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and the vast system of inter-oceanic communication that connects the civilised world together, has been framed.

At the date of Wheatstone's first experiment, guttapercha was undiscovered, and its insulating power unknown. By the employment of this gum, the electrical condition of the submarine cable, up to a certain standard, has been under ordinary circumstances rendered secure. Such being the case, and for the purpose of comparison hereafter, it is well to examine a little into the properties of this gum and that of india-rubber, another vegetable substance possessing insulating properties of the most remarkable kind, as applied to the construction of submarine cables. Gutta-percha, as is well known, is a vegetable gum, which becomes plastic and soft at a comparatively low temperature, about 100° F. Subjecting the gum to repeated cleansing processes to free it from impurities and extraneous vegetable matter, it is rendered tolerably dense and homogeneous, and in this state it is applied in successive layers or coats round the copper conducting wire as the insulating material, forming the 66 core" of the submarine cable, which is then termed "insulated," that is, capable to a certain extent of preventing the lateral escape of any electric current or charge which may be passed into the wire. A short investigation is now necessary to be made of some of the circumstances which take place when a wire thus insulated is submerged and subjected to the charge of an electric current. If the wire were absolutely insulated, that is, if gutta-percha were a perfect insulator offering an indefinite resistance to the passage of the current through its substance, any given quantity of electricity passed into the wire would remain there for a given time without loss, in the same way as when water is poured into a vessel, the level remains intact so long as there is no leakage. The amount of this leakage through the gutta-percha, or, in other words, its "conductive resistance," determines the insulating power of the cable. But this is not all that has to be considered; other circumstances affecting the value of the insulation come into play. The following analogous example will explain. When a leech is allowed to crawl through a glass tube, the head and body pass out first, while the tail-long and attenuated-is slowly withdrawn. So with the passing of an electric current through an insulated conductor, a portion of the current lags sluggishly behind, absorbed, as it were, into the substance of the insulating medium, and taking time to discharge itself in proportion to the amount of the sucking up, or "inductive capacity" of the insulator, for, in this respect, both guttapercha and india-rubber may be regarded as a sponge, the current penetrating into the pores of the substance. Without entering further into detail regarding the laws regulating the transmission of the current, it is sufficient to remember that the speed or power of transmitting a given number of messages in a given time over any cable depends materially upon the proportionate values of the "conductive resistance" and "inductive capacity" of the insulation. Thus there is at once established a measure by which the value of all known insulating materials may be determined and compared together, that is to say, if two cables of equal length and similar construction are taken the one insulated with gutta-percha, and the other with india-rubber (Hooper's india-rubber)-the relative value and working speed of each can be accurately determined and compared. The successful employment of india-rubber as an insulating medium for submarine cables is of more recent date, and the estimation in which it is now held for that purpose is entirely due to the beautiful process employed in its manipulation by Mr. W. Hooper, of Mitcham. It is well known that india-rubber possesses a much higher insulating power than gutta-percha; as a gum it is also denser, more homogeneous, and infinitely more pliable and elastic than gutta-percha, while it is not affected in any considerable degree by variation of temperature-all qualities of the

greatest importance as connected with submarine cable insulation.

Before entering upon a comparative statement of the insulation and speed of gutta-percha and Hooper's insulation, a short notice of the mode by which this insulating material is manipulated will be interesting, and will serve to give value to the practical data hereafter stated. The copper conductor, after being tinned, is coated with an insulation of pure india-rubber applied in the shape of a ribbon, lapped spirally round it. Next, two strips (one laid above and the other below) of indiarubber, chemically prepared to resist the action of sulphur, and called the "separator," are applied so as to completely surround the first rubber covering, as it were with a tube; a pair of grooved die-wheels giving the contour, and at the same time regulating accurately the guage of the core. Exterior strips are then similarly applied of a compound of rubber and a small percentage of sulphur. The whole is then lapped round with water-proof felt tape, and exposed for some hours in an oven to a heat of about 383° F. By this process the three successive coatings are welded into one solid, dense, homogeneous mass, having its distinctive features preserved as regards the individual character of the several layers. Thus the heat, in driving off the sulphur from the outside' coating, has converted that envelope into an indestructible vulcanised rubber jacket. The second layer, or "separator," has intercepted the passing of the sulphur by reason of its chemical properties, while at the same time it has allowed an infinitesimal trace of the sulphur to combine with the internal coating of pure rubber round the conducting wire, sufficient to change its character into an indestructible and nonliquifying material, without its becoming in any way vulcanised. It is by this beautiful chemical affinity between the several layers, each performing its special part towards the production of one individual whole, that the "Hooper insulation" has succeeded in establishing the durability of the preparation, the comparative value of which, as compared with that of gutta-percha, will now be given.

