1813.] Imperial Institute of France. 235 



force which produced them and the size of the particles of light 

 on which it acts, just as the duration of the oscillations of a 

 pendulum gives a relation between its length and the intensity of 

 gravity. 



Having arrived at this general result M, Biot shows, a poste- 

 riori^ that it really includes the two laws which he employed in 

 order to establish it 5 for he shows that we may draw from it the 

 very same formulas which he had obtained at first from the 

 experiments contained in his first memoir. He devotes the rest 

 of his paper to show how, from the same principle, we may cal- 

 culate and foretell all the other phenomena of polarization which 

 are exhibited by plates of sulphate of lime, of mica, and of 

 rock crystal, cut in any direction whatever, and exposed in any 

 way to rays polarized, either by refraction or reflection; but these 

 ulterior applications, though already calculated by M. Biot, being 

 the object of different memoirs which have not yet been read to 

 the Class, we cannot give an account of them here. 



Memoirs on different new Phenojnena of Optics. By M. Arago. 



We could have wished to have given as detailed an account of 

 the different memoirs in which M. Arago has exposed to the 

 Class his new experiments on light. We should have seen expe- 

 riments not less interesting, and theoretic ideas, which, to be 

 rendered sufficiently clear, require new experiments, of which 

 M. Arago has conceived the idea, and formed the plan; but 

 being able to devote to these experiments only the few moments 

 of leisure left him by his functions of Astronomer at the Impe- 

 rial Observatory, he has not been able to communicate his ideas 

 to the Class, but in proportion as he could notify them in de- 

 tached notices. He proposes to complete them, and to class 

 them in a luminous order. Thus we are obliged to defer to our 

 history for 1813, our detail of these experiments, made in order 

 to throw light on the most difficult points of optics, that is to 

 say, the explanation of the phenomena of the colours of bodies. 



Different Memoirs. By M. Rochon, 



M. Rochon, while communicating to the Class some new 

 researches in which he was engaged in the year 1812, had 

 occasion to notice some of his old labours, either little known, 

 or intimately connected with his recent speculations. In a 

 memoir on the art of multiplying copies he has noticed the 

 process of the celebrated Franklin, who first introduced into 

 France the art of multiplying copies of writings. M. Rochon 

 at that time improved these processes, by contriving a machine 

 for engraving, which was approved of by the Academy of 

 Sciences. In continuing the subject, he proved by his experi- 

 ments that the ancieiit bronze dies, composed of copper hardened 



