OBJECTS ILLUSTRATING SCIENCE. 83 



To judge by the number and the perfection of the modern French 

 optical instruments sent to the exhibition, there would be reason to 

 believe that this branch of science is more attended to in France than 

 anywhere else. 



It is true that we have been fortunate enough to secure, in the 

 various sub-divisions, historical instruments bearing well-known names. 

 Fresnel's first lens a true landmark in the History of Science is 

 accompanied by a large collection of models of the French light- 

 houses, from the first to those most recently constructed. And 

 thus all the improvements which have been effected in this powerful 

 means of averting loss of life at sea, can be seen at a glance. And 

 England is, indeed, the most appropriate place where we could have 

 exhibited such a collection which has been brought together, thanks 

 to the engineer who carries out, with so much skill, the administration 

 of our lighthouses. 



Electric light has lately been applied to industrial purposes to an 

 extent that cannot but go on increasing. The machines made by the 

 " Compagnie 1'Alliance," and the Gramme instrument, can light up vast 

 workshops or timber-yards. And now M. Carre has succeeded in 

 making carbon artificially, which, used instead of crayons of coke, 

 gives a much greater regularity, although it burns faster. There is 

 every reason to hope that this manufacture will allow of the use of 

 sufficient compression, so as soon to get rid of the defect entirely. 



The regulators used are those of M. Foucault, M. Dobosq, M. 

 Serrin, and of M. Carre himsc'f. 



With regard to the determination of the velocity of light, here are 

 the two instruments made use of by M. Foucault and M. Fizeau ; it is 

 known that it was by means of the latter one that M. Cornu succeeded 

 last year, in his experiments between the Observatory and the Tower 

 of Montlhery, a distance of twenty kilometres. We have placed next 

 to them Wheatstone's revolving mirror, which belongs to the Paris 

 Observatory. 



To this establishment we likewise owe Arago's interfcrential appa- 

 ratus, and the complete collection of his historical prisms ; I can 

 merely mention those of Biot, and Senarmont, and Jamin, and so 

 many others who have made themselves celebrated by their researches 

 in polarization, interference] and double refraction. M. Descloizeau 