First as regards temperature-it has been already stated that gutta-percha became plastic at about 100° F. At this temperature it loses also almost entirely its insulating properties; that is to say, if at a temperature of 32° F. the insulation of gutta-percha is taken as representing 100, at 75° it is reduced to 5'51, or little more than a twentieth part, while at the increased temperature of 100°, its insulating power has further decreased to 1'43, or about one seventieth part. Guttapercha as an insulator is therefore unsuited for hot climates, or any exposed position where the temperature rises above 70°. Taking now Hooper's india-rubber insulation at 32° F. to be the same, 100, at 75° we find its insulation to be 24'50, or about one-fourth part, while at 100° it is 10'60, or about one-tenth part. Thus at the ordinary temperature of 75°, Hooper's core establishes its superior insulating properties under temperature in the proportion of four to one. The" inductive capacity" of Hooper's core, from its superior density, is only about two-thirds that of gutta-percha, while its insulation or resistance of the dielectric is fully twenty times greater than that of gutta-percha core, as exemplified in the tests given of some of the best known cables now at work.

The following is a list of some of the more important cables insulated with Hooper's core laid up to the present

time :

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These two latter cables have recently been completed, and the Shanghae-Possiette cable is now in course of submergence; the Hong-Kong-Shanghae cable was successfully laid last month. These lines give a total distance of over 3,978 nautical miles of submarine cable with Hooper's indiarubber insulation. The following observations as regards the electrical conditions of these cables as compared with well-known gutta-percha insulated cables is remarkable. The electrical tests of well-known cables with both the gutta-percha and the Hooper core are taken at the temperature of 75° Fahr., and in terms of British Association (B.A.) units, the standard measure now most generally adopted in England for comparison :

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With such results, it is not to be wondered at that the relative speed of two cables of similar length and construction, the one employing a gutta-percha core and the other a Hooper core, should be found greatly in favour of the latter, in the proportion of 130 to 100; that is to say, in any given time the Hooper core, from its superior insutting properties, will transmit thirty per cent. more words than a gutta-percha core, a most important circumstance when it is considered that the earnings or dividend upon each cable is dependent upon the work it can perform in a given period. As regards the apparatus employed for transmitting the currents through submarine conductors, the "Wheatstone" automatic recording system is the most successful. By this apparatus an average speed of over thirty words a minute is regularly maintained upon the Danish-English cable, a distance of 363 nautical miles, exclusive of a further land circuit of over 140 miles, making a total distance of about 500 miles. This speed must be compared with that of seventeen words per minute, the highest result recorded over the same circuit by the most improved Morse system. From the esults of the "Wheatstone" apparatus working over this circuit since September 1868, it appears that to obtain maximum speed, the currents through a submarine cable require to be transmitted of equal duration, at equal intervals, in alternate directions, and the line discharged to earth between each successive reversal or current to neutralise the charge, all of which conditions are fulfilled in the "Wheatstone" Automatic Jacquard arrangement, which can only be compared to a loom weaving the currents into the line, the sequence of the currents representing the pattern on the cloth. This apparatus is now organised as the transmitting and recording register upon the vast system of submarine circuits belonging to the Great Northern Telegraph Company, and the extensions from Possiette Bay (RussianChinese frontier) to Nagasaki, Shanghae, and Hong Kong. The subject of high speed transmission through insulated conductors, both by land and sea, is one which demands

special attention, now that the telegraph is daily encroaching upon the postal service, a service in which both speed and accuracy are more than ever demanded by the public. NATH. J. HOLMES

