Jan. 16, 1873] December 10.-Professor E. C. Pickering exhibited a new form of theodolite magnetometer, which may be constructed at small expense from a common surveyor's transit. A mirror and magnet like that of a Thomson's galvanometer is attached to the cap of the telescope, and a right-angled prism and cross-hairs are placed in front of its eye-piece. The telescope is turned until the image of these cross-hairs is brought to coincide with those already in the eye-piece, when the axis of collimation will be exactly at right angles to the magnetic meridian. The remainder of the evening was devoted to a discussion of the great fire of November 9, by which sixty acres of the most valuable part of the city of Boston were destroyed. Numerous specimens of the effects of the fire were exhibited, among others a fused mass originally leather, but converted by the heat into a substance resembling resin. A strong wind with a velocity of twenty to twenty-five miles per hour was induced by the ascent of the heated air, although the velocity before the fire was but seven miles. This wind converted a narrow street into a sort of gigantic blow-pipe, and the flames were thus carried across Franklin Street, where it is over 100 ft. in width. The progress of the flames against the wind was noted, and explained by the radiant heat, which was so great that some of the engines were unable to get near enough to play on the fire. Buildings to windward might thus be set on fire, while those to leeward would be comparatively protected by the smoke. The carrying power of the air was remarkably great. Flakes of granite were carried across the water to South Boston, and fell in quantities on the side-walks and roofs, and papers were borne in some cases to a distance of over twenty miles. The light was so strong that it was easy to read by it in the higher parts of Belmont, over fifty miles distant; and the fire was seen at sea to a distance of ninety miles. RIGA. Society of Naturalists, March 6 (18 N.s.)—M. Frederking communicated a third section of his history of chemistry, in which he referred to the development of the electro chemical hypothesis, and the discovery of isomorphism, and to that of the vegetable alkaloids. April 3 (15 N.S.)-M. L. Taube presented a report on a work by M. Fischer, on the disease of bees, colled "foul brood," which is ascribed by the author to the dying and subsequent M. Fischer believes that putrescence of a portion of the larvæ. the fluid given by the worker-bees to the larvæ is secreted by the salivary glands, and that the mortality amongst the larvæ is caused by a deficiency of this secretion brought on by a scarcity of food. He considers that this is proved by the fact that "foul-broodedness" in a hive is caused by the removal of its own workers and the substitution of healthy workers from another hive. April 10 (22 N.S.)-M. Schroeder referred to the comet which was expected by some people to come in contact with the earth in August.-Colonel von Götschel read a paper on diseases of cage-birds, in which he especially recommended prophylactic measures. April 24 (May 6 N.S.)-M. C. Berg criticised Sir William Thomson's opinion as to the origin of the first organisms from germs conveyed by meteorites.-M. Teich communicated a contribution to the Natural History of Cucullia præcana. May 1 (13 N.S.)--A discussion took place on the means to be adopted for the protection of small birds, in which MM. Gögginger, Nauck, Westermann, and Burchardt, took part. May 15 (27 N.S.)-M. Schroeder presented a table of the rainfall at various stations during the summer of 1871, and called attention to the very small amount recorded at Riga. May 22 (June 3 N.s.)-Dr. Nauck communicated some observations on the torpidity of Myoxus nitela.-M. Westermann exhibited a pane of glass in which a circular hole of two inches diameter had been made by a hailstone on May 10. (22 N.S.) Dr. Nauck exhibited plaster-casts of hailstones from the same fall, and proposed a theory of the formation of hail by the production of a whirlwind caused by warm, moist winds meeting cold winds under angles of 90°, when the aqueous vapour is condensed, causing an inflow of air from above and below, and consequently an increase of precipitation, during which the water, striving to retain its fluid form, may easily fall several degrees below its freezing point, and its congelation into masses of ice may be accounted for by the fall into it of small grains.-M. J. H. Kawall gave an account of the publi. cations of the Society of Naturalists of Charkow, including the titles of all the papers. July 20 (August 1 N.S.)-The society assembled in the court of the Polytechnicum to hear an address in honour of Dr. G. Schweinfurth on his return from his African travels. August 21 (September 2 N.S.)-Dr. Schweinfurth described several types of the inhabitants of Central Africa, belonging to the Ujam-Ujam, Bongo, Djur, Dinka, Mittu, and Akka branches of the Negro, noticing especially their modes of adorning themselves, and a few peculiar habits.