Viscosity of Hydrogen, ^Sitrogen, and Oxygen. 585 



The time for the rotation is measured by a trace, on 

 a sheet of waxed paper covering the chronograph drum K, 



Fig. 1. 



made by a stylus which is elecfcromagnetically connected 

 to a standard clock in the Laboratory ami which travels from 

 one to the other end of the drum (luring one observation. 



The deflexion of the inner cylinder is indicated by a 

 very sharply defined spot of light reflected from a mirror. 