IN

PFLÜGER'S NERVE ENDINGS IN GLANDS N his "Archiv für die Gesammte Physiologie" (Bonn, 1871), E. Pflüger gives a short and summary answer to those many observers who have thrown doubt on the accuracy of his remarkable discoveries as to the continuity of nerves with the secreting cells of the salivary glands and liver. Pflüger's opponents in this matter have been Mayer, Hering, Krause, Henle, and Schweigger-Seidel. The objections which have been made are divided by him into three heads. 1st. It was said that the nerves he had seen were capillary vessels. 2nd. That they were threads of mucus. 3rd. They were disintegrated fat. These objections are successively shown to be groundless, and Pflüger stoutly maintains his original position. What is far more important in this short paper than these answers to objections is that the professor at length publishes an account of some of his methods as to which he has so long left every one in the dark. They are certain to be interesting to some of our readers. Salivary glands. A fresh submaxillary gland from the ox must be taken, and very fine sections made; these must be at once teased out in perosmic acid sp. gr. 1003, and covered with a thin glass in a shallow cell. A great many preparations should be made, and the best picked out. They will be sufficiently stained in 24 hours. As the water dries up it may be replaced by glycerine. Liver. A great number of very fine sections must be made from the fresh liver of a dog or pig. These sections must be placed 10 or 12 together in watch-glasses filled with Beale's carmine solution, and thus kept in a moist chamber 14 days. The sections must then be taken out, washed one by one in a drop of perosmic acid, sp. gr. 1003, transported to a fresh drop of the same on a slide, and carefully teased out, covered, and examined.

NOTES

ST. BARTHOLOMEW'S HOSPITAL has, we learn from the

British Medical Journal, sustained a great loss in the resignation by Mr. Paget of his active duties as Surgeon to the Hospital. Mr. Paget will, of course, receive the appointment of Consulting Surgeon to the Institution which he has served long and faithfully, and on which he has conferred lustre.

THE following excursions have been arranged by the Geologists' Association to take place in May :-To Oxford on Friday, 12th May. On arriving at Oxford the New University Museum will be visited. Subsequently the party, accompanied by the President, Prof. Phillips, and Prof. Morris, will walk to Shotover Hill, where the Middle and Upper Oolites are well exposed. To Grays, Essex, on Saturday, 20th May. Exposures of the Mammaliferous beds of the Thames Valley, and afterwards sections of the Upper Chalk will be visited, under the guidance of Prof. Morris. A four days' excursion to Yeovil, Weymouth, and Portland is proposed for Whitsuntide. Particulars of arrangements will be duly announced.

THE Edinburgh Naturalists' Field Club, which has since its formation carried on active operation only from April to July inclusive, held its adjourned annual meeting and conversazione on Saturday, the 22nd April, when Mr. Robert Scot-Skirving, the president, delivered an introductory address, enlarging mainly on entomology as a fit summer field study. The business meeting was held in November last, when, in addition to the

present president and committee, Prof. Liston was elected vicepresident, and Mr. Andrew Taylor honorary secretary and

treasurer.

THE following is the programme of the lectures on the Experimental and Natural Sciences in Trinity Term, in Trinity College, Dublin. Mineralogy, 11 A.M., on Mondays, Wednesdays, and Fridays. Demonstrations in Organic Chemistry, 12, Mondays, Wednesdays, and Fridays. Magnetism, 2 P.M., Mondays, Wednesdays, and Fridays. Comparative Anatomy, II A.M., Mondays, Wednesdays, and Fridays. Demonstrations in Botany, 11 A. M., Tuesdays, Thursdays, and Saturdays. Applied Geology, I P.M., Tuesdays, Thursdays, and Saturdays. THE grace for allowing French and German as an alternative for Greek, was submitted to the Senate of the University of Cambridge on Thursday last, and rejected by a majority of three only. The subject will doubtless be reopened, and probably some slight modification of the original scheme will ultimately be accepted.

THE following gentlemen have been elected, by the Senate of the University of London, Examiners in Science and Medicine for the ensuing year :-Logic and Moral Philosophy: Prof. G. Croom Robertson and Rev. John Venn. Political Economy: Prof. W. Stanley Jevons and Prof. T. E. Cliff Leslie. Mathematics and Natural Philosophy: Prof. H. J. S. Smith, F.R.S., and Prof. Sylvester, F.R.S. Experimental Philosophy: Prof. W. G. Adams and Prof. G. Carey Foster, F. R. S. Chemistry: Henry Debus, F.R.S., and Prof. Odling, F.R.S. Botany and Vegetable Physiology: Dr. J. D. Hooker, F.R.S., and Dr. Thos. Thomson, F.R.S. Geology and Paleontology: Prof. Duncan, F.R.S., and Prof. Morris. Practice of Medicine: John S. Bristowe, M.D., and Prof. J. Russell Reynolds, M.D., F.R.S. Surgery: Prof. John Birkett and Prof. John Marshall, F.R.S. Anatomy: Prof. Geo. Viner Ellis and Prof. John Wood. Physiology, Comparative Anatomy, and Zoology: Prof. M. Foster, M.D., and H. Power. Obstetric Medicine: Rob. Barnes, M.D., and Prof. W. M. Graily Hewitt, M.D. Materia Medica and Pharmaceutical Chemistry: Thos. R. Fraser, M.D., aid Prof. A. Baring Garrod, M.D., F.R.S. Forensic Medicine: E. Headlam Greenhow, M.D., F. R.S., and Thos. Stevenson, M.D.