-Baron F. Hoejningen-Huene communicated a continuation of his Phenological observations, containing notes on weather and other natural phenomena during the months of July and August, 1871. PHILADELPHIA "On a new Academy of Natural Sciences, July 2.Genus of Extinct Turtles." Prof. Leidy stated that he had determined that the fossil-turtle he had named Bæna undata beBesides other well-marked distinclonged to a different genus. tive characters, like the genus Platemys, it possessed an additional pair of plates to the usual number found in the sternum of the emydoids. These plates are intercalated between the hyo- and hypo-sternals. In Platemys Bullockis they are quadrate. In the new genus they are triangular, and the sutures defining them cross the plastron like a prostrated letter X, from which character it was proposed to name the genus Christernon. July 9.-Prof. Leidy directed attention to a bottle containing numerous specimens of a minute crustacean from Salt Lake, Utah, caught on the 22nd of June by Mr. C. Carrington, a member of Prof. Hayden's exploring party now in the field. They were received from Prof. Hayden with the remark "that Salt Lake has been supposed, like the Dead Sea, to be devoid of life, but its saltest water contains the most of these little creatures.' The crustacean is the Artemia salina, which has long been known in Europe, and has been previously found in other localities of this country. The animal has always been viewed with especial interest, in its order, from the fact that it lives and thrives best in a concentrated solution of salt, which would destroy most marine animals. It has not, I believe, been noticed in the ocean, but is found in salt lakes, and salt vats, in which, by evaporation, the brine has become more concentrated than sea water. Artemia is furnished with eleven pairs of limbs, which serve both for progression and respiration. The limbs are four-jointed, and the joints have leaf-like expansions fringed with long featherlike bristles. The narrow abdomen, or tail-like prolongation of The last the body is six-jointed, and traversed by the intestine. joint ends in a pair of processes, furnished each with a bunch of bristles like those of the limbs. The head exhibits a median, quadrate, black eye-spot, and in addition is provided with a pair of pedunculate, globular compound eyes. A short narrow pair of inarticulate antennæ project in advance of the eyes. The head of the male is furnished with a pair of singular organs for seizing the female. These claspers are large double-jointed hooks. In the female they are replaced by a pair of comparaThe first abdominal segment tively small horn-like processes. bears the ovarian sac in the female, and two cylindroid appendages in the male. The female of the Salt Lake Artemia ranges from four to seven lines in length; the male from three to four lines in length. The colour is translucent-white and ochreousyellow, with three black eye-spots, and a longitudinal line varying in The ovarian sac appears hue with the contents of the intestine. orange-coloured from the eggs within. The antennæ end in three or four minute setæ, and are considerably longer in the male than the female. The first joint of the claspers is provided on its inner side just below the middle with a spheroidal knob. The last joint forms a rectangular hook, the angle having an elbowlike prominence. When the clasper is thrown forward, the outer border of the hook is convex; the anterior border straight, slightly or deeply concave, and the inner or posterior border is sigmoid. The antenne are longer than in the female, and longer than the first joint of the claspers; and in the female are longer than their homologues. The ovarian sac is inverted flask-shaped, and has a pair of lateral conical or mamillary, finely tuberculated processes. The caudal setæ are longer than in the male, and are eight to each process. This description is taken from alcoholic specimens. They exhibit considerable variation in size, and to some extent in detail. Prof. Verrill has described what he views as two species of Artemia distinct from the well-known A. salina. One he names A. gracilis, from near Newhaven, Conn.; the other A. Monico, from Lake Mono, Cal. That from Salt Lake differs from either of them as much as they do from A. salina, and with the same propriety may be regarded as a distinct species. I am disposed to view them all as varieties merely of A. salina. Prof. Leidy stated that from time to time he had observed speci mens of teeth from various cretaceous formations which were identical in character with those of Lamna elegans and L. cuspidata of tertiary deposits, except that they were devoid of the lateral denticles. He had now in his possession well-preserved specimens of such teeth, unabraded, but exhibiting no trace of the existence of lateral denticles. There were teeth of the L. elegans variety found with the skeleton of Hadrosaurus Foulkii in New Jersey, and others from the cretaceous of Mississippi and Kansas. There were also teeth of the L. cuspidata variety from the creta. ceous of Kansas, and one in a block of chalk from Sussex, Eng. land. The absence of the lateral denticles in all the cretaceous specimens he thought could hardly be accidental, and suspected that these teeth represented the oxyrrhina ancestors, of the tertiary Lamna elegans and L. cuspidata, which lived during the cre taceous era. PARIS Academy of Sciences, Dec. 30, 1872.