SCIENTIFIC NEW9 77 



watches gave double the time of the propagation by the so- 

 lid substance, independent of the difference there might be 

 between them. Thus the time of the transmission by tl'.e 

 «oHd was found by repeated observations to be 0*26'', and of 

 thai by the air 2-76". The first result differs from that gi- 

 ven by the intervals of the sounds only 0-03"; and the se- 

 cond differs from the time deduced from the observations of 

 the academy j nil as much: an agreement that appears to 

 confirm the results. 



Mr. Biot likewise observed, that at this distance the low- 

 est voice could be heard perfectly froai one end tothe 

 other, and with sufficient distinctness to keep up a conver- 

 jtation. 



Mr. Leschevin, chief commissary of gunpowder and Native ^reea 

 salt-petre, has sent from Dijon to the Council of Mines a chmrai?, 

 collection of specimens af rocks, interesting on account of 

 the parts coloured green that they contain. Several pieces 

 of this stone, and a siliceous breccia, improperly called chal- 

 cedony of Creuzot, containing the same substance, had 

 been found in abundance on the road ; and Messrs. Guyton 

 and le Lievre had ascertained, that the green colour was not 

 owing to copper; but it was not known whence they came. 

 After much search Mr. Leschevin discovered these green 

 rocks in three contiguous mountains, and found that they 

 were coloured by oxide of chrome, combined in greater or less 

 quantity with silex, alumine, &c. On one of these moun- 

 tains he met with the graphic granite, which several authors 

 have mentioned as accompanying the emerald ; and he in- 

 tends to search for this stone also, which Mr. Vaoquelin has 

 discovered to be sometimes coloured with chrome. Since 

 Mr. Drappier has shown, that chrome united with lead 

 makes the most beautiful of all yellows, this may turn to 

 considerable account. 



Mr. Simon, of Berlin, has been making some experiments Electric repal- 

 onthe true law of electric repulsion. Coulomb appears to ^^^^ r ti of"" 

 have established this law by means o' the torsion of wire in the distanc* 

 his electrical balance, that the electrical repulsion is in the ^'"'i^y* 

 inverse ratio of the square of the distance. To prove this law 

 to his audience by a more simple and firm apparatus, Mr. 

 Simon constructed a pair of scales, all the parts of which were 



made 