present at the sitting on the 21st April, eighteen in number, viz., three astronomers, Yvon Villareau, Mathieu, and Langier ; one mathematiciau, Chasles; one physicist, Jamin, three chemists, Chevreul, Payer, Peligot; one mechanician, Ameral Paris; and the others medical men or naturalists, Milne-Edwards, Blanchard, Robin, Trécul, Bienaymè, Duchartre, and Quatrefages. M. Egger, of the Academy of Inscriptions, sat with his colleagues, and M. Simon Newcomb, the American astronomer, sat at the place allotted to foreign learned men.

THE seventh part of the illustrated work on the butterflies of North America, by Mr. Wm. H. Edwards, has just been published, containing numerous well-engraved and coloured plates of butterflies.

THE Commune has its own balloons, twelve in number, but they are kept apart for the private use of members when the final exit shall take place. One was sent up into the air, as it was said in the political newspapers for carrying away the masonic proclamation, but it was a little one without aëronaut.

THE Gardener's Chronicle for last Saturday prints an interesting letter from Dr. Hooker, dated Tetuan, April 12. In the journey from Tangier to Tetuan, Dr. Hooker notices that the general features of the flora of the low grounds and moderate hills in that part of North Morocco coincide with those of Southwestern Spain. Whole tracts are covered with masses of broom, so that the hills precisely resemble those of Scotland or Jersey. The previous day a guard had been obtained in order to ascend Beni-Hosmar, which mountain had only been visited previously by one botanist, Mr. Webb, some forty years since. The party ascended to 3,500 feet, and obtained a superb view across the Mediterranean to the Spanish coast, and south to the snowy crest of Beni-Hassan. It is a splendid rugged mass of limestone peaks, separated by very steep narrow-floored valleys, the flanks of which are crested with rifted white precipices. The whole is clothed with stunted shrubs up to 3,000 feet. They found some rare, and some probably new plants, but at a height of 3,400 feet no signs of a sub-alpine flora. The party did not succeed in reaching the summit.

THE principal object of interest at the soirée of the Linnean Society on the 26th ult., was again Mr. Wilson Saunders's collection of mimetic plants, which was even more remarkable than MR. C. T. CLOUGH, of Rugby School, has been elected to last year. The following is a list of the pairs exhibited : an exhibition at St. John's College, Cambridge, of 50%. per annum, for proficiency in Natural Science. There were ten Candidates.

SCIENCE appears to have penetrated even into the recesses of Christ's Hospital. Since October 1869, there has been a Chemistry ss of about fifty boys, in connection with St. Bartholomew's Kospital. The work done is both practical and theoretical; at the first, Dr. Matthiessen was the lecturer, and at his lamented death, 1. H. E. Armstrong. Since Christmas the class has been uder the care of Dr. W. T. Russell, F. C.S. For some weeks past, Prof. Tennant has been lecturing on Mineralogy, and next week commences on Geology. This class is very well attended. There has been established a permanent class for Natural ilosophy, under the care of Mr. James Noon, B. A. We believe ao that those boys who are intended for the Navy are ins ucted in theoretical and practical Astronomy. There have en wishes expressed for a Museum, and numerous speciens are constantly brought to Prof. Tennant for informa.

tin.

It is much to be wished also that some sort of a Natural Istory Society might be established, notwithstanding the city-site the Hospital.

WE continue to receive intelligence from the French Academy, and are in a position to give the full list of members who were

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A SERIES of scientific lectures, in connection with the School of Science and Art, has been for some time in contemplation at Taunton. It has recently commenced with a course of botanical lectures, by the Rev. W. Tuckwell, headmaster of the College School, which attract a large and diligent audience, consisting both of artisans and amateurs.

