage of about £2 per ton, are annually imported into Bombay, for the Company's steamers. Bituminous coals have been derived from much less distant sources ; among which the Burdwan coal-field, in the vicinity of Calcutta, may be named. Mergui Island, also, in the Bay of Bengal, has lately furnished some steam coal to Singapore. The steam ships on the China seas, during the war with that vast country, were supplied from these various sources. I do not propose to discuss the profitableness, or otherwise, of a Chinese market for our American anthracite. But as during the process of collecting statistical information for a proposed volume on " The Geological and Geographical Dis- tribution of Coal and other Mineral Combustibles \" some * From a pamphlet communicated by the Author. \ See in Philosophical Magazine, vol. xxvi. p. 263, the Prospectus of this work, by Mr. R. C. Taylor, for which subscriptions are received by Messrs. Wiley and Putnam. — Ed. and Bituminous Coal-fields in China. 205 notes reached me, of an interesting character, which are not generally accessible to the majority of readers, with relation to the Chinese coal-fields, it has struck me that a portion of these details, in an abridged form, might be just now acceptable, particularly as the intercourse with that country is on the in- crease. I venture even to omit, for the present, the author- ities for the facts I shall have to communicate ; reserving them in detail for the volume adverted to. It must, neverthe- less, be premised that to the Jesuit Fathers, the French Mis- sionaries who were permitted to reside at Pekin during the 18th and preceding centuries, we are indebted for details of the highest interest, not alone on this subject, but on many other objects of philosophical inquiry in that little-known region. It is probable that coal was discovered, and was in common use in China, long before it was known in the western world. It is mentioned by a noble traveller of the 13th century, as abounding throughout the whole province of " Cathay " of which Pekin is the capital, " where certain black stones are dug out of the mountains, which stones burn when kindled, and keep alive for a long time, and are used by many persons, notwithstanding the abundance of wood." The good missionaries were fully capable of describing the coals which were supplied to Pekin, since they there erected a furnace or stove, in which they experimented on the proper- ties of those combustibles ; particularly with reference to the ordinary domestic uses, and for the warming of apartments and the purposes of their laboratory. Among the people of Pekin three kinds are in use. 1 . That employed by the blacksmiths. It yields more flame than the other qualities ; is more fierce, but is subject to de- crepitate in the fire ; on which account, probably, the black- smiths use it pounded in minute particles. 2. A harder and stronger coal, used for culinary purposes, giving out more flame than the other sorts so employed ; it is less quickly consumed, and leaves a residuum of gray ashes. There are several gradations of these. The best are hard to break, of a fine grain, a deep black colour, soiling the hands less than the others. It sometimes is sufficiently siliceous to give fire with steel. Others have a very coarse grain, are easily broken and make a bright fire, leaving a reddish ash. Another species crackles or decrepitates when first placed on the fire, and falls down, almost entirely, in scales, which close the passage of the air, and stifle the fire. 3. A soft, feebly burning coal, giving out less heat than the 2nd class ; consuming more quickly, it breaks with greater fa- cility, and in general is of deeper black than the sorts previ- 206 Mr. R. C. Taylor on the Anthracite ously mentioned. It is commonly this description which, being mixed with coal-dust and a fourth part of clay, is em- ployed to form an artificial is ceconomical fuel. This being moulded in the form of bricks and balls is sold in the shops of Pekin. Wagon-loads of coal-dust are brought to that city for this sole purpose. The coal merchants have also an intermediate quality be- tween the classes 2 and 3. We cannot in this place recite the numerous details which are furnished by these intelligent Fathers. Suffice it to add, that nearly the whole of the properties and applications are now in every- day use in the United States, and are familiar to all. They are, in fact, the natural results suggested by quali- ties possessed in common by the combustibles of remote parts of the same globe. Even the modern method of warming all the apartments of our dwellings, which we view as the result of superior practical and. scientific investigation, was in use, with very little deviation, centuries ago by the Chinese. Many a patented artificial fuel compound both in Europe and Ame- rica, has been in practical operation in China at least a thou- sand years. 4. Anthracite. — Another description of coal abounding about thirty leagues from Pekin, but which was not then in such general use there as the other kinds, is called by the Chinese Che-tan. Che means a stone, but tan is the name they give to wood-charcoal. Therefore, according to the ge- nius of the Chinese language, this compound word signifies a substance resembling or having the common properties of stone and charcoal. There can be little difficulty here in re- cognising the variety of coal which in our day has been de- nominated anthracite, a compound word of similar meaning. The Chinese glance coal forms a remarkable exception to the unfavourable conclusion prevailing against Oriental coal ; and, according to more recent authority than those we before cited, deserves to rank at the head of the list, in respect of its purity as a coke, although in specific gravity it does not come up to the character of the Pennsylvania or Welsh fuel ; neither has it the spongy texture which contributes much to the glowing combustion of the latter. So late as 1840, a Russian officer has described the coal formations of the interior, as occupying the western mountain range of China, in such abundance that a space of half a league cannot be traversed without meeting with rich strata. The art of mining is yet in its infancy among the Chinese ; not- withstanding which, coal is thought to be at a moderate price in the capital. Anthracite occurs in the western range of and Bituminous Coal-fields in China. 207 mountains at about a day's journey, or thirty miles only from Pekin. The coal formation is largely developed, in which thick beds of coal occur. They appear to be of various qua- lities. Some of this coal, occurring in shale beds, is singularly decomposed, and its particles have so little cohesion, that they are almost reduced to a state of powder. Beneath these coal shales are beds of ferruginous sandstone, and below those occur another series, consisting of much richer seams of coal than the upper group. In this range are seen also both horizontal and vertical beds of conglomerate, accompanied by seams of coal which have the conglomerate for the roof and diorite or greenstone for the floor. As might be expected, this coal very much resembles anthracite. It is shining, of compact texture, difficult to ignite, does not flame in burning, or give out any smoke. Its sub- stance is entirely homogeneous. Every thing respecting it leads to the belief that there had been a great development of heat at the period of its formation, or subsequently. The horizon- tal coal beds are the most important and valuable, and are denominated large ; but no greater thickness than three and a half feet is quoted. The blacksmiths and those who work in copper, prefer this coal, on account of the intense heat which it gives out. Throughout the whole of this mountain range may be con- tinually seen the outcrops of this combustible, where they have never, as yet, been touched by the hand of man. In those parts of China where wood is very dear, coal is worked on a great scale for the Pekin market : but the process of mining is very little understood by those people, who excel in the preparation of charcoal. Coal in other parts of China. — The Missionaries and others inform us that coal is so abundant in every province of China, that there is perhaps no country in the world in which it is so common. The quays at Nankin are stored with the finest native coal. Some of the coal which was brought down to the coast, from the Pekin country, to the Gulf of Pe-tchee-lee, was anthracite, partaking of the character of plumbago or graphite. Coal, apparently of the brown coal species, exists extensively in the direction of Canton ; while all the coals seen on the Yang-tse-kiang river, south of Nankin, resembled can- nel coal. Nearer to Canton it possessed the comparatively modern characterof the brown coal. It was abundantly offered for sale in the different cities through which Lord Amherst's embassy passed, between the lake Po-yang-how and Canton, and the boats were largely supplied with it. It is there ob- tained by means of pits, like wells \ and we infer that, like 208 Mr. R. C. Taylor on the Anthracite nearly all the brown coal deposits, the beds were horizontal, and at no great depth. A sulphurous coal, interstratified with slate, and in the vicinity of red sandstone, also prevails towards Canton. Thus, therefore, we possess evidence, the main object which this communication was designed to exhibit, that extending over large areas in China, are beds of tertiary or brown coal, of cannel coal, a dozen varieties of bituminous coal, of anthra- cite, glance coal, and graphitic anthracite; all of which, for ages, have been in common use in this remarkable country, and have been there employed for every domestic purpose known to civilized nations of all times ; including gas lighting, and the manufacture of iron, copper, and other metals. Mode of Mining Coal in China. — It might be expected that in China, where most of the practical arts have from time im- memorial been carried on with all the perseverance of that industrious people, the operations of mining coal would be conducted with some regard to science, in relation to sinking, draining, and extraction. We have, however, good authority, especially in regard to the environs of Pekin, for stating that the process is still in a very imperfect state. Machinery to lighten labour is there unknown. They have not even an idea of the pumps indispensable to draw off the water. . If local circumstances allow, they cut drainage galleries ; if hot, they abandon the work whenever the inundation has gained too far upon them. The mattock and shovel, the pick and the hammer, are the mining instruments — the only ones, in fact, which the Chinese employ in working the coal. The water of the mine is emptied by the slow process of filling small casks, which are brought up to the surface by manual labour. Vertical shafts are not used. In working horizontal coal seams, the timbering is expensive, and the materials cost about two copecs per poud, = ^8,50 per ton, English wood being sold by weight in China. The coal, when mined, is put into baskets and drawn upon sledges, which are raised to the surface by manual strength. Each basket contains about three pouds of coal, and one man can raise about eight baskets in a day. This is equivalent to 1032 Russian pounds, or to 12 cwt. English per day. The miners' wages are at the rate of 30 copecs a basket ; which is equal to 240 copecs (copper currency), or 46 cents of United States currency, per day ; being ^0,76 U. S. per ton. Prices at Pekin. — At the pit's mouth, this coal is sold for 60 copecs per poud, = ^4,63 per ton of 20 cwt. It is then conveyed on the backs of mules, through the mountains, and thence on camels to Pekin, where the price is 1^ rouble, and Bituminous Coal-fields in China. 209 = 1£ franc,=29 cents United states, per poud; which, if our calculation be correct, is equivalent to «#" 11,60 United States, or £2 8s. 3d. per ton of 2240 pounds English. We perceive, therefore, that the best of fuel is expensive at Pekin, and hence the necessity for resorting to the artificial com- pounds and substitutes to which we briefly alluded. There is, however, a kind of coal sold in that city at a much lower price, particularly when it is mixed with one-half of coal- dust. This coal, in 1840, sold for one rouble per poud, which is at the rate of ^7*75, = £1 12s. 3d. per ton. It is of in- different quality, however ; giving out but little heat, and is quickly consumed. The compound fuel, consisting of coal-dust and clay, is still prepared after the mode described by the Missionaries last century ; but its use is chiefly confined to the indigent classes. Coal Gas Lighting in China. — Whether, or to what extent, the Chinese artificially produce illuminating gas from bitu- minous coal, we are uncertain. But it is a fact that sponta- neous jets of gas, derived from boring into coal-beds, have for centuries been burning, and turned to that and other cecono- mical purposes. If the Chinese are not manufacturers, they are, nevertheless, gas consumers and employers on a large scale ; and have evidently been so ages before the knowledge of its application was acquired by Europeans. Beds of coal are frequently pierced by the borers for salt water ; and the inflammable gas is forced up in jets twenty or thirty feet in height. From these fountains the vapour has been conveyed to the salt-works in pipes, and there used for the boiling and evaporation of the salt ; other tubes convey the gas intended for lighting the streets and the larger apartments and kitchens. As there is still more gas than is required, the excess is con- ducted beyond the limits of the salt-works, and there forms separate chimneys or columns of flame. One cannot but be struck with the singular counterpart to this employment of natural gas, which may be daily witnessed in the Valley of the Kanawha, in Virginia. The geological origin, the means of supply, the application to all the pro- cesses of manufacturing salt, and of the appropriation of the surplus for the purposes of illumination, are remarkably alike at such distant points as China and the United States. Those who have read, even within the present month, the account of the recent extraordinary additional supply of gas, and the services it is made to perform at the Kanawha salt-works, must be impressed with the coincidence of all the circumstances with those which are very briefly stated in the previous para- graph in relation to China. In fact the parallel is complete, Phil. Mag. S. 3. Vol. 28. No. 186. March 1846. Q 210 On the Anthracite and Bituminous Coal-fields in China. To the coals .and combustible minerals of China, I cannot further advert here. But what a conviction irresistibly presses upon the mind, as to the incalculable utility of the railroad system, and coal-mining improvements, in such an empire ! If ever there were concentrated at one point all the circum- stances especially and unequivocally favourable to that system, and imperiously calling for improvements of the character suggested, it seems to be presented in the case of the city of Pekin. Here, with its enormous population of 1,500,000 souls, it is situated only at a day's journey — computed at thirty miles — from an immense region of coal, comprising several varieties. Yet its inhabitants cannot purchase the best qualities of this coal, brought from the mountains on the backs of mules and camels, under &1 1,60 per ton, and the very worst for less than % 7375 per ton. Without making unnecessary or invidious comparisons, it might not unreasonably be suggested, that a Pekin railroad, in connection with the coal mines, would be a far more profit- able enterprise in its results, than the transportation of Ame- rican coals to China. I will only add one circumstance, which had nearly escaped me. Borneo, " the largest island in the world,"' which is only twenty degrees due south of Canton, has lately come into re- pute for the great quantity of coal which it contains, not only accessible to ships along the coast, but extensively occurring in the mountains of the interior. Much information has also been acquired from the natives ; and the facts which are al- ready elicited are regarded as of considerable importance, in respect to the facilitating the steam navigation in the China seas. Philadelphia will, of course, have her share in the en- larged commercial intercourse with China. Would it, then, be asking too much of those who are personally interested in this improving trade, to communicate any additional facts, which are either unknown to, or have been omitted by, the author of these scanty notes ? Respectfully, Philadelphia, April 28, 1845. Richard C. Taylor. Note. — The prices and admeasurements which are quoted in the fore- going article, were reduced to the United States and English currencies and measures from the Russian, as furnished by the Engineer Kovanko; who, in like manner, converted them into the Russian from the Chinese standards. In consequence of this triple conversion of standards, addi- tional care has been taken to avoid error in these calculations. [211 ] XXXVI IT. On the Conversion of the solid Ferrocyanide of Potassium into the Sesqui-ferrocyanide. By C. F. Schosn- bein*. N a former notice I have shown that a solution of the yellow prussiate of potash in water, placed in contact with an atmosphere of ozone, instantaneously destroys the latter, and is converted into the red sesqui-ferrocyanide. Since that communication was made I have ascertained that even the solid yellow salt very readily absorbs ozone and is changed into the red one. If a crystal of the common prussiate is suspended in a balloon containing an atmosphere strongly charged with ozone, and kept in that state by means of phos- phorus and water, it will soon assume the colour peculiar to the red cyanide, just in the same way as it would do when held in air containing chlorine. The surface of the crystal, after having remained in the ozonized air for about twelve hours, is changed into the red salt, which may be easily se- parated from the yellow nucleus by mechanical means. A crystal of about a cubic inch in bulk appeared after thirty- six hours' suspension in ozonized air covered with a crust of the red cyanide, at least one line thick; and in another case I saw a smaller crystal of the yellow salt entirely con- verted into the red one. I hardly need say that by changing the yellow compound into the sesqui-ferrocyanide, the cohe- sive state of the former undergoes a material alteration. The red crust surrounding the yellow nucleus is rather brittle, and consists of a heap of small crystals of the sesqui-ferro- cyanide. It is worthy of remark, that under the circum- stances mentioned the yellow prussiate becomes moist, and exhibits in that state a very strong alkaline reaction. XXXIX. On the Decomposition of the Yellow and Red Ferro- cyanides of Potassium by Solar Light. By C. F. Schcen- bein*. A SOLUTION of the yellow prussiate of potash kept in r*- the dark does not change its colour, but when exposed to the action of solar light it becomes of a deeper yellow. To render that change very perceptible, a weak, i. e. nearly co- lourless, solution must be used, in which case the liquid will assume a yellow colour after having been acted upon by strong sunlight only for a few minutes. If the bottle containing the solution be closed and not quite filled with the liquid, an odour of prussic acid is perceptible, and at the same time * Communicated by the Author. Q2 212 Prof. Potter on Physical Optics. a reddish yellow sediment subsides, which seems to be the peroxide of iron. The decomposition of the cyanide takes place much more rapidly when strips of filtering paper or linen are immersed in a solution of the salt and exposed to the action of solar light. In a very short time that part of the strip turned towards the sun becomes yellow, whilst the opposite side remains colourless, or nearly so. If strips of paper moistened with the solution of the common prussiate of potash are closed up in»glass bottles containing air, they also turn yellow by exposure to the sun, and a strong smell of prussic acid is perceptible in the vessels after a short time. In the shade no such action takes place. A large piece of linen cloth drenched with a solution of the yellow salt, after having been exposed in the open air to the action of solar light for thirty-six hours, had turned deeply yellow, and yielded, when treated with distilled water, a deep yellow solution, which on being filtered and heated to boiling became turbid, and depo- sited flakes of peroxide of iron. The same solution exhibited a stronger alkaline reaction than the solution of the common prussiate does. From the facts stated, it appears that the yellow ferro-cyanide is decomposed by light into prussic acid, oxide of iron and potash, and a compound formed yielding with water a yellow solution. Is that compound carbonate of potash and peroxide of iron ; and do the constituent gases of the atmosphere take part in the decomposition besides the solar light ? Further experiments must answer those ques- tions. A limpid solution of the red cyanide also becomes turbid when exposed to the action of solar light, prussic acid being evolved and peroxide of iron thrown down. XL. A Reference to former Contributions to the Philoso- phical Magazine, on Physical Optics. By Prof. Potter, A.M., F.C.P.S., late Fellow of Queen's College, Cambridge, $c* "l^TITHOUT the slightest wish to interfere in the contro- ™ ™ versies of others, I now beg to refer the readers of the Philosophical Magazine to my papers in the Magazines for January 1840 and May 1841. In the former, at page 20, I have shown Mr. Green's formula for the intensity of reflected light to fail entirely as a representation of nature ; and in the latter I have shown the peculiar refraction near the optic axes of biaxal crystals not to be represented by Sir William Ha- milton's analytical deductions from Fresnel's equation to the wave surface in biaxal crystals. * Communicated by the Author. On Differentiation as applied to Periodic Series. 213 The anonymous correspondent Jesuiticus in the last Num- ber, refers to those analytical researches triumphantly in fa- vour of the undulatory theory of light. I do not write to dis- turb the philosophical opinions of Jesuiticus, but to remind the readers of the Magazine where they will find the discus- sion of the points referred to. XLI. On Differentiation as applied to Periodic Series : with a Jew Remarks in reply to Mr. Moon. By J. R. Young, Professor of Mathematics in Belfast College*. F in the general expression at p. 430 of my paper on Periodic Series, in the last volume of this Journal, A be made equal to —1, we shall have the identity 1 a n t , « a o . COS (w + 1 ) fl + COS M 0 — = cos0 — cos 2 9 + cos 3 9— &c. -\ „ ,' — — tt ; 2 - 2(l+cos0) * and if we multiply this by d 0, and integrate, we shall further have 6 | J — = sin 0 sin 2 0 -f — sin 3 0 — &c. 2 2 ' 3 1 ±f cos (n -f 1)0 + cos n 0 , . 2(1 + cos0) Now it is demonstrable, from other and independent princi- ples, that, when n is infinite, the right-hand member of this equation, omitting the integral, is the true development of t — , for all values of 0 not exceeding it. Hence we may infer Z that, for n =s oo , this integral is necessarily zero. If we sup- press it therefore, we shall commit no error in the expression 0 for — ; but a very considerable error will be introduced if we S5 attempt to derive from that expression, thus limited to the particular case of n = oo , a series of other equations, by the aid of differentiation, as is commonly done. If the evanescent integral be restored, we may then apply the process of differ- entiation as far as we please : our resulting equations will all be identical equations ; holding, whatever be the value of w, and supplying the necessary corrections of those erroneous developments which, in the case of n = oo , are so commonly met with in analysis. I have elsewhere observed that differentiation fails to be applicable to the series * Communicated by the Author. 214- On Differentiation as applied to Periodic Series. a 111 — = sin 0 — — sin 2 9 + — sin 3 0 r sin 4 0 + . . . . 2 2 3 4 in the isolated case of n == oo ; and it is plain that in this case — sinra0 is 0, though sinw0 is itself indeterminate ; the inde- terminateness is therefore rendered nugatory. But if differ- entiation be allowed, this indeterminateness reappears in cos ii 0, in the right-hand member of the result, though the left-hand member remains determinate, which is absurd. Still we are not precluded from applying differentiation to the general forms above, since these are universally true ; they comprehend all values of w, and are identical. It is in virtue of this identity, and of this alone, that the results of differen- tiation may safely be extended to n = oo , although for this isolated value of n differentiation be inapplicable. I have very little to say in reference to Mr. Moon's attack in the last Number of this Magazine. The papers which have called it forth, — whether justly or not, I leave others to deter- mine,— Mr. Moon confesses that he does not understand ; and humiliating as such a confession may seem, the whole tenor of his remarks shows that he is sincere. I beg to say, that I did not write expressly for Mr. Moon, and Mr. Moon therefore cannot reasonably expect that I should attend to his demand, and define the terms I use. I have employed nothing but the recognised language of ana- lysis, and I cannot undertake to encumber the pages of this Journal with a glossary of scientific terms for Mr. Moon's especial benefit; if he will only take the trouble to turn to the Penny Cyclopaedia, Mr. De Morgan will fully instruct him in all these things. The occasion of my mentioning Mr. Moon's name was this : — I found Mr. Moon, in the June Number of this Magazine, floundering amidst difficulties which he showed himself un- able to cope with. I had long previously contemplated a paper, of which the main object was to remove those difficul- ties, and in drawing it up for this Journal, I could not well avoid the mention of Mr. Moon's name. But I mentioned it with the most scrupulous courtesy and i*espect; I was espe- cially anxious on this point, on account of the peculiarities which Mr. Moon had so often displayed in his published communications; so anxious indeed was I to avoid offence, that — at the risk of losing all credit for discrimination — I even went the length of calling him "an able contributor to this Journal !" As I have already said, I did not certainly write Mr. Moon in Reply to Jesuiticus. 215 expressly for Mr. Moon, but the instruction conveyed to him through my short papers, was precisely that of which he ob- viously stood in need. Instead of accepting this with thanks, he ungratefully turns round and bites the hand that brings him aid ; and, not content with this, he is ungenerous enough, artd unjust enough, to say, that everything in those papers, which is not erroneous, has already been given by himself! Belfast, February 9, 1846. J. R. YoUNG. [We omit the remainder of Mr. Young's letter, in which he animadverts upori Mr. Moon in terms which the communications of the latter seem well-calculated to provoke. The same discretion has been exercised with regard to some parts of Mr. Moon's letter in the present number, as from the character which the controversy has assumed, we are not disposed to devote any more of our space to its continuance. — Edit.] XLII. Mr. Moon in Reply to Jesuiticus*. A FTER the notice which appeared in the last Number of :**■ this Journal respecting his previous papers, there would be an obvious impropriety in the writer of the following re- marks attempting to force on the Editors of the Magazine any matter which would tend to produce further discussionf on the subject to which he has of late called attention, except so far as he be driven to do so in self-defence. As, however, the views to which the Editors afforded the means of publication have been openly attacked in this Journal, their author con- ceives he has a right to say a few words in their behalf. An anonymous writer, who subscribes himself Jesuiticus, commences certain animadversions on my first paper on Fres- nel's Theory of Double Refraction, by the remark, that " the hypothesis on which FresnePs Theory of Double Refraction is based is the following : — ' That the displacement of a mole- cule of the vibrating medium in a crystallized body is resisted by different elastic forces according to the different directions in which the displacement takes place.' " He then proceeds to make some remarks on the reason- ableness of this hypothesis, which it is not my present pur- pose to dispute; but I must beg to observe, en passant, that the above is not the hypothesis on which FresnePs Theory of * Communicated by the Author. + We omit some portions of Mr. Moon's communication, where he ap- pears to us to have lost sight of his declared purpose of confining himself to self-defence, and has introduced matter " tending to produce further discussion." — Ewt. 216 Mr. Moon in Reply to Jesuiticus. Double Refraction is based. It rests on a lower level still. The true basis of the theory is, that the eethereal medium consists of particles separated by finite intervals (to use a well- known, but improper mode of expression), and acting upon each other by their mutual attractions. From this principle, the so-called fundamental hypothesis of Jesuiticus is a suffi- ciently easy inference : I have thought it necessary to remark upon this inaccuracy, however, as from the extraordinary want of precision of the writers on this subject, it is somewhat dif- ficult to say what is their real starting-point ; at the same time, that in order to make a proper estimate of Fresnel's theory, and of the skill and judgement with which he has worked it out, it is very desirable that that fact should be clearly ascer- tained. Jesuiticus afterwards goes on to say, "It is then proved, that if any particle of the eether be suddenly displaced, the other particles remaining quiescent, the force of restitution developed by such disturbance will not in general be in the direction of the displacement, but only when such displacement is in the direction of the aforesaid axes of elasticity. The elegant de- monstration of Mr. Smith, quoted by Mr. Moon, is by Mr. Moon's own showing fully adequate to establish the theorem as I have enunciated it, which is doubtless the sense in which Fresnel conceived it." I admit that Mr. Smith's demonstration is fully adequate to establish the theorem as Jesuiticus has enunciated it, but I must beg to assure Jesuiticus, that unless the demonstration establishes a great deal more than the theorem so enunciated, it is not, for the purpose for which it is adduced, worth the paper it is written upon. What is the use of considering the impossible case of a single particle suddenly disturbed while all the other particles remain quiescent, and then reasoning upon what takes place in the beginning of the motion in that case, as if the same held good throughout the whole motion in the actual case, when all the particles are vibrating together, when it is perfectly certain that it does not? Jesuiticus says, "Any one who understands the subject must at once acknowledge that any theory of light must be, to a considerable extent, imaginative ; and that theory which can explain the greatest number of facts ought to claim the attention of the philosopher more than any other." Of the justice of the remark contained in the first part of the above sentence, Fresnel's theory is no doubt a remarkable confirma- tion ; in the sentiment of the second clause of it I am disposed to concur, with the reservation that some portion of the credit due to a theory depends on its antecedent probability. But Mr. Moon in Reply to Jesuiticus. 217 mark what follows: — " It is to this that the undulatory theory owes its great celebrity, and of all parts of the undulatory theory, that of double refraction is the most extraordinary. It ought to be regarded as a stupendous monument of human ingenuity. It must not be forgotten how admirably the pro- perties of uniaxal crystals follow from the general investiga- tion of the biaxal class ; but above all, how from this same investigation, conical and cylindrical refraction were disco- vered by Sir William Hamilton." I would ask of Jesuiticus, what is the hypothesis upon which Fresnel professes to explain the separation of the ray ? Whether it is not substantially what I have stated it to be in the early part of this paper ? And if so, I appeal to the world whether 1 have not shown incontrovertibly in my two papers on this subject contained in the last two Numbers of the Phi- losophical Magazine, that Fresnel entirely fails to explain the separation of the ray on that hypothesis. It may be true that some of Fresnel's expressions for the disturbance in doubly refracted and other polarized waves may involve in them cer- tain elements of truth (though for my own part 1 should be sorry to answer for any of them) ; but they do not on that ac- count afford any evidence of the truth of his principles, for this plain reason, that they do not follow from them. It may happen, that from the ruins to which this great theory must soon, if it be not already reduced, may be gathered some useful fragments which may form part of a new and more du- rable edifice ; but Jesuiticus may take my word for it, or if he do not choose to do that, he will not have long to wait for the verification of the prediction, that the time is at hand when Fresnel's theory will be considered as a " stupendous monu- ment " of anything else but ingenuity. As to the supposed discoveries of conical and cylindrical refraction, if Jesuiticus had been aware of their very doubtful character, he would hardly have ventured to have brought them so prominently forward. #i; '*•'•»' • * As to the investigation which I examined in the first of my two papers, I do not doubt that Mr. Airy considered it merely as an illustration ; but even in that point of view, and without adverting to the error which I pointed out in his reasoning, it would be entirely worthless, as it is obvious that the state of things he contemplates could only exist for a single mo- ment, whereas the results he deduces are supposed to be always subsisting. His object is to show that an undulation consisting of transversal vibrations might be propagated ac- cording to a certain law, when even on his own premises it is quite obvious that if the disturbance originally communicated 218 Mr. Moon in Reply to Jesuiticus. were of that character, it would immediately cease to be so, or in short, that a transversal undulation (if I may be per- mitted the expression) would not be propagated according to any law. With a full sense of the value of Mr. Airy's con- tributions to other departments of science, I cannot shut my eyes to the fact, that by allowing such investigations as the one under consideration (which but for its adopted parentage would not be worth a comment) to pass not merely Avithout censure, but with apparent sanction, he has introduced an absence of precision, — a laxity of principle (so to speak) into mathematical inquiries, which has produced the most injurious effects both in the mixed and the pure sciences. But to come to the error which Jesuiticus imagines he has found in my reasoning. He says, " that in substituting for u, and for w', du7 d*u W 0 du 7 d? u h2 n dx d xz 1 . 2 the substitutions stopping at 7i2, merely require that h should be small in comparison with the length of a wave, not in re- spect to u" It is true that if we suppose the initial disturbance to be 2 TV represented by a sin — (v t — x), the substitutions stopping at /i2 are defensible on the ground suggested by Jesuiticus ; but does Jesuiticus conceive that when Mr. Airy wrote out this demonstration, he ever thought about the length of the wave, or any other circumstance connected with the initial vibration ? If he does, I can only say that he is a very extraordinary per- son. In my paper I took Mr. Airy's investigation for what it purported to be, namely a proof that a certain hypothesis as to the disposition of the particles and the nature of their mutual action, without reference to the form of the initial dis- turbance, leads to the conclusion that transversal undula- tions may be propagated ; and in that point of view I have no hesitation in saying it entirely fails ; and, independently of all others, on the ground I have pointed out, i. c. of false approximation. If Jesuiticus has any doubt as to whether Mr. Airy did or did not consider himself to have proved the proposition generally, I would recommend to his attention Art. 127 of Mr. Airy's Tract, in which he takes the general integral of the equation Royal Society. 2 1 9 Jf~ n \ 2U h dt* to wit, u =

and o —• -" ■^CO^^CO^^UO^rf^Tt^-^T?T^T^^T^-<^Tr''^Tt-'3'"*t-e*CyiCOUOUOe^COUo6oOCOUO-''*e*-* CU-- •uik xbk IOf- CICOOM^MC OMNtM«00OO>-'HC<5Tj--iniO -*»g ©1 6 6* 6l 6i ON 6\ 6 6 6 WOlOlCTlOMJMJiCTidlOl^OO OM^OOQO ON ON ON ON CI *9 ooooMtM«sot)>ntNno«>ociO(NiOTro-iMooiot^oinio in»"*o win C0-ococ,5-ioiocifnoioin'*i>9 crie,o\rig\oo on 6 6 6 6 6 6n6n6i6n6i6n6noo on ob oo oo onoo oo on on on on on •WBf8 •uojsoa •q;aoH JO S^BQ 00 ^ loin r-iio ff\t>oD -h «- — ' oo^c^co^uouo— i^— up^otONop©©,— uo uo on 6 6 on 6\ on on 6 6 6 6 6>6non6i6n6nononoo onoo oo onoo oo on on on o> on c*cocoe*oie^oiococococ>iC}c^c^cNc^c*c^cie>'n<»oci'^ocnnP5»iM(<)oou5 y oo — ■ io r-» r- r~- © cVi<^d"iO o o i^c^6>i6 cr> CO CO CO «M (M * o ON CO ob 6^ UO CO — o O CO < ' CO 00 1 CO* -" co coco co Tf -* I© CTiCTl o ' THE LONDON, EDINBURGH and DUBLIN PHILOSOPHICAL MAGAZINE AND JOURNAL OF SCIENCE. ♦ [THIRD SERIES.] APRIL 1846. XLV. On the Oscillations of the Barometer^ with particular reference to the Meteorological Phenomena of November 1842*. By William Brown, Jun.\ [With Six Plates.] IN order to illustrate and confirm the views I have before advanced in this Magazine (vols. xx. and xxiii.), on the connexion between the direction of the currents of the atmo- sphere and the oscillations of the barometer, I have endea- voured to make a direct application of them to the explana- tion of the various phaenomena presented by the winds in this country during a great portion of the month of Novem- ber 1842, that month including an extremely unsettled and stormy period of weather. For this purpose, I have col- lected observations showing the state of the wind and the ba- rometer in various parts of this kingdom, and also at Chris- tiania in Norway, and at Paris; and exhibited the direction of the wind on diagrams, with the variations of the barometer in hundredths of an inch annexed. The data from which the diagrams are constructed, and which are given p. 262, with the exception of those for North Shields, the place of my own register, are extracted from the Shipping and Mercantile Ga- zette Newspaper; a newspaper containing daily reports from most of the parts of Great Britain and Ireland, of the state of the wind and weather, on which nautical men are accustomed to rely for that kind of information ; and the accordance of the observations at places situated near each other is sufficiently marked to confirm their general correctness, and thus give confidence in those of more isolated localities. The barometrical observations have been collected with * This essay, with the exception of some additions, although only now published, was written soon after this period. ■f Communicated by the Author. Phil. Mag. S. 3. Vol. 28. No. 187. April 1846. S 24«2 Mr. W. Brown on the Oscillations of the Barometer. great care : those for London and the Orkneys are taken from the tables published in the Philosophical Magazine and Athe- naeum, and those for Paris from the Annates de Chimie; but in general I have been indebted for them to the kindness of the observers themselves. I sought those from Christiania, which are from the register kept under the superintendence of Prof. Hansteen, in order to enlarge the field of the observa- tions ; it appears however from them that their locality is too far to the west to throw light on those of this country, except in a few instances ; for this reason they are placed at the foot of the columns, contrary to the general order of the positions of the observations ; and when reference is made to the ob- servations as a whole, they are never included, except when specifically mentioned. The whole of the facts brought to light by this investiga- tion may, I think, be resolved into this general principle; that all winds may be ultimately referred to the action of one or both of two contrary currents caused by the unequal distri- bution of temperature on the surface of the earth; the one ari- sing from the flow of colder and therefore denser air towards warmer, in the lower regions of the atmosphere; and the other from the descent to the surface of the earth of an opposite cur- rent belonging to the upper regions of the atmosphere, and formed by the elasticity or total weight of the atmosphere at any elevation in the warmer regions, being greater than that at the same elevation in colder, because of the greater height of the atmospheric column in the former than in the latter; the air in both being supposed of the same pressure at the surface of the earth. Thus in fig. 1, Plate V., the outline H b B A represents the general figure of a portion of the at- mosphere, of which the temperature decreases from A to B (A lying on the equatorial and B on the polar side of C, or A being south and B north); the lower current of heavy air will therefore set in from B towards A. But the pressure being equal at the surface of the earth, and greater at any equal elevation in the column H A than in b B, at some certain height above A the pressure or elasticity of the air will be so much greater than at the same height above B, that its force will there overcome the pressure of the colder air of the column Bb; and hence above this the air will flow from H A towards b B. But these currents can only be maintained by air descending and ascending in some part of them : let the upper current descend to the earth at A, it will continue to flow towards C, as represented in the figure, by the momen- tum acquired in its original position. These currents are the north and south winds. Mr. W. Brown on the Oscillations of the Barometer. 243 From this may be deduced the following results, which may be applied to the explanation of the general atmospheric phe- nomena of all latitudes of both hemispheres, though when the cardinal points are referred to, they are given in terms adapted only to the northern, and to extra- tropical latitudes; for the sake of convenient reference to each, they are placed in num- bered paragraphs. 1. An equality in the pressure of the atmosphere can only be maintained by the flow of these currents in their proper, that is, in their original positions, the one above and the other below; but on the descent of the upper current, which still, by its momentum, maintains wholly, or in part, its original direction, the lower is either more or less retarded, or entirely pushed back : thus whilst the air is carried away, either from the upper parts, or whole of the atmospheric columns, the flow to the lower is prevented, and consequently a diminution of air, or decrease in the atmospheric pressure, takes place in the regions where the descending current prevails on the sur- face of the earth : hence the great oscillations of the barome- ter in high latitudes, or the region of the " variable winds," and the maintenance of the equality of the atmospheric pres- sure in the region of the " trade winds," the ascent and de- scent of the air taking place at the extremities of the latter, and consequently without interruption to the course of the currents. 