22 Mr. R. J. Moss on the Condensation of [May 11, 



The projectile lias still 28 feet to fall through. 

 As an approximation let us put 



^.28 = sin3° 20' {%,,,,.,,~%^,^.^). 



We should get 



S,.ee3o .0=2502.3; 



.-. 5 sec 3° 20' = 1193-0. 

 .-. using equation (a), D=38'-2. 

 We may now put 



X = 28 cot (3^ 19''1) 

 = 482-8 



and ^""l^ ^^^^^^^ 



Summation of X's : — 



2929 

 2529-5 

 482-8 



Range = 5941-3 



Summation of T's : — 



2-183 

 2-028 

 -402 



Time of flight = 4-613 



The observed range and time of flight were in this particular case 

 6060 feet and 4-75 sec. 



III. ''Condensation of Vapour of Mercury on Selenium in the 

 Sprengel Vacuum. By R. J. Moss_, F.C.S., Chemical 

 Laboratory Royal Dublin Society. Communicated by G. 

 Johnstone Stoney, F.R.S. Received March 25, 1876. 



In the course of experiments on the electrical conductivity of selenium, 

 a cylindrical bar of this substance in the vitreous state was enclosed in 

 a glass tube which was attached to the exhaust-tube of a Sprengel pump. 

 The bar of selenium was 45 millims. long and 3*5 millims. in diameter. 

 Platinum wires were attached to the ends of it and passed through the 

 sides of the glass tube. The tube was exhausted, and allowed to remain 

 attached to the pump for four days. It was now found that the 

 selenium had acquired a conductivity greatly exceeding that of the pure 

 element in its most highly conducting condition. The experiment was 

 repeated with the intention of observing the time required to produce 

 conductivity. In forty-two hours the needle of a highly sensitive gal- 