At the annual dinner of the Institution of Civil Engineers held on April 22, Prof. Huxley, in responding to the toast of the learned societies in this country, gave the company some very sound advice as to the duty of the body of civil engineers in enforcing upon the public mind the truth that there can be no technical education of any value or soundness which is not based on a thorough preliminary training in abstract or theoretical practical science.

MR. JOHN GIBBS, of the Essex and Chelmsford Museum, publishes, at the price of a shilling, "A First Catechism of Botany," which has received the sanction of the Committee of Selection for the International Exhibition. Although the catechismal form always seems to us a needlessly cumbrous and for those who think otherwise a large amount circumlocutory one, of useful elementary information will be found in this little publication.

WE learn from Trübner's American and Oriental Literary Record that the American Ethnological Society was permanently reorganised under the name of "The Anthropological Institute of New York," on the 9th of March, and the following officers were elected :-E. Geo. Squier, president; J. C. Nott and Geo. Gibbs, vice-presidents; J. G. Shea, J. K. Merrill, E. H. Davis, C. C. Jones, jun., and W. H. Thomson, executive committee; A. J. Cotteral, treasurer; Charles Raw, foreign corresponding secretary; H. T. Drowne, domestic corresponding secretary; H. R. Stiles, recording secretary; and Geo. H. Moore, custodian. The objects of the institute are declared to be :-1. The study of man in all his varieties, and under all his aspects and relations. 2. Its special object the study of the history, conditions, and relations of the aboriginal inhabitants of America, and the phenomena resulting from the contact of the various races and families of men on this continent, before and since the discovery. 3. The physical characteristics, religious conceptions, and systems of men ; their mythology and traditions; their social, civil, and political organisations and institutions; their language, literature, arts, and monuments; their mode of life and their customs are specifically within the objects of the Institute. 4. The collection of manuscripts, books, and relics illustrating these several subjects; the stimulation and encouragement of inquiry and research, particularly in unexplored American fields; and by means of such publications as may be deemed proper, to utilise the results of its investigations and efforts for the benefit of science and of mankind. 5. It recognises the widest range of discussion, and a complete tolerance of individual opinions on all subjects within the scope of the Institute's objects. The Institute proposes to publish a series of Memoirs, and a Journal.

THE attention of astronomers throughout the world is directed toward the approaching transit of Venus, to occur on the 18th of December, 1874, and it is hoped, we learn from Harper's Weekly, that the United States Congress, with the same liberality that induced it to make an appropriation for the observation of the solar eclipse of December last, and for the polar exploration under Captain Hall, will also, at the proper time, advance the funds necessary for the research- in this case. Professor Hall, of the Washington Observatory, in a late communication to the Journal of Science, expresses the hope that a concert of action will be settled upon by American astronomers, in order that they may not be behind their European confrères in the attempt to secure satisfactory results. A committee has been appointed by

the National Academy of Sciences to take into consideration a general plan of operations, and it is expected that a report will be made on the subject at the approaching meeting in Washington city.

THE annual report of Professor Cooke, State Geologist of New Jersey, for 1870, has just been published; and although less in bulk than some of its predecessors, it contains some important information in regard to fertilisers used in the State, the marshes and tracts of land subject to protracted freshets, the soils, the iron and zinc ores, and other miscellaneous topics. The subject of drainage has attracted Professor Cooke's especial attention, on account of the vast tracts of land in the eastern portion of the State now either regularly overflowed at certain periods of the tide, or liable to freshets or inundations. In order more properly to qualify himself for this inquiry, Professor Cooke paid an extended visit to the drained lands of Holland and England, the results of which he presents in his report.

M. LONGET, the celebrated physiologist, member of the French Institute and of the French Academy of Medicine, died at the age of sixty-eight, at Bordeaux, a few days since. M. Longet is the author of works on the nervous system, which explain many of his own discoveries. His death was sudden, and was referred by his friends to the horror with which he was stricken when hearing the sad news from Paris.

IN the forthcoming number of the American Journal of Science will be found an article, by Professor Marsh, upon some new serpents of the Tertiary deposits of Wyoming. It will be remembered that in a previous notice of Professor Marsh's discoveries in the Rocky Mountains, we called attention to the difference observed by him between the contents of the Tertiary beds in the

vicinity of Fort Bridger and those of the Mauvaises Terres of the Upper Missouri, the former being especially characterised, as compared with the latter, by the presence of reptiles in great variety. Among these are many terrestrial species, including several kinds of land lizards; and among the forms generally serpents appear to be quite predominant. Of the latter, Professor Marsh has already determined the existence of five new species, belonging to three new genera; and others will probably be yet brought to light.