2. In the extent of the descending current, and for a space in front of it, following the line of its direction, the pressure of the atmosphere upon the surface of the earth will be distri- buted according to the curved line a deb, Plate V. fig. 1; and the lines A a, Dd and Cc, &c. will represent the pressure at the several points on which they are drawn, C being sup- posed the point at which the descending current terminates and meets the opposite or lower one, as shown by the arrows, whilst the southerly current is blowing above the north from c to b; the minimum pressure will be near C, or the place of meeting of the two currents. That this will be the case is evident from the consideration, that the descending current advances by reason of the superiority of its force to that of the lower one, which it drives back; but this superiority is constantly diminishing by the rarefaction of the air produced by its flowing from c to b, which rarefaction at last reduces the force of this current below that of the resistance of the opposite one in front of it ; hence it is clear that where the descending current terminates in advancing from the place of its descent, or is overcome, as at C, the pressure must be at the minimum, increasing from this point in both directions, S2 244 Mr. W. Brown on the Oscillations of the Barometer. but in the greatest degree towards B, because of the resistance given to the upper current in its How northwards after passing tliis point, and the increasing density of the air in the colder current. In my first paper on this subject (vol. xx.), I gave an illustration by a figure, in which for want of due consideration arise of the barometer was conceived to occur at the point C; but in a subsequent paper on the " Storms of the Tropics" (vol. xxiii.), it is assumed that this is, as here expressed, the point of the greatest barometric depression, though I omitted to notice the discrepancy. As this part of the subject is of great importance, it may be proper to give a further explana- tion of it. The upper current is supposed to descend to the surface of the earth between A and C, on which it will flow to a certain distance dependent on its power to overcome the opposite one from B, and C is the point at which it meets this current and advances upon it; here therefore there will be an influx of air from both sides at the surface, whilst that above is carried away in a continuous current from eg to b. Now it will at once be evident that in this position of the cur- rents, any change produced in the atmospheric pressure will depend upon their relative velocities; if that of the upper one is so much the greatest, that notwithstanding the check given it by the opposite force, more air is carried off from the higher parts of the atmosphere above C towards b than is brought to that point in the lower, the pressure at C must diminish. But the diminution of pressure thus begun by the force of the de- scending current, will go on until this force is reduced, by the loss of pressure sustained, to an equality with that of the op- posite one, and then its momentum being destroyed it will cease to advance, and the latter will begin to advance upon it, to restore the equilibrium of the atmosphere; hence the point of its furthest advance and first cessation must be near that where the diminution of the atmospheric pressure is greatest, or the point C; and at this point, in great storms, there will be a comparative calm throughout a certain extent of the atmosphere. That the conclusion resulting from this reasoning is in consonance with observed fact, may be seen from the observations of P. J. Espy, who has shown that the space between the opposite sides of a storm is in reality the place of minimum pressure in those storms of America which he has investigated*. * This, according to this observer, is the position of the fall of rain which occurs during storms, the fact upon which he has founded his theory; but it will be seen that in this case the conditions are precisely such as, accord- ing to the general opinion of meteorologists, are requisite to produce rain, — these are, the meeting of two currents in precisely opposite conditions Mr. W. Brown on the Oscillations of the Barometer, 24-5 3. It is not meant however in the foregoing paragraph that the greatest depression of the barometer throughout the course with regard to temperature and the quantity of aqueous vapour they con- tain; and hence the true nature of* the connexion between the occur- rence of rain and a falling barometer, both consequences of one common cause. The phaenomena attending the fall of rain are extremely dependent on geographical position, and are by no means sufficiently known to enable us fully to carry out these principles to the explanation of them, although I am firmly persuaded that when better known we shall be able to do so. I will however just refer to a few cases similar to that mentioned, of which they do give a sufficient explanation, and which are notorious weather laws : — the occurrence of rain ; — just before a change of the wind, or at the time of the change, whether it be from north to south, or from south to north, though the most conspicuous in the former case ; during a north- east wind with a falling barometer (§ 5), and with a south or south-east wind (occasioned by the junction of a north-east and south wind, see § 11). The last of these is the most conspicuous in the portions of storms to which § 16 refers, which in those parts where the wind is from south to south-east are always accompanied by abundance of rain. It may be thought that our dry winds from north-west (also formed by a north and south wind (§ 11)) are an exception to these results; but it is by no means necessary that rain should always occur at the meeting of these currents, for if the lower cur- rent greatly predominates in dryness or in quantity, then it is evident that there need be no precipitation of vapour in the form of rain. But there is another reason why these winds should be in general free from rain. The occurrence of rain in showers with squalls of wind, when the other portions of the day are fine, is a case to which the principle before us strikingly ap- plies, for these squalls almost always blow in a direction somewhat different from that of the wind in the intervals between their occurrence ; thus showing that they arise from an immediate onset of one or other of the op- posite currents : now it is very easy to conceive that two bodies of air may meet so as to produce rain, although their relative temperatures and quan- tities of vapour may be so adjusted, that the resulting temperature is suffi- cient to maintain the same quantity of vapour; for if the collision be sud- den, by the law of the diffusion of gases and vapours the vapour of the warm air will rush at once into the cold air, not waiting for the mixture to take place; and hence, being subjected to its temperature, it is immediately condensed and the rain is produced. Now (§ 11) the north-west wind is one of the most constant winds, hence one of the most favourably disposed for the gradual mixture of the opposite currents. This also explains the occurrence of fine weather with a steady barometer, for stability in the pressure of the atmosphere can only be produced by the stability of the currents. The formation and disappearance of clouds without rain may be explained in the same manner, — the precipitated vapour not being suffi- ciently dense to form rain is again aerified when the cold air acquires the temperature of the mixture. [For a full description of the differences and relations of the distinct atmospheres of air and vapour by which the globe is surrounded, and on which this reasoning is based, I need scarcely refer the reader to the * Meteorological Essays' of the late Professor Daniel!, where they are set forth with great perspicuity and precision.] But perhaps the fact most remarkably in accordance with this application of the principle set forth in this essay is that general one, established by W. Snow Harris by induction from a great number of particular instances, that thunder-storms result from the collision of opposite currents ; for the 246 Mr. W. Brown on the Oscillations of the Barometer. of a wind or storm* is at once attained at the point C, which is there supposed to be that of the furthest extent of the descend- ing current from the^rs^ place of its descent, and the place of the barometric minimum in the parts then occupied by the wind. The pressure continues to decrease for some time by the pro- gressive motion of the storm. It is evident that air having begun to descend at A and to flow forward with considerable velocity in the same direction as before its descent, the lower air on the south of A must at once begin to flow towards A to supply its place ; but as this air is either at rest or in a state of motion in another direction, it cannot at once begin to flow with suf- ficient velocity to supply the deficiency ; therefore the rare- faction thus produced will cause the upper current to descend into it, and thus the space upon which it flows will gradually extend itself backward from A, or southward. But at the same time that this is going on behind A, the advanced por- tion of the descending current has begun to retreat from C ; for its force there, at first superior to that of the opposite one, is at last overcome by it, and the heavy current of cold air then advances upon the receding wind, flowing with a force in some degree proportioned to the degree of the rarefaction, and restores the air to its ordinary pressure t» according to one general law of storms, that when the wind changes from south to north the barometer begins to rise. Thus the point of minimum pressure, C, or the furthest advanced portion of the storm, and the point of its first occurrence or descent, A, both move in one direction, from north to south, but not equally ; for it is obvious that the portions of air which de- scend after the first have an advantage over the latter in this, that the opposition in front being partially removed, by the first portions and the diminution of pressure begun, they flow towards a rarefaction ; and thus the force of the storm and the diminution of pressure at C are increased, and the motion of this point southward is retarded, whilst the wind is pro- gressing on the south from A. But this disproportionate motion of the two extremities cannot remain, for with the in- crease of the rarefaction there is an increase of the force of the torrents of rain which frequently fall during their occurrence seem to ma- nifest that the only difference between this and the fore-mentioned cases is in intensity. * The only distinction here inferred between wind and storm is that of force; in many instances I use the term storm, because of the phenomena being sufficiently striking only when the wind has great force. f In the hurricanes of the tropics, the returning current is a second storm, and it is sometimes so in those of high latitudes; but in the latter the rarefaction of the atmosphere is so extended, that the restoration of the pressure is frequently very gradual and produced by moderate winds. Mr. W. Brown on the Oscillations of the Barometer. 24<7 north current, which will after a time carry backward the point C with increasing velocity, and gradually put a period to the storm*. This is more conspicuous in storms of temperate regions than in those of the tropics, because the former consist, as it were, of one deep wide depression of the atmosphere, the pro- gressive motion of the storm being, so far as regards the movement from north to south, apparently in great measure an enlargement of this depression southward, whilst the latter occasion a much smaller one. 4>. As a direct consequence of the foregoing, and as also proved by P. J. Espy, the greatest reduction of atmospheric pressure in storms is not where the wind is most violent, but where its velocity is reduced by the resistance in front of it; and the depression of the barometer at any given place de- pends on its position with regard to the place of the mini- mum, or the point C, fig. 1, as well as on the violence of the storm. 5. A further consequence of the same result is, that a con- siderable diminution of the pressure of the atmosphere, and consequently, fall of the barometer, takes place on the loca- lity where a north-east wind is blowing, when this wind is immediately on the north of the northern range of the south wind which occasions the fall, (as at the point E in the cur- rent from B towards C), though, as explained in § 2, to a less extent than in the localities occupied by the south wind. This result explains a fact of very frequent occurrence, the falling of the barometer during a north-east wind. 6. As the impetus of the south wind may have reduced the elasticity or pressure of the air, in the column C c at any eleva- tion of the atmospheric columns, below that of the air of the same elevation on the north ; a very rapid increase of the pressure of the atmospheric columns on the north may give so great a check to the upper current at C, as to cause the air to accumulate so rapidly, that the increase of pressure or rise of the barometer extends to a great distance on the south ; but it is yet evident, from the state of the atmospheric columns shown by the figure, that the south wind will con- tinue to flow from A because of the greater pressure there; but the barometer will rise on account of the accumulation of air taking place at C and extending in a diminishing degree towards A ; hence a frequent phenomenon, the rise of the barometer during the continuance of the south wind ; as also * The deflection from south by the rotation of the earth is for the pre sent left out of consideration, see § 15. 248 Mr. W. Brown on the Oscillations of the Barometer. the beginning of the rise of the barometer, frequently some time previous to the setting in of the northerly current. 7. But an atmospheric pressure above the mean will also result from the opposition of these currents, but an opposition differing from that of § 2 in this respect; that whereas in that case the force of the descending current, originally much the greatest, is reduced at the place of its termination to an equality with that of the opposite one by the diminution of the pressure of the atmospheric columns composing it; in this, where a rise of the barometer takes place, the force of the lower, or current of gravity, is equal or superior to that of the descending one when at its full pressure, and the former is advancing upon the latter. Let then the two currents so circumstanced meet, as in fig. 1, at C, there will be at this station either simply a condensation of the air produced by the pressure of the two currents, or the air of the lower one will ascend, carrying with it an impetus which would tend to carry it on still in its first direction. In the case of § 2, air brought to the place of meeting is carried off in the upper current by the force of that current, but in this, if the air of the lower current does in this way ascend, it will simply check that flowing above in the contrary direction, and cause an accumulation of air to take place exactly similar to that of water occasioned by partially damming a stream. But even when the force of the former is in some degree inferior to that of the latter, it may yet be sufficient to retain so much air of the upper current by its opposition as to accomplish the same effect though in a less degree: thus the pressure will be re- presented by the dotted line a gb in fig. 1, and an elevation of the barometer will ensue in the localities where the south wind is blowing, as well as in those which have the north ; hence great elevations of the barometer occur with south winds as well as north. 8. The foregoing paragraph is intended to explain the great atmospheric pressure sometimes produced by strong north-east winds, and calms or very gentle breezes, as one or other of these is produced (§ 12) at places situated near the collision of the two currents, especially when the effect is in- creased, as shown in a previous essay, by reduction of tempe- rature; but increase of pressure will arise from other causes; as in some locality sufficiently far to the north of a strong southerly wind to be out of reach of its influence in depressing the barometer, and upon which the air from the depression flows; though probably in this case the barometer will not rise in a great degree, on account of the air, whose removal causes a deficit of pressure in one locality, being so extensively Mr. W. Brown on the Oscillations of the Barometer. 249 spread by the flowing of the upper current on others ; the reason why elevations of a degree corresponding to depressions at any given place have never been found by comparative ob- servations*. 9. An elevation of the barometer may also be the conse- quence of a previous reduction ; for let the pressure be re- duced, as at C, fig. 1, the returning air or northerly current which sets in after the cessation of the southerly one, will oc- cupy a portion at least of the higher regions of the atmosphere where it is not wont to flow, as is evident from the figure. On the restoration therefore of the usual pressure, the north current will be blowing not only in its own proper region, but also in part of that which properly belongs to the southerly one, and will continue there some time by reason of its acquired velocity after the original impulse has ceased to act ; and thus the upper current, not resuming at once the whole of its ac- tion, and consequently the air not being allowed to flow from the upper parts of the atmospheric columns as rapidly as it is brought to the lower, will accumulate. In like manner, the elevation of the barometer may be the cause of giving to the upper current a great velocity, for an elevation being any- where produced, the force by which the lower current causing it was urged on, must sooner or later be overcome by the in- crease in the pressure of the air towards which it flowed. But this current being overcome, the overplus of pressure will then increase the velocity of the upper one, and probably determine the flow of the air at the surface of the earth in the same direction ; which indeed is frequently the way in which an elevation of the barometer subsides; and in the ob- servations given in this essay, in which are included two pe- riods of stormy weather, both began with the occurrence of a southerly storm after a high barometer. 10. The direction of the wind when one current alone pre- vails, is determined by the relative situations of the warm air and cold, and the deflection of the current thus produced, by the rotation of the earth, as the "trade winds" and mon- soons of the tropics, and the north-east wind of high latitudes ; but when the opposite currents come into collision, the direc- tion is the resultant of their forces, and thus in the latter re- gions we have winds from every point of the compass, as has been pointed out by Prof. Kaemtz. 11. The action of these currents meeting together and pro- ducing the various winds may be considered as follows : — The south-west and north-east winds blowing from two stations, A and B, and meeting together at a station between them, C, * Daniell's Meteorological Essays. 250 Mr. W. Brown on the Oscillations of the Barometer. may cause a wind in any direction, according to their force and their inclination to one another; if it be on the eastern side from any point of the compass between a north-eastern point and some point between south and west, it will be very liable to change; for winds from these points being produced by the direct collision of the descending current with that from north-east, when the latter is blowing on the surface of the earth from some more northern station, require the conti- nuance and stability of a current whose direction, inasmuch as it is from east, depends upon its actual velocity, and which, in some parts of it at least, must be more or less interfered with by the flowing of the resulting wind; hence the winds from due south, or south of east, are the most inconstant and the least frequent of all the winds. But the case is very different with the winds on the contrary or western side of the compass ; for as the direction of the southerly current is formed in the upper regions of the atmosphere, and consequently is not in- terfered with by that of the resulting wind below, and the op- position of the air which ought to form the northerly current being simply that of a pressure from north when not actually flowing towards the south, and only in some degree affected by the rotation of the earth when the wind is north-west, the conditions which are necessary to produce the westerly winds are much more capable of giving them stability and duration. When these winds, instead of meeting with their forces di- rected more or less obliquely to each other, meet in direct opposition with nearly equal strength, a calm or very light wind is the consequence. 12. But a rarefaction of the air being anywhere produced, the direction of the wind may be further modified by the situ- ation of this rarefaction, with regard to the atmospheric co- lumns adjoining it, where the rarefaction does not exist; thus as storms in high latitudes move towards east (§ 15), the re- turning current in some parts of the storm is deflected from west. 13. The cause of these currents being the difference of temperature of adjacent portions of air, their force will depend upon the amount of this difference ; hence it is much greater in winter than in summer, when the great length of day in high latitudes lessens very greatly this difference*; hence also as the degree *to which the reduction of the atmospheric pres- sure can be carried by the flowing of the upper current (§ 2) depends on the force of that current, and the degree in which air can be accumulated (§ 7) likewise depends on that of * See Phil. Mag. S. 3. vol. xx. p. 467, "On the Oscillations of the Ba- rometer." Mr. W. Brown on the Oscillations of the Barometer. 251 the lower one, both the depressions and elevations of the ba- rometer are the greatest in winter. 14. The forces which urge on these currents are accelera- ting forces ; but the lower current being exposed to the fric- tion occasioned by its flowing along the surface of the earth*, as also to checks given by inequalities of temperature, its force is unequal to that of the upper one ; hence storms are by far the most frequent and violent from south. 15. The progressive motion of a south-west wind or storm has been in part previously considered (§ 3), but requires fur- ther notice ; it will be according to figure 2 of Plate V. Let the upper current descend upon a station A (the top of the page in this figure and those of § 16 and 1 7 being supposed the north) with more or less force ; as shown in § 3 and the essay on " The Storms of Tropics," the storm moves or recedes from A, in the direction from B to A ; but blowing from south, it is carried by the rotation of the earth towards east, or as if impelled in the direction C A; hence its actual path is the resultant of these motions, or that shown by the arrow at A. In this direction, therefore, the storm will arrive at the places which it visits, or as the line A D moving in a di- rection perpendicular to its length ; hence also H A will be a section of the two currents at their place of meeting, and con- sequently the line or parallel of the line of the minimum at- mospheric pressure (§ 3), extending in the same direction, or that shown by the arrow. The progressive motion however will not be in the same direction throughout; for let A be the place at which the current descends on the arrival of the storm, it will advance a certain distance along the surface. In the progressive motion just considered, there is a compara- tively rapid motion from west, because although this motion is opposed by the air in front of it, yet it is principally on the east and by air at rest, for as the storm recedes and one por- tion of air descends behind the previous one, the opposition on the north is in part removed by the first descending air from that which descends after it; but when the air, as in this part of the storm, advances from south to north, this opposi- tion is felt at every degree of its progress ; hence the path taken by the wind in this case is simply the resultant of the directions of the two forces, but that from south-west being much the strongest, it is from a point much nearer to this than to that from which the opposite force is directed. Now * See Phil. Mag., October 1843, "On the Storms of the Tropics," p. 277. I may here correct an error in the note on that page : it stated, that omitting the two months in which the change of the monsoons occurs, the differ- ence of the atmospheric pressure of the two seasons at Canton is nearly one-third of an inch : it ought to have been nearly half an inch, or 0*44. 252 Mr. W. Brown on the Oscillations of the Barometer. agreeably with this, we find that the direction of the wind in such cases is generally at first from S.S.E., but as the storm continues, it changes to S. or S.W. ; according to the explana- tion given of the lateral motion of the receding wind (one por- tion removing the opposition for that behind). Therefore let us suppose the direction of the advancing air to be from due south or along the line A B; then a, b, c will be stations at which it arrives in its progress; but at the time it reaches any of them the storm will have moved on a certain distance from A in the direction of the arrow ; therefore suppose A to be moved back along the line H A, then the wind will arrive on each point of the line E A from a point immediately south of it on the line H A ; and if the intervals of time which have elapsed on its arrival at stations equidistant with a, 6, c, from the line H A in a direction due north, or parallel to A B, be severally represented by the lines aft b e, and c d, parallel to the arrow, the wind will arrive at the stations a, b, c, or every point on the line A B, asf, e, d, or the correspond- ing points of the line E A, supposing it to move together with the line D A. Thus as fresh portions of air will advance as the point A moves forwards, the storm may be represented by a moving body of air, within which the wind is S.W., S. or S.E., and whose progressing front has the shape DAE; and we may name that part of it represented by A E the advancing portion*, and that by D A the receding portion, according to the nature of the motion. 16. In storms of the tropical regions, and in those of high latitudes commencing with the usual atmospheric pressure, the former of these is apparently insignificant ; but in some cases this portion of the storm extends over so great a space, and the phenomena presented by it are so peculiar, that it will require a distinct consideration. It is evident that its ex- tent, or the distance to which the wind advances, will depend not only on its force, but also on the greater or less resistance of the air, or in other words, the greater or less pressure of the atmosphere in front of it (the resistance from the differ- ence of temperature being supposed the same in all cases); hence we find that the cases in which it is traced in the fol- lowing observations to a considerable distance, and to which this paragraph is intended principally to apply, are those in which the height of the barometer has been much reduced by * This must not be confounded with the second period of storms, in which the north wind advances upon the receding south. For a descrip- tion of the winds in both the parts, A C and C B, fig. 1, of a progressing body of air, see this Magazine, vol. xxiii. p. 214; if the several directions there given be reversed, it will apply to this case. It is to tropical storms that we must look for an exhibition of these phenomena in their greatest simplicity. Mr. W. Brown on the Oscillations of the Barometer. 253 a previous storm, and not restored on the arrival of the advan- cing storm, which approaches from atmospheric columns on the south but little affected by the preceding one; which differ- ence indeed is apparently the cause of the storm; it occurs however after the returning or northerly current has set in in the north, and a little raised the height of the barometer there; and on its termination, the height of the barometer in the south is reduced as low as that in the north, in some parts of which it is depressed to a greater degree than before, the fall begin- ning in the south and advancing towards north as the wind itself. But not only this, the minimum height to which the barometer is reduced, and the setting in of the north wind (though always from north-west), occur first in the south, but on the western side (by the south being now meant the parts along the line H A of fig. 2, Plate V., where the upper current is supposed, with regard to localities north of them, first to de- scend); so that, in the south, the north wind is blowing and the barometer rising, whilst the south wind is blowing and the barometer falling in the north. The advance of the south wind northwards after its cessa- tion on the south, admits of very easy solution on the suppo- sition of the storm being carried forwards by means of por- tions of air descending from an upper current flowing in its proper position, and which the reduction of the height of the atmospheric columns towards which it is moving, allows to flow with its velocity little checked ; thus the south wind con- tinues below, not by the force of the original impulse received at its outset from the line H A, but by that of successive im- pulses received during its course: moreover, the rapid in- crease of the heights of the atmospheric columns in the south by the influx of air from north-west, still maintains the upper current of the atmosphere. The setting in of the northerly current from north-west in the south, and the consequent rising of the barometer before these changes occur in the north, may be explained by a consi- deration of the form of the space, on which the depression of the barometer previous to the occurrence of the second one produced by the advancing storm, exists. Suppose the greatest depression of the barometer to be produced along the line A B, fig. 3, Plate V. (H A of fig. 2), according to § 15, and the full effect of the first storm in depressing the barometer to have taken place ; as that storm moved from A to B, the pressure will be in some degree restored on the parts of this line towards A; hence the depression will decrease from B to A; but it also decreases towards C (§ 2) ; hence the form of this space on the west will be somewhat like that bounded by 254? Mr. W. Brown on the Oscillations of the Barometer. the line Fc A b, the pressure increasing from B towards nil parts of that line. Under these circumstances, then, the ad- vancing storm occasioned by the greater height of the atmo- spheric columns about C than of those about B, occurs, and reduces the barometer at C, so as to make it the place of the greatest depression, the line c C now representing the line H A of fig. 2. But whilst the south current is thus setting in from C, the north-east is blowing from b, and the two meet somewhere between these points ; and there, as at D, fig. 3, the wind is south-east (§ 11), though south-west in the localities south of it ; but as the direction of the current which carries off the air so as to produce the depression is from south-west, the depression will be produced in that direction also, or along the line C B. Now if we consider the storm to have advanced from any line drawn from C towards the circumference of the depression as C c, it is evident that whatever part of this we suppose a particular portion of the current to set out from, its condition will be the same, that of having at the time when the pressure of the atmosphere is reduced to the lowest point, a greater atmospheric pressure on the north-west side, or along lines drawn from it to the circumference cAb, as Ca and C A, because of that side being always adjacent to atmospheric co- lumns less and previously affected by the storm ; hence on the line Cc, the occurrence of the minimum in order of time will be in the direction from c to C, or that of the receding storm (§ 15). Let then the barometer be reduced to its minimum height at C (supposed the place where the storm is most in- tense), or to the limit of its equality with the resistance of the air in the direction from A to C, and let the air at d be re- duced to the same degree of rarefaction, or to one (as after- wards to be noticed) not quite so great. These stations are subject to the influence of the pressure increasing along the line C A ; hence from any station E on that line, the air will tend to flow towards them, as indicated by the arrows at E, the effect of which in the case of C is to oppose the southerly current, but in that of d rather to assist it ; hence whilst at C it is overcome and the wind sets in from north-west, it conti- nues its course at d. The commencement of the restoration of the pressure of the atmosphere advancing thus from C to- wards D, whilst its advance from west is, as before stated, along the line c C or A C, it is evident that every point of the line C D B in succession from C will be related to a line par- allel to A C, precisely as the point C is related to the line A C at the time of the setting in of the north wind ; and the restoration of the pressure will commence as the line A C ad- Mr. W. Brown on the Oscillations of the Barometer. 255 varices along the line A B, except that as it approaches B, from the great extension of the minimum depression in the north, the point A may move more slowly than the point C; near this time, however, the north wind begins to set in di- rectly in front of the storm from north-east, and then the re- storation of the atmospheric pressure proceeds throughout. But not only does the minimum of the barometer occur first at the point C, its depression is also sometimes the greatest at this point; thus at 9 a.m. on the 1 1th, its height at Cork was 28*93, at Belfast 29*10, and at Plymouth (to the south-east) 29*11. Thus it appears that the barometer in this instance was about one-tenth of an inch lower at a station similar to the point C than at the point d*. In § 2 it is stated merely that the minimum height of the barometer is near the point of meeting of the opposite currents, in order to simplify the reasoning of that paragraph ; but it is evident that it will be rather to the south of it, for at this point the resistance of the air in front of the south wind at the surface of the earth, is either equal to its force, in which case it advances no further, or if not equal to it, it is yielding to it and retreating. In either case the opposition will cause more or less condensation where it is immediately felt, but the opposition decreases to- wards the higher regions of the atmosphere; hence (§ 2) the upper current, whose force is only exhausted by the de- struction of its momentum, carries off the air from the point d (which, for the sake of illustration, let us suppose the limit of the south wind), and the positions south of it, so as still to carry on the reduction of pressure; but in the greatest degree a little south of d (or at C), on account of the condensation decreasing from d towards C. Now in storms in which the advancing portion is insignificant, the minimum pressure will be very near the point C of fig. 1 ; but in such as those now in consideration, it is apparently at a great distance, though the difference of the pressure at the point of the meeting of the currents, and that of the minimum pressure, is very slight. The distance, however, is in a great degree only apparent, being occasioned by the nature of the advance of the storm. 17. In high latitudes, the warmer regions, except when they * This appears to me a strong confirmation of the belief, that the origin of the south wind is that upon the supposition of which this theory is founded, for how upon any other than that of air descending from a cur- rent which flows by an acquired velocity, could a current flow from one station, C (fig. 3), to another, d, of a colder temperature and greater pres- sure? In this paragraph, as also in those which follow it, it will be ob- served that 1 have been obliged to depart from the form of the reasoning in the others, that of simple deduction from the principles stated at the outset, or from the results of previous paragraphs. 256 Mr. W. Brown on the Oscillations of the Barometer. are influenced by geographical situation, have their position, with regard to colder, constantly on the equatorial side of them, both in winter and summer; but in tropical regions these positions in summer are reversed by the change in the point over which the sun is vertical ; hence the currents also are either permanently reversed during this season, as in the monsoons of the Indian ocean ; or, as in the " trade winds," their position is altered and their constancy interrupted, and sometimes at least their direction reversed* ; thus the tropical hurricanes of the Atlantic, which occur only during summer, and the storms of the Indian ocean, which occur during the same season, that is when the south-west monsoon is blowing, have their relative parts precisely the reverse of those of high latitudes, the descending current being from north, from which quarter the storm commences, and the returning one from south, whilst the progressive motion is towards north-west. These storms visit only the western parts of the Atlantic, a fact which, on the supposition of their origin being the descent of the upper current, is readily explained by a glance at the position of the continents of Africa and America ; the western part of the Atlantic having the latter stretching out on the north of it and radiating the heat of the summer's sun, whilst the former extends on the south of the eastern parts, having only the waters of the ocean on the north. But these storms near the boundary of the tropics change their directionf and pass along the eastern coast of North America and parts ad- jacent, and present phaenomena different from those of storms which take their rise in extra-tropical latitudes, but to which the explanation given in the foregoing paragraph of the phae- nomena of the advancing portion of storms in the longitudes of Europe, may with some modification be applied. In my paper on the Storms of the Tropics, I have referred to two storms of this kind, which advanced along the coast of the United States in a direction from S.S.W. to N.N.E., of which the data collected by W. C. Redfield are given in Col. Reid's work on Storms. As a general explanation only was before given of their phaenomena, it may now be proper to give one * For a particular explanation of the phaenomena of these storms I must refer the reader to my essay in this Magazine, vol. xxiii. I may observe here, however, that the identity of the phaenomena of the storms of the Atlantic and Indian ocean is sufficient evidence of the same condition of the currents in the former as in the latter at the time of the occurrence of the hurricane; but in the western part of the Atlantic, which is the loca- lity of the hurricanes, the south is the prevalent wind in summer. (See an Essay on the Climate of Barbadoes, by Robert Lawson, in the Edin- burgh Phil. Journal for July 1845.) f On the Storms of the Tropics, Phil. Mag. vol. xxiii. p. 206. Mr. W. Brown on the Oscillations of the Barometer. 257 more explicit. I have therefore quoted below the principal data of the second of these storms (Law of Storms, p. 18), and from them constructed a chart (Plate IV.), showing the direc- tion of the wind at the different localities at the onset of the storm, and the time occupied by the first period of it. " At Charleston (S. C), on the 16th, the gale was from the S.E. and E. till 4 p.m., then N.E. and round to N.W. " At Wilmington (N. C.) the storm was from the E., and veered subsequently to the W. " In the vicinity of Cape Hatteras, at sea, the storm was very heavy from S.E., and shifted to N.W. "Early on the morning of the 17th, the gale was felt se« verely at Norfolk, and also in Chesapeak Bay from the N.E. " Off the Capes of Virginia, on the 17th, in lat. 36° 20', long. 74° 2', a 'perfect hurricane' from S. to S.S.E. from 5 a.m. to 2 p.m., then shifted to N.W. " Off Chincoteaque (M.d.), precise distance from the coast unknown, the gale was severe between S.S.E. and N.N.E. " Off the coast of Delaware, in lat. 38°, long. 72°, ' tremen- dous gale,' commencing at S.E. at I p.m. on the 17tb, and blowing six hours, then changed to N.W. "At Cape May (N. J.) the gale was N.E. off Cape May, in lat. 39°, long. 74° 15'; heavy gale from E.N.E. on the af- ternoon of the 17th of August. " Near Egg Harbour, coast of New Jersey, the gale was heavy at N.E. on the same afternoon. "Off the same coast, in lat. 39°, long. 73°, the gale was at E.N.E. " In the same latitude, long. 70° 30', \ tremendous gale,' commencing at S.S.E. and veering to N. " At New York and on Long Island Sound, the gale was at N.N.E. and N.E. on the afternoon and evening of the 17th. " Off Nantucket Shoals, at 8 p.m., the gale commenced se- vere at N.E. by E. "In the Gulf-stream, off Nantucket, in lat. 38° 15', long. 67° 30', on the night of the 17th, 'tremendous hurricane,' commencing at S., and veering with increasing severity to S.W., W., and N.W. "At Elizabeth Island, Chatham, and Cape Cod (Mass.), the gale was severe, at N.E., on the night between the 17th and 18th. " On the 18th, heavy gale from N.E. at Salem and New- bury Port (Mass.). "Early on the 18th, in lat. 39° 51', long. 69°, severe gale from S.E., suddenly shifting to N. Phil. Mag. S. 3. Vol. 28. No. 1 87. April 1 846. T 258 Mr. W. Brown on the Oscillations of the Barometer. " In lat. 41° 20', long. 66° 25', < tremendous hurricane ' from N.N.E. on the 18th." I cannot refer to the charts given by Col. Reid, because the directions of the wind marked out in them do not indicate the direction in any regular order with regard to the two periods of the storm. Now the general order of the phaenomena of the storms (for it is the same in both, the second being selected merely be- cause of the information concerning it being more full than in the first one, apparently on account of its position being more westerly, and therefore including a larger portion of the United States) are as follows: — The storm commences at S.E. or N.E., but in both cases terminates at N.W., excepting in a few instances — principally near the limit of the storm in the north — where the direction of the wind at both the onset and termination of the storm is from N.E. The veering of the wind is sometimes from S.E. to N.E. and then to N.W., but more generally at once from S.E. to N.W. ; and when the onset is from N.E., sometimes from N.E. to S.E., and after- wards to N.W., but more frequently directly from N.E. to N.W. The differences between the storms now under con- sideration, and those to which § 16 specially applies, are, — 1st, that in the former the rarefaction of the atmosphere is much more suddenly produced, on account of the much greater force of the wind, and hence the extent and duration of each continuous portion of the storm is much less than in the latter; thus instead of one wind prevailing at once over a large extent of surface, as from the extreme south to the north of England, and for a long period, an American storm, over the same length of tract, consists of many alter- nate portions, in which the direction of the wind varies, as shown in the account given of its changes, and continues only for a few hours; and, 2ndly, in British advancing storms the collision of the north and south current takes place from the flow of the opposite currents towards a rarefaction pro- duced by a previous storm ; but in American storms the rare- faction in the first instance is occasioned by the recession of the storms from localities where the directions of the atmo- spheric currents are the reverse of those which are now con- cerned in it. Now from the distribution of the arrows in the chart, we perceive that the localities where the wind is S.E. have a constant position with regard to those where it is N.E. ; and if we select any three or four positions in the track of the storm, at the time when the wind at the most southerly one has changed to N.W., the wind at the same instant of time will be blowing according to the directions shown by the ar- Mr. W. Brown on the Oscillations of the Barometer. 