-M. Faye, president, in the chair. The president read the second portion of his paper on the solar spots. He argued in favour of their cyclonic nature, and said that the pores were simply minute spots. He pointed out that Wilson, in 1783, had suggested that the spots were "eddies and whirlpools," and that Sir J. Herschel had made use of a similar phrase, but that the knowledge only recently ob tained was required before these suggestions could be accepted.M. Jamin read a note on concealed magnetism (magnétisme dissimulé). The author found that when a current used to magnetise a horse-shoe bar of iron attained a certain power, the bar appeared to return to its natural state; but that, with either stronger or weaker currents, magnetism was produced. This neutral state he calls "concealed magnetism," and supposes it to be due to a particular distribution of the magnetic force.—A note from Mr. A. Cayley on the condition under which a family of surfaces forms part of an orthogonal system, was next read.M. Janssen read the second part of his report on the eclipse of December 31. It was referred to the astronomical section. -M. F. P. Le Roux read a paper on peri-polar induction. The author applies the above name to a new form of electro-magnetic phenomena, in which the different points of the body acted on remain at the same distance from the active pole.-A paper on the dimensions of the pores of membranes by M. Guerout was presented by M. Becquerel.-M. Delafont sent a memoir on the first elements of the theory of conjugate points and right poles, which was submitted to the examination of M. Serret.— MM. Le Clère and Du Plantys sent a note on Phylloxera which were sent to that commission; and a second memoir on fermentation from M. Sacc was referred to a special commission. - General Doutrelaine sent a note relating to the questions of priority concerning the prolongation of the French meridian; M. Baillaud the elements and ephemerides of 127; and Mr. N. Lockyer an abstract of his late paper on spectrum analysis, communicated to the Royal Society.-MM. Troost and Hautefeuille sent a note on certain reactions of the chlorides of boron and silicon. These bodies decompose porcelain at a high temperature.-M. P. Pichard read a note on the estimation of manganese in iron ores, cast-iron, and steel, by a calorimetric process; and M. A. Houzeau, one on the volumetric estimation of minute quantities of antimony and arsenic.-M. Sorin read a note on the presence of methylamine in methylic nitrate and in methylic alcohol.-M. L. Colin's note on the passage of the blood pigment through the vascular sides in melanemia palustris was presented by M. Larrey, which was followed by a note on the distribution of the tympanic cord, by M. J. L. Prevost.-M. A. Béchamp read a note on the alcoholic and acetic fermentation of the liver, and on the physiological alcohol of human urine. The author has obtained from two litres of urine from a man of 50, enough alcohol to estimate. -M. A. Bernard presents a memoir on the "degeneration" of nerves after section, by M. L. Ranvier.-M. L. Posaoz sent a note on the estimation of sugar by cupric solutions. He stated that these liquids may be preserved from their usual faults by the passage of a stream of carbonic anhydride, or by the addition of alkaline bicarbonates.-M. J. Chautard sent a note on the absorption spectrum of delorophyll; and M. Sicc a note entitled, "Studies on Marmots," relating principally to the composition of the urine of these animals.-M. Decharme sent a paper on the ascending motion of liquids in very narrow vessels (bands of porous paper) compared with their ascent in capillary tubes.-M. Boileau sent a note on the preservation of potable water. The author kept eighty bottles of water fresh and free from bad odour during the siege of Paris, by leaving them simply covered with caps of paper.-M. Belgrand made some observations on this note.-M. Dausse sent a note on the best position for flood gauges in rivers. DIARY THURSDAY, JANUARY 16. ROYAL SOCIETY, at 8 30.-Note on an Erroneous Extension of Jacobi's Theorem: J. Todhunter.-On a New Formula for a Microscopic ObjectGlass F. H. Wenham.-Additional Note to the Paper On a Supposed Alteration in the Amount of Astronomical Aberration of Light produced by the Passage of the Light through a considerable Thickness of Refracting Medium: Sir G. B. Airy. ROYAL INSTITUTION, at 3.-On Oxidation: Dr. Debus. SOCIETY OF ANTIQUARIES, at 8. 30.-Election of Fellows.-Opening of Exhibition of Bronze Implements and Weapons. LINNEAN SOCIETY, at 8.-On the Recent Synonyms of Brazilian Ferns: J. G. Baker. CHEMICAL SOCIETY, at 8.