OBJECTS ILLUSTRATING SCIENCE. *>$ 



The French cases exhibit, through the original apparatus of our 

 principal inventors, the most complete history of the studies and dis- 

 coveries in heat. The measurement of heat is represented by the 

 instruments of Lavoisier, of Dulong, of Regnault, of Favre and 

 Silbermann ; observations on sideral heat by the actinometer and the 

 pyrheliometer of Pouillet, and by the actinometer with thermo-electric 

 pile of M. Desains. The metallic bars of Despretz are those which he 

 used for his first experiments on the conductibility of solids ; Gay- 

 Lussac, Despretz, M. Dumas, and M. Regnault remind one of the 

 uninterruoted series of studies on the density of gases and vapours ; 

 the collection of M. Regnault's apparatus is a proof of the gigantic 

 labours which he has successfully undertaken to place upon a firm 

 basis the actual facts connected with the science of gases and 

 vapours. 



With regard to the measurement of the expansion of bodies according 

 to the method of Newton's rings it has become, in the hands of M. 

 Fizeau, perhaps the most exact of all those connected with the science 

 of heat. 



For the very reason that discoveries relative to magnetism are com- 

 paratively of recent date, we have been able to procure some historical 

 objects of great value. 



M. Jamin has given us his great artificial magnet, made of thin plates 

 of steel, which can lift 200 kilogrammes, and which this skilful experi- 

 mentalist used as a starting point for his studies on the laws of magnetic 

 distribution, which had been, up to that time, so little understood. 



We have placed next to it the model of Gambey's deflecting compass, 

 one of the finest instruments from the hands of that celebrated man. 



In the collection of the Ecole Polytechnique, the small natural magnet 

 belonging to M. Obelliane is remarkable as being, with regard to its 

 weight, by far the most powerful magnet known ; it can lift forty times 

 its own weight. 



With regard to electricity we are necessarily less rich in historical 

 models, but nevertheless the series of discoveries made by French 

 scientific men is tolerably complete. 



Among the electrical piles may be noticed the fine collection of the 

 different models reproduced by M. Ruhmkorff and the considerable 

 effects of the secondary pile of M. Plantd ; among the thermo-electrical 