259 rows at ABCE, Plate V. fig. 4*. Now the upper current by which these storms begin within the tropic is from north- east, but after this change in their course the upper current is from south-west and the lower one north-east; let us then suppose A the station at which the storm first arrives after the change in the direction of the atmospheric currents, the upper one being now S.W., the rarefaction of the atmosphere is first produced here by the flowing of the air from it towards south, according to the recession of tropical storms, and into this rarefaction the south current descends, but instead of restoring the atmospheric pressure, it still further increases its diminu- tion by its momentum, and extends northwards and eastwards to B. But it is evident that the rarefaction will extend to a much greater distance in front of the storm than on the west- ern side of itf, hence the pressure on the line A C, fig. 3 (but now less inclined from C B), overcomes at length the force of the south wind at A where the depression of the barometer is the greatest and the wind sets in from N.W., as shown in the figure, and restores the pressure, so as to maintain by again raising the height of the atmospheric columns at A, the velo- city of the upper current now flowing to more northerly lo- calities. But whilst this is going on, the north-east wind is blowing at C and E, being produced there by two causes, its recession from A, and the flow of air produced by the rarefaction at the limit of the south wind, as at E, fig. 1, Plate V.; and as the direction of the upper current is from south-west, the diminu- tion of the atmospheric pressure is of course carried on in that direction ; and hence a rarefaction is maintained, into which the south current flows from columns at a point eastward of A, as B, which as yet is not subject in so great a degree as A, to the opposition of the air on the line A C of fig. 3. But the south wind meeting the north, the wind is S.E. But as the line A C advances, its pressure prevails both at B and C, and * I would just remark in passing, how well these positions would accord with the hypothesis of the wind moving in a whirl, could the fourth quarter wanting, when the wind should be south-west, be found,- but scarcely one observation of tlie wind from south-west occurs in the direct path of the storm, for when the wind is stated as blowing from south-west, it is either previous to the change in the progressive motion, or to the west of the " hurricane tract of the storm." The occurrence of the southerly current as a south-east wind in front of the north-east, as exhibited by the dia- grams, is a grand illustration of § 11. - f This is evident from the direction of the progressive motion, but an observation given in the data of the storm of 1821 (Law of Storms, p. 16) shows how abruptly the storm terminates on the west, for ''at Wilmington there was no gale," but " a severe gale was experienced thirty miles out* side of the American coast off Wilmington (N. Carolina)." T2 260 Mr. W. Brown on the Oscillations of the Barometer. changes the wind at both places to north-west, whilst the phe- nomena previously in existence at those stations are removed to others further north. Now it is obvious that whilst at a station C, fig. 4, where the wind is north-east, it may change directly to north-west, at another, E, more to the east, it will change first to south-east if the south wind has the greatest force; but if the north-east become the strongest, which at any particular spot may be the case, the wind in the first part of the storm from south-east may change to north-east before changing to north-west, as shown by some of the data; — a particular instance may be given. From the data of the hurricane of 1821 (Law of Storms, p. 17), "At Cape Henlopen, Delaware, the hurricane com- menced at 11| a.m. from E.S.E. ; shifted in twenty minutes to E.N.E. and blew very heavy for nearly an hour. A calm of half an hour succeeded, and the wind then shifted to the W.N.W. and blew, if possible, with still greater violence." " At Cape May, New Jersey" (a little to the north-east of the previous locality), " commenced at N.E. at 2 p.m. and veered to S.E." Thus it appears that at two stations situated with regard to each other as A and E, the phenomena were as follows: — At A the storm arrived at 11^ a.m., and blew as an E.S.E. wind, but about 12 p.m. the north current had in- creased in force and the wind changed to E.N.E., from which point it blew for an hour, or till 1 p.m. All this time it ap- pears there was no storm at E., but the N.E. wind had re- ceded to it at 2 p.m., and began to blow at that time, but the S. wind soon arrived with greater strength and the wind changed to S.E. But if this be the true explanation of the action of these storms, then according to that given of the mode of progression of receding storms, they ought to increase on the western side towards north-west by the recession of the north-east current; and on the south-west towards south-east by the recession of the south wind. Now with regard to the increase on the west side; as the direction of the north wind is opposed to that of the upper current, it is evident that by extending itself to the west, it cannot extend the rarefaction; and this being produced in a direction from south-west to north-east by the flow of the upper current, the resistance on the west side would soon overcome the advance from east : moreover, the north-east wind is not caused simply by its re- cession from south, but by the production or increase of the atmospheric rarefaction, as at E, fig. 1. § 2. None of these causes however operate as obstacles to its increase towards south-east, and hence we find that the storm actually does in- crease towards east, and that throughout its whole extent a Mr. W. Brown on the Oscillatio?is of the Barometer. 261 south wind progresses towards south-east. This is shown by the data, together with the report of the ship Blanche, whose log is given; for on the 17th (a.m.) she was in lat. 31° 42', long. 76° 59', with " fresh breezes and squally " from south by west, but at this time the hurricane was " off' the Capes of Vir- ginia in lat. 36° 20', long. 74° 2';" again, " off Nantucket Shoals (lat. 41° 5', long. 70°) the gale commenced at 8 p.m. of the 17th," and "off" Nantucket, in lat. 38° 15', long. 67° 30', on the night of the 17th; also early on the 18th, in lat. 39° 51', long. 69°." 18. It is obvious that the foregoing results, if correct, ought to enable us to explain the mode of veering of the wind, and so in great measure they will ; and when they are defective, the want arises from our ignorance of the circumstances imme- diately contingent on the descent of the upper current. If air simply descends upon the north-east current, or meets it from a position on the south, it is evident that whether it changes towards west or towards south of east, will depend on the degree of easterly deflection the north wind has attained ; hence, if the north wind be blowing briskly, the change would probably be towards south of east ; and if feebly, towards west. Also, if a station upon which the north-east wind is blowing receive a south wind approaching it as the line A D (fig. 2), it is obvious that it could not change to north-west and then to south-west, for the air sweeping along the surface in the direction of D A would gradually draw the air adjacent to it into its own direction ; consequently the wind would change first to south-east. Now this change does generally occur, but not always ; for on the 7th and 8th of the month chosen for these observations, the wind changed from north- east to north-west, and blowing in that direction some time, afterwards changed to south-west on the arrival of a storm moving like that of fig. 2. From this therefore we may infer, that portions of the upper current were already descending when it arrived in full force as a south-west storm. The change of the wind from south to north, however, is not so much dependent on circumstances. The position of the line A C, fig. 3, which must always exist with more or less inclination to the direction of the storm or D A, fig. 2, and C D B, fig. 3 (its peculiar effect in the case of § 1 6 being oc- casioned by the peculiarity in the distribution of the pressure of the atmosphere on the line C D), determines it in this case ; thus we find that in the southern and western portions of the locality of a south wind, the south wind first changes to north-west ; but as the north-east wind advances from the northern verge of the storm or wind, it changes again to 262 Mr. W. Brown on the Oscillations of the Barometer. north-east, — a change from south-west to south-east in this case, in the southern localities, being almost impossible whilst the wind continues to blow on the south-east side of the locality which the storm has left. Now it is matter of general observation that the wind very seldom changes in this direc- tion, or from south-west to south-east, being indeed termed by nautical men " backing" ; there is however a particular case in which the wind sometimes changes from S.W. to S.S.E. in the northern or central portions of a space occupied by a storm ; and that is in the occurrence of a storm as that of § 16, the circumstances of which fully explain the excep- tion, for the change is the consequence of the collision of the currents by which the S.S.E. wind is produced, and hence it takes place at what for the moment is on the northern verge of the south wind, where of course a change produced by a north-east wind meeting it may make it south-east*. Having carried out thus far the results of the principles stated at the beginning of this paper, I may now proceed to give the observations which I have collected, and first those of the wind, extracted from the Shipping Gazette. Scotland. — Orkney, Longhope. — " November 1. N., moderate. 2. S.E., fresh breeze. 5. N.W., moderate. 8. S.W., blowing hard; rain. 11. E., strong breeze; rain. 13. N.E., squally. 15. N.N.E., fresh. 16. N.E., frosty. 19. E., strong breeze; rain. 20, 21. N. to N.E., frost and sudden squalls. 22. E. to S.E. 23. E., fresh breeze." Pentland Frith. — "Nov. 7. N.W., moderate : night, S.W. ; very strong throughout the night. 8. S.W. 18. W., moderate. 19. S.E., moderate ; rain : 6 p.m., N.E., moderate." Thurzo.—" Nov. 2. S.E., moderate. 8. S.W., fresh breeze. 10. N.W., heavy gale. 11. N.E. 17. S.W. 18. N.E. 19. S.E., moderate weather. 23. S.E." Peterhead.—" Nov. 1. N.W., light. 3. S.E. to E.S.E., light breezes. 4. E., moderate. 5. N.E., fresh breeze. 8. S.W., fresh breeze. 9. S.W., strong gale. 19. S.E. to N.E., rainy. 20. N.E., strong breeze. 23. E.N.E., fresh breeze. 24. E., strong." Inverness. — "Nov. 19. N.E., calm and raining. 26. N.E., calm; rain." Aberdeen.— " Nov. 17. E.N.E. 18. Variable, E.N.E." Mull — Tobermorey. — "Nov. 3. S.E. 4. S.E., moderate breeze. 5. S.E. to E., light breeze. 7. Variable ; light airs and heavy showers of rain. 8. S-W., strong gales. 9. S.W., "fresh breeze, with rain at intervals. 10. E.N.E., fresh breeze. 11. E., strong breeze. 12. W. to S., light airs; variable. 13. E.N.E., fresh breeze. * In these paragraphs I have omitted any mention of the differences of the mean pressure on different latitudes of the surface of the earth, not because of its unimportance, but because it would merely be a transcript of my essay on that subject in this Magazine, vol. xx. p. 469. Mr. W. Brown on the Oscillations of the Barometer. 263 14. E.N.E., moderate breeze. 15. E.N.E., fresh breeze. 16. E. to S.E., fresh and squally. 17. S.S.W., moderate breeze. 22. S.S.E., strong gales ; heavy rain. 23. S., moderate breezes. 24. N.N.E., strong breezes." Islay. — Bowmore. — " Nov. 2. N.E. 10. S.W., blowing hard. 15. N.E. 16. S.E., a gale. 21. S.S.E. 23. N.W. 25. N.E. , fresh." Bute. — Rothsay. — " Nov. 1. W., blowing strong. 9. S.W., blow- ing strong. 20. S.W., blowing strong." Greenock.—1' Nov. 1. W., fine. 7. S.W., fine. 11. N.N.W. and S.E., moderate. 12. S., light airs; calm. 14. W., moderate. 18. S.E., moderate. 19. S., light airs; rain. 22. S.E., snow and sleet. 23. Variable; light airs and calm. 24. E., fresh breezes with showers." Glasgow *' Nov. 3. E., moderate. 6. N.E., fine. 8. 6 p.m. wind veered round to S.W., and blowing a gale outside. 10. Shortly after we had posted our letters (on the 8th) it began to blow a heavy gale, which towards night became a hurricane with rain, which continued all day (the 9th). Today (10th) wind N.E., fair. 14. 6-30' p.m., wind since Saturday last (12th) chiefly from N. to N.E., light. 17. N.E., light." Leith Roads. — "Nov. 14. N.N.E., fine. 17. Variable; fair." Ireland. — Donegal. — " On the night of the 8th, about 8 o'clock, there was a heavy gale of wind from W. to S.W. 26. W.N.W." Strangford.—" Nov. 1. W. 2. E.S.E., fine. 3 and 4. E.S.E., fresh. 5. E. by N., fine. 14, 15, 16. E., strong breeze. 17. E.S.E., strong. 18. W.S.W., heavy breeze with rain. 19. W. 21. E. 22. W.byN. 23. W.S.W. 25. E.S.E., strong; rain. 26. N.W., rain." Arklotv. — " Nov. 6. E.N.E., fresh breezes. 9. a.m. S.W., gtrong gales with rain : p.m. strong gales. 10. At day-break, E., strong gales with rain: p.m. S.S.W., blowing hard. 11. a.m. S.W., strong gales. 12. a.m. S.W. , strong gales and rain : p.m. W., fresh breeze. 13. a.m. W.S.W. , fresh gales with rain: p.m. S.W., moderate. 14. a.m. N.E., strong gales : p.m. E.N.E. to E.S.E., a gale after sunset with heavy incessant rain. 15. E. by S., a heavy gale with torrents of rain. 16. E., heavy gale. 17. E., strong gales : p.m. E.N.E., fresh gales. 18. a.m. S.W., strong gales : p.m. S.W., strong gales. 19. S.W., strong gales. 20. a.m. E.N.E., fresh gales : p.m. S., hard gales and rain. 21. E.N.E., a.m. moderate : p.m. freshened to a gale. 22. W.N.W., fresh gale. 23. a.m. W., moderate : p.m. S., squally. 24. W.S.W., fresh gales : p.m. W., more moderate. 25. a.m. W., moderate : p.m. W.N.W. , moderate. 26. W. by N., moderate." Waterford.— " Nov. 2. W.S.W., S.E., and S.S.E. 3. S.E. to S.S.E. 4. E. to S.E., E., and N.E. 14. W. by N. to W.S.W., S.S.W., and W." Youghall. — "Nov. 11. N.E., light breeze; hazy with rain. 12. W.S.W., fresh breeze ; rain. 20. E. by S., fresh breeze, with rain." Galway.-~ " Nov. 3. E.S.E. 5. E., fine. 6. E.S.E., moderate. 21. 264 Mr. W. Brown on the Oscillations of the Barometer. Hard gales from E.N.E. for some days past. 22. Much rain last night ; wind strong from E.N.E. ; today more moderate ; wind W.S.W. 26. N.N.W., light airs." Limerick. — "Nov. 10. S.S.E., moderate. 11. S., moderate. 14. S.S.E., moderate. 15. S.S.E., blowing hard, with rain." Cove of Cork. — "Nov. 2. Strong gales with rain. 3. S.E., stormy, with rain. 4. S.E., strong breezes. 5. N.E., a gale. 6. N.N.E., fresh breeze. 7. N.N.W., moderate. 9. S.W., stormy, with rain. 10. S.E., moderate; rain. 11. S.S.W., showery. 12. W.N.W., clear. 13. S.S.W. to W.N.W., variable; squally; heavy showers. 17. E., strong breeze. 18. S.W., stormy, with rain. 19. S.W., moderate. 20. E., strong breeze; rain. 21. S.E., moderate. 22. N.N.W., strong breeze ; fair. 23. S.E., strong breeze. 24. W.S.W., fresh; heavy showers. 25. N.N.W. 26. N.W., stormy and showers." England, West Coast. — Holyhead. — "Nov. 1. N. toN.E., moderate. 2. Variable and fine. 4 and 5. E. to E.N.E., strong; squally. 6. E. by N., fresh breeze. 7. N.E., fresh breeze. 8. W.S.W. , fine breeze. 9. S.W., strong gale ; hazy; wet. 10. a.m. E.S.E., fine breeze ; rainy : p.m. S. to S.S.W. , strong breeze and squally. 11. S., moderate. 12. W.N.W., strong breeze. 13. Variable; moderate; rain. 14. E., fine breeze. 15. E., strong gale; showery: 9 p.m. continued. 16. E., blowing excessively hard. 17. S.E., fine breeze : 8 p.m. S., moderate. 18. S.W., fresh breeze. 19. W.S.W., strong; rainy ; night variable. 20. E.S.E., fresh breeze: 8 p.m. E., fresh. 21. E., moderate. 22. N.W., strong gale. 23. Last night N.W., strong gale ; today veered to W.S.W., fine breeze : 8 p.m. S.S.E., fine breeze. 24. Vari- able from S.E. to S.S.W., fresh breeze; showery. 25. W.S.W. to S.W., fresh; showery. 26. W.S.W. to W., fresh; rain." Beaumaris. — "Nov. 11. S.W., much rain. 12. S.W., fresh ; rain. 13. S.W., much rain. 14. E., fresh. 17. E., fine. 18. S.S.W., fresh; rain. 19. S.S.W., fresh; rain. 20. S.S.E. 22. W., fine. 23. S.E., fresh. 25. S.W." Bristol. — " Nov. 4. E., strong. 8. E., moderate. 10. 4 r.M. S.S.W., very strong. 11. S.W. , showery. 13. It has continued squally from S.W. to W. since my last, and a great quantity of rain has fallen. 14. Variable ; moderate. 14. (second report) E., strong. 16. E., strong; constant rain. 19. S.W., a gale. 20. E., fresh. 21. N.E., fresh. 22. The wind this morning blew fresh from S.S.E. until 10 o'clock, when it gradually veered round to N.N.W., and afterwards it was very strong from that point; a quantity of rain fell last night. 23. N.W., fresh. 24. W.S.W., strong; showery." Scilly Islands. — St. Mary's. — "Nov. 1. S.E., fresh breeze. 2. S.E., strong wind and rain. 3. S.E., strong gales, with rain. 4. E.S.E., strong gales ; rain. 5 and 6. E., strong breeze. 7. E.N.E., strong, showers. 8. E., fresh breeze. 9 and 10. S.S.W., strong gales; rain. 11. W., strong; rain. 12. W. 13. W.S.W. 14 and 15. S.W. 16. S.W. to S.E., strong, with rain for the Mr. W. Brown on the Oscillations of the Barometer. 265 last four days. 17. E., fresh breeze. 19. S.W., strong; rain. 20. W.N.W., rain. 21. E.S.E., strong; rain. 25. W.N.W, strong gales and rain. 26. W.S.W., fresh breezes and rain." South Coast.— Falmouth.— " Nov: 1. N.E., light breeze. 2. E.S.E. toS.E. 3. E. by S. 4 and 5. E.N.E., strong. 6. E.N.E. 7. N.E., light. 8. N., light airs. 9. S. 10. S., a gale; rain throughout. 13. 8 a.m. S., a gale ; raining ; in the evening wind changed to W. 14. Weather moderated. 15. S., squally; rain; afterwards W. 16. Morning S.W. and raining; evening N.E., strong gale. 17. 1 a.m. N.E., moderate ; afterwards E. 18. S. 19. S.S.W., blowing hard. 20. W., light airs and rain: 10 p.m. veered to S.E. 21. E., showery. 22. N.N.W. to N.W., showery. 23. S.W., showery. 24. W. by S., heavy gale, with rain. 26. N.W., showers." Plymouth. — "Nov. 4. N.E., moderate. 5. N.E., fresh breeze. 6. N.N.E. to E.N.E. 8. N.E., light airs. 9. S.S.W., strong, with rain. 10. S.W. .strong; thick rain. 11. S.S.W., strong; rain. 12. W. by N. 13. It has blown very heavy through the night from S.S.W. with rain, which (at noon) still continues. 14. Calm; hazy. 15. W.S.W., strong. 18. S.E., fresh breeze. 19. S.S.W. , dirty. 21. Easterly, moderate. 22. N.W., fresh breeze. 23. W.N.W., fresh breeze. 24. W.S.W., strong; squally. 25. W.S.W., strong breeze, with showers. 26. W., moderate." Penzance. — " Nov. 26. W.N.W., strong gales." Portsmouth. — " Nov. 3. E.S.E. 4. E., fresh breezes. 6. N. to N.N.E., foggy ; slight showers of rain. 9. S.W., blowing fresh. 11. S.W., rain. 14. W. by S. : p.m. fresh breeze. 15. S.W., light breeze; rain all day. 17. N. by E., fresh breeze. 18. S. by E., fresh breezes. 21. N.E., hazy. 23. p.m. W.S.W., fresh breezes; rain. 24. W.S.W., rain. 25. W.S.W., rain and squalls." Isle of Wight Ryde.—" Nov. 12. W.S.W. to W. 13. S.W. to W.S.W., with rain; blowing hard. 14. W.N.W., fine. 15. S.W. 16. E.S.E., fresh. 17. N.E. to E.N.E., fresh. 18. S., fine. 21. E., fine. 24. W.S.W., strong, with rain." Deal. — " Nov. 1. W.N.W. and N. by E., moderate and fine. 2. E.N.E. to E.S.E. 3. N.E., moderate and fine. 4. S.E., light airs and rain: p.m. N.E., fresh and squally. 5 and 6. E.N.E., blowing fresh and squally. 7. E.N.E., fresh breeze ; squally. 10. S.W., fresh breeze ; squally. 11. S.W., blowing very strong, with rain. 12. It has blown very hard all day from W.S.W., with squalls of rain. 14. N.N.W. , light airs. 16. E., fresh. 17. a.m. E., blowing hard : 6-30' p.m. E.S.E. 18. S.W., mode- rate. 20. N.N.W. and N.E., moderate. 21. N.E. 22. a.m. S.S.W., blowing strong; rain: p.m. S.E. , moderate; rain. 23. W.S.W. and W.N.W., light airs. 24. W.S.W., blowing fresh. 25. It blew a gale of wind last night and nearly the whole of this day from S.W. 26. It blew very strong during last night from the S.W. or W.S.W., with squalls of rain." 266 Mr. W. Brown on the Oscillations of the Barometer. Dover. — " Nov. 3. 7 a.m. S.S.W., light : noon and 7 p.m. S.E., fresh. 4. N.E., light, with rain. 5. E.N.E., strong; cloudy. 6. a.m. E„ fresh : p.m. E.S.E., fresh; rain. 8. N.N.W., light. 9. S.W., fresh: 7 p.m. W.S.W., strong. 10. 7 a.m. W.S.W., fresh: noon, S.S.W., strong: 7 p.m. S.W., fresh. 15. E.S.E., strong. 16. 7 a.m. E., light wind; rain: noon and 7 p.m. E., strong. 17. E., strong. 21. N.E., fresh. 24. 7 a.m. S.S.W., strong, with rain: 7 p.m. W., strong; rain. 25. S.W., strong." East Coast. — The Downs. — " Nov. 1. N.W., light breeze. 2. East- erly, moderate. 8. N.W., very light. 9. S.W., blowing fresh. 10. S.W., blowing fresh. 14. W.N.W., light. 15. E. to S.E., fresh. 16. E.N.E., moderate breezes. 18. S.W., very light. 19. S., blowing fresh. 20. N„ moderate. 21. N.E., light breezes. 23. W., light. 25. W.S.W., blowing very fresh. 26. W.S.W., blowing fresh." North Foreland.—" Nov. 1. N.W. 2. E. to S.E., fresh. 3. Vari- able. 4. E., squally. 6. Blowing fresh. 12. S.W. : noon, W.N.W. : p.m. W., squally. 14. N.W. by W. to N., light. 15. E. to E.S.E., blowing strong. 16. E.S.E., blowing fresh. 17. E.S.E., fresh. 18. S.E. to S.S.W., light. 20. N. to E., moderate. 21. N.E. 22. S.E., moderate. 23. W.S.W., light. 24. S. to S.W., blowing hard; rain. 25. S.W., squally, with rain. 26. S.S.W. to S., blowing strong." Yarmouth (Norfolk).—" Nov. 1. N.W., fine. 2. N.N.E. 9. S.S.W., blowing fresh. 10. S.S.W. to S.W., fresh breeze. 11. S.S.W. to S.W., blowing strong, with rain. 12. 6 p.m. N.W., strong. 14. N. to W.N. W., fine. 15. S.S.E. 16. Last night and all this day the wind has blown fresh from E.N.E. to N.E. 17. E. 25. S. to S.S.W., blowing strong. 26. S.S.W., blowing fresh." Lowestoft.— "Nov. 1. W. 2. E.N.E., light breezes. 18. N.W., light. 21. N.N.E. , light breezes." Flamborough Head. — "Nov. 1. W. to N.W., light breezes. 2. E.S.E., light breezes. 3. E. to E.S.E., light breeze. 4. E.N.E. , strong breezes. 5. E.N.E., strong breezes and squally. 6. E.N.E., strong breezes. 7. N.E., strong breezes and squally. 8. W.N.W. , light breeze. 9. S.W., strong gales. 10. S.W., light breezes. 11. S. by E., strong breezes, with rain. 12. S.W. to W., fresh breezes. 13. S.W., light breezes : evening, E., light. 14. N. to N.E., moderate breezes. 15. E., moderate breezes. 16. E., strong breezes. 17. E.N.E., blowing fresh. 18. W., light breezes. 20. N.N.E., strong breezes. 21. N.E. , strong breeze. 22. S.S.W. to S., strong breeze. 23. W., moderate breeze. 24. S.E., strong gale ; rain. 25. S., strong breeze. 26. S.S.W. to S.W., strong breezes." North Shields. — " Nov. 1. N.W., brisk in the morning. 2. S.S.W. morning and evening ; light and S.S.E. in the middle of the day ; brisk. 3. S.E. and E. S.E. , moderate: evening, E. 4. E.N.E., strong. 5. N.E., strong, but moderate towards evening. 6. E.N.E., moderate. 7. 9 a.m. N.N.E., light: 9 p.m. W.N.W., fresh; light rain. 8. 9 a.m. W.N.W., light: 2 p.m. W.S.W., Mr. W. Brown on the Oscillations of the Barometer. 267 light: 9 p.m. S.W., almost calm. 9. Storm from S.W., which began early in the morning and continued till 5 p.m., at which time the wind had sunk down to a calm with rain ; the barometer being then at its minimum, 29*276. The calm continued through the night, with a hoar frost. 10. 9 a.m. W.N.W., very light; sky clear, but soon afterwards overcast: 2 p.m., wind extremely light and variable; rain falling: 9 p.m. wind strong from S.E., which continued, with heavy rain, all night; and until after- noon of the 11th, on which day the air became again calm in the evening. 12. 9 a.m. "W.N.W., very light wind: 9 p.m. strong from N.W. 13. 9 a.m. and 2 p.m. wind extremely light from W.S.W. and S.W. ; in the evening strong from N.E., with rain. 14. N.E., brisk. 15. N.E., brisk, with showers during the day, and strong at night. 16. N.E. and E.N.E., strong. 17. 9 a.m. E., very light; calm during the remainder of the day. 18. W.S.W., very light during most of the day, but strong at night. 19. Morning, W.S.W., brisk: evening, light from W.N.W., slight rain. 20. N.E., rather brisk; showers in the evening and during the night. 21. N. to N.W., rather brisk in the middle of the day; showers. 22. Morning, strong from S. S.W. ; changed to S.W. in the afternoon, and sunk down to a calm in the even- ing; rain and snow. 23. N.W., rather brisk. 24. A storm, with rain from S.S.E., which abated towards evening. 25. S.S.E., strong till evening, when the air became calm ; fine showers. 26. S.S.W. and S.W., light; rain in the evening." The Tables which follow contain the indications of the ba- rometer from the 1st to the 26th; each day is divided into three columns ; the second and third contain the observations for morning and evening, and the middle one those of the middle of the day. The hours of observation are given after the names of the places, which are placed in the order from north to south, but the western before the eastern. In a co- lumn previous to those containing the daily indications are given the mean heights of the barometer for each place, in order that the daily heights may be compared with each other*, in which comparison the difference of pressure due to the latitude ought to be borne in mind. With the excep- tion of the observations at Paris, Christiania, and North Shields, which are reduced to the temperature of 32° Fahr., the num- bers are those which are read off from the barometer ; as, * It is not meant by this to be understood that these means are given as representing by their differences the differences of height of the several barometers as read off from each scale, supposing them placed in juxtapo- sition, but only to serve in the following observations for standards for the comparison of their variations with each other in the absence of any other method of doing it; but the unusual equality of the mean pressure of the atmosphere of this month over so large a space, renders the means chosen sufficiently accurate for this purpose. 268 Mr. W. Brown on the Oscillations of the Barometer. however, one degree of Fahrenheit affects the barometer at 30 inches only *003 inch, and there is seldom a greater dif- ference than 3° between the temperatures of consecutive ob- servations, it will not affect any of the conclusions which may be deducible from them. The numbers representing the heights at Christiania in Paris lines, and at Paris in millime- tres, have been reduced to English inches. Names of places. Hours of observation. Mean of the month. Orkneys .. Glasgow*. . Belfast Armaghf.. Shields Cork Bristol Plymouth... London ... Paris Christiania . 9% a.m. & 8£ p.m. 9 a.m. & p.m. 9 a.m. & 3 p.m. 10 a.m. & p.m. 9 a.m. & 2 & 9| p.m. 9 a.m. & 3 p.m. 9£ a.m. & p.m. 9 a.m. & p.m. 9 a.m & 3 p.m. 9 a.m. & 3 & 9 p.m. 9 a.m. & 10 p.m. 29-70 29-53 2974 29-44 29-68 2974 29-70 2971 2972 2961 2971 3010 30-07 3035 30-14 30-22 30-22 30-27 30-23 3008 29-61 30-33 3017 3015 3017 30-22 3008 29-97 30-21 3014 3016 3000 29-96 30-24 3007 30-24 29-91 30-21 29-98 3009 30 09 3014 29-90 30-03 3018 30-19 29-92 3010 30-22 3001 29-82 3016 30-01 3000 29-83 30-20 Orkneys .. Glasgow .. Belfast Armagh .. Shields Cork Bristol Plymouth. . London .. Paris Christiania 3. 30-20 3000 3016 29-86 30-10 29-83 29-94 29-88 3000 29-76 3027 30-18 30-10 29-83 2996 30-28 3008 29-97 3015 2998 29-95 29-69 30-36 30-44 30-21 30-38 30-12 30-25 3016 30-07 3009 3006 29-75 30-42 30-45 30-34 3016 30-13 30-54 30-34 30-23 30-40 30-21 30-21 29-86 30-32 30-53 30-37 30-57 30-30 30-39 30-33 30-23 30-26 3019 2975 30-28 30-55 30-33 30-32 30-12 30-51 30-28 30-23 30-34 3016 3019 2975 30-27 * These observations give a mean much below the general one, which is probably the defect of the scale. I have compared them, however, with those given in the tables of the Philosophical Magazine for Applegarth Manse in Dumfries-shire, a locality not far distant, with which their varia- tions agree, with the exception of being a little in advance in movements coming from north, for which reason I have given them the preference here. I may add also, that the observations at Belfast were received with the information that they might be rather defective, which however is of little consequence, as those at Armagh are given. I have inserted the former, because of those at 3 p.m. f Height of the barometer 21 1 feet above the level of the sea. Mr. W. Brown on the Oscillations of the Barometer. 269 6. 7. 8. Orkneys ... 30-49 30-43 30-30 3000 29-83 29-42 Glasgow ... 30-24 30-27 30-23 3007 29-87 29 58 30-51 30-48 30-43 3019 3004 Armagh ... 30-26 30-24 30-20 3008 29-88 29-39 Shields 30-34 30-35 30-33 30-30 30-27 30-23 3005 29-97 29-77 Cork 30-30 30-30 30-32 30-18 30-33 30-18 3013 3014 3001 29-99 Bristol Plymouth... 30-23 30-24 30-24 30-24 30-21 3005 London ... 30-20 3016 3013 30-13 3015 30-08 29-85 29-83 29-87 29-84 29-94 29-93 29-88 Christiania . 30-27 3016 3009 29-95 29-75 29-58 9. 10. 11. Orkneys ... 28-70 28-90 29-29 29-50 29-37 29-12 Glasgow ... 2904 29-21 29-45 ^ 29-33 28-95 28-77 Belfast 29-36 29-41 29-65 29-57 29- 10 2902 Armagh ... 2911 29-30 29-34 28-97 28-74 28-68 Shields 29-37 29-28 29-37 29-62 29-58 29-43 2914 28-99 28-89 Cork 29-42 29-66 29-42 29-55 29-34 29-57 29-20 29-35 28-93 2905 28-91 2902 Plymouth... 29-78 29-66 29-61 29-34 2911 29-13 London ... 29-81 29-82 9Q-70 29-68 29-73 29-64 2918 29-33 2900 29-76 29-78 29-53 2917 Christiania . 29-46 29-28 2914 29-34 29-45 29-48 29-45 12. 13. 14. Orkneys ... 2905 2914 29-26 29-44 29-67 29-86 Glasgow ... 28-74 2901 29-08 29-13 29-65 29-72 2912 29-21 29-32 29-27 29-83 29-91 Armagh ... 28-87 2901 29-01 29-21 29-61 29-56 Shields 28-94 29-20 29-27 29-24 29-25 29-71 29-82 29-84 Cork 29-30 29-31 29-10 29-40 29-66 29-60 29-15 29-48 29-70 29-60 Plymouth... 29-30 29-63 29-44 29-49 29-75 29-61 London ... 2912 29-33 29-51 29-26 29-72 29-80 29-30 29-57 29-66 29-39 29-65 29-67 29-63 Christiania . 29-30 2909 28-96 28-94 28-97 29-16 29-54 15. 16. 17. Orkneys ... 29-97 3005 3015 30-30 30-38 30-32 Glasgow ... 29-73 29-71 29-85 30-08 30-28 30-30 29-85 29-82 29-96 30-06 30-47 30-51 Armagh ... 29-53 29-48 29-66 29-97 30-20 30-25 29-84 29-83 29-86 29-98 3003 30-15 30-40 30-51 Cork 29-40 29-60 29-37 29-61 29-49 29-68 29-70 29-88 30-30 30-25 JO-31 30-46 Plymouth... 29-61 29-67 29-63 29-78 30-25 30-47 London ... 29-69 29-62 29-76 29-79 30-23 30-36 29-57 29-55 29-58 29-53 29-50 29-57 29-79 30-19 Christiania . 29-69 29-72 29-80 29-92 29-98 29-94 29-95 270 Mr. W. Brown on the Oscillations of the Barometer. Orkneys Belfast , Armagh .. Shields Cork Bristol Plymouth.. London .. Paris Christiania 3016 30-25 30-48 3018 30-46 30-29 30-49 30-51 30-58 30-38 30-08 30-37 30-42 30-18 30-53 30-38 30-21 3011 29-82 30-34 30-35 30-43 30-41 3014 19. 29-90 29-68 29-93 29-68 29-88 29-98 3013 30-28 30-23 30-30 30-00 29-86 29-77 29-92 3006 29-93 29-66 29-64 29-73 29-82 3001 30-04 29-82 20. 29-97 29-78 29-94 29-64 »m 29-76 29-83 29-79 29-60 29-64 29-91 29-85 29-80 29-77 29-95 29-80 29-64 29-86 29-63 29-50 29-56 Orkneys ... Glasgow ... Belfast Armagh ... Shields Cork Bristol Plymouth... London ... Paris Christiania . 21. 29-95 29-82 30-01 29-74 29-90 29-84 29-83 29-78 29-80 29-51 29-56 29-95 29-89 29-83 29-82 29-54 29-77 29-62 29-43 29-78 29-76 29-79 29-63 29-56 22. 29-47 29-22 29-42 29-21 29-42 29-58 29-30 29-45 29-42 29-31 29-58 29-42 29-30 29-58 29-28 2913 29-55 29-39 2912 29-21 29-27 29-49 29-62 29-30 29-56 23. 29-36 2917 29-46 2919 29-31 29-34 29-48 29-59 29-50 29-50 29-61 29-32 29-27 2910 29-59 29-30 2901 28-70 2919 2904 29-02 29-33 29-63 Orkneys .. Glasgow .. Belfast Armagh .. Shields Cork Bristol Plymouth.. London . . Paris ..... Christiania 24. 2911 28-71 28-83 28-47 28-89 28-54 28-83 28-95 28-91 28-98 29-65 28-79 28-78 28-54 28-92 2908 28-58 28-40 28-75 28-75 28-87 29-07 29-67 25. 29-04 28-63 28-74 28-47 28-80 28-79 28-75 28-83 2S-90 28-95 29-66 28-82 28-82 28-80 28-88 2910 28-70 28-61 28-83 28-94 2903 29-08 29-58 26. 2910 28-76 28-97 28-73 2891 29-00 29-04 29 13 2909 29-07 29-58 29-04 2904 29-17 29-57 2910 28-90 28-88 29-07 29-24 29-28 29-28 29-60 In the columns which follow, interposed with the text, I have given the amount of the variations in lOOths of an inch between the consecutive observations given in the preceding tables, with the exception of those in which there are three daily observations ; for the 3rd column always contains the difference of the extreme observations of each day, so that in casting the eye down the columns the variations may always belong to the same periods, excepting when the time of the observations varies a little from 9 o'clock ; care however must be taken with regard to the first column to observe those which include a period beginning at 3p.m. on the day previous which is the case when there is no evening observation. For the sake of simplifying the diagrams as much as pos- Mr. W. Brown on the Oscillations of the Barometer. 271 sible, I have in the first place given a chart with the names and localities marked upon it (Plate IV.), and the subsequent ones merely contain the localities marked by dots, and set off in their several places from the chart, so that by reference to it they may easily be found. The arrow representing the direction of the wind at Christiania, placed in the north-east corner, is of course out of its relative position. I have endeavoured to re- present the force of the wind, as given in nautical language, by figures placed at the feet of the arrows : — 0 being a calm, 1 and 2 light airs or winds, 3 moderate, 4 brisk breeze, 5 strong breeze, 6 a gale or stormy, 7 hard gale ; v is variable : the veering of the wind backwards and forwards between points is represented by two arrows from these points, and a change of the wind in the latter part of the day, or night, by a line crossing the foot of the arrow showing its direction. A change in the force also is marked in the same way, by a line underneath the figure. The direction of the wind at Paris and Christiania is taken from the meteorological registers of those places ; and I have also occasionally introduced arrows showing its direction as noted in the registers of other places, but not without caution, as I am more disposed to rely on the mercantile reports, than on observations simply made by noting the direction of one particular vane generally only once in the day. It may also be remarked, that though the varia- tions given in the firstcolumnof each dayare those which have taken place during the previous night, they may yet be generally considered as caused by the wind indicated by the diagrams for that day, because the wind in the morning is usually that of the preceding night, and when a change occurs during the day it is marked as before stated *. Names of Places. Orkneys .. Glasgow .. Belfast Armagh . . Shields Cork Bristol Plymouth London .. Paris Christiania -•02 +•03 -•07 -•06 +•12 +•01 +-o; -•08 -11 -•08 +•35 +•02 -•01 -09 -•06 •00 -17 -•05 -•07 -•03 -•10 +•07 -•06 -•02 -•06 -•04 -02 -•06 -•09 -05 -•08 -•09 -•07 +•17 -•02 -•01 -02 +•04 -•06 -•09 -•07 -12 -•10 -•07 +•07 +•02 •00 •00 -•04 +•08 +•08 +•11 +•05 +•04 +•07 -•07 +•09 • The shipping reports however very frequently do not state the time of the clay the report refers to, when it is extremely probable the wind did not continue in the same direction the whole of the day; so as to occasion in some cases apparent discrepancies in the direction of the wind ; but they may generally be removed by reference to some other report from a neighbouring locality where a change in the direction of the wind is noted. 272 Mr. W. Brown on the Oscillations of the Barometer. Names of Places. Orkneys .. Glasgow .. Belfast Armagh .. Shields Cork Bristol Plymouth London .. Paris Christiania +•16 +•13 +•20 + 15 +•10 +•33 +•09 +•14 +•10 +•06 +•06 +•07 +•09 •00 +•07 +•10 + 13 + 11 + 15 +•14 + 12 +•11 -•10 5. -•01 +•03 +•12 +•07 -•01 +•17 +•02 +•05 +•06 -11 -04 -02 -•06 -•01 -07 6. -02 -•04 + •06 •00 -•02 +•04 +•08 +•10 •00 +•02 •00 -04 -•02 -•06 -02 •00 + 01 +•02 -•11 The first very conspicuous atmospheric phenomenon is an elevation of the barometer, which at Orkney reached the highest point at the p.m. observation of the 4th, and advanced towards south. Its maximum was in the north and north-west, affording an excellent illustration of § 7 ; for on the 4th, the day on which the principal rise took place, we find the col- lision of the currents on the western and south-western side of the chart : thus at the Irish ports and the Scilly islands the wind was south-east, whilst in England and Scotland and at Paris it was north-east. Hence at the Orkneys the barometer stood at 30*54 and at Belfast 30*57, these places being situated in the line of the meeting currents ; whilst at London, which, so far as the observations go, was in the line of the north-east current moving freely, the barometer reached an elevation of only 30*19 ; the advance of the north wind and of the eleva- tion of the barometer likewise accorded with each other, both being from north to south. The observations of the 1st are particularly illustrative of § 5 and § 8 ; in them the opposition of the southern current is seen only in the extreme south, where it is blowing with some strength, causing a fall of the barometer in the south, where the north wind is blowing immediately in front of the south wind (§ 5), and a slight rise in the north by the arrival of the air removed from the south (§ 8). It might be thought that the setting out of the currents in somewhat different directions from the western part of England might give rise to this fall, but it is evidently not so, because it decreases towards the lo- cality where the current takes the easterly deflection. The deflection of the southern current is also worthy of remark. At the Scilly islands the south wind meeting a north-east blows from the south-east, but at Paris meeting a north-west it is south-west or west-south-west (§ 11). The cause of the north wind being north-west in the north and eastern parts, appears to be owing to a deficit of pressure in the east (the barometer at Christiania being '39 inch below that at the Mr. W. Brown on the Oscillations of the Barometer. 273 Orkneys), which on this day was rapidly removed by the air flowing towards it, for at Christiania the height of the baro- meter in the morning was 29*61 and in the evening 29*96. The strength of the south wind after this increases, and on the 2nd and 3rd prevailed almost throughout, occasioning a slight general fall of the barometer until 9 a.m. on the 3rd ; we still however have evidence of the north-east wind blowing on the east, as on the 2nd, on the south-east coast of England, and on the 3rd in the same part, as at the North Foreland, where it was variable (the one and the other of the currents alternately prevailing), and at Deal, where it was north-east, these being almost the most easterly parts of England. After this, however, the north-east wind advanced, becoming ge- neral on the eastern side on the 4th, and raising the baro- meter as before described, the south wind only appearing on the west, blowing there, according to § 11, from south-east. On the 5th and 6th the north-east prevailed throughout, and the barometer was slightly depressed in all the northern sta- tions, beginning at the Orkneys ; the cause of which might be, either the subsidence of an elevation above adjacent loca- lities on the south, by the flowing of the air towards them, or it might be the beginning of the descent of the upper current on the north, which manifested itself at the Orkneys on the 6th by changing the wind to north-west. Names of Places. Orkneys ... Glasgow... Belfast ... Armagh ... Shields ... Cork Bristol ... Plymouth London ... Paris Christiania -13 -•13 -04 -•03 +•02 •00 -03 -03 -•18 -•05 -•03 +•01 •00 -•30 -•16 -12 -•07 •00 •00 +•10 -•14 -•17 -•20 -•24 -•20 -•18 -•20 -•04 -03 +•02 -01 -•20 -•15 -•08 -12 —07 •41 .--72 •29 --54 -•68 +•05 48 -•28 28 -•40 -•09 -•59 •00 If) -•33 •16-27 -•27 •05 --06 17 --12 -11 -•06 +•20 +'17 +•19 •00 -11 -12 -•04 -•18 Names of Places. Orkneys .... Glasgow.... Belfast .... Armagh .... Shields Cork , Bristol .... Plymouth , London ... Paris , Christiania 10. +•39 +•24 +•24 +•04 +•25 -•08 +•02 -•05 -•02 -•05 -14 -•08 -•03 -14 +•21 -•12 -•37 -•19 -•22 -•27 -•04 -•20 +•20 11. -•13 -•38 -•47 -•23 -•29 -•27 -•30 -•23 -•46 -•20 +•11 -•08 -•15 -•02 -•25 -•18 -•06 -•25 -•03 +•02 -•18 -16 •00 Phil. Mag. S. 3. Vol. 28. No. 187. April 184-6. U 274 Mr. W. Brown on the Oscillations of the Barometer. The elevation of the barometer indicated by the foregoing observations, though gradually decreasing from the 4th, did not subside till the approach of a storm from south-west (§15); which began at the Orkney islands on the night of the 7th, was blowing at the island of Mull on the 8th, and arrived at Glasgow at ii p.m. of the same day; in the north of Ireland (Donegal) at 8 p.m.; and at North Shields (a little to the north of Donegal in latitude, but on account of its more easterly position later in receiving the storm) at a very early hour on the morning of the 9th. The change of the wind as the storm progressed is well-marked by the diagrams. On the 7th, the wind remained north-east throughout the day in almost the whole of England, but at the Orkneys had changed to north-west (§ 18), and was variable at Mull island in the evening: at North Shields it changed to north-west after mid-day, and at night the storm began at the Orkneys from south-west. On the 8th, the south-west wind is blowing in the greater part of Scotland, whilst to the southward the wind is still north, but in some cases north-west. In the evening the changes before noticed take place, the wind being yet northerly in the south. On the 9th the storm became pre- valent throughout, on which day the barometer attained its minimum in the north (§ 3), its height in the south being very little reduced (§ 2), although it appears that on that day the wind was blowing as strongly in the south as in the north (§4). The approach of the storm from north is seen also by the falling of the barometer, as indicated by the observations. At North Shields the barometer attained its minimum (there 29-276) at 5 p.m., and at 9 p.m. it had risen (HO, though reckoning simply from the extreme observation, it had not risen at all ; whilst at Orkney it had risen 0*20, and in the south it was yet falling (§ 3). On the morning of the 10th the barometer at the Orkneys had risen 0*39, with a strong gale from north-west (§ 3 and 12) ; but at Shields, from 5 p.m. on the previous day to about the same hour on this, although the barometer rose, the air was almost calm. The diagram, however, together with the barometric heights, fully explains this ; for we see that its position was that of the meeting of the two currents, the north current blowing on the north and the south one on the south (§11), the latter continued by the state of the barometer ; the barometer rising however by reason of the strength of the north wind setting in in the north (§ 6). The north wind in the middle and southern parts of Scotland appears (on account of the low state of the barometer at Orkney) to arise from the impetus which it has received in blowing in the Mr. W. Brown on the Oscillations of the Barometer. 275 extreme north, together probably with a higher barometer on the east (shown by its easterly deflection) : thus we find the wind decreases in strength as it advances, being at Mull is- land only brisk. The equality in the force of the two currents is not however of long continuance, for that of the south wind, evidently because of the great depression of the barometer in the north below its height in the south (Orkney, barometer 28*70, London 29'81), on the 9th, greatly increases and ad- vances as a storm towards the north. But this difference of the atmopheric pressure requiring, on account of the great distance of the localities of the extremes of pressure, and the resistance of the opposite current blowing in the north, a long interval of time to produce its effect, does not arrive at North Shields till the latter part of the 10th as a S.E. or rather S.S.E. storm (being deflected by its collision with the contrary cur- rent) (§11 and 16), and continues until about the same time of the 11th. In the phaenomena now before us we have a good example of an advancing portion of a storm (§ 16). The fall of the barometer, which continues in the south whilst the rise is going on in the north, increases on the 10th, and advances, together with the wind, towards the north, where, excepting in the extreme north, it falls to a greater degree than before, and, as noticed in § 16, the greatest depression is in the south. The progressive motion of the storm may however be traced in both the directions of the figure of § 15, but the south-east movement is in the south : thus at Cork and Ply- mouth the minimum depression occurred on the evening of the 10th, at Bristol about noon of the 11th; for out of four observations that at noon was the lowest (2999); and at Paris (south-east) and at North Shields (north-east) it happened simultaneously about 9 p.m. Hence if we suppose Cork to represent the point C, fig. 3, then the line c C prolonged would extend to Paris, the storm however diminishing in in- tensity, and the line C B from Cork to North Shields. The limit of this storm may be observed in the north; for at Orkney the wind continued northeast, and at Mull island east, but yet the barometer at Orkney falls, though during a north- east wind, but not to so great a degree as the next station (Glasgow) (§ 5), for on the next day (the 12th) the minimum depression, or the point C, was in the south of Scotland or north of England ; hence Orkney would represent the point E. of fig. 1. The diagrams of the 10th and 11th (Plate VII.) are also of interest as regards the deflection of the currents produced by their meeting: on the north the wind is N.E., in the south U2 276 Mr. W. Brown on the Oscillations of the Barometer. of England and in Ireland it is S.W., and at the localities between the two it is S., S.S.E., or S.E. Names of Places. 