-On Ethylamyl: Mr. Grimshaw -On the Heptanes from Petroleum: C. Schorlemmer-On the Vanadates of Thallium: T. Carnelley. On the Formation of Sulphide of Sodium by the Action of Sulphuretted Hydrogen upon Sodium Chloride: C. T. Kinggeth. NUMISMATIC SOCIETY, at 7. IT THURSDAY, JANUARY 23, 1873 THE NAVY AND SCIENCE T would be difficult to estimate the many excellent effects that are likely to result from the establishment of the Royal Naval College, which, as has been at last authoritatively intimated, is to be opened on February 1, in those noble halls at Greenwich that for so long have been associated in another way with the British Navy. Her Majesty's Government deserve the highest praise for the wisdom-provokingly tardy though it has been-displayed in the thorough and handsome provision they have made for the scientific education of our naval officers. Much that is sarcastic, no doubt, might be said on this tardiness of a Government which seldom moves until it is driven; but as we fear this would do little good, we shall only express a hope that in future when they are compelled to take action in any matter, especially if it be scientific, they will do so as decidedly and sweepingly as they have done in the present instance. It is usually acknowledged that the very existence of Britain as a first-rate Power depends upon the efficiency of her navy, and yet it is a lamentable fact that hitherto no nation in the world of any consequence has made less systematic provision for the training of the members of her navy than has our own. Our naval officers and seamen have been left pretty much to haphazard to gain a knowledge of their profession, and, indeed, until recently it would have been generally thought derogatory to what is vaguely known as "British pluck," had it been hinted that it would be not less plucky were it well informed; that it would have a better chance to beat all the forces in the universe, did it know the scientific principles on which a few of these forces rested. Happily this is no longer the case; the strong light of science, "the irresistible logic of facts," has shown this old knowledge to be but ignorance; and let us rejoice that this great light has at last dawned upon the magnates of our navy, and dispersed the great darkness in which they have for so long sat. The college to be opened on Feb. 1, if we may judge from the prospectus, will furnish as thorough a scientific education in the branches to be taught as can be obtained at any similar institution in any country in the world. The immense advantages that are likely to accrue to the British Navy as such, from the excellent training which its officers must undergo at the new Naval College, are evident to all, and have been already pointed out in the columns of the general press. For one thing it will reduce the incompetents and idlers to a minimum. We are inclined to think that the gains to Science from the establishment of such an institution will be of not less importance than the increase in the efficiency of the navy which must be its special result. Our naval officers form a large, important, and influential body, having opportunities for scientific research all over the world which all students of nature must envy. Even under the old régime many of the most important additions to scientific knowledge in various departments were made by naval officers, some of whom have won for themselves 'deathless names as scientific explorers. What then No. 169-VOL. VII. must be the conquests of Science in the future when every naval officer who is capable of profiting by the instruction to be furnished at Greenwich will go forth trained and equipped to wrest from Nature some of the many secrets which she still holds in her grasp? What an immense advantage must it be to any scientific or exploring expedition when the officers that command the ship are as capable of unravelling the mysteries of Nature as they are of boxing the compass. But it would be impossible to enumerate all the advantages that we may reasonably expect to accrue to Science from the step taken by the Lords of the Admiralty. The scheme of education as it stands on paper is admirable, and most comprehensive as to subject and as to the classes for whose advantage it has been drawn out; with Rear-Admiral Kay as President of the College, and Dr. Hirst as Director of Studies, we have every reason to hope that the Royal Naval College will "become, not only an educational establishment affording the means of the highest training in theoretical subjects to naval officers of all classes, but also a nucleus of mathematical and mechanical science specially devoted to those branches of scientific investigation which have most interest for the navy." We can only hope that the excellent example set by the Lords of the Admiralty will in a very short time be followed by the authorities of the War Office. Does not the profession of a military officer at the present day require as thorough a training to be able to fill it efficiently, as does that of a naval officer? Are not the very highest scientific principles being brought to bear on the elaboration of military weapons, and military tactics? and would not military officers, like naval officers, perform the duties of their profession more efficiently if they had a systematic training in the sciences from which modern tactics draw their life? But sad to say, the military authorities have recently shown a tendency to take the very opposite course to that which our more advanced naval authorities have so commendably followed. We hope the example of the latter will ere long shame the former into mending their ways. The following are some of the principal points in the minute issued by the Lords of the Admiralty : "The College, subject to the subjoined Regulations, will be open to officers of the following ranks :-1. Captains and Commanders. 