September io, 1908J 



NA TURE 



447 



Mascart's earliest researches were chiefly devoted to 

 optics; later electricity, magnetism, and the determin- 

 ation of the electrical units claimed his attention. The 

 pages of the Coinptes rendus, of the Annales scicii- 

 tifiqiies de I'Ecole normale, and of the Journal de 

 Physique attest his industry and his scientific insight. 

 It must suffice here to indicate a few of his principal 

 investigations. He was one of the first to apply photo- 

 graphy to the study of spectrum analysis, and in 

 1862 constructed a spectrograph with a quartz train 

 with which he photographed the ultra-violet spectra 

 of many of the metals, adding many new lines to those 

 already known, and directing attention to the har- 

 monic relations presented by groups of lines, for 

 example, by those of magnesium. He then made a 

 number of standard determinations of wave-lengths 

 by use of Nobert's gratings. Fizeau reported to the 

 Academy of Sciences that this was the most thorough 

 and satisfying piece of work on wave-lengths that had 

 been made since the researches of Fraunhofer, and on 

 his recommendation Mascart was awarded the Prix 

 Bordin. He also prepared tables of the dispersion of 

 the principal kinds of glass used by opticians, and of 

 Iceland spar. He devised, with M. Perrin, a novel 

 optometer, and studied the distribution of the colour- 

 sensation over the retina of the eye. In the theory of 

 'ight he presented, in 1S71, an elaborate memoir on' the 

 calculation of the interference fringes formed in 

 different circumstances, carrying out the investigation 

 with great generality, and giving the results of com- 

 parison between theory and experiEiient. He investi- 

 gated the phase-relations in the light reflected from 

 metallic films of great tenuity ; and he wrote a series 

 of didactic articles in the journal de Physique, then 

 ( 1872) newly-founded, on the application of the spectro- 

 scope to the observation of interference phenomena. 

 He also produced an improved apparatus for the study 

 cf interference, based on the phenomenon of Talbot's 

 fringes. For the study of colour-mixtures he devised 

 .'in instrument producing three parallel spectra, each of 

 variable intensity, which could be superposed on one 

 another, and displaced so as to yield a mixture of any 

 three spectrum tints in any proportion. An important 

 paper in 1874, followed by another in 1878, was devoted 

 to refraction and dispersion in gases, some twenty 

 being examined. Another research dealt with the 

 index of refraction of water under pressure. Doppler's 

 theory also was examined, and an investigation was 

 made, of great interest in the light of recent ether 

 tlieories, whether the proper motion of the earth had 

 any appreciable effect on the phenomena of optics. 

 The conclusion was that optical phenomena give no 

 indication of the absolute motion of a body, but only 

 of its relative motion. This memoir was awarded the 

 Grand Prix des Sciences mathematiques in 1S74 on 

 the report of M. Fi.^eau. 



» In 1876, M. Mascart published a treatise on statical 

 electricity greatly in advance of any previously existing 

 on the Continent in that it introduced to Continental 

 readers the potential theory developed on the basis of 

 Green's book, and the electrometric work of Lord 

 Kelvin. The volume included several matters of ori- 

 ginal interest, comprising a research on discharges 

 across long distances, and on the measurement of 

 great differences of potential. About this time also 

 he made new observations on atmospheric electricity, 

 on the influence of ozone {i.e. air ionised by the pas- 

 sage of sparks) on the formation of fogs, and on the 

 influence of electricity on evaporation. In 1877 he 

 published in the Journal de Physique an elegant ex- 

 position of the elementary theory of magneto-electric 

 and electrodynamic machines, based on the energy 

 formula; of Hclmholtz and Thomson. In this article 

 the law of efficiency of motors, at that date generally 

 NO. 2028, VOL. 78] 



misunderstood, was correctly stated. In the succeed- 

 ing year, in collaboration with M. Angot, he made 

 many tests on Gramme machines and others, to test 

 his formula". The influence of Lord Kelvin's volume 

 of reprinted papers on electrostatics and magnetism 

 now became very great on Mascart's work. He com- 

 municated to the Acadcmie des Sciences a paper on the 

 reciprocal action of two electrified spheres, employing 

 Thomson's method of electric images; another paper 

 on the propagation of electric impulses along con- 

 ductors; and another on the theory of induction. 



Public work began to fall upon M. Mascart, in 

 connection with the electrical machinery shown in the 

 Paris Exhibition of 1S78; and. still more, in connection 

 with the Electrical Exhibition and the International 

 Electric Congress of iSSi. In the congress he took 

 an active part, particularly in the debates on the then 

 burning question of the electric units. He contributed 

 to the settling of these matters by a fine determination 

 of the absolute electrochemical equivalent of silver, 

 which he deposited from a nitrate solution, measuring 

 the current in absolute terms by means of a current- 

 weigher, a balance of his own design. The value 

 found was about one-half of one per cent, below those 

 rospectivelv found by L.ord Rayleigh and Prof. 

 Kohlrausch. Between '1S81 and 1884 he completed a 

 re-determination of the unit of resistance, by the 

 methods of \\"eber and Kirchhoff, finding as a result 

 io6'3 centimetres for the length of the mercury column 

 to represent the ohm, Lord Rayleigh 's figures being 

 io6'28 and io6'24. In these years also, he had, in 

 conjunction with his friend M. Joubert, prepared a 

 text-book of electricity and magnetism, based on his 

 courses at the College de France. It introduced many 

 points from the treatise of Maxwell, and the use of 

 the C.G.S. system of units. 



In 1884 he was elected to the Acad<!'mie des Sciences 

 in the place of Jamin. Of that distinguished body he 

 became an active member, being at various times vice- 

 president, perpetual secretary, and in 1904 president. 



Being a man of affairs he was frequently in request 

 to advise the Government on matters within his 

 competence. He was vice-president of the consultative 

 committee on arts and manufactures, and president 

 of the commission on inventions for the War Minis- 

 try. He was also a member of the Bureau of Longi- 

 tudes, and of the International Bureau of Weights 

 and Measures. In recognition of his public services 

 he was created Grand Officer of the Legion of 

 Honour. He took a prominent part in organising the 

 electrical sections of the exhibitions of 1889 and 1900, 

 and in the latter year was president of the electrical 

 congress which met in the exhibition. He was widely 

 travelled, and had been an active member of the 

 Chicago congress in 1893, which he followed up by a 

 visit to the Yellowstone Park. He was profoundly 

 interested in the establishment of the meteorological 

 station at the top of the Eifi'el Tower, and it was a 

 particular pleasure with him, during the exhibition of 

 1900, to conduct parties of scientific friends to the 

 special gallery above the highest to which the public 

 had access, to show them the observing instruments 

 therein installed. 



Amidst these busy avocations he still found time to 

 write. His " Traite d'Optique," in four volumes, which 

 appeared between 1890 and 1893, possesses all the 

 elegance of style peculiar to writers trained in the 

 school of Laplace and .Arago and Verdet. It is parti- 

 cularly rich in the sections of interferences and 

 meteorological optics. In 1900 he published a " Traits 

 de IMagnetisme terrestre " in one volume. 



Mascart was president of the Soci^t^ francaise de 

 Physique, and at another time of the Soci^t^ Inter- 

 nationale des Electriciens. He was elected in 1885 an 