12. Orkneys !— *07 Glasgow J--03 Belfast J+-10 Armagh +"19 Shields Cork Bristol .... Plymouth . London .... Paris Christiania . +•05 +•39 +•13 +•17 + 12 +•13 -15 +•09 + 01 +•21 +•09 +•27 +•14 +•26 +•33 +•33 +■27 -•21 13. + 12 +•07 + 11 •00 +•07 -•21 -•19 +•18 +•09 -13 -•05 03 +•30 •25 +•18 +•05 +•20 -•02 +•05 -•27 + •01 14. — +•23 +•52 +•56 +•40 +•46 +•26 +•26 +•46 +•26 +•19 +•08 +•11 -06 +•08 +■02 +•19 +•07 -•05 + 13 -10 -14 -02 +•38 Namei of Places. 1"). Orkneys .v. +'H Glasgow +*01 Belfast --06 Armagh — *03 Shields -00 Cork --20 Bristol -00 Plymouth -00 London — *11 Paris --06 Christiania...... +*15 -•03 + -01 + •03| '+ .,7 + • •02 + + 16. +•10 +•14 +•14 +-10 +•181 +-12I+-06 +•12 +-21 +•07 04 +•14 -•05 + •08 +•03 -03 + •15 +•23 +•31 + •17 +•21 +•15 +•04 +•12 17. +•08 +•20 +•41 +•23 +•25 +•60 +•37 +•47 +•44 +•22 -•06 +•04 +•01 +•13 -•06 +•02 +•05 +•11 +•21 +•22 +•40 -03 The phaenomena on the 12th commence a period during which the restoration of the atmosphere to its usual pressure and the rise of the barometer above its mean elevation take place; but their chief interest is in their being those ensuing on the cessation of an advancing storm. The occurrence of the minimum of the atmospheric pressure in the south before its taking place in the north has already been noticed, and is also very apparent from the whole of the observations. Thus at Cork, which seems to represent the point C, § 16, as being in the line of the greatest intensity of the storm, the barometer at 9 a.m. has risen 0'39 inch, and the rise lessens in both di- rections towards south-east, or along the line eC of fig. 3 prolonged, and towards north on the line C B; and in the latter direction at Orkney the barometer still continues to fall, though very slightly. In accordance with this state of the barometer (referring to the same paragraph), the wind is blowing strongly from north-west in the south-west and mid- dle portions, though still opposed by the south wind on the extreme south. In the north, we have clear evidence of the extensive low state of the barometer on the west, for at Chris- tiania, about 10° to the east of the Orkney islands, the height Mr. W. Brown on the Oscillations of the Barometer. 27*7 of the barometer at 9 a.m. was 29*30 inches, and at Orkney the wind is from east, hence at the same distance on the west of these islands the barometer is probably below this. If we now suppose, whilst the wind is blowing as shown by the dia- gram, the point C of fig. 3, by the motion of the line A C (§ 16), to moye considerably northwards, and to be a little to the north of Holyhead, where the wind is strong from north-west, the phaenomena will be simply a particular case of the general result of the paragraph, for the wind is strong from north-west on the localities in the direction which would be that of the line C A, and variable between west and north-west at Flamborough-head, and west-north-west and very light at North Shields, places, which with regard to the figure would be nearly on a horizontal line with the point C; and in the north, but not extending to Orkney (where the ba- rometer is just beginning to rise), the wind is variable between south and west, and extremely light; but at the locality near- est to Orkney, Greenock, it appears to change to north-east in the latter part of the day. This however is the extreme portion of the storm, and accordingly, soon after this, the north wind sets in briskly from north-east instead of from north-west. It may be observed that in the south the rise of the baro- meter ceases at Cork whilst it continues at Plymouth; the phaenomena of the next day (13th) however, explain this, for by the setting in of the current from north-west on the south- west, which opposing the south wind blowing in the more southern parts, causes a very rapid rise of the barometer in the south, but more especially in the south-west, a dispro- portionate pressure there is again produced, and the conse- quences are in some degree the same as before ; for on the 13th, although the barometer rose rapidly at the Orkney islands, and the north-east wind fully set in in Scotland, the south wind blowing previously only in the extreme south, in- creases in strength and becomes prevalent in all the southern part, causing a considerable fall of the barometer in the south, which, as before, occurs first at Cork, confirming the view that the rarefaction of the atmosphere is greatest in the north- west. At North Shields, where on the night previous the wind was strong from the west, it changed to south-west, though extremely light, and caused a slight fall of the barometer be- tween 9 a.m. and 2 p.m. The phaenomena presented by the diagrams of this day, together with the variations of the barometer given in the first column of the 13th, though of the same kind as in two previous instances, afford so striking an example of the case 278 Mr. W. Brown on the Oscillations of the Barometer. of $ 2, because of the blowing of both currents being so fully pointed out, that I cannot pass it over. We see that on the south the south wind is prevalent and strong, and the north is blowing as a fresh breeze in the north, the two cur- rents meeting and balancing one another a little to the north of the centre of the field of observation, and yet in this place the barometer falls, the fall increasing towards south on account of the greater height of the barometer there at its commencement; but at the same time a rise takes place in the north. Now it is certain that if these winds were simply the flow of exactly similar currents, the one flowing from north and the other from south to a space between them, on this space the barometer would rise. What then becomes of the air brought to the place of meeting if the southern current does not carry it off in the upper regions of the atmosphere, as shown in fig. 1 by the upper arrows be- tween c and b ? That it does not arise from any atmospheric change, originating in a central portion, such as a change in the elasticity of the atmospheric columns, causing a portion of air to roll off from their upper parts and a current to set in towards their bases, is very evident, because the diminution of pressure begins and is greatest at the most remote parts of the south wind flowing towards it; but if we admit the ex- planation given by § 2, the phenomena presented by the barometer are perfectly consistent with the action of the two contrary currents, which appear to have met so directly that a calm, or a state of the air nearly approaching to it, is pro- duced*. On the afternoon of the 1 3th the north wind becomes the most prevalent, and the barometer rises rapidly throughout, * As the north and south winds are deflected, the one from east and the other from west, the relative position of England and Scotland might at first sight give rise to the opinion, that when the north was blowing in Scotland and the south in England, they do not blow in opposition to each other, but in parallel bands; in the cases of the 13th and 15th, however, as well as others in which this opposition has been remarked, the observations in Ireland and the extreme west of England remove all doubt as to the actual collision of the currents, for we see by these the two currents blow- ing directly towards each other in the more remote parts, and variable winds, calms, or the deflections of the south current from east, near the place of meeting. It is evident, however, that when the north-east wind prevails in a much greater degree on the eastern parts than on the western, as appears to be the case in some days of this period, the opposite currents may blow in par- allel bands for some distance ; but on the parts immediately adjacent to the north wind, the south wind will be south-east ; hence a northern loca- lity may have a south-east wind when a north-east blows on a southern one more to the east, a case frequently occurring in this country, as on the 2nd and 3rd. Mr. W. Brown on the Oscillations of the Barometer. 279 although in the south during the blowing of a south wind ($ 6). On the remaining clays of this series the north wind continues on the whole to gain in predominance over the south, and to cause the barometer to rise, not however without a check in the south, where the south wind again increases in strength for a time, and causes a slight depression of the barometer on the 14-th and 1 5th, which has its limit northward in the north of England or south of Scotland, where the force of the wind is balanced by the opposite current, repeating the phaenomena of the 13th, though with this difference, that on the 15th the north wind prevails to a greater degree than on the 13th, so that at North Shields the north-east wind itself is blowing; still however there is a slight fall of the barometer (§ 5). On the 16th the south wind has greatly decreased, and serves only to produce the great comparative rise of the barometer at Ork- ney (§ 7), where it attains a height considerably above the mean. On the 17th, the day on which the barometer attains its maximum elevation, we have very little indication of the south wind blowing on the south; it is however blowing on the west, and accordingly we find the elevation beginning in the north-west and extending itself towards the south-east ; now as this is the direction in which the point of C of fig. 1, whether the point of depression or elevation moves, and this elevation differs from that of the 4th, during which also the opposition of the south wind was on the west, in extending eastward and south ; and also as in many previous instances the south wind merely retreated, and did not altogether dis- appear when the north wind advanced; we may infer that in the present case it is yet blowing in localities southward of the latitudes included in the diagram. If not, the phaeno- mena yet admit of easy explanation, on the supposition that the north-east wind, which is blowing with great strength, occupies (j 9) a greater proportion of the height of the at- mosphere than the equal flow of the upper current admits of. Names of Places. Orkneys ... Glasgow ... Belfast ... Armagh ... Shields ... Cork Bristol ... Plymouth London . . . Paris Christiania IS. -•16 -•05 -03 -•07 -05 -02 +•03 +•04 +•22 +•19 -13 -11 -•04 -•11 +•05 -14 -•36 -12 -14 -•08 +•03 +•06 19. -•44 , — -07 -•30: --17 +-o;j -•02 -•04 -•15 -•31 -•27 -•26 -•18 20. +•04 + 12 +•08 •00 + •12 -•16 •00 -•18 -•27 -•44 -■18 -•03 ■00 +•04 -•02 -02 +•02 •00 +•01 -•20 -•70 -•08 280 Mr. W. Brown on the Oscillations of the Barometer. Names of Places. Orkneys ... Glasgow ... Belfast ... Armagh ... Shields ... Cork Bristol ... Plymouth London ... Paris Christiania 21. •00 +•02 +•10 +•10 +•04 +•04 +•15 + 03 +•01 •00 -•06 -•01 -•01 +•02 -•18 -•20 -•31 -•12 -•07 +•01 +•12 •00 22. -•30 -•40 -•53 -•23 -•36 -•25 -•46 -•34 -•40 -•32 +•02 •00 -•12 •00 -14 -•18 -•08 -10 •00 -15 +•19 +•17 -•01 -•02 23. -•03 +•05 +•04 -•02 +•04 -•24 -•01 -•03 +•22 +•20 +0-5 -14 -04 -•24 +•09 -•06 -•16 -•49 -12 -•44 -•57 -17 +•02 Names of Places. Orkneys ... Glasgow ... Belfast ... Armagh ... Shields ... Cork Bristol ... Plymouth London ... Paris Christiania 24. + • •19 •30 •49 -04 •23 •30 -•01 •56 •00 •21 •07 •68 +•01 •35 02 -•03 -•13 -•07 -•14 -•08 -•08 +•09 +•02 25. — 04 +•05 -01 +•07 + •05 +•25 •00 -04 -01 -12 -•01 +•08 +•02 +•01 -•02 +•06 +•07 +•14 + 03 +•19 +•20 +•13 -•08 26. •00 +•06 +•15 +•12 +•08 +•20 +•10 +•10 +•21 -01 •00 +•07 +•04 +•08 00 + 14 +•15 +•16 +•20 + 15 +•21 +•02 Having now given a detailed explanation of the several phaenomena of the preceding observations, it will be sufficient to give a very general account of those of the succeeding ones ; they are however of great interest. The first in occurrence, whose approach is indicated by the p.m. observation of the barometer at the Orkneys on the 17th, is a depression of the barometer by a south wind of just sufficient strength to be called a storm, and its subsequent rise; both progressing from north-west to south-east. Before the restoration of the usual pressure of the atmosphere a second storm occurs, prevailing in Ireland on the night of the 21st, and in England on the 22nd ; and whilst the storm was blowing in the latter country the returning current set in strong from north-west in the former, raising the barometer there to a height considerably above that in England (§ 16) ; its height however on the fol- lowing day was rapidly reduced by the setting in again of the south wind, as we have before seen in cases of a dispropor- tionate elevation of the barometer in the south, and continued the following day (the 24th). Both these storms, but more particularly the latter, approached this island from about the north of Ireland, as appears from the fall of the barometer occurring first at Armagh. It must be recollected however that the observation there is registered at 10 p.m., thus one hour and Mr. W. Brown on the Oscillations of the Barometer. 28 1 a half later than that at the Orkneys ; and as the observation at 3 p.m. at Belfast shows that it occurred between these hours, the difference in time accounts for part of the difference in the variation of the barometer; but in accordance with this view of the direction of its motion, we observe that the greatest depression of the barometer, as shown by the observations, is at Glasgow, and therefore, if not precisely there, it must be somewhere between this and the Orkney islands, and hence it is that the south wind during these storms very seldom extends to the north of Scotland, and that the north wind is generally prevalent there; and when it is not, the south wind is very inconstant, as there is always a northerly direction given on the same locality, excepting when the wind is simply stated east, when there can be little doubt it was from the north of that point ; and if not so, it at least shows that the south wind had little strength. On the 23rd and 24th, how- ever, the days on which the principal depression of this period occurred, the north wind in the north is well-marked, whilst the south wind is blowing in the south. The latter of these storms offers an example of the case of § 16, but one in which there is a more equable division between both portions of the storms of § 15. The two remaining days of the period represent by simi- larity, the remaining portion of the month not included in the observations given; the weather continued stormy, and the barometer fluctuating according to the prevalence of the north or south wind, the north however being on the whole pre- dominant, so that the barometer attained its mean height on the 1st of December. As a very remarkable depression of the barometer occurred on the 13th of January, 1843, I included the first fifteen days of this month in my collection of observations, but with the exception of the storm which occasioned that depression, they do not offer anything sufficiently worthy of notice, after what has already been given, to make it necessary to insert them here. That storm however I notice particularly, because it presents an additional illustration of the action of the storms of § 16, its phaenomenaconfirming the account given of storms, derived from a consideration of those of the 10th and 11th of November 1842. It advanced to the north of England from a line running somewhat in the direction from Cork to Ply- mouth ; thus at Plymouth it began at 1 1 p.m. of the 12th, and at North Shields about half an hour after 5 a.m. of the 13th, six and a half hours later ; but in the south its progress to- wards south-east, or its recession along the line c C of fig. 3, is well-marked, for it began at Cork at 7 p.m. of the 12th, 282 Mr. W. Brown on the Oscillations of the Barometer. four hours sooner than at Plymouth, and at Portsmouth at 2 a.m. of the 13th, three hours later than at Plymouth. At London and Bristol it began at the same hour as at Ports- mouth, 2 a.m.*, so that its "progress in both directions is clearly seen. In this case also, as in the previous one, the storm succeeded a great depression of the barometer in the north. The order of time in which the minimum height of the barometer was attained, coincides exactly with that of the beginning of the storm, and is very conspicuously marked in both directions ; thus in that of the receding portion, or along the line c C of fig. 3, the time of the minimum at Cork was early in the morning, or during the night; at Falmouth 9 a.m.; at Ply- mouth 10 a.m., and at Paris about noon; again in the direc- tion of the advancing portion, or along the line C B, it was two hours later at Bristol than at Falmouth, and at Shields five hours later than at Bristol. I have not thought it necessary to give a diagram showing the directions of the wind, because they may be so easily described. The wind was south-west in the south of Ireland and of England, east and north-east in the north of Scotlandf, and south-east or south-south-east (§11) between the two extremes, as in the north of England and south of Scotland. This storm affords also an illustration of § 4; for though, as on the 11th and 12th of November, 1842, the height of the barometer at its cessation was not very far from equal through- out, the reduction was greater in the north of England than in the extreme south, yet in the former region it was a storm of short continuance and no extraordinary violence, whilst in the latter it is described as a perfect hurricane. Height of Barometer, January 1843. Names of Places. Orkneys .... Glasgow Belfast ..., Armagh .... Shields .... Bristol .... Cork Falmouth , Plymouth , London ... Paris , Christiania 11. 28-76 2875 2910 28-85 28-80 2914 29-08 29-24 29-22 29-11 29-12 28-55 12. 28-99 28-88 2900 8909 2903 28-79 28-65 28-57 28-81 28-78 28-83 28-79 28-79 28-67 28-84 28-74 29-02 28-78 28-84 28-84 29-20 28-80 28-71 28-74 28-07 28-83 2905 28-90 29-20 29-22 29-17 28-97 28-77 28-82 28-70 28-55 28-93 2913 29-23 29-22 2911 28-98 * Shipping Gazette Newspaper, January 1843. t At Tobermorey (Mull) a hard gale from E.N.E. (§ 2), at North Shields S.S.E., and in Leith Roads a gale Iroin ES.E. Mr. W. Brown on the Oscillations of the Barometer. 283 Names of Places. 13. Orkneys 28-57 Glasgow 2790 Belfast 28-10 Armagh .... Shields .... Bristol Cork Falmouth . Plymouth . London .... Paris Christiania . 27-83 28-18 28-18 28-58 28-45 28-44 28-35 28-79 28-96 2805 28-81 28-78 1 28-51 12812 28-22 28-48 • 28-15 j 28-75 2903 28-70 ! 2901 28-32 28-74 28-93 28-91 Minimum on 13th. 28032 27-975 28-45 28-436 28-74 Time of minimum. 14. 4 P.M. 11 A.M. 9 A.M. 10 A.M. about noon 28-52 28-56 28-90 28-61 28-62 2903 28-70 29-08 2917 2905 2919 28-71 28-75 28-72 28-74 28-51 28-61 28-84 28-64 28-77 28-85 29-04 2901 28-68 28-56 Variations of Barom eter. Name* of Places. 11. 12. 13. 14. Orkneys ...!+-28| +•03 +•051 -•02 -•25 --06+-01 -•01 Glasgow ..-(-'19, -•10 +•09 -04 -•80 — 22,+-44 +•05 Belfast ...+-06--11 +•03'+ -03 -•95 +•12 |+-68 -•06 Armagh ... --03 -•28 +•20 -•23 -•72 +•65—13 +•03 Shields ...—01 +-0J +•03 +•09 +•09 -•75 -•13 -03+ -47 +•15 Bristol ... -01 -•36 + •06 +•29, --95 +-57i+-28 -•18 -•20 +•32 •00 -•62 +-23 -•11 +•05 Falmouth . --10 -•41 -03 +•42 +•43 _ -78—33 +-58—03 -•04 Plymouth -•22 -•43 -•08 +•46 +•51 -•78+-26;+-57|+-16 -•45 •16 London ...'+-06 -•09 -•28 -•23 +•44 -•62 -03 —73 -•31 Paris —08 -•33 -•12 -•32 +•14+ -26 -•51 Christiania 1 1 +•12+16 +•15 -02 -■05—20 -15 An extraordinary depression of the barometer (height 28*612) for that latitude occurred about the same time at Parisf as that in England ; it however occurred at 6 a.m. of the day previous to that in this country, for which reason I have noticed it here, as at first sight it might seem opposed to the general order of the phaenomena presented by the fore- going observations; but it did not occur during "the hurri- cane," for the wind in the Paris meteorological register for the 12th is quoted merely " strong," but on the following day, when the fall corresponding to the great depression in En- gland took place, the wind is quoted " very strong," and the tables show also a fall of the barometer in England on the 12th corresponding with that at Paris. I may now conclude this part of the subject by remarking that observations for other periods than those chosen might exhibit difficulties which do not appear in these, although I have made no selection in publishing them, but merely given those I collected on account of the period included in them * Time of minimum not noted but during the night of 12-13. f Annates de Chimic el de Physique. 284 Mr. W. Brown on the Oscillations of the Barometer. being more than usually stormy. Whatever difficulties do arise, however, it must be borne in mind that the situation of this island is peculiar, having in summer a temperature be- low that of parts of Europe on the north, and in winter above that of part of the continent on the south; hence a very con- siderable complexity in the directions of the currents must occasionally occur. The results given in the first portion of this paper are de- duced from the simple fact of the descent of the upper current of the atmosphere, and are altogether independent of the im- mediate cause of its descent; that it must always be descend- ing in some portion or other of its course, to supply the place of the air flowing in the surface current towards the equator, is very evident; but the indications of the barometer show that the acting cause of its descent at any particular time is not — always at least — a deficiency or rarefaction of the air, such as would be occasioned by the flowing of the lower current, were its effect uncompensated by the arrival of air from above, for the south wind often sets in when the barometer is high. I have alluded to this subject before (Phil. Mag. Oct. 1843, p. 280), noticing the effect of the difference of the opposite currents with respect to the quantity of aqueous vapour in each ; but though there appears no reason to doubt that effect being, in a greater or less degree, as there supposed, I stated a difficulty which it is probable does not exist, that of the descending air being warmer than the air previously in its place — an opinion derived simply from the fact of the upper current having, from its origin, generally the higher tempera- ture. Now it may very often be observed, though not always, that the temperature does actually become colder immediately at the change of the wind from north to south, though it rises again on the continuance of the wind ; for when once it has found its way to the surface, then of course, whatever its tem- perature subsequently, it will continue there until its force be overcome, one portion making way for the next following. The cases in which the temperature rises immediately on the change of the wind may be those in which the change either takes place, not from an immediate descent of the current, but simply from its advance (§ 16) from southern localities, where it has previously descended, or perhaps been blowing for some time, and advanced by reason of an increase of force; or by its recession (§ 15) from north*. * This is a distinction which must be carefully borne in mind during the reading of these remarks, and during all consideration of this subject, in order to guard us from drawing inferences in any one particular case of a change of wind, when its nature in this respect is not known. Mr. W. Brown on the Oscillations of the Barometer. 285 Now the south wind descends or blows in the greatest de- gree during the winter half of the year *, and then most at night; that is, when the temperature of the earth and the at- mosphere is falling by radiation; whilst in spring and summer — the temperature increasing — the lower current, or north- east wind, prevails more than at any other time of the year. Now it is obvious that were the cooling of the atmosphere un- affected by that of the earth, its upper strata, notwithstanding the facility with which heat passes through it, would be first and most cooled by radiation ; but we know that within small heights — to the extent of about 100 feet — above the surface of the earth, in which such observations can be easily conducted, the lower strata are much the coldest in nights when radiation is vigorous, by reason of the cooling of the earth. It is ob- vious however that it does not at all necessarily follow from this that this increase of temperature in ascending, or rather as it would be after a certain height, increase compared with the general progressive decrease of the temperature, should go on towards the higher regions of the atmosphere; for it is evident, from the very great rapidity in which the temperature decreases towards the surface, that it is very much, if not al- most entirely, owing to contact ; but on the contrary there will be a certain elevation, perhaps not very great, at which the cooling of the atmosphere by the greater radiation of heat into space in the strata above than in those below it, is so much greater than the cooling in the air below, occasioned by radiation to the earth, that the previous relation of the temperatures of the air of the two currents may become at any time, when this difference is not very great, reversed, and the upper one, being then comparatively the colder, descends. The cooling may also be materially affected by the presence of clouds, and by the heights above the surface of the earth at which they are formed; as these would present a compa- ratively dense radiating body, and by cooling the particles of air in contact with them, would cause currents of cold air to * The blowing of the wind from west, whether north or south, may of course (except in the case (§ 12) where it is caused by the flowing of air to restore the atmospheric pressure as in storms) be taken as evidence of the descent of the upper current; thus in the cold months of the year, although the north wind is strongly urged on towards warmer regions by the greater difference of temperature between adjacent latitudes, due to the season, and frequently prevails, — it is generally from north-west. The phenomena of tropical regions correspond to those of high lati- tudes ; thus the time of descent, or of hurricanes, is after the sun has at- tained its greatest northern declination, consequently when solar radiation is decreasing ; the temperature however is very little fallen, and is in some- what of the variable state of high latitudes, the blowing of the trade-wind being then nearly suspended. l286 Mr. W. Brown on the Oscillations of the Barometer. descend; and also prevent radiation from the earth and atmo- spheric strata beneath them. Admitting such a cause of de- scent of cold air, we shall have an explanation of those sudden colds often experienced, which cannot be accounted for on the supposition of the arrival of air from colder regions. But in the summer half of the year the time of descent of the upper current is not in the night more especially than during the day. Being desirous of confirming the opinion that the south wind prevailed most at night, I selected from my own register of the wind, made three times a day, all the changes of wind from north to south and from south to north for one year, noting the time (whether night or day) at which they oc- curred, and met with the unexpected result, that whilst with regard to the winter months the opinion was amply confirmed, in those of summer the result was rather the opposite to it, the change on the whole taking place most frequently in the daytime ; and in order to confirm this conclusion, the changes were selected from two other years, with the same result. I have presented in a table the average number of changes for the three years, merely remarking that with scarcely an exception the same month of each of the three years gave a result in accordance with the mean one. The table also con- tains the changes from south to north, which are in general opposite to the contrary ones. Number of Changes of Wind. Night. Day. Month. Night. Day. From From From From From i From From From N. to S.'S. to N. N. to S. 1 1 S. to N. N. to S. S. to N. N. to S. S. to N. Jan. 73 1-7 1-7 60 April 23 5-3 6-3 2-7 Feb. 3-7 20 1-7 3-7 May 40 4-0 3-3 3-7 March 6-3 4-3 2-3 4-3 June 33 2-7 13 1-3 Oct. 43 3-3 27 3-3 July 33 53 5-3 43 Nov. 5-3 1-3 1-7 60 Aug. 3-7 50 5-0 3-7 Dec. 50 40 2-3 33 Sept. 3-7 30 2-3 3-3 Total 31-9 166 12-4 266 Total 20-31 , 2.1 32 23-6 190 The want of exact consistency which appears in the results of the summer months is easily accounted for by the lightness of the wind and its arising often from merely local circum- stances ; the total result however is sufficiently decided to show the difference of character of the winter months. Now in summer the temperature of the lower strata of the atmo- sphere with respect to those above, from the heat derived from the ground, is comparatively much greater than in winter, On the Derivation of the Word Theodolite. 287 the difference of course being greatest in the daytime; thus then the daytime is more favourable for the descent of air from the upper strata than in winter. Hence then I think it may be concluded that the air of the upper current becomes relatively colder than the lower strata of the atmosphere by loss of its heat by its own radiation, and that when the cold has arrived at a certain degree, it de- scends, if other conditions which influence its descent are fa- vourable; these conditions being the state of the temperature and pressure of the air of adjacent latitudes, by which the force urging forward the surface current of the atmosphere is affected; and the state of the opposite currents with respect to aqueous vapour. XLVI. On the Derivation of the Word Theodolite. By Professor De Morgan *. T^HE word theodolite has puzzled all who have tried to trace p it to its origin. Some have connected it with the roots of dedofiat, and SoXivo9, and made it a seer of lengths, though the instrument neither does, nor ever did, see anything but angles. In a modern dictionary of good reputation, it is con- nected with deaofxai and 80X09, and made a seer of stratagems, which might apply to a telescope: but unfortunately the use of the term theodolite was prior to the invention of the tele- scope. The word is exclusively English, never having obtained any mention from foreigners till comparatively recent times. The Encyclopedic Melhodique (1789) does indeed give the word without allusion to its origin; but Saverien's dictionary (1753) says that the theodotile (as it is spelt) is an instrument used by the English, much resembling the graphomelre. I find that the use of the word runs back to the " Geometri- call practise named Pantometria," begun by Leonard Digges, and finished by Thomas Digges his son (published London 1571, quarto, reprinted in 1591). But it seems as if the name was not then new. Chapter 27 is on " the composition of the instrument called Theodelitus," and it is plain from various modes of speaking that the word is here an adjective or par- ticiple. This "circle called Theodelitus," or "planisphere called Theodelitus," is nothing but a graduated circle with a revolving diameter furnished with sights, and placed horizon- tally. Held vertically, it would have been the astrolabe of the period, and nothing else. In Leybourn's ' Compleat Sur- veyor,' 1657, we learn that the altitude circle was sometimes * Communicated by the Author. 288 On the Derivation of the Word Theodolite. added; and in Stone's Mathematical Dictionary (1726) that it was sometimes furnished with a telescope. A ruler with sights, travelling upon a graduated circle, was a constituent part of various astronomical instruments im- ported into Europe from the East, and was accompanied by the Arabic term alhidada to express it. The word alidade or alhidade (for it is spelt both ways) is completely naturalized in France, and appears in the common dictionaries. It was also used by the English writers of the sixteenth century, and among others by Digges himself. The original theodolite being nothing but a graduated circle with an alidade, some connexion between the terms might be suspected by those to whose notice they are brought. But so different do the words appear, that I, for one, should never have been reminded of the first by the second, if I had not happened to find, in a writer contemporary with Digges, an intermediate formation, which brings the two words nearer together. William Bourne's * Treasure for Travailers ' was published in 1578 ; he does not use the word theodelite, but calls the instrument the " hori- zon tall or flatte sphere." He begins by spelling the word alhidada thus, alydeday, but soon changes it, and keeps very steadily to athelida, which is the only technical term intro- duced in his description of what Digges calls theodelitus. From these premises, I cannot help inferring that the theo- delited circle of Digges, and the athelidated circle of Bourne, which are certainly the same things, are but described by dif- ferent corruptions of the Arabic word whose earliest Euro- pean form is alhidada. In our day such a transformation might not be easy; but when the works above-mentioned were written, nothing was more common than to spell the same word in two different ways in the course of one sentence. Bourne himself, though he sometimes spells the name of Digges's work correctly, Pantometria, yet in the first place in which it occurs, he makes Pantometay of it, possibly a misprint for Pantometry. The fact seems to have been thus in this and many other instances. In the sixteenth century, before the language was well-settled, an author more accustomed to Latin than En- glish, would try to anglicize some technical terms; and, not finding his results please his own fancy, would then fall back upon the Latin. Bourne has done this with both athelida and pantometria ; and, were it worth while, I could show abundance of similar instances in other writers. Nor is it against the connexion of the words that Digges uses them both. Instances are not wanting in which two dif- ferent spellings of the same word are used by the same writers On the Proportion of Water in the Magnesian Sulphates. 289 for different things. For example, the original English sense of the word square applies to an angle, not a figure; a right angle is a square corner; and to this day the carpenter's right angle is called a square. But I could name half-a-dozen writers of the end of the sixteenth century who use the two spellings square and squire* the former in the modern sense, the latter for the carpenter's instrument. XLVII. Reply to the Observations of M. Pierre, on the Pro- portion of Water in the Magnesian Sulphates and Double Sulphates. By Thomas Graham, Esq., F.R.S.* IN a late number of the Annates de Chimie, a paper by M. Isidore Pierre appears, On the Double Salts formed by the Oxides of the Magnesian Group, of which an abstract is also given in the March Number of the Philosophical Maga- zine, containing statements which demand some remark from myself. It presents new analyses of the sulphate of magne- sia and potash, and other double sulphates of the same type, from which the author infers that these well-known double salts possess seven atoms of water crystallization, and not six atoms, as resulted from my own analyses and the analyses of all other chemists who have of late years examined these salts. The double salts in question are thus made by M. Pierre to have the same proportion of water as sulphate of magnesia itself; while the latter salt, also, is not found to retain its seventh atom of water more strongly than the other six, but to become anhydrous at 212°, or a few degrees above that temperature, in a current of dry air. The author then infers that his results are subversive of the theory which was ori- ginally published by myself, of the constitution of the mag- nesian sulphates, and to which I still adhere, namely that they contain an atom of water strongly attached and not easily- expelled by heat, but readily replaced by an alkaline sulphate, with formation of a double salt. Although confident of the accuracy of the analyses thus im- pugned, I considered it due to M. Pierre, who, although a young chemist, has afforded every evidence of habitual care and accuracy in another experimental inquiry of importance, to repeat my experiments. Of the double sulphate of zinc and potash, 31*46 grains by- drying at 212° for several days, lost 7*75 grains of water ; and by fusion at a heat verging on redness, 0'08 grain of water additional, making the whole loss 7*83 grains. Hence the composition of the salt with reference to water is as follows : * Communicated by the Author. Phil. Mag. S. 3. Vol. 28. No. 1 87. April 1846. X 290 On the Proportion of Water in the Magnesian Sulphates. Theory of Theory of Experiment. 6HO. 7HO (Pierre). Water 24-89 24*03 27*32 Sulphate of zinc and potash 75*11 75*97 72*68 100* 100* 100* The experiment obviously indicates six and not seven equi- valents of water. The slight excess of 0*86 per cent, of water is not more than is usually found in crystallized salts, arising from the difficulty of divesting them entirely of water me- chanically interposed between the plates of the crystals. The peculiarly high disposition of this particular class of salts to retain mechanical water, has been noted by Mitscherlich, my- self, and almost every one else who has made them the sub- ject of investigation. It has probably been the cause of the error into which M. Pierre has fallen, in over-estimating their proportion of water. Although it is scarcely necessary to extend the inquiry to the other double salts of the class, which being isomorphous with the last have necessarily the same proportion of water, still I may be allowed to avail myself of a series of five analyses of the double sulphate of copper and potash lately executed in the laboratory of my friend Prof. Fownes, and which he has kindly communicated to me. Expt. 1. Water 25-20 24-00 7600 100- 25:00 7500 4. 25-2 74-8 100- Theory of Theory of ?HO 5. 6HO. (Pierre). 24-4 24-44 27*40 Sulph. of copper "1 74.cn and potash ... j 75-6 75-56 72-60 100- 100- 100- 100- 100- These experiments all concur in proving that six equiva- lents is the proportion of water in the double sulphate of copper and potash, and not seven equivalents. Although M. Pierre gives seven atoms of water to the double sulphate of magnesia and potash, he adds, near the end of his paper, as if to qualify the statement, that when he communi- cated his results to M. Balard, that chemist informed him that the double sulphate of magnesia and potash contained no more than six equivalents of water, and was therefore consist- ent with the views of Mr. Graham. With reference to the single atom of water strongly retained by the magnesian sulphates, an experiment was made on sul- phate of zinc. The crystallized salt dried for several days at 212°, in the same circumstances as those in which the double sulphate of zinc and potash became anhydrous, still retained water. The heat being continued for three or four days after M. Donny on the Cohesion of Liquids. 293 the salt ceased to lose weight, it was thereafter found to con- sist of — Experiment. With one equivalent of , • ■ A • > water. Sulphate. of zinc . 20-42 89*20 90*03 Water .... 2'46 10-75 9-97 22-88 100- 100- It is sufficiently evident, therefore, that sulphate of zinc, which is admitted by M. Pierre to contain seven equivalents of water, retains one equivalent of water by a stronger affinity than the other six, contrary to his observation ; while, more- over, this strongly retained atom of water is absent in the double sulphate of zinc and potash, the last containing only six atoms of water — the experimental data on which the view of the constitution of these salts controverted by that chemist is founded. XLVIII. On the Cohesion of Liquids and their Adhesion to Solid Bodies. By M. F. Donny, Agrege a V Universite de Gand, Pre'parateur du Cours de Chimie. To the Editors of the Philosophical Magazine and Journal. Gentlemen, THE twenty-sixth volume of your valuable Magazine (p. 541) contains an account of two communications made by Prof. Henry to the American Philosophical Society, on the 5th of April and 17th of May 1844, both relative to the cohesion of liquids. I have been investigating the same subject from the begin- ning of 1841 to the end of 1843, when I gave a full descrip- tion of my experiments on cohesion and adhesion in a written communication addressed to the Academie Royale de Brux- elles. The reception of this memoir is recorded in the Bul- letin de la Seance du 2 Decembre 1843 (tome x. p. 457), and the memoir itself is printed in the Memoires Couronnees et des Savants Etra?igers, tome xvii. I beg leave to direct your at- tention to the contents of this communication. Having discovered, in 1841, as Prof. Henry did in 1844, that the cohesion of liquids is a powerful attraction, entirely misrepresented in the works on natural philosophy, I en- deavoured to find out the cause of this misrepresentation. With this object I constructed a very simple instrument, which enabled me to observe accurately how the separation of water from water is effected, in the well-known experiment of a X2 292 M. Donny on the Cohesion of Liquids, plate suspended from a scale-beam over a vessel of water. The use of this new instrument convinced me immediately that there is no similitude whatever between the rupture of a solid body and this mode of separating water from water. I perceived plainly that such a separation was the final result of a series of successive transformations undergone by that portion of the liquid which is lifted up during the ascension of the plate; which transformations ultimately reduce the thin- nest part of that ascending liquid to so small a diameter, that it gives way, even without any further exterior exertion. The first experimenters, not being aware of this mode of acting, considered the separation of water from water as if it were similar to the rupture of a solid body; they made their calcu- lations accordingly, and so doing, reduced to the lowest pro- portions that very strong molecular attraction which fixed my attention in Europe and Prof. Henry's in America. The learned Professor has proved the magnitude of this molecular attraction by observations on soap-bubbles. I fol- lowed quite a different course, and arrived at more extensive results. I constantly employed liquids placed in glass tubes, whose interior diameter measured from eight to ten millimetres (from three-tenths to four-tenths of an English inch). In similar circumstances, two distinct molecular forces are acting, — the attraction of water for water, or cohesion', and the attraction of water for glass, or adhesion. In my experiments, both co- hesion and adhesion appeared very weak when the liquid was not deprived of that portion of air which it usually contains ; and, on the contrary, proved very powerful when air was ex- cluded. In order to exhibit this power of attraction in airless liquids*, I have made use of two different disjunctive forces; that of mechanical traction in my first two experiments, and that of repulsive caloric in the other. My first experiment was made on sulphuric acid deprived of air by means of a very powerful air-pumpf. In that case molecular attraction proved to be superior to the weight of a column of acid, whose height was 1250 millimetres (more than 4> English feet). * By airless liquids, I mean liquids deprived of air by one of the pecu- liar processes described in my memoir. In this sense, distilled water, al- though containing less air than common water, is far from being an airless liquid. •f- This pump, constructed on a new plan, without either cock or valve, was described in 1841. It is recorded in the Rapport du Jury et Docu- ments de r Exposition de l' 'Industrie Beige en 1841, p. 161. and their Adhesion to Solid Bodies. 