2. Lieutenants. 3. Navigating Officers. 4. Naval Instructors. 5. Acting Lieutenants and Acting Sub-Lieutenants. 6. Officers, Royal Marine Artillery; ditto, Royal Marine Light Infantry. 7. Officers gineers, 1st Class Assistant Engineers, Acting 2nd Class of the Engineer Branch, viz.:-Chief Engineers, EnAssistant Engineers. 8. A limited number of Dockyard Apprentices will be annually selected, by competitive examination, for admission to the College. A course of instruction at the College will also be open to a limited number of:-9. Private students of Naval Architecture or Marine Engineering. 10. Officers of the Mercantile Marine. "It is not intended to provide at Greenwich for the education of the Naval cadets. My Lords intend that the Royal Naval College at Greenwich shall be so organised as to provide for the education of naval officers of all ranks above that of midshipman, in all branches of theoretical and scientific study bearing upon their profession; but my Lords will continue the instruction given in the Excellent gunnery-ship as heretofore, and arrangements for instruction in practical surveying will also be con N tinued at Portsmouth. My Lords desire by the establish. ment of the College, to give to the executive officers of the navy generally every possible advantage in respect of scientific education; but no arrangements will be made at all prejudicing the all-important practical training in the active duties of their profession. The object of securing, in the interest of the naval service, the highest possible scientific instruction is, in the opinion of my Lords, most effectually to be attained by bringing together in one establishment all the necessary means for the higher education of naval officers and of others connected with the navy. . . . Complete courses of study suitable for the different classes of students admitted will be organised, and will be carried out by professors, lecturers, and instructors. Officers and others admitted as students will have the advantage of these courses of study, whether they reside or not. But officers and others who may not become students will, under certain regulations, have free access to separate courses of lectures, the benefit of which it is desired to extend as far as possible." now afforded at South Kensington. Further regulations will be issued by their lordships in regard to the admission of private students to the course of study at the College on similar conditions to those now existing at South Kensington. My Lords have further determined to admit a limited number of officers of the Mercantile Marine as students of the College, enjoying the full advantages of the whole course of instruction and tuition by the educational staff, while officers of the Mercantile Marine generally will, on application, be allowed to attend courses of lectures. "The paramount object which my Lords have pursued in the organisation of the College has been to provide the most efficient means for the higher education of naval officers adequate to the constantly increasing requirements of the service; but my Lords also anticipate great advantages from the results likely to accrue from the connection which will be established through the College between men distinguished in the various departments of mathematical, physical, and chemical science, and those practical problems which so vitally interest the navigator, the naval architect, and the naval engineer. My Lords expect the College to become, not only an educational establishment affording the means of the highest training in theoretical subjects to naval officers of all classes, but also a nucleus of mathematical and mechanical science specially devoted to those branches of scientific investigation which have most interest for the navy.” The following are the proposed courses of study:— "1. Pure Mathematics, including co-ordinate and higher Pure Geometry, Differential Calculus, Finite Differences, and the Calculus of Variations. 2. Applied Mathematics, viz., Pneumatics, Mechanics, Optics, and the Theories of Sound, Light, Heat, Electricity, and Magnetism. 3. Applied Mechanics, including the Theory of Structures, the principles of Mechanism, and the Theory of Machines. 4. Nautical Astronomy, Surveying, Hydrography, with Maritime Geography, Meteorology, and Chart Drawing. 5. Experimental Sciences :-a. Physics, viz., Sound, Heat, Light, Electricity, and Magnetism; b. Chemistry; c. Metallurgy. 6. Marine Engineering, in all its branches. 7. Naval Architecture, in all its branches. 8. Fortification, Military Drawing, and Naval Artillery. 9. International and Maritime Law; Law of Evidence and Naval Courts Martial. 10. Naval History and Tactics, including Naval Signals and Steam Evolutions. II. Modern Languages. 12. Drawing. 