400 



NA TURE 



[August 21, 1890 



duction of the spectroscope considerably extended the 

 limits of investigation. The chemical constitution of the 

 stars was determined in spite of their immense distances ; 

 the sun was shown to contain sodium, iron, magnesium, 

 calcium, hydrogen, in a state of vapour at its surface — that 

 is, the same elements as those which make up the earth's 

 crust ; it also contains nickel, an important constituent 

 of meteorites, those nomadic bodies which fill inter- 

 planetary space. The sun and the bodies revolving 

 round it are therefore composed of the same elements. 



By means of the spectroscope it has been proved that 

 the moon and the planets shine by reflected light, and 

 that the stars, like the sun, are self-luminous, and made 

 up of the same elements, thus demonstrating the unity of 

 the chemical composition of the whole universe. 



But the spectroscope has not only revealed the sub- 

 stance of the stellar world, it affords a means of investi- 

 gating a component of stellar motion. The principle 

 enunciated by Doppler, viz. that light-waves, like those of 

 sound, vary in length with the relative velocity of the 

 source producing it, remained unapplied for some time 

 because there was, of course, no means of determining the 

 proper colour of a star in repose and comparing it with 

 thatreceivedjthevariationbeingproducedby motion in the 

 line of sight. Fizeau showed, however, that by substituting 

 lines in the spectrum for the idea of colour the conditions 

 necessary for the application of the principle were met ; 

 all that was required being a line common to a star and 

 some terrestrial element, and the measurement of the dis- 

 placement of this line. This method was proposed by 

 Fizeau in 1859, and has been considerably developed ; 

 numerous lines in stellar spectra are coincident with those 

 of terrestrial substances. If they are all shifted towards the 

 red the star is receding from the earth ; if towards the 

 violet the star is approaching us. The displacement of 

 the line is measured with a micrometer, and a simple 

 calculation gives the velocity with which the star is 

 moving, whatever may be its distance. 



It has been shown that for the application of the 

 Doppler-Fizeau principle it is necessary to find in the 

 spectrum of the star the lines of a terrestrial element. 

 This common element is most often hydrogen — the simple 

 body -par excellence, the elementary substance of those 

 who hold in the unity of matter. 



Among all the methods of rendering impurities manifest, 

 the simplest and most delicate is that of spectrum 

 analysis. With the spectrum of hydrogen observed in 

 the laboratory feeble lines of other substances are always 

 present, and to decide upon the true hydrogen spectrum 

 becomes therefore a difficult matter. But it was an 

 astronomer and not a chemist who first described the 

 pure hydrogen spectrum ; the lines photographed by Dr. 

 Huggins in the spectra of the white stars having since 

 been shown to be reproduced in the laboratory when the 

 spectrum of approximately pure hydrogen is observed. 



In physics, the centre of natural philosophy, many 

 branches have made rapid and definite advances. The 

 results of the development of electrical science is seen on 

 all sides, yet no science has had a more humble beginning. 

 The first electrical experiment was made six centuries 

 before our era : this was the attraction of light bodies by 

 rubbed amber. The knowledge remained in this stage 

 for more than twenty centuries ; then the two electrical 

 states were gradually recognized, and conductors and 

 non-conductors were separated. In the establishrnent of 

 the identity of atmospheric electricity with that obtained by 

 electrical machines the death of Richmann at St. Peters- 

 burg should be noticed, and the discovery of the lightning 

 conductor by the illustrious Franklin. 



Everyone knows the story of the convulsive movements 

 of a frog's leg in contact with a bimetallic arc observed 

 by Galvani, an Italian physiologist. Volta saw in this 

 circumstance that electricity might be developed by the 

 contact of different substances ; he discovered the law 



NO. 1086, VOL. 42] 



which permitted the energy to be multiplied ; and in 1794 

 summed up all his works in an imperishable monument 

 — the voltaic pile. 



All the sciences benefited by the discovery, but 

 chemistry gained the most. Carlisle and Nicholson 

 decomposed water ; Davy, with the great pile belonging to 

 the Royal Institution of London, decomposed the alkalies 

 and alkaline earths, formerly supposed elementary bodies. 

 Later, Davy performed an experiment which eclipsed 

 everything accomplished with the invention of Volta. 

 By joining two carbon poles to his colossal pile, he pro- 

 duced a dazzling and continuous light, and discovered 

 the electric arc now so commonly seen. 



In 1820, Oersted discovered that the wire joining the 

 poles of a pile exercised an influence on a magnetic 

 needle. Ampere discovered the mutual action of electric 

 currents, the mathematical law governing it, and, finally, 

 the production of magnetism by the sole action of the 

 voltaic current. 



The discovery of the electro-magnet was a great event, 

 not only in the history of science, but in that of humanity. 

 In telegraphy it is the electro-magnet which transmits 

 messages from one end of the world to the other with the 

 velocity of light ; in the telephone, the v/ord itself ; in 

 the powerful machines derived from the memorable 

 discoveries of Faraday, it is that which causes the 

 transformation of energy. 



Great advancements have also been made on the 

 purely theoretical side. Ampere, Poisson, Fourier, Ohm, 

 Gauss, Helmholtz, Thomson, and Maxwell have done 

 much to connect electricity with mechanical laws. 

 Again, electro-magnetic and optical phenomena obey 

 the same elementary laws, and appear to be two mani- 

 festations of the movement of the same medium— the 

 ether ; thus optical problems may be settled with the 

 equations of electro-magnetism. From an experimental 

 point of view, results full of promise have already been 

 obtained ; the velocity of light, found by optical methods, 

 has also been determined by measures purely electrical ; 

 and recently M. Hertz has accomplished experimentally 

 the identification of electrical discharges with light- 

 waves. 



All these facts show that as our knowledge increases the 

 distinctions between different branches of science vanish ; 

 the limits which have been traced between them are 

 shown to be artificial, and only testify to ignorance of 

 natural laws ; but the efforts of successive generations 

 have not been in vain, and we look forward to the time 

 when these limits will be effaced, and all the branches of 

 natural philosophy be united in one harmonious whole. 



Prof. Cornu's discourse, of which the foregoing is but 

 a sketch, was received with much applause. 



After an address by the Mayor of Limoges, the Secre- 

 tary of the Association, M. A. Gobin, read the report for 

 1889-90, and gave an account of the meeting in Paris 

 last year. The financial statement by M. Gallante shows 

 that the Association is in a prosperous condition, and 

 increasing its number of members. 



Many interesting and important communications were 

 made in the different sections. The series of excursions 

 included one of three days' duration, and visits were 

 made to all places of interest in or near Limoges. The 

 Congress will be remembered as a very successful one by^ 

 all who were fortunate enough to be present. 



C. H. F. PETERS. 



Y the death of Prof. C. H. F. Peters, Director of the 

 Litchfield Observatory, Hamilton College, Clinton,. 

 N.Y., astronomy has lost an assiduous observer. An in- 

 teresting sketch of his career is given in the Astronomische- 

 Nachrichten, from which the following details are taken. 



B' 