293 The second experiment was made on airless water, and the molecular force exceeded the weight of one atmosphere. The third experiment proved the molecular attraction of airless water to be superior to the weight of three atmospheres, and exhibited^ery curious phaenomena. The liquid had been placed in such circumstances as to be free from any pressure whatever; its temperature was carried to -f- 135° Centigrade (about +275 Fahr.) ; and, nevertheless, it did not exhibit the least symptom of ebullition, but by still increasing heat, a part of it was suddenly vaporized with a kind of explosion. A fourth experiment was tried by placing distilled water (not deprived of air) in a tube similar to that used in the third experiment; an external pressure equal to three atmospheres was applied to the liquid, which was then carried to the above- mentioned temperature of 4- 135° Centigrade: a calm, ordi- nary ebullition ensued, without any symptom of explosion. In a fifth experiment, airless water was placed in a situation comparable to that of water in a steam-boiler working under low pressure. Continually increasing heat could not bring the airless liquid to ordinary ebullition ; but the molecular at- traction gave way from time to time by distinct explosions, becoming successively more and more violent, till a final one, blowing up the liquid mass and fracturing the instrument, put an end to the experiment. My sixth experiment exhibited the molecular force in a still more striking form. A tube quite open at one end, half-filled with airless water, was heated over a lamp : no ebullition en- sued, but a violent explosion took place, the water being at the same time suddenly projected out of the tube and con- verted into a cloud of vapour. After a complete description of the experiments, a new theory of the ebullition of liquids is proposed as a consequence of the above-mentioned results, and of some peculiar consi- derations fully expounded in my memoir, and whereof it will be sufficient to mention here two of the most striking. 1. The molecules composing the surfaces of volatile bodies are very much inclined to assume a gaseous form, even whilst the internal molecules are kept together by a strong attrac- tion. 2. Ordinary ebullition does not take place at once in the whole mass of a boiling liquid, the ebullitive motion being ge- nerated from some points of that portion of the boiler's inter- nal surface which is near the source of heat; which points evolve a succession of large bubbles of vapour, tumultuously ascending through the liquid to its uppermost surface. According to this new theory, ebullition is a peculiar kind 294? Dr. Faraday's Researches in Electricity. [Series xix of very rapid evaporation generated on those internal liquid surfaces which surround one or more bubbles of a gaseous Jluid. I am, Gentlemen, Your most humble Servant, Ghent, March 2, 1846. F. DoNNY. XLIX. Experimental Researches in Electricity. — Nineteenth Series. By Michael Faraday, Esq., D.C.L., F.R.S., Fidlerian Prof. Chem. Royal Institution, Foreign Associate of the Acad. Sciences, Paris, Cor. Memb. Royal and Imp. Acadd. of Sciences, Pelersburgh, Florence, Copenhagen, Berlin, Gottingen, Modena, Stockholm, SfC. fyc* §26. On the magnetization of light and the illumination of magnetic lines of force f. Tf i. Action of magnets on light. 2146. Y HAVE long held an opinion, almost amounting to -*- conviction, in common I believe with many other lovers of natural knowledge, that the various forms under which the forces of matter are made manifest have one com- mon origin ; or, in other words, are so directly related and mutually dependent, that they are convertible, as it were, one into another, and possess equivalents of power in their ac- * From the Philosophical Transactions for 1846, Part I., having been read November 20, 1845. f The title of this paper has, I understand, led many to a misapprehen- sion of its contents, and I therefore take the liberty of appending this ex- planatory note. Neither accepting nor rejecting the hypothesis of an aether, or the corpuscular, or any other view that may be entertained of the nature of light; and, as far as I can see, nothing being really known of a ray of light more than of a line of magnetic or electric force, or even of a line of gravitating force, except as it and they are manifest in and by sub- stances; I believe that, in the experiments I describe in the paper, light has been magnetically affected, i. e. that that which is magnetic in the forces of matter has been affected, and in turn has affected that which is truly magnetic in the force of light: by the term magnetic I include here either of the peculiar exertions of the power of a magnet, whether it be that which is manifest in the magnetic or the diamagnetic class of bodies. The phrase " illumination of the lines of magnetic force " has been understood to imply that I had rendered them luminous. This was not within my thought. I intended to express that the line of magnetic force was illuminated as the earth is illuminated by the sun, or the spider's web illuminated by the astronomer's lamp. Employing a ray of light, we can tell, by the eye, the direction of the magnetic lines through a body; and by the alteration of the ray and its optical effect on the eye, can see the course of the lines just as we can see the course of a thread of glass, or any other transparent substance, rendered visible by the light : and this was what I meant by il- lumination, as the paper fully explains. — December 15, 1845 M.F. Nov. 184-5.] Rotation of a Ray of Light by Magnetism, 295 tion *. In modern times the proofs of their convertibility have been accumulated to a very considerable extent, and a com- mencement made of the determination of their equivalent forces. Imml 214-7. This strong persuasion extended to the powers of light, and led, on a former occasion, to many exertions, ha- ving for their object the discovery of the direct relation of light and electricity, and their mutual action in bodies subject jointly to their power f; but the results were negative and were afterwards confirmed, in that respect, by WartmannJ. 2148. These ineffectual exertions, and many others which were never published, could not remove my strong persuasion derived from philosophical considerations; and, therefore, I recently resumed the inquiry by experiment in a most strict and searching manner, and have at last succeeded in magne- tizing and electrifying a ray of 'light '; and in illuminating a magnetic line of force. These results, without entering into the detail of many unproductive experiments, I will describe as briefly and clearly as I can. 2149. But before I proceed to them, I will define the mean- ing I connect with certain terms which I shall have occasion to use : — thus, by line of magnetic force, or magnetic line of force, or magnetic curve, I mean that exercise of magnetic force which is exerted in the lines usually called magnetic curves, and which equally exist as passing from or to magnetic poles, or forming concentric circles round an electric current. By line of electric force, I mean the force exerted in the lines joining two bodies, acting on each other according to the principles of static electric induction (1161, &c), which may also be either in curved or straight lines. By a diamagnetic, I mean a body through which lines of magnetic force are passing, and which does not by their action assume the usual magnetic state of iron or loadstone. 2150. A ray of light issuing from an Argand lamp, was po- larized in a horizontal plane by reflexion from a surface of glass, and the polarized ray passed through a Nichol's eye- piece revolving on a horizontal axis, so as to be easily exa- mined by the latter. Between the polarizing mirror and the eye-piece, two powerful electro-magnetic poles were arranged, being either the poles of a horse-shoe magnet, or the contrary poles of two cylinder magnets ; they were separated from each other about two inches in the direction of the line of the ray, * Experimental Researches, 57, 366, 376, 877, 961, 2071. f Philosophical Transactions, 1834. Experimental Researches, 951- 955. \ Archives de FElectricite, ii. pp. 596-600. 296 Dr. Faraday's Researches in Electricity. [Series xix. and so placed, that, if on the same side of the polarized ray, it might pass near them ; or, if on contrary sides, it might go between them, its direction being always parallel, or nearly so, to the magnetic lines of force (2149.). After that, any trans- parent substance placed between the two poles, would have passing through it, both the polarized ray and the magnetic lines of force at the same time and in the same direction. 2151. Sixteen years ago I published certain experiments made upon optical glass*, and described the formation and general characters of one variety of heavy glass, which, from its materials, was called silicated borate of lead. It was this glass which first gave me the discovery of the relation between light and magnetism, and it has power to illustrate it in a degree beyond that of any other body ; for the sake of per- spicuity 1 will first describe the phasnomena as presented by this substance. 2152. A piece of this glass, about two inches square and 0*5 of an inch thick, having flat and polished edges, was placed as a diamagnetic (2149.) between the poles (not as yet mag- netized by the electric current), so that the polarized ray should pass through its length ; the glass acted as air, water, or any other indifferent substance would do; anGjifSthe eye- piece were previously turned into such a position that the polarized ray was extinguished, or rather the imagflyproduced by it rendered invisible, then the introduction of this glass made no alteration in that respect. In this state of circum- stances the force of the electro-magnet was developed, by sending an electric current through its coils, and immedi- ately the image of the lamp-flame became visible, and conti- nued so as long as the arrangement continued magnetic. On stopping the electric current, and so causing the magnetic force to cease, the light instantly disappeared ; these phasno- mena could be renewed at pleasure, at any instant of time, and upon any occasion, showing a perfect dependence of cause and effect. 2153. The voltaic current which I used upon this occasion, was that of five pair of Grove's construction, and the electro- magnets were of such power that the poles would singly sus- tain a weight of from twenty-eight to fifty-six, or more, pounds. * Philosophical Transactions, 1830, p. 1. I cannot resist the occasion which is thus offered to me of mentioning the name of Mr. Anderson, who came to me as an assistant in the glass experiments, and has remained ever since in the Laboratory of the Royal Institution. He has assisted me in all the researches into which I have entered since that time, and to his care, steadiness, exactitude, and faithfulness in the performance of all that has been committed to his charge, I am much indebted. — M. F. Nov. 1 845.] Rotation of a Ray of Light by Magnetism. 297 A person looking for the phenomenon for the first time would not be able to seent with a weak magnet. 21 54-. The character of the force thus impressed upon the diamagnetic is that of rotation ; for when the image of the lamp-flame has thus been rendered visible, revolution of the eye-piece to the right or left, more or less, will cause its ex- tinction ; and the further motion of the eye-piece to the one side or other of this position will produce the reappearance of the light, and that with complementary tints, according as this further motion is to the right- or left-hand. 2155. When the pole nearest to the observer was a marked pole, i. e. the same as the north end of a magnetic needle, and the further pole was unmarked, the rotation of the ray was right-handed ; for the eye-piece had to be turned to the right-hand, or clock fashion, to overtake the ray and restore the image to its first condition. When the poles were re- versed, which was instantly done by changing the direction of the electric current, the rotation was changed also and became left-handed, the alteration being to an equal degree in extent as before. The direction was always the same for the same line of magnetic force (2149.). 2156. When the diamagnetic was placed in the numerous other positions, which can easily be conceived, about the mag- netic poles, results were obtained more or less marked in ex- tent, and very definite in character, but of which the phaeno- mena just described may be considered as the chief example : they will be referred to, as far as is necessary, hereafter. 2157. The same phenomena were produced in the silicated borate of lead (2151.) by the action of a good ordinary steel horse-shoe magnet, no electric current being now used. The results were feeble, but still sufficient to show the perfect identity of action between electro-magnets and common mag- nets in this their power over light. 2158. Two magnetic poles were employed end-ways, i. e. the cores of the electro-magnets were hollow iron cylinders, and the ray of polarized light passed along their axes and through the diamagnetic placed between them : the effect was the same. 2159. One magnetic pole only was used, that being one end of a powerful cylinder electro-magnet. When the heavy glass was beyond the magnet, being close to it but between the magnet and the polarizing reflector, the rotation was in one direction, dependent on the nature of the pole ; when the dia- magnetic was on the near side, being close to it but between it and the eye, the rotation for the same pole was in the con- 298 Dr. Faraday's Researches in Electricity. [Series xix. trary direction to what it was before ; and when the magnetic pole was changed, both these directions were changed with it. When the heavy glass was placed in a corresponding position to the pole, but above or below it, so that the magnetic curves were no longer passing through the glass parallel to the ray of polarized light, but rather perpendicular to it, then no effect was produced. These particularities may be understood by reference to fig. 1, where a and b represent the first positions of the diamagnetic, and c and d the latter positions, the course of the ray being marked by the dotted line. If also the glass were placed directly at the end of the magnet, then no effect was produced on a ray passing in the direction here described, though it is evident, from what has been already said (2155.), that a ray passing parallel to the magnetic lines through the glass so placed, would have been affected by it. 2160. Magnetic lines, then, in passing through silicated borate of lead, and a great number of other substances (21 73.), cause these bodies to act upon a polarized ray of light when the lines are parallel to the ray, or in proportion as they are parallel to it: if they are perpendicular to the ray, they have no action upon it. They give the diamagnetic the power of rotating the ray; and the law of this action on light is, that if a magnetic line of force be going from a north pole, or coming from a south pole, along the path of a polarized ray coming to the observer, it will rotate that ray to the right-hand; or, that if such a line of force be coming from a north pole, or going from a south pole, it will rotate such a ray to the left- hand. 2161. If a cork or a cylinder of glass, representing the dia- magnetic, be marked at its ends with the letters N and S, to represent the poles of a magnet, the line joining these letters may be considered as a magnetic line of force; and further, if a line be traced round the cylinder with arrow heads on it to represent direction, as in the figure, such a simple model, held up before the eye, will express the whole of the law, and give every position and consequence of direction resulting from it. If a watch be considered as the diamagnetic, the north pole of a magnet being imagined Nov. 1845.] Rotation of a Hay of Light by Magnetism. 299 against the face, and a south pole against the back, then the motion of the hands will indicate the direction of rotation which a ray of light undergoes by magnetization. 2162. I will now proceed to the different circumstances which affect, limit, and define the extent and nature of this new power of action on light. 2163. In the first place, the rotation appears to be in pro- portion to the extent of the diamagnetic through which the ray and the magnetic lines pass. I preserved the strength of the magnet and the interval between its poles constant, and then interposed different pieces of the same heavy glass (2151.) between the poles. The greater the extent of the diamag- netic in the line of the ray, whether in one, two, or three pieces, the greater was the rotation of the ray ; and, as far as I could judge by these first experiments, the amount of rota- tion was exactly proportionate to the extent of diamagnetic through which the ray passed. No addition or diminution of the heavy glass on the side of the course of the ray made any difference in the effect of that part through which the ray passed. 21 64. The power of rotating the ray of light increased with the intensity of the magnetic lines of force. This general effect is very easily ascertained by the use of electro-magnets; and within such range of power as I have employed, it ap- pears to be directly proportionate to the intensity of the mag- netic force. 2165. Other bodies, besides the heavy glass, possess the same power of becoming, under the influence of magnetic force, active on light (2173.). When these bodies possess a rotative power of their own, as is the case with oil of turpen- tine, sugar, tartaric acid, tartrates, &c, the effect of the mag- netic force is to add to, or subtract from, their specific force, according as the natural rotation and that induced by the magnetism is right- or left-handed (2231.). 2166. I could not, perceive that this power was affected by any degree of motion which I was able to communicate to the diamagnetic, whilst jointly subject to the action of the mag- netism and the light. 2167. The interposition of copper, lead, tin, silver, and other ordinary non-magnetic bodies in the course of the mag- netic curves, either between the pole and the diamagnetic, or in other positions, produced no effect either in kind or degree upon the phaenomena. 2168. Iron frequently affected the results in a very consi- derable degree ; but it always appeared to be, either by alter- ing the direction of the magnetic lines, or disposing within 300 Dr. Faraday's Researches in Electricity. [Series xix. itself of their force. Thus, when the two contrary poles were on one side of the polarized ray (2150.), and the heavy glass in its best position between them and in the ray (2152.), the bringing of a large piece of iron near to the glass on the other side of the ray, caused the power of the diamagnetic to fall. This was because certain lines of magnetic force, which at first passed through the glass parallel to the ray, now crossed the glass and the ray ; the iron giving two contrary poles oppo- site the poles of the magnet, and thus determining a new course for a certain portion of the magnetic power, and that across the polarized ray. 2169. Or, if the iron, instead of being applied on the oppo- site side of the glass, were applied on the same side with the magnet, either near it or in contact with it, then, again, the power of the diamagnetic fell, simply because the power of the magnet was diverted from it into a new direction. These effects depend much of course on the intensity and power of the magnet, and on the size and softness of the iron. 2170. The electro-helices (2190.) without the iron cores were very feeble in power, and indeed hardly sensible in their effect. With the iron cores they were powerful, though no more electricity was then passing through the coils than be- fore (1071.). This shows, in a very simple manner, that the phsenomena exhibited by light under these circumstances, is directly connected with the magnetic form of force supplied by the arrangement. Another effect which occurred illus- trated the same point. When the contact at the voltaic bat- tery is made, and the current sent round the electro-magnet, the image produced by the rotation of the polarized ray does not rise up to its full lustre immediately, but increases for a couple of seconds, gradually acquiring its greatest intensity; on breaking the contact, it sinks instantly and disappears ap- parently at once. The gradual rise in brightness is due to the time which the iron core of the magnet requires to evolve all that magnetic power which the electric current can deve- lope in it; and as the magnetism rises in intensity, so does its effect on the light increase in power; hence the progressive condition of the rotation. 2171. I cannot as yet find that the heavy glass (2151.), when in this state, i. e. with magnetic lines of force passing through it, exhibits any increased degree, or has any specific magneto-inductive action of the recognized kind. I have placed it in large quantities, and in different positions, between magnets and magnetic needles, having at the time very deli- cate means of appreciating any difference between it and air, but could find none. Nov. 1845.] Rotation of a Ray of Light by Magnetism. 301 2172. Using water, alcohol, mercury, and other fluids con- tained in very large delicate thermometer-shaped vessels, I could not discover that any difference in volume occurred when the magnetic curves passed through them. 2173. It is time that I should pass to a consideration of this power of magnetism over light as exercised, not only in the silicated borate of lead (2151.), but in many other sub- stances ; and here we perceive, in the first place, that if all transparent bodies possess the power of exhibiting the action, they have it in very different degrees, and that up to this time there are some that have not shown it at all. 2174. Next, we may observe, that bodies that are exceed- ingly different to each other in chemical, physical, and me- chanical properties, develope this effect; for solids and liquids, acids, alkalies, oils, water, alcohol, aether, all possess the power. 2175. And lastly, we may observe, that in all of them, though the degree of action may differ, still it is always the same in kind, being a rotative power over the ray of light ; and further, the direction of the rotation is, in every case, inde- pendent of the nature or state of the substance, and dependent upon the direction of the magnetic line of force, according to the law before laid down (2160.). 2176. Amongst the substances in which this power of action is found, I have already distinguished the silico-borate of Lead (2151.) as eminently fitted for the purpose of exhibiting the phaenomena. I regret that it should be the best, since it is not likely to be in the possession of many, and few will be in- duced to take the trouble of preparing it. If made, it should be well-annealed, for otherwise the pieces will have consider- able power of depolarizing light, and then the particular phae- nomena under consideration are much less strikingly observed. The borate of lead, however, is a substance much more fusi- ble, softening at the heat of boiling oil, and therefore far more easily prepared in the form of glass plates and annealed; and it possesses as much magneto-rotative power over light as the silico-borate itself. Flint-glass exhibits the property, but in a less degree than the substances above. Crown-glass shows it, but in a still smaller degree. 2177. Whilst employing crystalline bodies as diamagnetics, I generally gave them that position in which they did not affect the polarized ray, and then induced the magnetic curves through them. As a class, they seemed to resist the assump- tion of the rotating state. Rock-salt and fluor-spar gave evi- dence of the power in a slight degree ; and I think that a cry- stal of alum did the same, but its ray length in the transparent 302 Dr. Faraday's Researches in Electricity. [Series xix. part was so small that I could not ascertain the fact decisively. Two specimens of transparent fluor, lent me by Mr. Tennant, gave the effect. 2178. Rock-crystal, four inches across, gave no indications of action on the ray, neither did smaller crystals, nor cubes about three-fourths of an inch in the side, which were so cut as to have two of their faces perpendicular to the axis of the crystal (1692, 1693.), though they were examined in every direction. 2179. Iceland spar exhibited no signs of effect, either in the form of rhomboids, or of cubes like those just described (1695.). 2180. Sulphate of baryta, sulphate of lime, and carbonate of soda, were also without action on the light. 2181. A piece of fine clear ice gave me no effect. I can- not however say there is none, for the effect of water in the same mass would be very small, and the irregularity of the flattened surface from the fusion of the ice and flow of water, made the observation very difficult. 2182. With some degree of curiosity and hope, I put gold- leaf into the magnetic lines, but could perceive no effect. Considering the extremely small dimensions of the length of the path of the polarized ray in it, any positive result was hardly to be expected. 2183. In experiments with liquids, a very good method of observing the effect, is to inclose them in bottles from 1^ to 3 or 4 inches in diameter, placing these in succession between the magnetic poles (2150.), and bringing the analysing eye- piece so near to the bottle, that, by adjustment of the latter, its cylindrical form may cause a diffuse but useful image of the lamp-flame to be seen through it: the light of this image is easily distinguished from that which passes by irregular re- fraction through the striae and deformations of the glass, and the phaenomena being looked for in this light are easily seen. 2184. Water, alcohol, and aether, all show the effect; water most, alcohol less, and aether the least. All the fixed oils which I have tried, including almond, castor, olive, poppy, linseed, sperm, elaine from hog's lard, and distilled resin oil, produce it. The essential oils of turpentine, bitter almonds, spike lavender, lavender, jessamine, cloves, and laurel, produce it. Also naphtha of various kinds, melted spermaceti, fused sulphur, chloride of sulphur, chloride of arsenic, and every other liquid substance which I had at hand and could submit in sufficient bulk to experiment. 2185. Of aqueous solutions I tried 150 or more, including the soluble acids, alkalies and salts, with sugar, gum, &c, the Nov. 1845.] Rotation of a Ray of Light by Electric Force, 303 list of which would be too long to give here, since the great conclusion was, that the exceeding diversity of substance caused no exception to the general result, for all the bodies showed the property. It is indeed more than probable, that in all these cases the water and not the other substance present was the ruling matter. The same general result was obtained with alcoholic solutions. 2186. Proceeding from liquids to air and gaseous bodies, I have here to state that, as yet, I have not been able to de- tect the exercise of this power in any one of the substances in this class. I have tried the experiment with bottles 4 inches in diameter, and the following gases: oxygen, nitrogen, hydrogen, nitrous oxide, defiant gas, sulphurous acid, mu- riatic acid, carbonic acid, carbonic oxide, ammonia, sulphu- retted hydrogen, and bromine vapour, at ordinary tempe- ratures; but they all gave negative results. With air, the trial has been carried, by another form of apparatus, to a much higher degree, but still ineffectually (2212.). 2187. Before dismissing the consideration of the substances which exhibited this power, and in reference to those in which it was superinduced upon bodies possessing, naturally, rota- tive force (2165. 2231.), I may record, that the following are the substances submitted to experiment: castor oil, resin oil, oil of spike lavender, of laorel, Canada balsam, alcoholic solu- tion of camphor, alcoholic solution of camphor and corrosive sublimate, aqueous solutions of sugar, tartaric acid, tartrate of soda, tartrate of potassa and antimony, tartaric and boracic acid, and sulphate of nickel, which rotated to the right-hand; copaiba balsam, which rotated the ray to the left-hand ; and two specimens of camphine or oil of turpentine, in one of which the rotation was to the right-hand, and in the other to the left. In all these cases, as already said (2165.), the superinduced magnetic rotation was according to the general law (2160.), and without reference to the previous power of the body. 2188. Camphor being melted in a tube about an inch in diameter, exhibited high natural rotative force, but I could not discover that the magnetic curves induced additional force in it. It may be, however, that the shortness of the ray length and the quantity of coloured light left, even when the eye- piece was adjusted to the most favourable position for dark- ening the image produced by the naturally rotated ray, ren- dered the small magneto-power of the camphor insensible. ^[ ii. Action of electric currents on light. 2189. From a consideration of the nature and position of the lines of magnetic and electric force, and the relation of a magnet to a current of electricity, it appeared almost certain 30* Dr. Faraday's Researches in Electricity. [Series xix. that an electric current would give the same result of action on light as a magnet; and* in the helix, would supply a form of apparatus in which great lengths of diamagnetics, and especially of such bodies as appeared to be but little affected between the poles of the magnet, might be submitted to exa- mination and their effect exalted: this expectation was, by experiment, realized. 2190. Helices of copper wire were employed, three of which I will refer to. The first, or long helix, was 0'4< of an inch internal diameter ; the wire was 0'03 of an inch in diameter, and having gone round the axis from one end of the helix to the other, then returned in the same manner, forming a coil sixty-five inches long, double in its whole extent, and con- taining 1240 feet of wire. 2191. The second, or medium helix, is nineteen inches long, 1*87 inch internal diameter, and three inches external dia- meter. The wire is 02 of an inch in diameter, and eighty feet in length, being disposed in the coil as two concentric spirals. The electric current, in passing through it, is not divided, but traverses the whole length of the wire. 2192. The third, or Woolwich helix, was made under my instruction for the use of Lieut.-Colonel Sabine's establish- ment at Woolwich. It is 26*5 inches long, 2'5 inches inter- nal diameter, and 4*7.5 inches external diameter. The wire is 0*17 of an inch in diameter, and 501 feet in length; It is disposed in the coil in four concentric spirals connected end to end, so that the whole of the electric current employed passes through all the wire. 2193. The long helix (2190.) acted very feebly on a mag- netic needle placed at a little distance from it; the medium helix (2191.) acted more powerfully, and the Woolwich helix (2192.) very strongly ; the same battery of ten pairs of Grove's plate being employed in all cases. 2194. Solid bodies were easily subjected to the action of these electro-helices, being for that purpose merely cut into the form of bars or prisms with flat and polished ends, and then introduced as cores into the helices. For the purpose of submitting liquid bodies to the same action, tubes of glass were provided, furnished at the ends with caps; the cylindri- cal part of the cap was brass, and had a tubular aperture for the introduction of the liquids, but the end was a flat glass plate. When the tube was intended to contain aqueous fluids, the plates were attached to the caps, and the caps to the tube by Canada balsam ; when the tube had to contain alcohol, aether or essential oils, a thick mixture of powdered gum with a little water was employed as the cement. 2195. The general effect produced by this form of appa- Nov. 1845.] Rotation of a Ray of Light by Electric Force. 305 ratus may be stated as follows: — The tube within the long helix (2190.) was filled with distilled water and placed in the line of the polarized ray, so that by examination through the eye- piece (2150.), the image of the lamp-flame produced by the ray could be seen through it. Then the eye-piece was turned until the image of the flame disappeared, and, afterwards, the current often pairs of plates sent through the helix; instantly the image of the flame reappeared, and continued as long as the electric current was passing through the helix ; on stop- ping the current the image disappeared. The light did not rise up gradually, as in the case of electro- magnets (2170.), but instantly. These results could be produced at pleasure. In this experiment we may, I think, justly say that a ray of light is electrified and the electric forces illuminated. 2196. The phaenomena may be made more striking, by the adjustment of a lens of long focus between the tube and the polarizing mirror, or one of short focus between the tube and the eye; and where the helix, or the battery, or the substance experimented with, is feeble in power, such means offer assist- ance in working out the effects : but, after a little experience, they are easily dispensed with, and are only useful as accesso- ries in doubtful cases. 2197- In cases where the effect is feeble, it is more easily perceived if the Nichol eye-piece be adjusted, not to the per- fect extinction of the ray, but a little short of or beyond that position ; so that the image of the flame may be but just visible. Then, on the exertion of the power of the electric current, the light is either increased in intensity, or else diminished, or extinguished, or even re-illuminated on the other side of the dark condition ; and this change is more easily perceived than if the eye began to observe from a state of utter darkness. Such a mode of observing also assists in demonstrating the rotatory character of the action on light; for, if the light be made visible beforehand by the motion of the eye-piece in one direction, and the power of the current be to increase that light, an instant only suffices, after stopping the current, to move the eye-piece in the other direction until the light is ap- parent as at first, and then the power of the current will be to diminish it; the tints of the lights being affected also at the same time. 2198. When the current was sent round the helix in one direction, the rotation induced upon the ray of light was one way ; and when the current was changed to the contrary di- rection, the rotation was the other way. In order to express the direction, I will assume, as is usually done, that the cur- Phil. Mag. S. 3. Vol. 28. No. 1 87. April 1846. Y 806 Dr. Faraday's Researches in Electricity. [Series xix. rent passes from the zinc through the acid to the platinum in the same cell (663. 667. 1627.) : if such a current pass under the ray towards the right, upwards on its right side, and over the ray towards the left, it will give left-handed rotation to it; or, if the current pass over the ray to the right, down on the right side, and under it towards the left, it will induce it to rotate to the right-hand. 2199. The law, therefore, by which an electric current acts on a ray of light is easily expressed. When an electric current passes round a ray of polarized light in a plane per- pendicular to the ray, it causes the ray to revolve on its axis, as long as it is under the influence of the current, in the same direction as that in which the current is passing. 2200. The simplicity of this law, and its identity with that given before, as expressing the action of magnetism on light (2160.), is very beautiful. A model is not wanted to assist the memory; but if that already described (2161.) be looked at, the line round it will express at the same time the direction both of the current and the rotation. It will indeed do much more ; for if the cylinder be considered as a piece of iron, and not a piece of glass or other diamagnetic, placed between the two poles N and S, then the line round it will represent the direction of the currents, which, according to Ampere's theory, are moving round its particles ; or if it be considered as a core of iron (in place of a core of water), having an electric current running round it in the direction of the line, it will also re- present such a magnet as would be formed if it were placed between the poles whose marks are affixed to its ends. 2201. I will now notice certain points respecting the de- gree of this action under different circumstances. By using a tube of water (2194.) as long as the helix, but placing it so that more or less of the tube projected at either end of the helix, I was able, in some degree, to ascertain the effect of length of the diamagnetic, the force of the helix and current remaining the same. The greater the column of water sub- jected to the action of the helix, the greater was the rotation of the polarized ray ; and the amount of rotation seemed to be directly proportionate to the length of fluid round which the electric current passed. 2202. A short tube of water, or a piece of heavy glass, being placed in the axis of the Woolwich helix (2192.), seemed to produce equal effect on the ray of light, whether it were in the middle of the helix or at either end ; provided it was always within the helix and in the line of the axis. From this it would appear that every part of the helix has the same effect ; Nov. 184-5.] Rotation of a Ray of Light by Electric Force. 307 and, that by using long helices, substances may be submitted to this kind of examination which could not be placed in suf- ficient length between the poles of magnets (2150.). 2203. A tube of water as long as the Woolwich helix (21.92.), but only 0'4 of an inch in diameter, was placed in the helix parallel to the axis, but sometimes in the axis and sometimes near the side. No apparent difference was pro- duced in these different situations ; and I am inclined to be- lieve (without being quite sure) that the action on the ray is the same, wherever the tube is placed, within the helix, in re- lation to the axis. The same result was obtained when a larger tube of water was looked through, whether the ray passed through the axis of the helix and tube, or near the side. 2204. If bodies be introduced into the helix possessing, naturally, rotating force, then the rotating power given by the electric current is superinduced upon them, exactly as in the cases already described of magnetic action (2165. 21S7.)« 2205. A helix, twenty inches long and 0'3 of an inch in diameter, was made of uncovered copper wire, 0*05 of an inch in diameter, in close spirals. This was placed in a large tube of water, so that the fluid, both in the inside and at the out- side of the helix, could be examined by the polarized ray. When the current was sent through the helix, the water within it received rotating power ; but no trace of such an action on the light was seen on the outside of the helix, even in the line most close to the uncovered wire. 2206. The water was inclosed in brass and copper tubes, but this alteration caused not the slightest change in the effect. 2207. The water in the brass tube was put into an iron tube, much longer than either the Woolwich helix or the brass tube, and quite one-eighth of an inch thick in the side ; yet when placed in the Woolwich helix (2192.), the water rotated the ray of light apparently as well as before. 2208. An iron bar, one inch square and longer than the helix, was put into the helix, and the small water-tube (2203.) upon it. The water exerted as much action on the light as before. 2209. Three iron tubes, each twenty-seven inches long and one-eighth of an inch in thickness in the side, were selected of such diameters as to pass easily one into the other, and the whole into the Woolwich helix (2192.). The smaller one was supplied with glass ends and filled with water; and being placed in the axis of the Woolwich helix, had a certain amount of rotating power over the polarized ray. The Y2 308 Dr. Faraday's Besearches in Electricity. second tube was then placed over this, so that there was now a thickness of iron equal to two-eighths of an inch between the water and the helix; the water had more power of rota- tion than before. On placing the third tube of iron over the two former, the power of the water fell, but was still very con- siderable. These results are complicated, being dependent on the new condition which the character of iron gives to its action on the forces. Up to a certain amount, by increasing the development of magnetic forces, the helix and core, as a whole, produce increased action on the water; but on the ad- dition of more iron and the disposal of the forces through it, their action is removed in part from the water and the rotation is lessened. 2210. Pieces of heavy glass (2151.), placed in iron tubes in the helices, produced similar effects. 2211. The bodies which were submitted to the action of an electric current in a helix, in the manner already described, were as follows: — Heavy glass (2151. 2176.), water, solution of sulphate of soda, solution of tartaric acid, alcohol, aether, and oil of turpentine; all of which were affected, and acted on light exactly in the manner described in relation to magnetic action (2173.). 2212. I submitted air to the influence of these helices care- fully and anxiously, but could not discover any trace of action on the polarized ray of light. I put the long helix (2190.) into the other two (2191. 2192.), and combined them all into one consistent series, so as to accumulate power, but could not observe any effect of them on light passing through air. 2213. In the use of helices, it is necessary to be aware of one effect, which might otherwise cause confusion and trouble. At first, the wire of the long helix (2190.) was wound directly upon the thin glass tube which served to contain the fluid. When the electric current passed through the helix it raised the temperature of the metal, and that gradually raised the temperature of the glass and the film of water in contact with it, and so the cylinder of water, warmer at its surface than its axis, acted as a lens, gathering and sending rays of light to the eye, and continuing to act for a time after the current was stopped. By separating the tube of water from the helix, and by other precautions, this source of confusion is easily avoided. 2214. Another point of which the experimenter should be aware, is the difficult}', and almost impossibility, of obtaining a piece of glass which, especially after it is cut, does not de- polarize light. When it does depolarize, difference of posi- tion makes an immense difference in the appearance. By al- ways referring to the parts that do not depolarize, as the black Rotation of Light by Magnetic and Electric Forces. 309 cross, for instance, and by bringing the eye as near as may be to the glass, this difficulty is more or less overcome. 2215. For the sake of supplying a general indication of the amount of this induced rotating force in two or three bodies, and without any pretence of offering correct numbers, I will give, generally, the result of a few attempts to measure the force, and compare it with the natural power of a specimen of oil of turpentine. A very powerful electro-magnet was em- ployed, with a constant distance between its poles of 2\ inches. In this space was placed different substances: the amount of rotation of the eye-piece observed several times and the ave- rage taken, as expressing the rotation for the ray length of substance used. But as the substances were of different di- mensions, the ray lengths were, by calculation, corrected to one standard length, upon the assumption that the power was proportionate to this length (2163.). The oil of turpentine was of course observed in its natural state, i. e. without mag- netic action. Making water 1, the numbers were as follows : — Oil of turpentine . . . 