13. Hygiene-Naval To obtain any adequate idea of the present state of and Climatic. A certain latitude in selecting such courses of study as they may prefer will be allowed to officers voluntarily attending the College. Officers and others required to attend by the Regulations will follow such courses of study as may from time to time be prescribed. "The general organisation of the College will be as follows: A flag officer will be president; he will be assisted by a captain in the Royal Navy in matters affecting discipline, and in the internal arrangements of the College unconnected with study. A director of studies will, under the president, organise and superintend the whole system of instruction, and the various courses of study. There will further be-A professor of mathematics, a professor of physical science, a professor of chemistry, a professor of applied mechanics, a professor of fortification. Such instructors in mathematics and the other branches specified as may be necessary to assist the professors will be added to the staff. Lecturers will be appointed to deliver courses of lectures in naval architecture, metallurgy, civil and hydraulic engineering, maritime law, naval history and tactics, and hygiene. A naval officer will conduct instruction in nautical astronomy and surveying, and there will be two instructors in steam. Such provision will be made for instruction in French and German and in draw ing, as the number of students desirous of following courses in these branches may render necessary. . . "Arrangements have been made for the admission of naval engineer officers to the College, which will prevent time spent at the College from entailing any pecuniary loss upon them. The School of Naval Architecture at South Kensington will be absorbed in the Royal Naval College, Greenwich. The regulations for the admission of engineer students and of dockyard apprentices have been so framed as to provide as nearly as possible the same aggregate time for their instruction as that which is ELECTROSTATICS AND MAGNETISM Reprint of Papers on Electrostatics and Magnetism. By Sir W. Thomson, D.C.L., LL.D., F.R.S., F.R.S.E., Fellow of St. Peter's College, Cambridge, and Professor of Natural Philosophy in the University of Glasgow. (London: Macmillan and Co., 1872.) 'O T° electro-magnetic science we must study these papers of Sir W. Thomson's. It is true that a great deal of admirable work has been done, chiefly by the Germans, both in analytical calculation and in experimental researches, by methods which are independent of, or at least different from, those developed in these papers, and it is the glory of true science that all legitimate methods must lead to the same final results. But if we are to count the gain to science by the number and value of the ideas developed in the course of the inquiry, which preserve the results of former thought in a form capable of being employed in future investigation, we must place Sir W. Thomson's contributions to electro-magnetic science on the very highest level. science-forming ideas, is that which forms the subject of One of the most valuable of these truly scientific, or the first paper in this collection. Two scientific problems, each of the highest order of difficulty, had hitherto been considered from quite different points of view. Cavendish and Poisson had investigated the distribution of electricity on conductors on the hypothesis that the particles of electricity exert on each other forces which vary inversely as the square of the distance between them. On the other hand Fourier had investigated the laws of the steady conduction of heat on the hypothesis that the flow of heat from the hotter parts of a body to contiguous parts which are colder is proportional to the rate at which the temperature varies from point to point of the body. The physical ideas involved in these two problems are quite different. In the one we have an rature at any point in the solid, and to draw the isothermal surfaces. One of these surfaces is a sphere, and if, in the electrical problem, this sphere becomes a conducting surface in connection with the earth, and the external source of heat is transformed into an electrified point, the sink will become the image of that point, and the temperature and flow of heat at any point outside the sphere will become the electric potential and resultant force. attraction acting instantaneously at a distance, in the other heat creeping along from hotter to colder parts. The methods of investigation were also different. In the one the force on a given particle of electricity has to be determined as the resultant of the attraction of all the other particles. In the other we have to solve a certain partial differential equation which expresses a relation between the rates of variation of temperature in passing along lines drawn in three different directions through a point. Thomson, in this paper, points out that these two problems, so different, both in their elementary ideas and their analytical methods, are mathematically identical, and that, by a proper substitution of electrical for thermal terms in the original statement, any of Fourier's wonderful methods of solution may be applied to elect-mation of the external electrified system by reciprocal rical problems. The electrician has only to substitute an electrified surface for the surface through which heat is supplied, and to translate temperature into electric potential, and he may at once take possession of all