AT the present day, when the columns of our newspapers teem with advertisements of various preparations for promoting the growth or changing the colour of the hair, the following account of the results of the use of a preparation of boxwood for that purpose may be of interest. Boxwood, according to the old herbalists, was used from a remote period to render the hair auburn; and we are told by Phillips that a young woman in Lower Silesia, whose hair had fallen off after a severe attack of dysentery, was advised to wash her head with a decoction of boxwood, in order to induce it to grow again. This she did; and "hair of a chestnut colour grew on her head, as she was told it would do ; but, having used no precaution to secure her face and neck from the lotion, they became covered with red hair to such a degree that she seemed but little different from an ape or a monkey!"

MR. JAMES BOYD, of Panama, published some time ago in the Panama Stur and Herald, under the head of "The Migration of Butterflies across the Isthmus," an account of the phenomenon of the migration in one direction of the Urania Leilus. This being republished in England has led to some correspondence with Mr. Boyd, particularly from a naturalist resident at Liverpool. This gentleman states that in January 1845, he observed the same habit of the Urania in the Island of Caripi, one of those near Para, in the Brazils. From an early hour in the morning until nearly dark these insects passed along the shore in amazing numbers, but most numerously in the evening. It was very seldom that one was seen in the opposite

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direction. The main course was from west to east.
saw it at Pernambuco, at Rio Janeiro, and in the Southern
States of America, but nowhere so abundant as on the Amazons.
The Urania is scarcely a butterfly; but between the day and
night butterflies, something between a skipper and a hawk moth.
By Latreille they were called Hespero-Sphyngida. The larva
and pupa are supposed not to have been adequately examined.
The Liverpool naturalist could not identify them, and as yet they
have not been able to find them at Panama. In Central America
the Urania is found as far north as Guatemala. Mr. Darwin
observed a butterfly of similar habits, the Papilio feronia, which
frequents orange groves.

THE ROYAL SOCIETY'S LIST FOR 1871

ON COLOUR VISION *

ALL vision is colour vision, for it is only by observing differences of colour that we distinguish the forms of objects. I include differences of brightness or shade among differences of colour. century, that Thomas Young made the first distinct announceIt was in the Royal Institution, about the beginning of this ment of that doctrine of the vision of colours which I propose to illustrate. We may state it thus :-We are capable of feeling three different colour-sensations. Light of different kinds excites these sensations in different proportions, and it is by the different combinations of these three primary sensations that all the varieties of visible colour are produced. In this statement there is one word on which we must fix our attention. That word is, Sensation. It seems almost a truism to say that colour is a sensation; and yet Young, by honestly recognising this elementary truth, established the first consistent theory of colour. So far as I know, Thomas Young was the first who, starting from the well-known fact that there are three primary colours, sought for the explanation of this fact, not in the nature of light, but in the constitution of man. Even of those who have written on colour since the time of Young, some have supposed that they ought to study the properties of pigments, and others that they ought to analyse the rays of light. They have sought for a knowledge of colour by examining something in external nature

Now, if the sensation which we call colour has any laws, it must be something in our own nature which determines the form of these laws; and I need not tell you that the only evidence we can obtain respecting ourselves is derived from consciousness.

The science of colour must therefore be regarded as essentially a mental science. It differs from the greater part of what is called mental science in the large use which it makes of the physical sciences, and in particular of optics and anatomy. But it gives evidence that it is a mental science by the numerous illustrations which it furnishes of various operations of the mind. In this place we always feel on firmer ground when we are dealing with physical science. I shall therefore begin by showing how we apply the discoveries of Newton to the manipulation of light, so as to give you an opportunity of feeling for yourselves the different sensations of colour.

Before the time of Newton, white light was supposed to be of all known things the purest. When light appears coloured, it was supposed to have become contaminated by coming into contact with gross bodies. We may still think white light the emblem of purity, though Newton has taught us that its purity does not consist in simplicity.