11*8 Heavy glass (2151.) . . 6*0 Flint-glass 2*8 Rock-salt 2-2 Water 1*0 Alcohol less than water. iEther less than alcohol. 2216. In relation to the action of magnetic and electric forces on light, I consider, that to know the conditions under which there is no apparent action, is to add to our knowledge of their mutual relations ; and will, therefore, very briefly state how I have lately combined these forces, obtaining no appa- rent result (955.). 2217. Heavy glass, flint-glass, rock-crystal, Iceland spar, oil of turpentine, and air, had a polarized ray passed through them; and, at the same time, lines of electro- static tension (2149.) were, by means of coatings, the Leyden jar, and the electric machine, directed across the bodies, parallel to the polarized ray, and perpendicular to it, both in and across the plane of polarization ; but without any visible effect. The tension of a rapidly recurring, induced secondary current, was also directed upon the same bodies and upon water (as an electrolyte), but with the same negative result. 2218. A polarized ray, powerful magnetic lines of force, and the electric lines of force (2149.) just described, were com- bined in various directions in their action on heavy glass 310 Dr. Faraday's Researches in Electricity. [Series xix. (2151. 2176.), but with no other result than that due to the mutual action of the magnetic lines of light, already described in this paper. 2219. A polarized ray and electric currents were combined in every possible way in electrolytes (951-954). The sub- stances used were distilled water, solution of sugar, dilute sul- phuric acid, solution of sulphate of soda, using platinum elec- trodes; and solution of sulphate of copper, using copper elec- trodes; the current was sent along the ray, and perpendicular to it in two directions at right angles with each other ; the ray was made to rotate, by altering the position of the polarizing mirror, that the plane of polarization might be varied; the current was used as a continuous current, as a rapidly inter- mitting current, and as a rapidly alternating double current of induction; but in no case was any trace of action perceived. 2220. Lastly, a ray of polarized light, electric currents, and magnetic lines of force, were directed in every possible way through dilute sulphuric acid and solution of sulphate of soda, but still with negative results, except in those positions where the phaenomena already described were produced. In one arrangement, the current passed in the direction of ra- dii from a central to a circumferential electrode, the contrary magnetic poles being placed above and below; and the ar- rangements were so good, that when the electric current was passing, the fluid rapidly rotated; but a polarized ray sent horizontally across this arrangement was not at all affected. Also, when the ray was sent vertically through it, and the eye- piece moved to correspond to the rotation impressed upon the ray in this position by the magnetic curves alone, the superin- duction of the passage of the electric current made not the least difference in the effect upon the ray. % iii. General considerations. 2221. Thus is established, I think for the first time*, a * I say; for the first time, because I do not think that the experiments of Morrichini on the production of magnetism by the rays at the violet end of the spectrum prove any such relation. When in Rome with Sir H. Davy in the month of May 1814, 1 spent several hours at the house of Morrichini, working with his apparatus and under his directions, but could not suc- ceed in magnetising a needle. I have no confidence in the effect as a direct result of the action of the sun's rays ; but think, that when it has occurred it has been secondary, incidental, and perhaps even accidental ; a result that might well happen with a needle that was preserved during the whole experiment in a north and south position. January 2, 1846. — I should not have written "for the first time" as above, if I had remembered Mr. Christie's experiments and papers on the Influence of the Solar Rays on Magnets, communicated in the Philoso- phical Transactions for 1826, p. 219, and 1828, p. 379.— M.F. Nov. 1845.] Relation of Light to the Magnetic Force. 311 true, direct relation and dependence between light and the magnetic and electric forces ; and thus a great addition made to the facts and considerations which tend to prove that all natural forces are tied together, and have one common origin (2146.). It is, no doubt, difficult in the present state of our knowledge to express our expectation in exact terms ; and, though I have said that another of the powers of nature is, in these experiments, directly related to the rest, I ought, per- haps, rather to say that another form of the great power is distinctly and directly related to the other forms ; or that the great power manifested by particular pheenomena in particular forms, is here further identified and recognised, by the direct relation of its form of light to its forms of electricity and mag- netism. 2222. The relation existing between polarized light and magnetism and electricity, is even more interesting than if it had been shown to exist with common light only. It cannot but extend to common light; and, as it belongs to light made, in a certain respect, more precise in its character and pro- perties by polarization, it collates and connects it with these powers, in that duality of character which they possess, and yields an opening, which before was wanting to us, for the appliance of these powers to the investigation of the nature of this and other radiant agencies. 2223. Referring to the conventional distinction before made (2149.), it may be again stated, that it is the magnetic lines of force only which are effectual on the rays of light, and they only (in appearance) when parallel to the ray of light, or as they tend to parallelism with it. As, in reference to matter not magnetic after the manner of iron, the phaenomena of elec- tric induction and electrolysation show a vast superiority in the energy with which electric forces can act as compared to magnetic forces, so here, in another direction and in the pe- culiar and correspondent effects which belong to magnetic forces, they are shown, in turn, to possess great superiority, and to have their full equivalent of action on the same kind of matter. 2224. The magnetic forces do not act on the ray of light directly and without the intervention of matter, but through the mediation of the substance in which they and the ray have a simultaneous existence ; the substances and the forces giving to and receiving from each other the power of acting on the light. This is shown by the non-action of a vacuum, of air or gases ; and it is also further shown by the special degree in which different matters possess the property. That magnetic force acts upon the ray of light always with the same 312 Dr. Faraday's Researches in Electricity. character of manner and in the same direction, independent of the different varieties of substance, or their states of solid or liquid, or their specific rotative force (2232.), shows that the magnetic force and the light have a direct relation : but that substances are necessary, and that these act in different degrees, shows that the magnetism and the light act on each other through the intervention of the matter. 2225. Recognizing or perceiving matter only by its powers, and knowing nothing of any imaginary nucleus, abstract from the idea of these powers, the phsenomena described in this paper much strengthen my inclination to trust in the views I have on a former occasion advanced in reference to its na- ture*. 2226. It cannot be doubted that the magnetic forces act upon and affect the internal constitution of the diamagnetic, just as freely in the dark as when a ray of light is passing through it ; though the phenomena produced by light seem, as yet, to present the only means of observing this constitu- tion and the change. Further, any such change as this must belong to opake bodies, such as wood, stone, and metal ; for as diamagnetics, there is no distinction between them and those which are transparent. The degree of transparency can at the utmost, in this respect, only make a distinction be- tween the individuals of a class. 2227. If the magnetic forces had made these bodies mag- nets, we could, by light, have examined a transparent magnet ; and that would have been a great help to our investigation of the forces of matter. But it does not make them magnets (2171.)? ar,d therefore the molecular condition of these bodies, when in the state described, must be specifically distinct from that of magnetized iron, or other such matter, and must be a new magnetic condition; and as the condition is a state of ten- sion (manifested by its instantaneous return to the normal state when the magnetic induction is removed), so ihe force which the matter in this state possesses and its mode of action, must be to us a ?icw magnetic force or mode of action of matter. 2228. For it is impossible, I think, to observe and see the action of magnetic forces, rising in intensity, upon a piece of heavy glass or a tube of water, without also perceiving that the latter acquire properties which are not only new to the substance, but are also in subjection to very definite and pre- cise laws (2160. 2199.), and are equivalent in proportion to the magnetic forces producing them. 2229. Perhaps this state is a state of electric tension tending * A speculation, &c. Philosophical Magazine, 1844, vol. xxiv. p. 136. / Difference between the Magnetic and Natural Rotation. 313 to a current ; as in magnets, according to Ampere's theory, the state is a state of current. When a core of iron is put into a helix, every thing leads us to believe that currents of electricity are produced within it, which rotate or move in a plane perpendicular to the axis of the helix. If a diamag- netic be placed in the same position, it acquires power to make light rotate in the same plane. The state it has received is a state of tension, but it has not passed on into currents, though the acting force and every other circumstance and condition are the same as those which do produce currents in iron, nickel, cobalt, and such other matters as are fitted to receive them. Hence the idea that there exists in diamagnetics, under such circumstances, a tendency to currents, is consistent with all the phaenomena as yet described, and is further strength- ened by the fact, that, leaving the loadstone or the electric current, which by inductive action is rendering a piece of iron, nickel, or cobalt magnetic, perfectly unchanged, a mere change of temperature will take from these bodies their extra power, and make them pass into the common class of diamagnetics. 2230. The present is, I believe, the first time that the mole- cular condition of a body, required to produce the circular polarization of light, has been artificially given ; and it is there- fore very interesting to consider this known stats and condi- tion of the body, comparing it with the relatively unknown state of those which possess the power naturally : especially as some of the latter rotate to the right-hand and others to the left ; and, as in the cases of quartz and oil of turpentine, the same body chemically speaking, being in the latter instance a liquid with particles free to move, presents different speci- mens, some rotating one way and some the other. 2231. At first one would be inclined to conclude that the natural state and the state conferred by magnetic and electric forces must be the same, since the effect is the same* but on further consideration it seems very difficult to come to such a conclusion. Oil of turpentine will rotate a ray of light, the power depending upon its particles and not upon the arrange- ment of the mass. Whichever way a ray of polarized light passes through this fluid, it is rotated in the same manner ; and rays passing in every possible direction through it simul- taneously are all rotated with equal force and according to one common law of direction ; i. e. either all right-handed or else all to the left. Not so with the rotation superinduced on the same oil of turpentine by the magnetic or electric forces : it exists only in one direction, i. e. in a plane perpendicular 314 Dr. Faraday's Researches in Electricity. [Series xix. to the magnetic line ; and being limited to this plane, it can be changed in direction by a reversal of the direction of the inducing force. The direction of the rotation produced by the natural state is connected invariably with the direction of the ray of light; but the power to produce it appears to be possessed in every direction and at all times by the particles of the fluid: the direction of the rotation produced by the induced condition is connected invariably with the direction of the magnetic line or the electric current, and the condition is possessed by the particles of matter, but strictly limited by the line or the current, changing and disappearing with it. 2332. Let m, in fig. 3, represent a glass cell filled with oil of turpentine, possessing naturally the power of producing right-hand rotation, and a b a polarized ray of light. If the ray proceed from a to b, and the eye be placed at b, the rota- tion will be right-handed, or accord- Fig. 3. ing to the direction expressed by the arrow-heads on the circle c ; if the ray proceed from b to a, and the eye be placed at a, the rotation will still be right-handed to the observer, i. e. ac- cording to the direction indicated on the circle d. Let now an electric cur- rent pass round the oil of turpentine in the direction indicated on the cir- cle c, or magnetic poles be placed so as to produce the same effect (2155); the particles will acquire a further / rotative force (which no motion / amongst themselves will disturb), and " a ray coming from a to b will be seen by an eye placed at b to rotate to the right-hand more than before, or in the direc- tion on the circle c; but pass a ray from b to «, and observe with the eye at a, and the phenomenon is no longer the same as before ; for instead of the new rotation being according to the direction indicated on the circle d, it will be in the con- trary direction, or to the observer's left-hand (2199). In fact the induced rotation will be added to the natural rotation as respects a ray passing from a to b, but it will be subtracted from the natural rotation as regards the ray passing from b to a. Hence the particles of this fluid which rotate by virtue of their natural force, and those which rotate by virtue of the induced force, cannot be in the same condition. 2233. As respects the power of the oil of turpentine to rotate a ray in whatever direction it is passing through the liquid, it may well be, that though all the particles possess \ Nov. 1845.] Magnetic Rotation of Light. 315 the power of rotating the light, oniy those whose planes of rotation are more or less perpendicular to the ray affect it; and that it is the resultant or sum of forces in any one direc- tion which is active in producing rotation. But even then a striking difference remains, because the resultant in the same plane is not absolute in direction, but relative to the course of the ray, being in the one case as the circle c, and in the other as the circle d, fig. 3 ; whereas the resultant of the mag- netic or electric induction is absolute, and not changing with the course of the ray, being always either as expressed by c or else as indicated by d. 2234. All these differences, however, will doubtless disap- pear or come into harmony as these investigations are ex- tended ; and their very existence opens so many paths, by which we may pursue our inquiries, more and more deeply, into the powers and constitution of matter. 2235. Bodies having rotating power of themselves, do not seem by that to have a greater or a less tendency to assume a further degree of the same force under the influence of mag- netic or electric power. 2236. Were it not for these and other differences, we might see an analogy between these bodies, which possess at all times the rotating power, as a specimen of quartz which rotates only in one plane, and those to which the power is given by the induction of other forces, as a prism of heavy glass in a helix, on the one hand ; and, on the other, a natural magnet and a helix through which the current is passing. The natural condition of the magnet and quartz, and the constrained con- dition of the helix and heavy glass, form the link of the ana- logy in one direction ; whilst the supposition of currents ex- isting in the magnet and helix, and only a tendency or tension to currents existing in the quartz and heavy glass, supplies the link in the transverse direction. 2237. As to those bodies which seem as yet to give no indi- cation of the power over light, and therefore none of the as- sumption of the new magnetic conditions ; these may be di- vided into two classes, the one including air, gases and vapours, and the other rock crystal, Iceland spar, and certain other crystalline bodies. As regards the latter class, I shall give, in the next series of these researches, proofs drawn from phe- nomena of an entirely different kind, that they do acquire the new magnetic condition ; and these being so disposed of for the moment, I am inclined to believe that even air and gases have the power to assume the peculiar state, and even to affect light, but in a degree so small that as yet it has not been made sensible. Still the gaseous state is such a remarkable condi- 316 Dr. Faraday's Researches in Electricity. tion of matter, that we ought not too hastily to assume that the substances which, in the solid and liquid state, possess properties even general in character, always carry these into their gaseous condition. 2238. Rock-salt, fluor-spar, and, I think, alum, affect the ray of light; the other crystals experimented with did not; these are equiaxed and singly refracting, the others are un- equiaxed and doubly refracting. Perhaps these instances, with that of the rotation of quartz, may even now indicate a relation between magnetism, electricity, and the crystallizing forces of matter. 2239. All bodies are affected by helices as by magnets, and according to laws which show that the causes of the ac- tion are identical as well as the effects. This result supplies another fine proof in favour of the identity of helices and mag- nets, according to the views of Ampere. 2240. The theory of static induction which I formerly ven- tured to set forth (1161, &c), and which depends upon the action of the contiguous particles of the dielectric intervening between the inductric and the inducteous bodies, led me to expect that the same kind of dependence upon the intervening particles would be found to exist in magnetic action ; and I published certain experiments and considerations on this point seven years ago (1709 — 1736). I could not then dis- cover any peculiar condition of the intervening substance or diamagnetic ; but now that I have been able to make out such a state, which is not only a state of tension (2227), but de- pendent entirely upon the magnetic lines which pass through the substance, I am more than ever encouraged to believe that the view then advanced is correct. 2241. Although the magnetic and electric forces appear to exert no power on the ordinary or on the depolarized ray of light, we can hardly doubt but that they have some special influence, which probably will soon be made apparent by ex- periment. Neither can it be supposed otherwise than that the same kind of action should take place on the other forms of radiant agents as heat and chemical force. 2242. This mode of magnetic and electric action, and the phamomena presented by it, will, I hope, greatly assist here- after in the investigation of the nature of transparent bodies, of light, of magnets, and their action one on another, or on magnetic substances. I am at this time engaged in investi- gating the new magnetic condition, and shall shortly send a further account of it to the Royal Society. What the possi- ble effect of the force may be in the earth as a whole, or in magnets, or in relation to the sun, and what may be the best Lieut.-Col. Sabine on the Cause of Mild Winters. 317 means of causing light to evolve electricity and magnetism, are thoughts continually pressing upon the mind ; but it will be better to occupy both time and thought, aided by experi- ment, in the investigation and development of real truth, than to use them in the invention of suppositions which may or may not be founded on, or consistent with fact. Royal Institution, Oct. 29, 1845. L. On the Cause of remarkably Mild Winters which occa- sionally occur in England. By Lieut.-Colonel Sabine, R.A., For. Sec. R.S. To the Editors of the Philosophical Magazine and Journal. Gentlemen, THE unusual character of the winter which we have just experienced, together with its effects which we are now witnessing upon our gardens and fields, and its influence on the public health as evidenced by the bills of mortality, should make it an object not only of scientific, but of general interest, to endeavour to trace out the cause of so remarkable a phe- nomenon. By a memorandum with which the Astronomer Royal has been so obliging as to furnish me, it appears that the mean temperature in December, January and February, exceeded the mean temperature of the same months in the preceding year by the amounts respectively of 80,7, 50,3, 11°*2; on an average above 8° for three months. An excess of temperature of such amount and such continuance, must surely, one would suppose, have some sufficiently notable cause. I am not aware that any probable cause has yet been suggested ; but should you oblige me by inserting this com- munication, it may at least be of use in commencing the dis- cussion, and possibly in eliciting the opinions of others, whose views on the subject the public may naturally desire to know. The winter which within my recollection most nearly re- sembled the present, was that of 1821-1822, and undoubtedly the resemblance is in many respects very striking. For the peculiarity in that year there was a cause assigned, adequate 1 believe to account for all the phenomena, and of which the existence was proved : I allude to the extension of the Gulf- stream in that year to the coast of Europe, instead of its ter- minating as it usually does about the meridian of the Azores. In the winter of 1821-1822, the warm water of the Gulf-stream spread itself beyond its usual bounds over a space of ocean which may be roughly estimated as exceeding 600 miles in lati- tude and 1000 in longitude, carrying with it water several de- 318 Lieut.-Col. Sabine on the Cause of Mild Winters grees higher than the temperature of the sea in ordinary years in the same parallels. The facts, both in respect to the Gulf- stream, and to the peculiarities of the winter in that year, were stated in the volume of Pendulum and other observa- tions which I published in 1825 ; perhaps the statement of them now will be most satisfactorily given in the words which were then used : and I have the less hesitation in introducing an extract from that work, because it was published many years ago, and is, I believe, but little known, at least in this country. The statement was as follows : — i( In the passage of the Iphigenia from England to the coast of Africa, a remarkable and very interesting evidence was ob- tained, by observations on the temperature of the sea, of the accidental presence in that year of the water of the Gulf- stream, in longitudes much to the eastward of its ordinary extension. " The Iphigenia sailed from Plymouth on the 4th of Ja- nuary [1822], after an almost continuous succession of very heavy westerly and south-westerly gales, by which she had been repeatedly driven back and detained in the ports of the Channel ; the following memorandum exhibits her position at noon on each day of her subsequent voyage from Plymouth to Madeira, and from thence to the Cape Verd Islands, the temperature of the air in the shade and to windward, and that of the surface of the sea ; it also exhibits in comparison, the ordinary temperature of the ocean at that season, in the respective parallels, which Major Rennell has been so kind as to permit me to insert on his authority, as an approximation founded on his extensive inquiries ; the last column shows the excess or defect in the temperature observed in the Iphi- genia's passage. Date. Latitude N. Longitude W. Surface-water. Excess or Air* Observed. Usual. defect. 1822. "Jan. 5 47 30 7 30 470 49-0 500 -1 6 44 20 9 30 52-5 55-7 525 -r-3-2 Plymouth to 7 41 22 11 37 540 58-2 540 +4-2 Madeira. 8 38 54 13 20 54-2 61-7 55-7 +6 9 No obser vation. 56-0 630 58-0 +5 10 33 40 15 30 607 640 600 +4 19 26 00 17 50 660 65-5 67-0 -1-5 Madeira to 20 24 30 18 50 68-0 670 68-4 -1-4 Cape Verd 1 21 23 06 20 00 69-0 690 69-5 -0-5 Islands. 22 21 02 21 27 69-5 69-5 71-2 -1-7 23 19 20 23 00 706 702 716 -1-4 which occasionally occur in England. 319 " It is seen by the preceding memorandum, that in the pas- sage from Plymouth to Madeira, the Iphigenia found the temperature of the sea, between the parallels of 44|° and 33§°, several degrees warmer than its usual temperature in the same season; namely 3°'2 in 44^°, increasing to 6° in 39°, and again diminishing to 4° in 33§° ; whilst at the same period, the general temperature of the ocean in the adjoining parallels, both to the northward and to the southward, even as far as the Cape Verd Islands in 19f°, was colder by a degree and upwards than the usual average. The evidence of many care- ful observers at different seasons and in different years, whose observations have been collected and compared by Major Rennell, has satisfactorily shown, that the water of the Gulf- stream, distinguished by the high temperature which it brings from its origin in the Gulf of Mexico, is not usually found to extend to the eastward of the Azores. Vessels navigating the ocean between the Azores and the continent of Europe, find at all seasons a temperature progressively increasing as they approach the sun ; the absolute amount varies according to the season, the maximum in summer being about 14° warmer than the maximum in winter; but the progression in respect to latitude is regular, and is nearly the same in winter as in summer, being an increase of 3° of Fahr. for every 5° of lati- tude. It is further observed, that the ordinary condition of the temperature, in the part of the ocean under notice, is little subject to disturbance, and that in any particular parallel and season, the limits of variation in different years are very small ; after westerly winds of much strength or continuance, the sea in all the parallels is rather colder than the average temperature, on account of the increased velocity communi- cated to the general set of the waters of the north-eastern Atlantic towards the south. To the heavy westerly gales which had prevailed almost without intermission in the last fortnight in November, and during the whole of December, may therefore be attributed the colder temperatures observed in the latitude of 47|°, and in those between 26° and 19^°. " If doubt could exist in regard to the higher temperatures between 44^° and 33§° being a consequence of the extension in that year of the Gulf-stream in the direction of its general course, it might be removed by a circumstance well-deserving of notice, namely, that the greatest excess above the natural temperature of the ocean was found in or about the latitude of 39°, being the parallel where the middle of the stream, in- dicated by the warmest water, would arrive, by continuing to flow to the eastward of the Azores, in the prolongation of the great circle in which it is known to reach the mid- Atlantic. 320 Lieut.-Col. Sabine on the Cause of Mild Winters " One previous and similar instance is on record, in which the water of the Gulf-stream was traced by its temperature quite across the Atlantic to the coast of Europe ; this was by Dr. Franklin, in a passage from the United States to France, in November ] 776*. The latter part of his voyage, i. e. from the meridian of 35° to the Bay of Biscay, was performed, with little deviation, in the latitude of 45°; in this run exceeding 1200 miles, in a parallel of which the usual temperature, to- wards the close of November, is about 55^°, he found 63° in the longitude of 35° W., diminishing to 60° in the Bay of Biscay; and 61° in 10° west longitude, near the same spot where the Iphigenia found 5 5 °* 7 on the 6th of January, being about five weeks later in the season. At this spot then, where the Iphigenia crossed Dr. Franklin's track, the temperature in November 1776 was 5^°, and in January 1822, 30,2 above the ordinary temperature of the season. "There can be little hesitation in attributing the unusual extension of the stream in particular years to its greater ini- tial velocity, occasioned by a more than ordinary difference in the levels of the Gulf of Mexico and of the Atlantic; it has been computed by Major Rennell, from the known velocity of the stream at various points of its course, that in the summer months, when its rapidity is greatest, the water requires about eleven weeks to run from the outlet of the Gulf of Mexico to the Azores, being about 3000 geographical miles ; and he has further supposed, in the case of the water of which the temperature was examined by Dr. Franklin, that perhaps not less than three months were occupied, in addition, by its passage to the coasts of Europe, being altogether a course ex- ceeding 4000 geographical miles. On this supposition, the water of the latter end of November 1776 may have quitted the Gulf of Mexico, with a temperature of 83°, in June ; and that of January 1822, towards the end of July, with nearly the same temperature. The summer months, particularly July and August, are those of the greatest initial velocity of the stream, because it is the period when the level of the Ca- ribbean Sea and Gulf of Mexico is most deranged. " It is not difficult to imagine that the space between the Azores and the coasts of the old continent, being traversed by the stream, slowly as it must be, at a much colder season in the instance observed by the Iphigenia than in that by Dr. Franklin, its temperature may have been cooled thereby to a nearer approximation to the natural temperature of the ocean in the former than in the latter case ; and that the difference * Franklin's Works, 8vo, London, 1806, vol. ii. pp. 200, 201. which occasionally occur in England. 321 between the excess of 5°*5 in November, and of 30,2 in Ja- nuary, may be thus accounted for. " If the explanation of the apparently very unusual facts ob- served by Dr. Franklin in 1776, and by the Iphigenia in 1822, be correct, how highly curious is the connexion thus traced between a more than ordinary strength of the winds within the tropics in the summer, occasioning the derangement of the level of the Mexican and Caribbean seas, and the high temperature of the sea between the British Channel and Ma- deira, in the following winter ! " Nor is the probable meteorological influence undeserving of attention, of so considerable an increase in the temperature of the surface water over an extent of ocean exceeding 600 miles in latitude and 1000 in longitude, situated so import- antly in relation to the western parts of Europe. It is at least a remarkable coincidence, that in November and Decem- ber 1821, and in January 1822, the state of the weather was so unusual in the southern parts of Great Britain and in France, as to have excited general observation ; in the meteo- rological Journals of the period it is characterized as ' most extraordinarily hot, damp, stormy, and oppressive ;' it is stated, 1 that an unusual quantity of rain fell both in November and December, but particularly in the latter ;' that ' the gales from the west and south-west were almost without intermission,' and that in December, the mercury in the barometer was lower than it had been known for thirty-five years before*/' * " The following description of this very remarkable winter is extracted from Mr. Daniell's Essay on the Climate of London (Meteorological Essays. London, 1823, pages 297 and 298), and becomes highly curious when viewed in connexion with the unusual temperature of the ocean in the di- rection in which the principal winds proceeded. "'November 1821 differed from the mean, and from both the preceding years, in a very extraordinary way. The average temperature was 5° above the usual amount ; and although its dryness was in excess " (the relative dryness in consequence of the increased temperature) " the quantity of rain exceeded the mean quantity by one-half. The barometer on the whole was not below the mean. All the low lands were flooded, and the sowing of wheat very much interrupted by the wet. '"In December the quantity of rain was very nearly double its usual amount. The barometer averaged considerably below the mean, and de- scended lower than had been known for thirty-five years. Its range was from 3027 inches to 28- 12 inches. The temperature was still high for the season, and the weather continued, as in the last month, in an uninter- rupted course of wind and rain; the former often approaching to a hurricane, and the latter inundating all the low grounds. The water-sodden state of the soil, in many parts, prevented wheat-sowing, or fallowing the land at the regular season. The mild temperature pushed forward all the early- sown wheats to a height and luxuriance scarcely ever before witnessed. The grass and every green production increased in an equal proportion. " ' January, 1822. This most extraordinary season still continued above Phil. Mag. S. 3. Vol. 28. No. 187. April 1846. Z 322 Lieut.-Col. Sabine on the Cause of Mild Winters It is impossible to read this description of the winter of 1821-1822 without being- struck with the many features which it has in common with that of the present year. The excess of heat in both amounted to several degrees, and continued through several months. There were similar floods in many parts of England in the early part and middle of this winter ; and these were not confined to England only, but extended, as in 1821-1822, to many of the rivers of western Europe. The tension of the vapour conveyed to the shores of the British Channel in December, January and February last, was nearly ^rd part greater, as appears by the Greenwich Observations, than in the same months of the preceding year ; although in consequence of the much higher temperature, the humidity of the air, or the ratio of the humidity to saturation, has been less. This was also the case in 1821-1822. We have had an unusual prevalence of westerly and south-westerly winds at the season when they are ordinarily replaced in a much greater proportion by the dry and cold winds which come to us from the interior of the great continents of Europe and Asia. If in the southern parts of Britain, and on the shores of the British Channel, we have been less severely affected by storms and extreme barometrical depressions than was the casein 1821-1822, we may possibly owe the comparative ex- emption to the fact that the excess of heat above the mean has been greater in the winter of 1845-1846 than it was in 1821-1822 ; whence we may infer perhaps that the conflict of the opposing currents of the atmosphere has been removed in the present year further to the north and north-east than on the former occasion ; it is at the limits which are reached by the warm and humid current proceeding from the south-west, and in the localities where it encounters the dry and cold stream pressing from the east and north-east, that the greater atmospherical derangements are produced, and these have been experienced in the northern parts of Britain. The similarity of the two winters having thus been shown, and specially their agreement in those features in which they differ from ordinary winters, it will naturally be asked, what evidence we have to prove or disprove an extension of the Gulf- the mean temperature, but the rain, as if exhausted in the preceding month, fell much below the usual quantity in this. There was not one day on which the frost lasted during the twenty-four hours. " ' Serious apprehensions were entertained, lest the wheats, drawn up a9 they had been by the warm1 and moist weather, without the slightest check from frost, should be exhausted by excessive vegetation, and ultimately be more productive in straw than corn. "' The month of February, still 5° above the mean temperature, ended a winter which never has been paralleled.'" which occasionally occur in England. 323 stream in the present year, similar to that which took place in 1821. To this it must be replied, that strange as it may- appear, this remarkable phaenomenon may take place in any year without our having other knowledge of it than by its effects, although it occurs at so short a distance from our ports, from whence so many hundred vessels are continually crossing and recrossing the part of the ocean where a few simple ob- servations with a thermometer would serve to make it known. We have no organized means of learning an occurrence which, whether it be or be not the cause of the present extremely mild winter, cannot fail whenever it does occur to affect ma- terially and for a considerable length of time the climate of an extensive district of the globe including our own islands. History-has recorded two instances in which the extension of the Gulf-stream is known to have taken place ; and in both we owe our knowledge of it to the casual observations of an acci- dental voyager. Some one there may be in the present winter whose curiosity may have induced him, in the well-frequented passage between England and Madeira, to dip a thermometer in the sea once or twice a day, and who may therefore, perhaps unconsciously, be in possession of the very facts which it is desirable to know ; in such case this communication, should it meet his eye, may be the means of inducing their publica- tion. It is desirable however that we should not be thus altogether dependent on accident for information w7hich may have even greater practical than scientific value ; happily it is well known that suggestions of this nature, when really de- serving attention, do not pass unheeded by our excellent Hy- drographer, to whose department such subjects seem naturally to belong*. But not only might we by such means be occasionally in- formed in November or December that we had probably to expect a continuance of very mild weather through January and February; it is not unreasonable to suppose that such winters might well be anticipated at a still earlier period of the year ; ships sail faster than the Gulf-stream flows, and a more than usual difference existing in the levels of the Gulf of Mexico and the Atlantic, or a more than usual initial ve- locity of the stream itself, with the consequent probability of a winter of unusual mildness in Europe, might be known in England in the summer or in the early autumn ; or even going * It is much to be wished that a society existed in England which should charge itself with the many interesting and important considerations be- longing to physical geography. Did the object and scope of the Royal Geographical Society embrace physical as well as descriptive geography, it cannot be doubted that science and the public would be greatly benefited. Z2 324 M. Pouillet on the Recent Researches q/Trof. Faraday. back to a yet earlier stage of the phenomenon, we might be apprised that the causes which operate in producing the de- rangement of the level of the Caribbean and Mexican seas were prevailing in any particular year in an unusually high degree. I wish in conclusion to guard against the possibility of being understood to suppose that amidst the variety of incidents by which our climate is affected, there may not be others which may be influential in the production of winters of un- usual mildness in an equal, or even in a greater degree than the extension of the Gulf-stream ; or, that whenever the stream reaches the coasts of Europe, its influence on our cli- mate must necessarily occasion winters like that of 1821- 1822, or 1845-1846. It is reasonable to believe that there may be degrees of initial velocity between that which is usual and that which is extreme. There may also be counteracting or qualifying causes with which we are as yet wholly unac- quainted. The object of this communication is rather to re- call to recollection, on the occasion of the present remarkable winter, the coincidence that was discovered between the simi- lar winter in 1821-1822, and the extension of the stream; and to promote the adoption of such simple means as may supply additional evidence, whereby we may discern between coincidence observed on a single occasion, and connexion which may be established by the observation of repeated co- incidence. I am, Gentlemen, Your obedient Servant, Woolwich, March 17th, 1846. Edward Sabine. LI. Observations on the Recent Researches of Prof. Faraday. By M. Pouillet*. TTpOR some months past there has been much talk about a -*- hew series of researches by M. Faraday, the result of which was one of the most important discoveries, the action of magnetism on light. Two authentic documents have at length reached us on this subject ; one is published in the January number of the Philosophical Magazine, being an ab- stract of the sitting of the Royal Society of the 27th of No- vember, the other was communicated at the last meeting of the French Academy by M. Dumas in the name of Mr. Faraday himself. Various results are announced in these two publi- cations, but only one fact is presented with some development, * Translated from the Comptes Rendus, for January 26, 1846. — The re- searches of Prof. Faraday, referred to in this paper, are given entire in our present Number. M. Pouillet on the Recent Researches of Prof. Faraday. 