Fourier's solutions of the problem of the uniform flow of heat. To render the results obtained in the prosecution of one branch of inquiry available to the students of another is an important service done to science, but it is still more important to introduce into a science a new set of ideas, belonging, as in this case, to what was, till then, considered an entirely unconnected science. This paper of Thomson's, published in February 1842, when he was a very young freshman at Cambridge, first introduced into mathematical science that idea of electrical action carried on by means of a continuous medium which, though it had been announced by Faraday, and used by him as the guiding idea of his researches, had never been appreciated by other men of science, and was supposed by mathematicians to be inconsistent with the laws of electrical action, as established by Coulomb, and built on by Poisson. It was Thomson who pointed out that the ideas employed by Faraday under the names of Induction, Lines of Force, &c., and implying an action transmitted from one part of a medium to another, were not only consistent with the results obtained by the mathematicians, but might be employed in a mathematical form so as to lead to new results. One of these new results, which was, we have reason to believe, obtained by this method, though demonstrated by Thomson by a very elegant adaptation of Newton's method in the theory of attraction, is the "Method of Electrical Images," leading to the "Method of Electrical Inversion." Poisson had already, by means of Laplace's powerful method of spherical harmonies, determined, in the form of an infinite series, the distribution of electricity on a sphere acted on by an electrified system. No one, however, seems to have observed that when the external electrified system is reduced to a point, the resultant external action is equivalent to that of this point, together with an imaginary electrified point within the sphere, which Thomson calls the electric image of the external point. Thus Thomson obtained the rigorous solution of electrical problems relating to spheres by the introduction of an imaginary electrified system within the sphere. But this imaginary system itself next became the subject of examination, as the result of the transfor radii vectores. By this method, called that of electrical inversion, the solution of many new problems was obtained by the transformation of problems already solved. A beautiful example of this method is suggested by Thomson in a letter to M. Liouville, dated October 8, 1845, and published in Liouville's Journal, for 1845, but which does not seem to have been taken up by any mathematician, till Thomson himself, in a hitherto unpublished paper (No. xv. of the book before us), wrote out the investigation complete. This, the most remarkable problem of electrostatics hitherto solved, relates to the distribution of electricity on a segment of spherical surface, or a bowl, as Thomson calls it, under the influence of any electrical forces. The solution includes a very important case of a flat circular dish, and of an infinite flat screen with a circular hole cut out of it. If, however, the mathematicians were slow in making use of the physical method of electric inversion, they were more ready to appropriate the geometrical idea of inversion by reciprocal radii vectores, which is now well known to all geometers, having been, we suppose, discovered and re-discovered repeatedly, though, unless we are mistaken, most of these discoveries are later than 1845, the date of Thomson's paper. But to return to physical science, we have in No. vii. a paper of even earlier date (1843), in which Thomson shows how the force acting on an electrified body can be exactly accounted for by the diminution of the atmospheric pressure on its electrified surface, this diminution being everywhere proportional to the square of the electrification per unit of area. Now this diminution of pressure is only another name for that tension along the lines of electric force, by means of which, in Faraday's opinion, the mutual action between electrified bodies takes place. This short paper, therefore, may be regarded as the germ of that course of speculation by which Maxwell has gradually developed the mathematical significance of Faraday's idea of the physical action of the lines of force. We have dwelt, perhaps at too great length, on these youthful contributions to science, in order to show how early in his career, Thomson laid a solid foundation for his future labours, both in the development of mathe Now if in an infinite conducting solid heat is flowing out-matical theories and in the prosecution of experimental wards uniformly from a very small spherical source, and part of this heat is absorbed at another small spherical surface, which we may call a sink, while the rest flows out in all directions through the infinite solid, it is easy, by Fourier's methods, to calculate the stationary tempe research. Mathematicians however will do well to take note of the theorem in No. xiii., the applications of which to various branches of science will furnish them, if they be diligent, both occupation and renown for some time to come. |