440 Prof. TyndalFs Contributions to Molecular Physics. 



plates of rock-salt. It was skilfully constructed for me by Mr. 

 Becker, and the same two plates have already done service in 

 more than six hundred experiments. 



The apparatus consists of the following parts : — AB C (fig. 1) 

 is a plate of brass, 3*4 inches long, 2'1 inches wide, and 0*3 of 