325 it is that which relates to the action of an electro-magnet on a ray of polarized light in turning its plane of polarization either to the right or left, according to the relative directions of the luminous ray and of the resultant of the magnetic actions. This fact is justly considered by Faraday as a fundamental one, for hitherto there is nothing analogous in science ; and it constitutes of itself a discovery of the very highest import- ance. Undoubtedly many persons have hastened to repeat and investigate it in order to ascertain its perfect accuracy, and to find out the most marked characters and the most essential conditions. Immediately after having read the Philo- sophical Magazine I set to work, as I stated at the last meeting of the Academy, but my first trials having been without re- sult, and other persons not having been more fortunate than myself in the attempt, it appeared to me necessary to resume them with greater attention, varying the mode of experiment and making up in the best manner I was able for the want of precision in the directions which had come to my know- ledge. I hasten to lay before the Academy today the result of these researches, and with a twofold motive ; in the first place, to render homage to the author of the discovery, and in the next place, to furnish those physicists who may desire to follow this new path of science with some indications that may be of service to them, if, as I believe, they add anything to what has hitherto been published on the subject. The apparatus employed by me* is composed, — 1st, of a Bun- sen's battery; 2nd, of one or more electro-magnets ; 3rd, of M. Soleil's instrument for exhibiting the least angular displace- ments of the planes of polarization ; 4th, of the various sub- stances to be submitted to examination. The elements of the Bunsen's battery are of the ordinary size ; in the majority of cases ten suffice to render the phenomenon perceptible ; but to measure it and to compare the intensities with a certain approximation, forty, fifty, and even 100 elements must be employed. The electro-magnets are capable of supporting 1600 pounds when excited by a battery of twenty pairs. They are soft iron cylinders, seven to eight centimetres in diameter and about fifty centimetres in length, which are curved in a horse-shoe form, the distance of the axes of the two arms or poles being not more than fifteen to twelve centi- metres. From 500 to 600 metres of copper wire, coated twice with silk, are wound round each arm. The instrument of M. Soleil is composed of two parts, one objective, the other ocular. The objective part, or that which is turned towards the light, is nothing more than a Nicol's prism, behind which 326 M. Pouillet on the Recent Researches o/'Prof. Faraday. is a system of two juxtaposed plates of quartz cemented by one margin, and worked together in order to fulfill a double condition of giving them exactly the same thickness and ren- dering each perfectly perpendicular to the axis. The surface of junction of these plates being parallel to the pencil of light and occupying the centre of its breadth, it is evident that the first half of the pencil traverses one of the plates only, and the second half the other plate ; and as they were selected of opposite rotatory power, the first half of the polarized pencil is found to have its planes of polarization deviated, for instance towards the right, by a certain angle, and the second half, on the contrary, has its planes of polarization deviated towards the left by a perfectly equal angular magnitude. The magni- tude of these deviations depends on the common thickness of the two plates, which is usually from five to six millimetres. The ocular portion, or that directed towards the eye, con- sists, in the first place, of a thick plate of rock-crystal, like- wise perpendicular to the axis, having for instance a rotatory power to the right, and a thickness of five millimetres very accurately determined by the spherometer. Behind this plate is the compensator, composed of two equal prismatic plates, provided with a similar rotatory power towards the left, i. e. in a contrary direction to the first. These two prisms, op- posed like two wedges by their acute angle, are moved simul- taneously by the same spring ; they slide one upon the other, to be arranged sometimes by their less sometimes by their greater thickness, and thus always form a system equivalent to a parallel plate, but one which would vary from the thick- ness 0 to nearly double that of the base of each prism. To avoid the deviations which the light might experience from the variable distance of these prisms and the obliquity of the surfaces, each one is compensated by a glass prism. Lastly, behind the compensator is a doubly refracting achromatic prism and a small Gallilean telescope, to which the eye is applied to observe the pencil of light which has passed both the objective portion, the intermediate bodies submitted to examination, and the ocular portion of the instrument. The graduation of the compensator is easily made; and when this has once been done with sufficient care, the instrument indicates that the cause, whatever it be, which produces the deviation in the plane of polarization has an intensity equiva- lent to that of a plate of quartz of a known thickness ; always, be it understood, on the condition that this cause exercises on the various simple lights actions comparable to that which the quartz exercises. M. Pouillet on the Recent Researches q/'Prof. Faraday. 327 The instrument of M. Soleil, the construction of which I have just described, must be separated into two parts for the experiments under consideration. The objective and the ocular parts were mounted separately on my frame of diffrac- tion*, which is most readily adapted for all the researches in which it is required to centre the apparatus on the same axis. A common lamp is placed before the objective part, and a strong magnifier gives a pencil of light closely parallel, which being propagated in the direction of the common axis, traverses successively the object-glass, the pieces subjected to the test, and the ocular; the distance between the objective and the ocular may vary between tolerably distant limits, for it may extend to nearly two metres, or only to a few centi- metres, according to the nature of the observations. It is "important to remark that the pencil of light is always horizontal, and the apparatus was accidentally arranged so that the light was propagated from south to north, which may assist us to define more easily the relative positions of the polarized ray, of the electro-magnets, and of the bodies on which they act. The electro-magnet is horizontal, that is to say, the plane of the axes of its two branches is horizontal, and precisely at the height of the pencil of light which traverses the appara- tus ; moreover, the vertical plane, formed by the extremities of the two branches or by the poles of the electro-magnet, is parallel to this pencil, and may approach it more or less. This being settled, if it be desired to submit to experiment, for example, a parallelopipedon of flint-glass of ten or twelve centimetres in length and terminated perpendicularly to its length by two parallel planes, this parallelopipedon is first arranged so that the ray polarized by the objective traverses it in the direction of its axis, and if the flint-glass is pure and well-annealed, as it must be for the success of the experiment, its interposition produces neither deviation nor coloration in the ray of light. The electro-magnet is then approached, ar- ranging it in the same manner as if the piece of flint-glass were a piece of iron to close it, and there is even no inconvenience in arranging it so that the two poles of the electro-magnet are in contact with the flint-glass ; the middle of the length of the latter corresponds consequently to the interval which exists between the two arms of the electro-magnet. When these arrangements have been made, a current is passed, and suddenly it is seen that the two tints of the red image, which correspond to the two opposed plates of the quartz of the object-glass, cease to be identical. Let us sup- * See my Elements de Physique, 4th edition, vol. ii. pi. 26. 328 M. Pouillet on the Recent Researches of Prof. Faraday. pose, for example, that the one on the right has turned blue ; if the current is passed in a contrary direction, it is that on the left which this time turns blue in the same manner. Thus, by reversing the poles of the electro- magnet, the action which it exercises on the flint-glass, or on the light which traverses it, is also suddenly reversed. Here then we see the action in question rendered evident in the most striking and incontestable manner. In the circumstances of which I have just spoken, ten ele- ments are more than sufficient to exhibit it to a practised eye ; but with a hundred elements, it assumes such an intensity that persons the most unaccustomed to these kind of observa- tions could not fail to perceive it as a perfectly characterized phaenomenon. Before seeking to ascertain whether this effect, at once so novel and so extraordinary, results from a direct action of the magnetic fluid upon light, or from an indirect action, in which the ponderable matter of the flint-glass intervenes, or at least the collective forces to which this matter is subjected in order to exist in molecular equilibrium, it is necessary first to de- termine precisely what is the nature of the effect produced, and to seek above all to measure its intensity, in order to ascertain what are the conditions under which the phaenome- non is shown with the greatest energy. For this purpose, instead of observing directly the coloured tints which the quartz gives by the lamp perpendicular to the axis, it is necessary to recompose what M. Biot has called the tint of passage. This is done by placing before the ob- jective several systems of blue and greenish glasses ; but I found in the cabinet of the Conservatoire some glasses very slightly coloured blue, which give to this tint a sensitiveness still greater than that obtainable by other means. When these glasses are interposed in the pencil, the tints of the quartz become of a light lilac, on which the least changes of shade are appreciable ; the uncertainties which are presented by the zero of the compensator disappear, and it becomes possible not only to perceive, but to measure the effects which correspond to thicknesses of quartz of a hundredth of a milli- metre. The instrument thus modified, the compensator being at zero, and the polarizing prisms of the object-glass and of the ocular being suitably regulated in their relative positions, the experiment may be proceeded with ; only there is one thing which requires mention, not to pay attention to the yellow image, but to look exclusively at the lilac image, the two halves of which are then exactly of the same shade. M. Pouillet on the Recent Researches of Prof. Faraday. 329 As soon as the current passes, one of the halves of this image, for instance that on the right, is seen to turn blue ; we observe that this tint is persistent as the current itself, and we may be convinced that, from the first instant, it acquired its whole value, that is to say, that the prolonged duration of the action adds nothing perceptible to it. The compensator is then moved in the proper direction ; the difference of the tints gradually disappears in proportion as it advances, and with a little practice the point at which the equality is re-established is soon found. The number of divisions is noted down, and we thus obtain a measure, or at least an approximate measure of the effect produced, — say twenty divisions. When subsequently the current is passed in a contrary di- rection, it is the other half of the tint, that to the left, which turns blue, and it is in the other direction that the compen- sator has to be moved to re-establish the equality. No inter- val of time is appreciable between the change of the current and the change of effect upon the light, and it is again instan- taneously that the tint takes all its value. When the optical ap- paratus is well-adjusted, and the electrical communications are equally good in both directions, the ground gone over by the compensator is the same in the two cases, that is to say, that if it progressed in the first twenty divisions to the right, it should in the second proceed twenty degrees to the left. These opposite effects and the corresponding measures may be repeated indefinitely, either with the same or a different number of pairs of the battery ; and a few hours are sufficient, during which the action of the battery is nearly constant, to pass in review a great number of diaphanous substances, and to obtain a first approximation on the relative sensitiveness with which they obey the magnetic influence. When the substances submitted to the test are more or less coloured, it is necessary to vary the systems of glasses intended to produce the tint of passage, and we do not always succeed in composing a tint equally delicate and easy of observation. It might happen consequently that some substances, even slightly coloured, when submitted to these modes of observa- tion, would appear much less energetic than they are in reality. Let us pause then at the diaphanous substances, and ob- serve that in the experiment with the flint-glass cited above, it was necessary to advance the compensator twenty divisions to the right and twenty divisions to the left, according as the current passed in one direction or the other. Let us bear in mind, that if, instead of interposing on the passage of the pencil a prism of flint-glass submitted to the electro-magnet, 330 M . Pouillet on the Recent Researches of Prof. Faraday. there had been interposed, without magnetic action, a lamina of quartz perpendicular to the axis, of a proper thickness, turning to the right in the first case and to the left in the second, it is certain that the equality of the tints would have been re-established by the same movements of the compen- sator. Now, it is known that the effect produced by such a lamina of quartz would have been to turn the plane of pola- rization from right to left, whence it seems very natural and legitimate to conclude, that the flint-glass subjected to the magnetic action has produced the same effect as this lamina of quartz, that is to say, that it has also turned the plane of polarization to the right for one direction of current, and to the left for the contrary direction. This is, in fact, the con- clusion to which Mr. Faraday has come, and he has charac- terized this new action of magnetism upon light, by stating that the magnetism turns the plane of polarization of the luminous ray submitted to its influence under certain condi- tions, and that the direction of this rotation is connected with that of the current. Quartz, and the other substances which, of themselves, by their nature or structure have, without the intervention of magnetism, the permanent property of turning the planes of polarization, exert this action with variable intensities on the different elements constituting white light; and there are dispersive powers for this rotation, as there are dif- ferent dispersive powers for refraction. It would be very important to make in this respect some researches upon the substances which acquire this property by the magnetic action, analogous to those very remarkable ones which M. Biot made upon the former. The apparatus which I have used must be very much modified to be adapted to this class of experiments ; it serves to show the phaenomena very di- stinctly, rather than to measure them in their more delicate details. Such an investigation, however, cannot be under- taken with phaenomena so little developed as those which I have obtained; for in such limits they might perhaps be as well explained by partial depolarizations towards the right and left as by the rotation itself of the plane of polarization, which, moreover, would not detract anything, and would perhaps add to their importance. As I just stated, the plane of polarization, in that specimen of the flint-glass which gave the most energetic effects, was diverted by the magnetic action as much as it would have been by the action of a plate of quartz two-tenths of a millimetre in thickness ; now, since by changing the direction of the cur- rent, the rotation takes place in an opposite direction, it is seen M. Pouillet on the Recent Researches o/Prof. Faraday. 331 that the total effect obtained by passing from the magnetic action which is exerted in one direction to that which is ex- erted in the other, is equal to that which would be produced by a plate of quartz four-tenths of a millimetre in thickness. Such, up to the present time, is the maximum effect which I have been able to obtain. As we have now a means of com- paring the intensities of this force, it will be very easy to see how it will be modified by the different relative positions of the electro-magnet and of the piece of flint-glass. The following are the observations I have made with respect to this point : — 1. If, instead of placing the electro-magnet in contact with the piece of flint-glass, it is removed parallel to itself in the same horizontal plane, and so that the vertical plane separa- ting the two arms corresponds always to the middle of the flint-glass, the action diminishes, but feebly in proportion as the distance increases, so that at the distance of ten centi- metres, it is still a considerable proportion of what it was when it was actually in contact. 2. If the electro-magnet is again placed in contact, and the piece of flint-glass slid in the direction of the ray of light to subject it to the action of one only of the poles of the magnet, a moment arrives when the action is wholly null ; then, if it is still slid in the same direction, removing it more and more from its primitive position, until it is placed beyond the pole to which it is submitted, the action begins anew ; but then it is contrary to what it was at first. These observations appear to lead to three important con- sequences : — It first results, that if we consider the unknown action of the magnet on the flint-glass as being produced by attractions and repulsions, the effect is null when the resultant of these attractive and repulsive forces is perpendicular to the direc- tion of the polarized ray ; and it is at its maximum, on the contrary, when this resultant is parallel to the ray. We may thus, from these considerations, form a just idea of the direc- tion in which it acts, for in considering, always hypothetically, the piece of flint-glass as a piece of soft iron, acquiring two poles from the influence of the magnet, the movement of the plane of polarization occurs to the right when the light enters by the south pole, and proceeds from the south to the north pole, and it occurs to the left when the light enters by the north pole ; consequently, whatever be the position of the piece of flint-glass, if two observations are made on it without touching it, and without disarranging the electrical apparatus, but merely turning the optical apparatus to cause the light 332 M. Pouillet on the Recent Researches o/Prof. Faraday. to enter successively in the two directions, we shall see, in the first case, the effect to the right, and in the second the effect to the left, which establishes, as Mr. Faraday has pointed out, a difference, at least apparent, between the substances which have the permanent property of turning the planes of polarization and those which acquire it by magnetic action. In the second place it results, that on experimenting in this way care must be taken to give to the pieces subjected to the electro-magnet a length greater than the distance of the axes of the two arms ; for the portions which would exceed those axes would receive similar modifications among one another, and opposed to that which the central portion would receive ; it may even be presumed that the compensation might obtain exactly, so that with a connecting piece exceeding the breadth of the magnet, the action might be perfectly null. This re- sult seems to me opposed to that which is pointed out by Mr. Faraday, namely, that the effect is proportional to the length of the piece subjected to the experiments. It results, lastly, that in order to obtain a greater effect, two electro-magnets, opposed to one another, may be presented to the piece of flint-glass, so that the poles of the same name face one another. This I have verified, and it is even by the assistance of two electro-magnets thus opposed that I have obtained, the maximum effect of which I have spoken above. By placing thus several similar systems in succession on the same pencil, the effect would be, without doubt, tripled, &c. It has appeared to me very important to examine whether the position of the plane of polarization, with relation to the horizontal plane of the electro-magnet, had any influence on the energy of the action ; but whether the plane of polariza- tion be itself horizontal, vertical or intermediate, the results appeared to me to remain perceptibly the same. I have hitherto spoken only of flint-glass, but I have sub- jected to experiment all the other solid transparent bodies which I have been able to procure ; for instance, various kinds of flint-glass, and doubtless of different composition, crown-glass, and glass of all kinds, coloured with copper, gold, chromium, &c, and also rock-salt. All these bodies present, although with less intensity, the same phenomena as the flint-glass ; unfortunately the samples of crown-glass are sometimes so annealed as to modify the colours, and which does not allow of their being compared with other bodies ; nevertheless, after the attempts which I have been able to make on some less imperfect specimens, I am led to think that the action of the crown-glass has an intensity comprised between the half and the two- thirds of that of the flint-glass. M. Pouillet on the Recent Researches of Prof. Faraday. 333 The chloride of sodium has an action very analogous to that of the flint-glass. I have also subjected to experiment some transparent or coloured liquids ; these experiments were made in a trough formed of parallel glasses, having a length of thirteen centi- metres, equal to the distance of the axes of the electro-mag- nets, a breadth of three centimetres, and a depth of five centi- metres. The trough being empty, and the electro-magnets being in action, no sensible effect was produced by the pa- rallel glasses which formed the extremities. The intensity of all these liquids is very nearly equal to that of the crown-glass; the most energetic however ap- peared to me to be olive oil, distilled water, concentrated ammonia, and pure nitric acid ; and the less energetic, acetic acid, sulphuric acid, ferrocyanide of potassium, and ferrocya- nate of magnesia. It appeared to me certain that several bodies dissolved in distilled water weakened its effects. Mr. Faraday states that manganese, chromium, and cerium are magnetic after the manner of iron, and that all the com- pounds of these bodies preserve this property more or less. I had long ago proved the first fact for manganese, and in the course of last summer I proved it for very pure chromium obtained by the battery, both from chromic acid and from sulphate of chromium. With regard to the magnetic com- pounds, I have studied them recently by a very simple and very easy process, which consists in arranging a powerful electro-magnet, with its poles at top, forming a horizontal plane ; a thin paper is stretched over each pole, in contact with the iron itself, and it is then only requisite to throw upon this paper some very fine particles of the substance to be examined, and to give the paper some slight vibrations, which put them in motion. The particles arrange and fix themselves on the circle which corresponds to the terminal bar of the iron of the electro-magnet, and describe the circle with great precision. By this means I have ascertained that almost all the compounds of magnetic metals are, in fact, more or less magnetic ; prussian blue and the sesquichloride of chromium (of M. Peligot) are so in a remarkable manner. There are some compounds however which are exceptions to this rule ; such, for example, are the double cyanide of iron and of potassium, the chromate of silver, and the bichromate of potass. Other metals, as platina sponge and arsenic, exhibit a per- ceptible action ; but it would require to be verified on per- fectly pure specimens. Bismuth presents other phenomena; instead of forming a 334 M. Pouillet on the Recent Researches of Prof. Faraday. circle, like the magnetic metals, it forms two concentric circles, leaving thus a narrow white band, in the very place where the other metals form a circle, as if it were repelled by the more lively action of the iron armature of the magnet. The effect is so marked, that on mixing, for example, some sesquichloride of chromium very finely pulverized with some bismuth, likewise in very fine powder, the violet circle of the chloride is seen, and the two circles of the bismuth which are separate from them, although very near. Amber seems to give the same appearances as the bismuth, though in a much weaker degree. No attractive or repulsive effect is observed by this means, either on very pure antimony or on the other metals, binary or other compounds (among the rare metals, I have only experimented on tellurium and the uranium of M. Peligot), nor on the alkalies, sulphur, iodine, charcoal, and diamond. I regret that I had not at my disposal either cerium or any of its compounds. These negative results cannot invalidate in the least the general proposition of M. Faraday, who has doubtless ope- rated with more delicate means or with more energetic mag- nets. I merely mention them here to point out the easy pro- cess which I have employed, and the limit of its sensibility. There is another process for investigating the magnetic properties, — that which was employed by Coulomb when he discovered that all bodies are subject to the influence of mag- nets, and which has been since employed in the same view by many experimentalists, and very recently by M. Ed. Becquerel (Comptes Rendus, vol. xx. p. 1708). Mr. Faraday appears to have employed it ; but doubtless, from the weakness of my electro-magnets, although excited by a battery of 100 pairs, I have not obtained the same results as he ; in my experi- ments, bismuth and amber are the only two substances which took a direction perpendicular to the line of the poles, and without doubt the relation existing between this direction of the bismuth and the effect of repulsion which the fine pow- der of that body experiences from the part of the armature of the magnet will appear highly remarkable. These two me- chanical actions of magnetism upon bodies — the attraction and repulsion of fine powders, placed almost in contact with one of the poles, and the direction given to more considerable masses, oscillating in the presence of the two poles — appear therefore to be dependent one upon the other ; but in what degree are they connected with the third action, the optical action which Mr. Faraday has just discovered? Admitting with this philosopher that all the substances Mr. G. G. Stokes on the Aberration of Light. 335 which are not magnetic after the manner of iron, are diamay- netic or magnetic after the manner of bismuth, we should be led to conclude immediately that the optical action being con- comitant with a certain mechanical action, it is at least pre- sumable that this action is exerted upon the bodies, and not, directly and immediately on the light which passes through them. But if it happens, as in my experiments, either from the relative weakness of my magnets or from the imperfection of the methods which I have employed, or from other causes — if it happens that the various kinds of glasses, distilled water, the fatty bodies, &c, which are so sensitive to the optical action, are nevertheless insensible to the mechanical action of the magnetism, it would not be a reason to conclude that magnetism acts directly upon the light itself; a conclusion which, moreover, would only have a precise meaning in the system of emission, for in the undulatory theory, which seems at present so completely demonstrated, it is the aether of the body submitted to the experiment which would be modified by the magnetism, and it would doubtless be very difficult to recognise whether it is modified without any par- ticipation of the ponderable matter of the body with which it is so intimately connected. LI I. On the Aberration of Light. By G. G. Stokes, M.A., Fellow of Pembroke College, Cambridge*. T WISH to say a few words more on the subject of aberra- " tion, to prevent misapprehension. It is evident from Prof. Challis's last communication, that we differ merely as to the phenomenon which we understand by the term " aberration of light." When the position of a star has been corrected for refraction, precession, and nutation, and proper motion if it has any, let s be its mean annual place referred to the celestial sphere, sx the point to which the star is referred by astrono- mical measurement, and s2 the point in which the sphere is cut by the line along which the light comes from the star, produced backwards, s2 being corrected in the same manner as sv It is shown by observation that sx is displaced from s towards the point towards which the earth is moving, through an angle equal to the ratio of the velocity of the earth to that of light multiplied by the sine of the earth's way. This is the phenomenon which I understand by the aberration of light, and which it was the object of one of my former communis * Communicated by the Author. 336 Intelligence and Miscellaneous Articles. cations to account for on the theory of undulations. But it is evident that what Prof. Challis means by aberration, is the circumstance that sx is displaced from s2 through the angle which I have mentioned. Prof. Challis's reasoning, by his own confession, does not explain aberration in the sense in which I used the word ; for he says that it follows from ob- servation (not theory alone), that s2 coincides with s. LI II. Intelligence and Miscellaneous Articles. ANALYSIS OF DIASPORE FROM SIBERIA. BY M. A. DAMOUR. rr,HE remarkable characters of diaspore have frequently attracted ■*• the attention of mineralogists, and have been extremely well de- scribed and analysed by MM. Children, Dufrenoy, and Hess. The author observes, that he should therefore have abstained from re- ferring to them, if he had not had occasion lately to observe a sin- gular property of this mineral which had not been previously noticed. The diaspore is a well-known hydrate of alumina. It is shown by the experiments of M. Dufrenoy, that tbis mineral, even when long boiled in sulphuric acid, not only resists its action, but retains all its water. M. Damour, on repeating this experiment, obtained the same result ; but he afterwards found that the diaspore, when de- prived of its water by calcination, was almost totally soluble in sul- phuric acid when assisted by heat. This property is the inverse of that which chemists always ob- serve with respect to hydrates, and in general with respect to sub- stances which have not been calcined. In fact, the greater number of these substances lose their solubility in acids after they have been heated to redness. In this case the contrary occurs : the peculiar molecular condition of the crystallized hydrate of alumina, consti- tuting the diaspore, appears then to be the only obstacle to the na- tural affinity of this hydrate for the sulphuric acid ; for calcination, by destroying this arrangement of the molecules, restores the usual properties of alumina. M. Damour took advantage of this circumstance in order to sim- plify the method of analysing diaspore. The mineral was first purified by digesting it, reduced to very fine powder in dilute hydrochloric acid at a moderate heat. There was dissolved a notable quantity of oxide of iron accidentally mixed with it. The powder, after washing, was perfectly white. The propor- tion of water was found to be nearly similar in three different ope- rations : to determine this the dried powder of the mineral was suf- fered to remain under a receiver over a stratum of pumice moistened with sulphuric acid, this powder was weighed and placed in a small covered platina crucible : in order to prevent the projection of the powdered mineral, the crucible was placed in another of the same metal ; the whole being weighed, the crucibles were submitted to Intelligence and Miscellaneous Articles. 337 the highest temperature which could he produced hy the flame of an alcohol eolipyle. The crucibles were cooled in a receiver with a glass stopper, containing fragments of chloride of calcium. When perfectly cool they were again weighed, and the difference between the first weighing and that after calcination was attributed to the quantity of water disengaged, and was 14*97, 1496, and 14*90 in three experiments. In order to act upon the diaspore deprived of water, hydrated sul- phuric acid was poured upon the mineral remaining in the crucible in which it had been calcined. The whole was heated in a sand- bath so as to volatilize the greater part of the sulphuric acid ; when the matter had become of a pasty consistence, water was added, which dissolved a great quantity of sulphate of alumina ; the solu- tion was poured off, and more sulphuric acid was added, and this operation was repeated five times. The aluminous solution was fil- tered in order to separate a small portion of a white earthy deposit ; this, which had resisted the prolonged action of sulphuric acid, still contained much alumina ; when moistened with nitrate of cobalt and heated to redness, it acquired a very decided blue tint, and rea- dily dissolved in the salt of phosphorus. The solution of sulphate of alumina was supersaturated with car- bonate of ammonia ; the alumina was collected, washed and heated for a long time to strong redness. It was very white, and nitrate of cobalt gave a fine blue tint to it. One hundred parts of diaspore yielded — Alumina 79*91 Water 14*90 Mineral unacted upon .... 5*80 100*61 M. Damour admits that this analysis is superfluous after those of MM. Dufrenoy and Hess, and gives it merely to exhibit a property worthy of attention, and which had not been previously noticed with respect to any mineral whatever. — Ann. de Ch. et de Phys., Mars 1 846. ON BOllACIC iETHER. M. Ebelmen having ascertained that boracic acid is volatilized by the vapour of water and of alcohol, succeeded in preparing, after some trials, boracic aether by the following process: — fused and finely-powdered boracic acid was put into a tubulated retort, and an equal weight of absolute alcohol was added to it. In a few minutes the temperature of the mixture became 122° Fahr., that of the atmo- sphere being only 64°. The retort was heated, and a thermometer placed in it showed that the liquid did not begin to boil until heated to about 203°, and its temperature continued rising from this point. At about 230° the distillation was stopped to cohobate the distilled liquid, and it was again distilled at 230°. The boracic acid swelled much during the operation, and the liquid which covered it while the distillation was going on, had completely imbibed it the following day. The distilled liquid had the slightly alliaceous smell of abso- lute alcohol, became very turbid on admixture with water, deposited Phil. Mag. S. 3. Vol. 28. No. 187. April 1846. 2 A 338 Intelligence and Miscellaneous Articles. boracic acid, burnt with a perfectly green flame, and yielded abun- dant white fumes of boracic acid. The semi-solid mass remaining in the retort was bruised and di- gested during twenty-four hours in anhydrous aether, which com- pletely disintegrated it ; the aethereal solution, when clear, was poured into a retort placed in an oil-bath, and fitted with a conden- sing apparatus. It was requisite to employ a temperature of about 392° Fahr. to obtain the last traces of aether and of alcohol. There remained in the retort a large quantity of a viscid liquid, of a slight amber colour, yielding at 392° Fahr. thick vapours in contact with the air, and which became solid on cooling. The author considers this product as boracic aether, and it ap- proximates in physical properties to boracic acid and the borates, which are well-known to assume the vitreous state by fusion. It is in fact a true transparent glass, but one which is rather soft at common temperatures ; at about 104° Fahr. it may be drawn into fine threads. It has a weak ^ethereal odour and burning taste ; when applied to the skin, it occasions a strong sensation of heat, and is converted into a white powder, which is hydrated boracic acid ; the same effect is produced by the contact of air with the boracic aether, but when the fragments are of considerable size, it takes place slowly, eventu- ally however they become quite opake. When boracic aether is tri- turated with water, it is very rapidly decomposed with the extrication of much heat ; alcohol is reproduced and may be obtained by distil- ling the aqueous liquid. Boracic aether is volatile, but not distillable ; at about 392° Fahr. it emits thick vapours into the air; but when distillation is attempted, it is decomposed, leaving a considerable residue of fused boracic acid. When it is dissolved in absolute alcohol and the mixture di- stilled, the alcohol volatilizes such a quantity of boracic aether, that on the addition of water it becomes almost a solid mass. It is combustible, and burns with a white smoke and a fine green flame, leaving a residue of fused boracic acid. It is soluble in aether and alcohol in all proportions, and retains these fluids with great affinity, for it is requisite to heat them to 392° Fahr. to remove the last traces of them ; these solutions become solid masses by the ad- dition of water. When boracic aether is heated, it first fuses, then decomposes, swells, and becomes less and less liquid. There are simultaneously disengaged alcohol, which retains a large quantity of boracic aether, and a colourless gas which burns with a green flame before it is washed in water. After having been passed through water, the gas burns with a bright flame, and possesses all the properties of olefiant gas. The residue of the decomposition is but unmixed anhydrous boracic acid, much swelled with carbonaceous matter ; it is requisite to heat it to redness for a long time to expel the inflammable gas. Great difficulty attends the analysis of boracic aether ; it was ef- fected by converting the boracic acid, first into borate of ammonia, and afterwards into anhydrous boracic acid. The mean of several experiments gave — Intelligence and Miscellaneous Articles. 339 Boracic acid 66*7 Carbon 19'8 Hydrogen 4*4 Oxygen (estimated by loss) . 9*1 100*0 The author observes that the carbon and hydrogen are in the same proportions as in aether, while the oxygen is obviously in excess. The formula BO6 O H5 O is the nearest approach to the above mean ; it gives — Boracic acid . . 8720 65 A Carbon 3000 224 Hydrogen .... 62*5 47 Oxygen 1000 7'6 13345 100-0 M. Ebelmen observes that the difference between the results of experiment and calculation are too considerable to be attributed to errors of analysis. It must be admitted, he says, that the boracic aether contains a certain excess of boracic acid disseminated uni- formly throughout the vitreous mass ; this supposition, he further observes, is not at all improbable, when the mode of preparing bo- racic aether is considered. — Ann. de Ch. et de Phys., Fevrier 1846. ACTION OF BORACIC ACID ON PYItOXYLIC SPIRIT. M. Ebelmen states that the action of boracic acid upon pyroxylic spirit is similar to that which it exerts upon alcohol ; when equal weights of them are mixed, great increase of temperature is pro- duced. On heating the retort from 212° to 230° Fahr., but little distilled product is obtained ; on allowing the retort to cool, and treating the matter which it contains with anhydrous aether, and ope- rating in other respects as for boracic aether of alcohol, boracic me- thylic aether is obtained, the properties of which are perfectly compa- rable with those of boracic aether. It is soft and may be drawn into threads at common temperatures ; when treated with water it is im- mediately decomposed, with the disengagement of much heat, into boracic acid and pyroxylic spirit ; it burns like boracic aether, with a fine green flame. Pyroxylic spirit is preferable to alcohol as a reagent for determi- ning the presence of boracic acid by the colour of the flame ; when the alcoholic solution does not contain much boracic acid, the edges only of the flame are green, and it is often difficult to discover it. But with pyroxylic spirit it requires only a small quantity of the acid to give the whole flame a green colour ; this result is doubtless de- pendent upon the fact, that the flame of the pyroxylic spirit by itself has less colour than that of alcohol. When pyroxylic spirit is distilled with a great excess of boracic acid, a colourless gas is obtained which is soluble in water, and whose properties resemble those of boracic methylic aether, C2 H3 O ; the mode in which boracic methylic aether is decomposed is therefore en- tirely different from that of the corresponding compound of alcohol. M. Ebelmen found that boracic methylic aether yielded 69 -5 and 70*6 per cent, of fused boracic acid by ammonia ; the acid was black and contained a small quantity of charcoal disseminated through it ; 2 A 2 340 Intelligence and Miscellaneous Articles. the proportion of acid correspondent to the formula BOG CQ H3 O would be 75-2 per cent. The product obtained was evidently a little impure, and contained, besides some boracic methylic aether, some of the compounds of boracic acid with the pyrogenous compounds, which it is so difficult to separate from pyroxylic spirit. — Ibid. ON A SIMPLE METHOD OF PROTECTING FROM LIGHTNING, BUILDINGS WITH METALLIC ROOFS. BY PROF. HENRY. On the principle of electrical induction, houses thus covered are evidently more liable to be struck than those furnished either with shingle or tile. Fortunately, however, they admit of very simple means of perfect protection. It is evident, from well-established prin- ciples of electrical action, that if the outside of a house were encased entirely in a coating of metal, the most violent discharge which might fall upon it from the clouds would pass silently to the earth without damaging the house, or endangering the inmates. It is also evident, that if the house be merely covered with a roof of metal, without pro- jecting chimneys, and this roof were put in metallic connexion with the ground, the building would be perfectly protected. To make a protection, therefore, of this kind, the Professor advises that the me- tallic roof be placed in connexion with the ground, by means of the tin or copper gutters which serve to lead the water from the roof to the earth. For this purpose, it is sufficient to solder to the lower end of the gutter a riband of sheet copper, two or three inches wide, sur- rounding it with charcoal, and continuing it out from the house until it terminates in moist ground. The upper ends of these gutters are generally soldered to the roof ; but if they are not in metallic contact, the two should be joined by a slip of sheet copper. The only part of the house unprotected by this arrangement will be the chimneys ; and to secure these, it will only be necessary to erect a short rod against the chimney, soldered at its lower end to the metal of the roof, and extending fifteen or twenty inches above the top of the flue. Considerable discussion in late years has taken place in reference to the transmission of electricity along a conductor ; whether it passes through the whole capacity of the rod, or is principally con- fined to the surface. From a series of experiments presented to the American Philosophical Society, by Professor Henry, on this subject, it appears that the electrical discharge passes, or tends to pass, prin- cipally at the surface ; and as an ordinary-sized house is commonly furnished with from two to four perpendicular gutters (two in front and two in the rear), the surface of these will be sufficient to conduct, silently, the most violent discharge which may fall from the clouds. Professor Henry also stated, that he had lately examined a house struck by lightning, which exhibited some effects of an interesting kind. The lightning struck the top of the chimney, passed down the interior of the flue to a point opposite a mass of iron placed on the floor of the garret, where it pierced the chimney ; thence it passed explosively, breaking the plaster, into a bedroom below, where it came in contact with a copper bell- wire, and j^sed along this hori- zontally and silently for about six feet ; thence it leaped explosively Intelligence and Miscellaneous Articles. 