358 



NATURE 



{Sept. 3, 1874 



will be inaugurated next year ; and Nantes. It was gene- 

 rally supposed that Clermont Ferrand would be selected, 

 but Nantes had sent a special delegate with the power of 

 offering the grant of a large sum of money. Clermont 

 Ferrand is poor and has drained its exchequer in helping 

 M. Alluard in his admirable work ; consequently Nantes 

 was all but unanimously selected. The president for the 

 Nantes meeting (1S75) '^'^ be iVI. d'Eichtal, a gentleman 

 of great fortune and influence, largely connected with the 

 railway interest, and possessed of high scientific quali- 

 fications, having been educated at the Polytechnic School. 

 The assembly appointed j\l. Fayc, the astronomer, to be 

 president of the 1876 meeting, but the town where it is to 

 be held has not been decided on. The meeting was 



brought to a close by a banquet given at the Hotel de 

 Ville, by the Mayor of the city. 



The number of the members of the Association is 

 Soo ; it is an excess of 200 on the number of the Lyons 

 meeting. The ladies are very few. JSIadame Thureau de 

 Villeneuve, the wife of the secretary of the .Societe de 

 Navigation Ardenne, was the only lady who delivered an 

 address. This was in the section of Geography. 



The Paris papers have published very short articles on 

 the proceedings of the Association ; none have shown 

 so much interest as the Times, who sent a special re- 

 porter and published long telegrams on the work of the 

 Sections. 



Lille, August 29 W. de Fonvielle 



THE SIDEROSTAT* 

 'X'HERE is in use at the present moment in the Paris 

 -'■ Observatory an instrument of a new construction, 

 which is destined to play a large part in the Astronomy of 

 the future. It is not too much to say that the new instru- 

 ment will play as important a part in, and will be as 

 essential to the new Astronomy, as the transit instrument 

 plays in the Astronomy of position. 



For this instrument in its present form we are indebted 

 to the genius of Foucault, who also gave it its name, the 

 Siderostat. 



The use of the present instruments obliges the astro- 

 nomer to change h is position to follow the eye-piece, and 

 consequently to observe frequently in uncomfortable 

 positions. To escape this inconvenience the Germans 

 have long employed the bent telescope, meridian circles 



* In p.->rt translated fioin an .uticle by M. A. Fraissenct, in La Kalurt. 

 For the woodcuts we are indebted to the kindness of M. Gauthier-Villars. 



Eic. 2— Clockwoik movement, with isoclironous regulator 



and theodolites. But the use of this arrangement is 

 limited to small instruments, while it is precisely in the 

 case of the largest instruments that it would be most 

 useful. 



Foucault, who died in the midst of his most im- 

 portant labours, wished in the latter years of his life to 

 give to the equatorial the power of making the entire 

 heavens pass before the observer without his having to 

 disturb himself or to displace the instrument. A telescope 

 fixed horizontally in an invariable position, before which 

 a plane mirror brings successively the various points of 

 the sky — such was the Siderostat in his mind, the idea in 

 all probability having occurred to him from a singular em- 

 ployment of the hcliostat by M. Laussedat in observations 

 of the eclipse of 1S60. (See Fig. i.) 



The instrument was constructed after the death of its 

 inventor, by M. Lichens, under the direction of the Com- 

 mission charged with the carrying out and the pubUca- 



