168 



Louis Schwendler — On tlie Emj>lopnent of 



[No. 3, 



permai)ently to earth. The earth consists of 3 copper plates* joined 

 parallel and offering a parallel resistance of 167 ohms.t 



T is a tangent galvanometer for measuring the main current. In this 

 case it was the tangent galvanometer employed in my electric light 

 experiments in London in 1878. The resistance of the copper ring of this 

 instrument is nil. Taking the late Mr. Brough's value for H, the hori- 

 zontal component of the Earth's magnetic intensity at Calcutta to be 

 H = 0'37158 dynes, the formula for calculating the currents c from the 

 deflections observed by this tangent galvanometer, is :— 

 c = 47330 tang a (milli-oersted). 



r is a coil of iron wire (No. 2i i. w. g., 0-21" diameter) offering a 

 resistance of 1-517 ohms at 85" F. The wire is coiled on a large wooden 

 drum and serves as the constant resistance by which from time to time 

 the efficiency of the dynamo-electric machines at Howrah^an be gauged. 



?72/, 



m 



4 



T'oorru. 



J represents an electric light, in this case produced by a large Serrin- 

 1am p. 



In the following experiments, either r or J was used as the external 

 resistance for closing the poles of the dynamo-electric machine to produce 

 the miain current ; but never the tivo joined parallel. 



Jj is the telegraph line from the dynamo-electric machine to the 

 Calcutta Telegraph Office. This line is 1-75 miles in length and consists, 

 from the electric light room to the Howrah Eailway Station, of Hooper's 

 india-rubber cable core, from the Howrah Station to the Kirk, of No. 6 



* The three single earths measured gave : 7'7, 3-1, and 6'9 B. A, U. 

 t The dimensions are 4' x 2' and yL". 