34 1 through the air a distance of about ten feet, through a dormer win- dow, breaking the sash, and scattering the fragments across the street. It was evidently attracted to this point by the upper end of a perpendicular gutter, which was near the window. It passed silently down the gutter, exhibiting scarcely any mark of its passage until it arrived at the termination, about a foot from the ground. Here again an explosion appeared to have taken place, since the windows of the cellar were broken. A bed, in which a man was sleeping at the time, was situated against the wall, immediately under the bell- wire ; and although his body was parallel to the wire, and not distant from it more than four feet, he was not only uninjured, but not sen- sibly affected. The size of the hole in the chimney, and the fact that the lightning passed along the copper wire without melting it, show that the discharge was a small one, and yet the mechanical effects, in breaking the plaster, and projecting the window-frame across the street, were astonishingly great. These, effects the Professor attributes to a sudden repulsive energy, or expansive force developed in the air along the path of the discharge. Indeed, he conceives that most of the mechanical effects which are often witnessed in cases of buildings struck by lightning, may be re- ferred to the same cause. In the case of a house struck within a few miles of Princeton, the discharge entered the chimney, burst open the flue, and passed along the cockloft to the other end of the house ; and such was the explosive force in this confined space, that nearly the whole roof was blown off. This effect was, in- all probability, due to the same cause which suddenly expands the air in the experiment with Kinnersly's electrical air thermometer. — From the Proc. of the American Philosophical Society, June 20, 1845. OBSERVATIONS ON CAPILLARITY. BY PROF. HENRY. In 1839, the author presented the results of some experiments on the permeability of lead to mercury ; and subsequent observation had led him to believe that the same property was possessed by other metals in reference to each other. His first attempt to verify this conjecture was made with the assistance of Dr. Patterson, at the United States Mint. For this purpose, a small globule of gold was placed on a plate of sheet iron, and submitted to the heat of an as- saying furnace ; but the experiment was unsuccessful ; for, although the gold was heated much above its melting-point, it exhibited no signs of sinking into the pores of the iron. The idea afterward sug- gested itself, that a different result would have been obtained had the two metals been made to adhere previous to heating, so that no oxide could have been formed between the surfaces. In accordance with this view, Prof. Henry inquired of Mr. Cornelius, of Philadelphia, if, in the course of his experience in working silver-plated copper, in his extensive manufactory of lamps, he had ever observed the silver to disappear from the copper when the metal was heated. The an- swer was, that the silver always disappears when the plate is heated above a certain temperature, leaving a surface of copper exposed ; and that it was generally believed by the workmen, that the silver evaporates at this temperature. 342 Intelligence and Miscellaneous Articles. Professor Henry suggested that the silver, instead of evaporating, merely sunk into the pores of the copper, and that by carefully re- moving the surface of the latter by the action of an acid, the silver would reappear. To verify this by experiment, Mr. Cornelius heated one end of a piece of thick plated copper to nearly the melting-point of the metal ; the silver at this end disappeared, and when the metal was cleaned by a solution of dilute sulphuric acid, the end which had been heated presented a uniform surface of copper, whilst the other end exhibited its proper coating of silver. The unsilvered end of the plate was next placed, for a few minutes, in a solution of muriate of zinc, by which the exterior surface of copper was removed, and the surface of silver was again exposed. This method of recovering the silver before the process of plating silver by galvanism came into use, would have been of much value to manufacturers of plated ware, since it often happened that articles were spoiled, in the process of soldering, by heating them to the degiee at which silver disappears. It is well-known to the jeweller, that articles of copper, plated with gold, lose their brilliancy after a time, and that this can be restored by boiling them in ammonia ; this effect is probably produced by the ammonia acting on the copper, and dissolving off its surface, so as to expose the gold, which, by diffusion, has entered into the copper. A slow diffusion of one metal through another probably takes place in cases of alloys. Silver coins, after having lain long in the earth, have been found covered with a salt of copper. This may be explained by supposing that the alloy of copper, at the surface of the coin, enters into combination with the carbonic acid of the soil, and being thus removed, its place is supplied by a diffusion from within ; and in this way it is not improbable that a considerable portion of the alloy may be exhausted in the process of time, and the purity of the coin be considerably increased. Perhaps, also, the phenomenon of what is called segregation, or the formation of nodules of flint in masses of carbonated lime, and of indurated marl in beds of clay, may be explained on the same prin- ciple. In breaking up these masses, it is almost always observed, that a piece of shell or some extraneous matter occupies the middle, and probably formed the nucleus, around which the matter was accu- mulated by attraction. The difficulty consists in explaining how the attraction of cohesion, which becomes insensible at sensible distances, should produce this effect. To explain this, let us suppose two sub- stances uniformly diffused through each other by a slight mutual at- traction, as in the case of a lump of sugar dissolved in a large quan- tity of water, every particle of the water will attract to itself its pro- portion of the sugar, and the whole will be in a state of equilibrium. If the diffusion at its commencement had been assisted by heat, and this cause of the separation of the homogeneous particles no longer existed, the diffusion might be one of unstable equilibrium ; and the slightest extraneous force, such as the attraction of a minute piece of shell, might serve to disturb the quiescence, and draw to itself the diffused particles which were immediately contiguous to it. This would leave a vacuum of the atoms around the attracting mass : for example, as in the case of the sugar, there would be a portion of the Meteorological Observations. 34-3 water around the nucleus deprived of the sugar ; this portion of the water would attract its portion of sugar from the layer without, and into this layer the sugar from the layer next without would be dif- fused, and so on until, through all the water, the remaining sugar would be uniformly diffused. The process would continue to be re- peated, by the nucleus again attracting a portion of the sugar from the water immediately around it, and so on until a considerable ac- cumulation would be formed around the foreign substance. We can in this way conceive of the manner by which the molecu- lar action, which is insensible at perceptible distances, may produce results which would appear to be the effect of attraction acting at a distance. — From the Proc. of the- American Philosophical Society. Obituary. — The University of Konigsberg has sustained a severe loss by the death of the celebrated astronomer Bessel, who died, after long suffering, on the 17 th of March, in the 62nd year of his age. METEOROLOGICAL OBSERVATIONS FOR FEB. 1846. Chiswick. — February 1. Very fine : rain. 2. Fine. 3,4. Overcast : rain. 5, 6. Very fine. 7. Overcast : windy, with showers. 8. Clear : cloudy : very clear at night. 9. Frosty: fine, but cold. 10. Frosty: cloudy and cold. 11. Frosty: fine: partially overcast. 12. Foggy: cloudy and fine. 13. Densely clouded. 14,15. Cloudy and fine. 16. Densely overcast. 17,18. Overcast and fine. 19. Hazy. 20. Overcast. 21. Exceedingly fine. 22. Cloudy: boisterous, with rain at night. 23, 24. Rain. 25. Heavy clouds and mild. 26. Cloudy in the morning : afterward cloudless and exceedingly fine. 27. Slight haze : showery. 28. Very fine. Mean temperature of the month 4S0,32 Mean temperature of February 1845 33 '07 Average mean temperature for the last twenty years 39 '36 Average amount of rain 1 "61 inch. Boston. — Feb. 1. Fine. 2. Fine : rain early a.m. 3. Cloudy. 4. Fine. 5. Cloudy : rain early a.m. 6. Fine. 7. Stormy : rain early a.m. 8. Fine : rain early a.m. 9. Fine : snow early a.m. : snow a.m. and p.m. 10. Fine: snow on the ground. 1 1. Cloudy : snow on the ground. 12. Fine : snow on *he ground. 13. Cloudy : snow all gone : melted snow. 14 — 22. Cloudy. 23. Cloudy : rain early a.m. 24. Cloudy. 25. Fine : rain early a.m. 26. Cloudy. 27. Fine : rain a.m. 28. Fine. This month has been usually fine. Sandwich Manse, Orkney. — Feb. 1. Sleet-showers. 2. Cloudy. 3. Cloudy: sleet-showers. 4, 5. Hail-showers. 6. Showers : rain. 7. Showers : snow- showers. 8. Snow-showers. 9. Snow-showers : frost. 10. Snow : showers. 11. Clear : cloudy. 12. Cloudy: damp. 13. Showers. 14,15. Cloudy: showers. 16. Rain: cloudy. 17. Showers : cloudy : drizzle. 18. Showers : drizzle : cloudy : drizzle. 19. Bright : cloudy. 20. Clear : cloudy. 21. Rain : cloudy. 22. Rain. 23. Clear. 24. Damp: showers. 25—27. Clear: cloudy. 28. Cloudy: showers: clear. Api>legarth Manse, Dumfries-shire. — Feb. 1. Occasional showers. 2. Fair and fine. 3. Heavy rain. 4. Sleet and rain p.m. 5. Showers. 6, 7. Heavy showers. 8. Slight fall of snow. 9. Frost: fine: clear. 10. Frost: fine. 11. Thaw: fair: mild. 12. Slight frost. 13. Very slight frost. 14,15. Fine. 16. Very fine. 17. Fine. 18. Frost a.m. 19. Fine, but cloudy : shower. 20. Slight showers: mild. 21. Wet and stormy. 22, 23. Damp and drizzling. 24, 25. Heavy rain. 26. Wet. 27. Remarkably fine. 28. Damp and drizzling. Mean temperature of the month 430-4 Mean temperature of February 1845 34 "5 Mean temperature of Feb. for twenty-three years . 37 "0 Mean rain in February for eighteen years 2 -0 inches. « r> 'jpiMpaBS 'ajiqs -saujiunfl •uojsog •jpi.visiqo •JfOIAipuBS •aaiqs -saujiunfi •uojsog •urd i •^aiMstq^ c « ■a? •urd *8 •ui-c 'S <" as •uijv •xerc •urn ?8 •uoisog -wg *E. •ui-b?8 ■uojsoa •q;uoj\[ «■ (soHinH-ciHaoo 1 1 * I *' 1 1 i i i i s I' i * ► £ * * i 'tiiiiii * & £ if is * * £ * I * * IS te s £ e s * * B IS £ £ s: fe > > « « 5 f * > : a J -J J -JiSSSjBJsEEJaSijEjjSjga £ is is is £ s if * i p » * s g £ * * £ (s* £ >' ► * i i * i * i Odf^lMOO -rf ""# •"tfco-'tcococo-'tcOCOOl COCOCOCOCO'<*cocOCOT''tf'**'3,Tt-«3<-<3<-<3*tOtOtOiOtOiO>0>0^0 ^T?<.')T5'lP?0P99??vl?'?????,cP^,^T,"?'(?l?l'?"?in C'lCJ'iC^O't^©^©^©*!© © © O^O^O © © © dC^i^CPi^C^C^oo ©n ©\ ©^ ©i©!©!©!©!^©1!© O © O ©i ©i © O © ©i©i©i©\©i©>©\©i©,©i©>©> C10O O WOOD OlONOO - 'OdlO- INCMflO^COCOOOOOtllOON ©i©v©i©\©i©i©i©i© o o o ©> o © o o ©i©©©i©\©i©>db © 6\ ©> OMJ>^ONcr\c><^osd\o ©©i©©©©©©©©©*©!©©©©,©© O "* <-> *o O — -©©i ■<*C0CM t>- r^ ©00 © © © © © O — 00 — --XCfl CO CO— — 1 MNO00 000 - r- -H>-iCM(M(NC«CM(M'64> per cent. Sulphur 35-36 from which it is obvious the substance is a sub-sulphuret, that its constitution is Co2 S, a rather remarkable result, consider- ing that the iron compound, doubtless of simultaneous forma- tion, is different. The cobalt pyrites has the specific gravity of 5*4<5. It is used by Indian jewellers for staining gold of a delicate rose- red colour; the modus operandi which they follow I have been unable to learn ; it is a secret with them, which they are unwilling to disclose. LVII. On the Structural Relations of Organized Beings. By H. E. Strickland, M.A,, F.G.S.* [" PROPOSE to make a few observations on the Relations *- which subsist between different organized beings in re- spect of the similarities of their physical structures. This limitation will exclude — first, the relations between individuals, such as that of parent to offspring, for in individuals of the same species the essential points of structure are not similar, but identical; and secondly, the relations between an organized being and the external circumstances of soil, climate, or food, to which it is adapted, in other words, between structure and function ; for these adaptations of the one to the other, how- ever interesting and admirable in themselves, are not relations of similarity. On comparing together the innumerable species of organ- ized beings, we find their structures to present every possible degree of variation, from an almost perfect identity to the ut- most amount of difference which the mind can conceive any two organized bodies to possess. These agreements and dif- ferences are not however devoid of laws and principles ; they admit of being classed under certain general heads, and we thus discover the traces of Divine workmanship not merely * Read before the Ashmolean Society of Oxford, March 10, 1845, and communicated by the Author. Relations of Organized Beings. 355 in the structure of an individual organism, but in the mutual relations of those organisms, the due combinations of which constitute the Natural Systems of Botany and Zoology. When the human mind first began to observe and to com- pare the structures of organic life, to generalize the points of agreement, and thus to lay the foundation of the Science of Natural History, no inherent principles of classification were even suspected to exist, characters were compared and gene- ralized at random, and the arrangements which resulted were of the rudest and most unphilosophical kind. The most su- perficial and arbitrary characters were selected as the basis of classification, and no man was able to give a reason why one mode of arrangement should not be as correct and as true to Nature as another. Thus we find the older naturalists class- ing Lizards, Tortoises and Frogs with terrestrial Mammalia, under the name of " Four-footed Beasts," while Serpents were made into a distinct Class ; and Whales, whose physio- logical organization is as highly developed as in any other Mammal, were dismissed among the cold-blooded Class of Fish, into which the humble Lobster and the Oyster entered from the other side to keep them company. By some authors we find the Echinus and the Hedge-hog approximated, be- cause both are covered with spines; the Ammonite and the Rock-crystal were described in the same chapter "de lapi- dibus"; Shrew-mice and Spiders were classed together, be- cause both were supposed to be venomous ; Bats were referred to Birds, Corals to Plants, and so on. In the course of the seventeenth century, the few who cul- tivated natural science began to be conscious that these crude arrangements were not satisfactory, or consistent with the realities of Nature; and in the works of Ray and of Lister, we perceive many instances of an instinctive preference for essen- tial instead of arbitrary characters. But it was Linnasus who first pointed out in express terms the great principle of the Subordination of Characters. This principle teaches us to give to each point of structure its due weight, and to attach more value to those peculiarities whose immediate influence on the mysteries of Life often renders them the most difficult for our senses to appreciate, than to those external characters which, though most conspicuous to the eye, are but remotely con- nected with the real Essence of the creature. This principle has been further developed by later naturalists, especially by Cuvier, and accordingly we now find that in the modern sy- stems of Zoology the primary divisions of the Animal King- dom are based on characters derived chiefly from the nervous system, as being the most important feature in organization, 356 Mr. H. E. Strickland on the Structural the secondary subdivisions are grounded on the organs of re- spiration, groups of a lower rank on the digestive system, and so on, the most superficial peculiarities, such as external form and colour, being reserved to characterize the ultimate groups of genera and species. These improved principles of classi- fication are gradually bringing the systems of Zoology and Botany into a state of permanence, consistent with Nature, and satisfactory to that Truth-seeking Instinct which is inhe- rent in the human mind. A further advance of philosophical Classification has shown that the characters of organized beings require not only to be subordinated according to their importance, but subdivided according to their kinds. There are many instances of cor- respondence of structural characters in organic beings which can never by any process of subordination become elements in a natural classification, and it is important to distinguish those which can from those which cannot be so employed. Zoologists had long been aware that certain sets of characters produced an arbitrary or artificial method if employed for classification, while others seemed to lead to a natural system, but the question was involved in obscurity till the time of MacLeay, who was the first to give us clear definitions on the distinction between Affinity and Analogy. He applied his views indeed in support of a theory, the Quinary System, which few naturalists are now disposed to support, and with which we are not now concerned ; but his elucidation of Affi- nities and Analogies is not the less valuable on that account. Although I am not disposed to take the same view of these principles as that of Mr. MacLeay, yet as the principles them- selves are at the foundation of all sound classification, whether in Zoology or Botany, I may be allowed to make a few further remarks upon this subject. It appears to me that the instances of resemblance or agree- ment of structure between any two species of organized beings should be reduced, not into two, but into three distinct classes, Affinity, Analogy, and a third, for which I propose to adopt the name of Iconism*. I. The highest class of these structural agreements is that of Affinities, which appear to be the direct result of those Laws of Organic Life which the Creator has enacted for his own guidance in the act of Creation. Affinity consists in an essential and physiological agreement in the corresponding parts of organic beings, resulting from a uniformity of plan * This term, suggested by the Rev. Dr. Ingram, President of Trinity College, appears preferable to Mimesis, which I had originally proposed to Relations of Organized Beings. 357 which pervades the System of Nature*. These essential agreements of parts consist rather in a similarity of organic composition and of relative situation, than olform. A micro- scopic examination of the primary tissue, or a chemical ana- lysis of its substance, will often demonstrate the true affinities of a structure when its external form would only mislead us. And when we have proved an affinity to subsist between the structures of two organic beings, we then apply the term to the beings themselves, and say that an affinity subsists between them, greater or less, according to the number and import- ance of the organs in which such affinity is shown. Take for example the long, straight weapon of offence in the Narwhal, its general appearance is that of a horn, and such the vulgar accordingly call it; but if we examine its organization and its chemical composition, we find that both are utterly unlike those of real horns, but correspond to the structure of teeth. Further, if we examine the mode of its connexion with the skull, we find that it is inserted into a socket like other teeth, instead of being attached in the manner of horns, and we ac- cordingly pronounce it to be not a horn but a tooth, deve- loped for purposes of offence to an extraordinary extent. And having thus shown that the weapon of the Narwhal has no affinity to real horns, we no longer appeal to this structure in proof of any affinity between the Narwhal and the truly horned animals. Again, the Narwhal in its external form much re- sembles a Fish ; but when we look to its nervous, circulatory, and reproductive organizations, which rank much higher in the scale of characters than external form, we find that it is no Fish, but a true Mammal, agreeing in every essential point with the warm-blooded quadrupeds of the land, to which its affinities are real and direct. Similar instances of the dis- cordance between outward form and real affinity might be multiplied to a great extent; and it forms a constant employ- ment for the scientific zoologist to distinguish real affinities from apparent ones, and thus to refer every organized being to its true position in the Natural System. It will thus be seen that every instance of asserted affinity * We may suppose, for instance, that it was a law of organic creation that all Birds should have the anterior extremities modified into the form of wings ; and in obedience with this law we find that there is no Bird which is absolutely without wings, though there are several kinds in which the wings are perfectly incapable of flight. Again, it is a law that Mam- malia have neither more nor less than seven cervical vertebrae ; and we find this law to hold good, without an exception, through the whole Class of Mammals, from the slender-necked Giraffe to the Whale, which can hardly be said to have any neck at all. The above, out of countless other exam- ples, will show what is meant by laws of organization. 358 Mr. H. E. Strickland on the Structural between two organic beings is merely a corollary deduced from an observed affinity between the corresponding organs in each ; and though it is not usual to apply the term affinity to the similarities between parts, yet as the similarity between the wholes results from the similarities of their parts, the word affinity may be as correctly applied to the one as to the other. In works of comparative anatomy it is customary to speak of those members which are essentially equivalent in two organic beings as analogous organs, but we shall soon see that the word analogy has a very different sense ; and as the relation between equivalent organs is one of real affinity, and forms the sole ground on which we assert the affinity of the whole beings, we may introduce the adjective qffine or homologous in place of analogous, when referring to structures which es- sentially correspond in different organic beings. When we say that Affinity consists in an essential agree- ment of structure resulting from a fixity of purpose in the mind of Creative Wisdom, it must not be supposed that all affinities are equally strong, direct, and palpable. Any agree- ment, however slight, or however concealed by more palpable differences, which forms part of the plan of organic existence, is a true affinity ; and the principle of subordination of cha- racters before referred to is merely the arranging of these affi- nities in the true order of their proximities. The proximity of affinities is in the inverse ratio of their essential importance, the most important agreements of characters being those which have the widest extent, and which therefore form affinities be- tween the remotest points in the System of Organized Beings. We will illustrate this by an example showing the successive series of affinities which the same species bears to others, com- mencing with the most remote, and proceeding to the closest affinity which can subsist between two distinct species. We will take as an example the species Raven (Corvus cora.v). A Raven has an Affinity to an it is the same Affinity which exists hetween and is derived from the Affinity between their respective supplying the dia- gnostic characters of the Oak-tree ; Locust ; Salmon ; Swan; Humming Bird Sparrow; Jay; Magpie ; Carrion Crow ; all Animals and all Plants, Vertehrata and Insects, Birds and Fish, Inscssores and Natatores, Conirostres and Tenuirostres, Corvidae and Fringillidae, Corvinae and Garrulinas, Corvus and Pica, one species of Corvus and an- other, Organic Life, &c. nervous systems, &c. vertebral columns, &c circulatory systems, &c. structure of feet, &c. conical beaks, &c. structure of nostrils, &c. short elevated beaks, &c. even tails, black plumage, &c. Organic Empire. Animal Kingdom. Province, Vertehrata, Class, Birds. Order, Insessores. Tribe, Conirostres. Family, Corvidce. Subfamily, Corvince. Genus, Corvus. Relations of Organized Beings. 359 The affinities in this series are seen to accumulate succes- sively as we proceed from the remotest organism to the ap- proximate species. The Raven and Carrion Crqw not only possess that superficial resemblance of form which constitutes their generic character, but they have in addition all the other points of affinity which extend from them to a greater or less distance into the realms of organic existence. Thus we find that The Raven has organization in common with all Organized Beings, a nervous system ... Animals, a vertebral column ... Vertebrata. a peculiar circulatory system ... Birds, perching feet ... Insessores. a conical beak ... Conirostres. the nostrils covered by feathers ... Corvidae. ridge of the beak arched ... Corvinae. an even tail ... Corvus. and a wholly black plumage ... Carrion Crow. It will be seen from the above example, that the whole pro- cess of classification consists in observing the affinities of structure in different beings, in estimating their importance, and in arranging them according to that estimate. It follows that a clear comprehension of affinities, as distinguished from the other kinds of resemblance, is essential to the objects of the scientific zoologist. Although affinity consists in an essential and intimate agree- ment in the structure of certain organs, yet it by no means implies an identity of function in those organs. The modifi- cations of external form are so various that we frequently find the same organ applied by different animals to purposes the most remote from its normal function ; and on the other hand we see very different organs applied to discharge the same function. Thus, as a general proposition, it is certain that the proper function of wings is flying, of legs walking, of fins swimming; and yet we find examples where each of these organs is applied to any other function but its own, as in the case of the Bat, Seal, Ostrich, Penguin, Gurnard, and Flying Fish. Hence, although it-is generally true that certain organs are destined to perform certain definite functions, yet the ex- ceptions are so frequent as to make us attach a minor degree of importance to function, while we give the fullest weight to those essential properties which form the only test of real af- finity. 360 Mr. H. E. Strickland on the Structural II. We have next to consider that class of structural agree- ments known by the name of Analogies. These consist in a similarity of external form and of function connected with it, but without that agreement of essence which constitutes Affi- nity. These analogous agreements are equally the result of natural laws, but of laws of a different class from the former. Agreements of affinity are produced in conformity with the laws of the organic Creation, while analogies have a reference to the laws and properties of external and often inorganic matter. In obedience to these laws, it follows that when- ever an instrument is required to produce a given effect upon external objects, or to resist their influences in a given manner, there is in general one method, and one only, of effecting the object in the best and most effectual way. Accordingly, what- ever be the organ or instrument employed, that organ must have a certain and definite mechanical structure bestowed upon it to obtain the desired end. As a general rule, the same end is attained in different organic beings by means of the same set of organs ; but when those organs are required for any other purpose, or are so modified as to be unfit for that special end, then some other set of organs are endowed with the requisite external structure and are called upon to act as substitutes for the legitimate instruments. Examples of this adaptation of organs to purposes remote from their normal destination are numerous and well-known ; and I cannot do better than refer to the late Mr. John Duncan's work on the Analogies of Organized Beings, where there are numerous examples of such analogies arranged in a tabular and highly perspicuous form. We need only take the Elephant as an in- stance. We may suppose that this animal required horns for the purpose of defence, but it belongs to an order, the Pachy- dermata, in which horns are uniformly absent, and the laws of Affinity forbade their introduction. To supply this defect, the incisor teeth are removed from their usual duties of mas- tication, and are so developed as to assume the form and dis- charge the function of horns. Further, the great size and weight of these lengthened tusks required a great strength and shortness of neck, and the animal was consequently unable to reach the ground with his mouth. A hand was therefore re- quired to convey the food to the mouth, but the vast weight of the animal required a massive structure in the feet, which forbade them to be adapted to the purpose of hands. To supply this want then the nose is lengthened out, furnished with muscles, divided at the end into a finger and thumb, and in this proboscis behold a hand ! almost equal in delicacy of manipulation to the hand of Man. And thus we see the Ele- Relations of Organized Beings. 361 phant, endowed in one respect with an analogy to the Ox, and in another respect to Man, yet having no immediate affinity with either. As then Analogy consists in an agreement of function, and only of form so far as it tends to discharge that function, it follows that real and genuine Analogies may take place be- tween the works of Nature and the works of Man, while no such relation of Affinity can possibly exist. When, for in- stance, the inventive powers of Man are called upon to imi- tate any of the operations of Nature, the external matter to be acted on being in both cases the same, a similar arrange- ment of form is adopted by both. If the problem be to make a floating body adapted for rapid motion through water, Man either by practical experiment or mathematical calculation produces the form of a boat, and thus uncon- sciously imitates the structure of the Whale and Seal among Mammals, the Penguin among Birds, the Ichthyosaurus and Turtle among Reptiles, the Fish among Vertebrata, the Dy- tiscus among Coleoptera, the Notonecta among Hemiptera, Sepia among Mollusca, Physalia among Acalephae, &c. &c. Nor is the analogy between a ship and a Fish confined to the external form only ; the keel of the one represents the spine of the other, the " ribs " of both agree in name as in nature, the rudder coincides with the tail, the oars with the fins, the masts with the spinous processes, the running rigging with the tendons, the seamen with the muscles, the look-out man on the forecastle with the eye, and the captain in the cabin with the mental faculties in the Fishes' brain. Again, what can be more striking than the analogy between a locomotive steam-engine and a living Animal ? We see in both an ana- logous respiratory and digestive system, the same necessity for food and drink and oxygen to sustain that internal combus- tion which is the source of the vital action, the same obedience of the organs of motion to the impulse of the governing mind, and the same wear and tear of the system, terminating in old age and sudden or gradual death. Yet in all these cases there is no set purpose on the part of Man to imitate the works of Nature, he merely applies the faculties which God has given him to elicit the properties which the same God has given to matter ; and by this process alone he often arrives at the same or similar results to those at which Creative Wisdom had ar- rived before him. It appears to me therefore, that relations of Analogy, that is to say, agreements in structure in conse- quence solely of an agreement in the function to be performed, may be as truly and as correctly asserted to exist between ar- Phil. Mag. S. 3. Vol. 28. No. 188. May 1846. 2 C 362 Mr. H. E. Strickland on the Structural tificial and natural productions, as between one object of the latter class and another. It is clear from this how much lower Analogies ought to stand in our estimation than Affinities. The latter form an essential part of that magnificent plan of Creation, which notwithstanding the amount of attention which Man has given to it, is of so transcendental a nature, that it may almost be said to be yet " to us invisible or dimly seen." Analogies, on the contrary, appear not to form any element whatever in the great System of Nature, but are merely examples of the recurrence of certain mechanical forms whenever the production of a certain mechanical action called for them ; and so far from their being at or beyond the verge of human comprehension, we have seen that Man enjoys the high privilege of copying by these Analogies, at a humble distance, the far transcendent works of his Maker. It would be an improvement in the language of Compara- tive Anatomy, if the term analogous organs were limited to the sense above defined. The serrations in the beak of a duck, for instance, are analogous in form and in function to teeth., but in their essential nature they are only a corneous modifi- cation of the lips. Most anatomists, however, would habitu- ally say that the beak of a bird is analogous to the lips of a Mammal, though it must be evident how much more precise their language would become if they spoke of this essential relation as an affinity, and applied the word analogous to for- mal or functional relations only. A similar inaccuracy is committed by geologists in speaking of the recent analogue of a fossil species, meaning thereby that living species which has the nearest affinity to the extinct one. It would be more cor- rect if they would term it the recent ajjine, or the recent homo- logue. III. There is yet a third species of relation of structural similarity between organized beings which has usually been confounded with Analogy, but which appears to me to be di- stinct from it in kind, as well as far inferior to it in import- ance,— I refer to those cases where a resemblance in form or configuration exists, but without any perceptible identity either of essence or of function. Such, for example, are the resem- blances between the flower of the Bee Orchis and a Bee, be- tween the shell of Murex haustellum and a Woodcock's head, between a Fungia and a Fungus, Ovulum and an egg, Haliotis and an ear, &c. To this class also belong the numerous in- stances of similarity of colour between Birds whose affinities are remote, such as the resemblance of Oriolus to Xanthomas, of Dicrurus to Corvus, of Cissopis to Pica, of Agelaius phceni- Relations of Organized Beings. 363 ceus to Campephaga phcenicea. Many errors of classification have been caused by mistaking these similarities for true affi- nities. Not only are such cases of external resemblance uncon- nected with any agreement in the essential structures of the bodies compared, but there is no conceivable similarity in the functions which they are created to discharge. I think there- fore that it is not going too far, nor departing from that vene- ration which the true naturalist will always feel for Nature's God, to call such superficial coincidences of form accidental. They seem to arise from the exuberant variety of the works of Nature which causes an occasional recurrence of similar forms, without any express design for such coincidences. Nothing can be inferred from such resemblances, either as to essential affinity or functional design ; and they would almost have been beneath our notice, were it not that some authors have regarded them as examples of real analogies. The ad- vocates of the Quinary theory of classification, who regard Analogies to be as important an element in the Natural System as Affinities, often speak of these mere resemblances in the light of true Analogies, and appeal to them in confirmation of their views. Regarding however, as I do, those views to be erroneous, I think it important that the distinction between functional Analogy and mere resemblance should be clearly pointed out; and to render the distinction more marked, I would distinguish the latter by the new term Iconism. We must beware indeed of too hastily pronouncing an in- stance of resemblance to be an Iconism, merely because we cannot immediately detect any functional analogy. There may be real reasons for these resemblances, real agreements in the functions to be discharged, which we have not yet de- tected, and perhaps may never discover. A person might say, for instance, that the species of Mantis called the " walk- ing leaf" presents a mere Iconism or accidental resemblance to true leaves ; whereas it is highly probable that this very re- semblance is given to the animal to enable it to remain con- cealed from its foes amid the verdant foliage. Such at least is undoubtedly the intention of numerous instances in which animals present an analogous colour to the surrounding sur- face, and even undergo corresponding changes with it, such as that of the Ptarmigan, which during summer is of a speckled gray plumage, like the lichen-covered rocks which it frequents, while in winter it becomes a pure white when those rocks are covered with snow. I have now endeavoured to show that the relations of re- semblance in organized beings are of three kinds, diminishing 2 C2 564 Abstract of Meteorological Observations successively in importance ; that Affinities are expressions of the real and elementary and esoteric Plan of Creation which the Author of Nature has been pleased to follow ; that Analo- gies are coincidences of structure consequent solely upon an identity of external physical conditions ; and that Iconisms are merely accidental recurrences of similar forms resulting from the exuberance of Nature's riches. It is evident that these distinctions must be clearly understood before we can make any progress in Natural History as a Science, and the re- marks above offered may perhaps aid in drawing attention to the subject or removing the difficulties which surround it. LVIII. Abstract of Meteorological Observations made during the year 184-5 at Gongo Soco, in the interior of Brazil. By William Jory Henwood, F.R.S., F.G.S., Member of the Geological Society of France, Chief Commissioner of the Gold Mines of Gongo Soco and Catta Preta, fyc. fyc. * HPHE rich gold mines of Gongo Soco are situated in the ■■- province of Minas Geraes, about forty-eight miles north- west of the city of Ouro Pretof (Villa Rica), in long. 43° SO' west and lat. 19° 58' 30" south, in a vale bounded on the north by the wooded mountain-range of Tejuco, and on the south by undulating grassy lowlands, which at the distance of about eight miles are terminated by the mountain- chain of the Caracas, which rises from 4000 to 5000 feet above the plain. Barometrical measurements J give Gongo Soco an elevation of about 3360 feet above the sea at Rio de Janeiro. The thermometrical observations were made at such times as my occupations permitted, but the hours are probably not the best possible §. The midnight observations were made by Captains Blarney, Luke, and Guy, and the thermometer they used needed a constant correction of 20,8 + ; all the others are my own, and the thermometer I employed was a standard one (No. 89) of the British Association. The thermometer is suspended in a wooden box pierced with numerous holes, and hangs at about six feet above the ground, in a shed open at all sides, and is well protected, — as well from reflected heat as from the direct rays of the sun, * Communicated by the Author. f Mr. Caldcleugh estimates the elevation of Ouro Preto at 3969 feet above the sea. — DanieWs Meteorological Essays, p. 345. % Made by the Austrian Mining Engineer, M. Virgil von Helmreichen. § The observations at 4 and 8 p.m. give higher results than would have been afforded at 3 and 9 respectively. G3 s X 50©©©©U5»<5"5©©©© GCcoccccccccGpcccpccapcp o^«ii©c»*?»©c©c*isotbabe*i © © © lf5 lO »3 -^ ifS »Q "9 "^_©_ coooooecaoooaoaococooocc in so ^ f-iqjfC(N^)» «>» t^ tO © © ©>>»»>» l>» «>» h<- i ep -"J1 "7" © ^5 lf5 *> "* 0^^0004fiCOcb(NM05"-<'-i t>«i>«*-»«o«o«5i«tototot>>«^» 00 . . °p . . $* *? 9s . f8 . °«>» oo»He«OTi'©idD«bN'*'b tom©©©mioiom©©© 00 CO CM Ki "^ *js 9P t»i>»«>.»^©©©©<>»«>»i>»«>» »co''*© !<»>.t>.l>»©©©©W«>.*>»«>» co «5 . •? . 9P . . 9P OCO CO^eb<>»:ob»ifSib.("» to tO©©©^^©^©©© «? U5 lfl US tD 00 1» >>»«>» >>»©©>>«t>»coccce ostpcpifsirsipfijiwcpepapifj °o ©Tf> t»t>.t>»«>.t-»©©«>»t^«>»t^*>» °© -^di4t»»^ih-^iot>»'fl CO CO COt'»»»*'»t'»t>»COGO coco lp-rjtsptpcpt^oq'^on^cpcp Oii} ibsO'-i©l~»ib©©tf5*,»*,» »>.i>.t>»i>»«^©©©©t>«t»*^ OM ^COJflirSff^OOCOO-^lfl"^1 tO*-»"* , © © # op^w ^•^©©©©m©©©*-**-* o 1 !>. t» t>» »>»»>.© ' °tb »>» to © so cp so © tb ifl ^ ap cq -rti cb © •** tb tb IS |Q |Q (S (S (D °© ^l»^-lCO00-T)<©-^'>f5©©© ©*>»»>.©©©©©©*>.«>»l>» S F o — i 3 «> JS p*J3 § 3 3 » o o « III I j; u o 0> a o e — o eS . b © © so . to © ift © 0) 0) :- XI 3 CS e3 M H & s May June July Augu ■4-J a a £S Ml* h, pn ^ (g, h ...) such that (D' + D^ + ...)♦& *.») = <>. * Communicated by the Author. 374 Rev. B. Bronwin on certain Definite Multiple Integrals. Then, separating the symbols of operation from those of quantity, D* + Dx2 + D22 + ... = o Dl = - (D2 + D,2... + DJU,). I><=-D*(D2 + D12+...) = -(D2 + D12 + ...)D* =, (D2 + D12+ ..,)«, B6n = - (D2 + Dx2 + ...)3, &c. Therefore {«2D2 + &D*... + a2D* }s = (a2D2 + g2D!2... + 02DLi)s + s {a? D2 + £ Dx2 ... + 02 DLi)-5"1 *? D* + ^i"^ («2D2 + 6*I>ia - + ^DJi-O-'x^i + &c. = (a2D2 + ^D^... + fl*D|[_1)' -5(a2D2... + fi2DLi)s-1(^D2 + x2DI2...+x2DL1)+&c.. = {a2 D2 + g2 Dj2 ... - x2 D2 - x2 Dx2 ... y = {(a2-x2)D2 + (&-k*)D*... + p-Wjptiiy. In this case therefore #s$ ('.) + (g2-x2)D12...}^(o-, /,...) Change in this last a, 6 ... A into «, b ... £, but so that «2 - x2 = a* -1% & - A2 = 62 - /2, &c. ; and let this change vj/ into $, we have obviously , « § ... + = ^r.* w This is an extension of Laplace's theorem relative to the attraction of ellipsoids on a point exterior. And if a, £, &c., a, b, &c. be independent of g, /i, &c, we have also To give an example or two, let R = {(g-^+ik-y)*...}*, and let Rx stand for the same quantity when a, £, &c. are changed into «, Z>, &c. ; then, since (&_ d*_ \_J_ W2 + ^2"7R'1-2"0' w being the number of variables, we have Rev. B. Bronwin on certain Definite Multiple Integrals. 375 /»/* dxdy ... _ otS ... /»/» dxdy ... . . JJ '"~WZ^~ ab..JJ '" R?~2 ' ' * ( j In the next two examples, by way of distinction, let #, y, &c. be changed into ax, a,r, 6y, 6y, &c. ; and let there be three variables, « § y dx dy dz fffi {(g-ux)2 + (k-fy)*+{k-yz)*}t _*§y rrp abcdx dy dz ~ aTcJJJ { {g - axf + {h- byf + {k - czf}* = rp>Sydxdys/l-x*-f +Ac,Bc2 + &c aSydxdy V\ — x2 — y2 {(g-axf + (k-byf-tkz}i SJ\ (2.) the equation of limits for the first member being x2+y2 + 22= 1, that for the second x* + y'2=l. This result is obtained by de- veloping into series relative to z, then integrating for this quantity, and lastly diminishing c without limit, the quanti- ties A, B, &c. being finite. In the second member it must be observed, that since c=0, a= VV— 72, b= VSP—y2. If we differentiate (2.) for (&), we have M (fc — yz) dx dy dz {{g-«x?+{h-Sy?+(k-ys?Y ~m kdxdy V ' l—x2 —y2 {{g-ax)* + {h-by)* + Ji*}% } (30 By integrating the first members of (2.) and (3.) relative to z, we should obtain very singular results. Let R={Cg-*)H (*-#+(*-*)«}*> v=J£f*^v±, U the same integral when «, £, y are changed into a, b9 c. Make v Vto — tL ^ J' =sm u, — & — sin v. R S{g-xy + {h-yf Then x=g— Rsinwsinv, y—h — Rsinwcosw, z=k— Rcosm, dx dy dz= — d R sin u du dv ; or rather 376 Rev. B. Bronwin on certain Definite Multiple Integrals. dxdydz = d R sin u du dv, because (R) decreases while (x) increases. Therefore U = III R d R sin u du dv = — / /R2sin u du do. Putting the values of .r, y, and z in ^LlISI z! - 1 a2 + & + c2 - j> and making 1 . . 1 1 A = -o sin2 « sin2 fl + to sin2 « cos2 v + -s a"1 tr c2 = -^ sin u sin » + 75 sin ^* cos u + -a cos m, a b c o-2 A2 yfc2 55+j5 + ?=> W we find 2 B /*/»B2 R = -spi and U = 2 / / -^ sin w c?« afr;. Between # = 0 and u = tt, R will be positive, and then negative up to u = 2ir. We must therefore integrate from «=0, tt=0 to u — TTf v=7r. If we leave out terms containing the first power of cos u, cos v, as these would give nothing in the value of the integral, we may make p-2 ^2 £2 B2 _ s sin2 u sin2 v + 7-3 sin2 a cos2 u + -r cos2 u. cr tr 2_ g«\| Rev. B. Bronwin on certain Definite Multiple Integrals. 577 J Lp + q p—q. '■ — n\ sin u du p + q p-qj V{p + q)(p-q) b c4g2 sin2 u + a4 k2 cos2 u a c2 sin2 u + a2 cos2 u . a c4^2 sin2 u + b4 k2 cos2 «"l sin « rfw "r os2 «1 sin w du b c2 sin2 w + W- cos2 # J A ' where A = (c2 sin2 m + a2 cos2 w)* (c2 sin2 « + b2 cos2 «)*• If we transform this by making sin2 u = -g , and to abridge A = ^/(a^ + x) (£2 + #)(c"2 + .r), we find tt / /'/g2 , ^2 , 1 a2k2-c2g2 J \_al bl c2 az-\-x 1 Z»2F-c2^2\k S* /*sinu cos2 ududv _^itk /* sin u cos2 u du c2JJ p + qcosll) c2 J Vp2— q2 . 7 7 /*2 cos2 u sin u du =4w ab k I *S o .(5.) V (c2sin2w + a2cos2 w)(c2sin2?^ + 62cos2w) „ And if we transform this by making sin2w = — , it will J * Vc2 + x become Phil. Mag. S. 3. Vol. 28. No. 188. May 1846. 2 D 378 Rev. B. Bronwin on certain Definite Multiple Integrals. ' dx 1 2nabck J? c2+x ^(a* + x) (b*+x) (c2 + «*•)' We have therefore in the general case dV rrr(g—x)dxdydz n p r dx ~ (a2+.r)A ^v „ 0 , r dx % a £ Y h J - ^v £ i r dx d & ' */ (