524 



NA TURE 



[OCTOISKK 1, I< 



markable researches by which he has partially answered 

 some of the most difficult questions as to the relation of 

 matter to ether, which are perplexing the best physical 

 investigators of the time. 



Born in i8ig, Fizeau was only thirty years of age when 

 his paper, " Sur une experience relative a la vitesse de 

 propagation de la lumi&re," appeared in the Comptes 

 rciidus. In this he put forward his plan of rotating a 

 wheel having round its rim alternate teeth and spaces 

 of equal width, so that these teeth and spaces should 

 alternately intercept and allow to pass a beam of light 

 from a source, and so adjusting the speed of rotation 

 that the time occupied by the light in travelling from 

 the wheel to a mirror and back again, should be equal 

 to the time taken by the rim of the wheel to advance 

 through a space equal to an integral number of times 

 the width of a tooth or space. Curiously enough, the 

 other experimental method of finding the velocity of light 

 was described by Foucault in the very next volume of 

 the Comptes rcndiis. In some respects the latter method 

 — that of the revolving mirror — was e\en more striking 

 than that of Fizeau. It allowed the velocity of light to 

 be determined within an ordinary room, and, besides, 

 enabled the question as to whether light travelled more 

 or less quickly through a more refractive medium to be 

 decided by direct experiment. 



Another experiment of capital importance with which 

 the name of Fizeau will ever be honourably associated 

 is that by which he determined the amount of drift of 

 light-waves in a transparent medium in motion. Accord- 

 ing to a theory given by Fresnel, the velocity of drift of 

 ether-waves in a medium moving with velocity u is 

 (i - i//i^)?/,- where /i is the index of refraction of the 

 medium. This conclusion of Fresnel was verified more 

 lately by the experiments of Airy and Hoek, which 

 proved, in opposition to the statement of Klinkerfues, 

 that no change in the constant of aberration is observed 

 when the tube of the observing telescope is filled with 

 water. But it was tested directly by Fizeau in the most 

 simple and beautiful manner. Two tubes were arranged 

 side by side, and water was forced at a considerable 

 speed (as much as seven metres per second) along one 

 tube and back by the other, while a beam of light was 

 split into two parts, which were sent round the tubes, 

 one with the stream, the other against the stream, and 

 then brought together again and tested for interference 

 produced by the virtual difterence of path traversed, 

 arising from the motion of the water. The result gave 

 exactly the formula quoted above, and has been con- 

 firmed by very careful experiments made comparatively 

 recently by Michelson and Morley. 



Fizeau made some notable observations on the number 

 of interference bands observable with approximately 

 homogeneous light, and, in conjunction with Foucault, 

 carried out a most important series of observations on 

 the light in different parts of the field of illumination 

 in interference experiments. The method consisted in 

 applying the spectroscope to examine the light taken 

 from a narrow part of the field parallel to the bands, 

 and proved inter alia that there is really interference in 

 that region of the field which seems to be uniformly 

 illuminated in consequence of overlapping produced by 

 want of perfect homogeneity of the light. 



One very important recent result of such observations 

 has been to show that the detection of interference is 

 limited only by the resolving power of the spectroscope 

 employed, and that the usual inference as to the regu- 

 larity of the vibrations in a source of light is unjustifiable. 



Like Joule in this country, Fizeau carried on scientific 

 research largely from his own private resources ; and by 

 a long series of most valuable papers published in the 

 Memoirs of the French Academy and elsewhere, he has 

 earned the gratitude of his countrymen and the world. 

 But his most enduring memorial will doubtless be his 



NO. 1405, VOL. 54] 



determination by simple laboratory apparatus of the 

 velocity of light (a velocity sufficient to enable the earth's 

 path round the sun to be traversed in about twenty-six 

 minutes !), and with his great colleague Foucault he will 

 be held in honoured remembrance so long as men study 

 the science of optics. 



Fizeau was elected a Foreign Member of the Royal 

 Society in 1875, and he received the Rumford Medal of 

 the .Society in recognition of his scientific work. 



A. Gray. 



NOTES. 



The monument to Lobachevsky, erected at Kazan, in a square 

 which bears the name of the great geometer, was unveiled on 

 September 13, in the presence of the Bishop of Kazan, the 

 Governor of the province, the University, the local Physical and 

 Mathematical Society, and a great number of sympathisers. 

 The Mayor of Kazan made a statement as to the funds raised 

 for the erection of the monument. Prof. Suvorofif referred to the 

 scientific work of Lobachevsky in mathematics and physics, 

 and Prof, ^'asilieff spoke of the great geometer as one whcse 

 life was worthy of emulation, and as an energetic worker for 

 spreading scientific knowledge. In the evening the Physical 

 and Mathematical Society held a special commemoration meet- 

 ing before a distinguished gathering of visitors of both sexes. 



A SERIES of fltes have been celebrated at Alais, in the centre 

 of the great mulberry and silkworm district of France, in com- 

 memoration of the services rendered by Pasteur to sericulture. 

 A statue of Pasteur was unveiled during the celebrations ; and, 

 on Saturday last, a solemn service was celebrated in the cathedral 

 in commemoration of the first anniversary of his death, which 

 occurred on September 28, 1895. 



The Harveian oration is to be delivered before the Royal 

 College of Physicians, on October 19, by Dr. J. Frank Payne. 



It is proposed to establish an International Botanical Station 

 at Palermo, under the superintendence of Prof. Borzi, who 

 desires the co-operation of botanists of all countries. 



Dr. a. Zimmermann has been appointed botanist to the 

 section of the Botanic Garden, Buitenzorg, Java, devoted to the 

 cultivation of coffee. 



The Graefe gold medal, which is awarded by the German 

 Ophthalmological Society every ten years, has this year been 

 awarded to Prof. Theodore Leber, of Heidelberg, in recognition 

 of his work on inflammation. Prof von Helmholtz was the 

 first to receive the medal, the award being made for his dis- 

 covery of the ophthalmoscope, and his treatise on physiological 

 optics. 



A c.As exposition, beginning on January 25, 1897, is to be 

 held for two weeks in the Madison Square Garden, New York. 

 The object of the exposition, according to the prospectus, 

 is to bring together a collection of gas apparatus and appliances 

 of every description, for the purpose of afiording the general 

 public and the gas engineer an opportunity to study the develop- 

 ments that have taken place in the gas industry during recent 

 years. 



The French Medical Press Association is organising a 

 memori.al festival in honour of the jubilee of the discovery ol 

 anresthesia. The festival will take place in Paris, on October i.S 

 and following days. The programme includes a ceremonial 

 meeting at the Sorbonne, a banquet, and a special performance 

 at one of the theatres. A suitable commemoration of iht 

 event is being arranged in Boston (Mass.), where the fir^i 