HE following fifteen have been selected by the Council THE of the Royal Society out of the fifty candidates, and recommended to the Fellows for election:- William Henry Besant, M.A., Mathematical Lecturer at St. John's College; Senior Wrangler and First Smith's Prizeman in 1850, Moderator in 1856, Examiner in the University of London from 1860 to 1865; author of Treatises on "Hy--something out of ourselves. dromechanics and the Theory of Sound," 2nd ed. 1867; "Elementary Hydrostatics," 2nd ed. 1867; “Geometrical Conic Sections," 1869; "Roulettes and Glissettes," 1870. William Budd, M.D. (Edin.), physician, author of various medical papers, especially relating to contagious diseases. George W. Callender, F.R.C.S., lecturer on Anatomy at St. Bartholomew's Hospital School, and Assistant Surgeon to Bartholomew's Hospital; author of Anatomical papers. William Carruthers, F.L.S., F.G.S., keeper of the Botanical Department, British Museum; author of "Fossil Cycadean Stems from the Secondary Rocks of Britain," "On the Structure and Affinities of Sigillaria and Allied Genera;" "The Cryptogamic Forests of the Coal Period;""On the Structure of the Stems of the Arborescent Lycopodiaceæ of the Coal-measures;" "Revision of the British Graptolites," &c. Robert Etheridge, F.R.S.E., F.G.S., Palæontologist to H.M. Geological Survey of Great Britain; Demonstrator on Palæontology, Royal School of Mines; author of numerous geological papers. Frederick Guthrie, B.A., F.R.S.E., F.C.S., Professor of Physics in the Royal School of Mines; author of various papers on Chemistry and Physics. Captain John Herschel, R.E., of the Great Trigonometrical Survey of India. Captain Alexander Moncrieff, Militia Artillery, C.E., inventor of the Moncrieff gun-carriage, and author of the Moncrieff system of defence. Richard Quain, M.D. (Lond.), Fellow and late Censor of the Royal College of Physicians; author of a paper "On Fatty Degeneration of the Heart," which has exerted a marked influence on certain branches of Pathological Science; and of numerous communications published in the Transactions of the Pathological Society, of which Society he was President (1869-70). Carl Schorlemmer, Senior Assistant in Owens College Laboratory, Manchester; author of a series of papers on the Constitution of the Paraffins, chiefly published in the Proceedings of the Society since 1862. Edward Thomas, Treas. R.A.S., author of numerous papers on Indian Coins and Gems. Edward Burnet Tylor, author of "Researches into the Early History of Mankind;" "Primitive Culture ;" and various memoirs on Savages and their Customs. Cromwell Fleetwood Varley, Civil and Telegraphic Engineer, M.I.C.E.; Consulting Electrician to the Electric and International Telegraph Company, the Atlantic Telegraph Company, la Société du Cable Transatlantique Français; author of many inventions in connection with the Electric Telegraph. Viscount Walden, President of the Zoological Society of London; author of various papers on Ornithology. John Wood, F.R.C.S., Examiner in Anatomy at the University of London; author of a number of anatomical papers published in the Phil. Trans.

These

We now form the prismatic spectrum on the screen. are the simple colours of which white light is always made up. We can distinguish a great many hues in passing from the one end to the other; but it is when we employ powerful spectroscopes, or avail ourselves of the labours of those who have mapped out the spectrum, that we become aware of the immense multitude of different kinds of light, every one of which has been the object of special study. Every increase of the power of our instruments increases in the same proportion the number of lines visible in the spectrum.

All light, as Newton proved, is composed of these rays taken illuminated by white light, make a selection of these rays, and in different proportions. Objects which we call coloured when our eyes receive from them only a part of the light which falls on them. But if they receive only the pure rays of a single colour of the spectrum, they can appear only of that colour. If I place a disc containing alternate quadrants of red and green paper in the red rays, it appears all red, but the red quadrants brightest. If I place it in the green rays both papers appear green, but the red paper is now the darkest. This, then, is the optical explanation of the colours of bodies when illuminated with white light They separate the white light into its component parts, absorbing some and scattering others.

Here are two transparent solutions. One appears yellow, it tains sulphate of copper. If I transmit the light of the electric contains bichromate of potash; the other appears blue, it con. lamp through the two solutions at once, the spot on the screen appears green. By means of the spectrum we shall be able to explain this. The yellow solution cuts off the blue end of the spectrum, leaving only the red, orange, yellow, and green. The blue solution cuts off the red end, leaving only the green, blue, and violet. The only light which can get through both is the * Lecture delivered before the Royal Institution, March,24th.

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