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Mr. F. C. Webb on one of Ohm's Laws 



operations on the part of Messrs. Bright and Clark, I performed 

 an experiment to test the accuracy of this law. In order to 

 render the whole problem and experiment intelligible, it will be 

 better to illustrate it geometrically. 



Let C A represent the resistance of the battery of seventy- 

 one elements and having a resistance of 520 Siemens' s units, and 



Q.'' 



A B the resistance of 78 nautical miles of cable having a resistance 

 also of 520 units, the number of elements having been selected in 

 order to equal this resistance. Let C Q represent the electro- 

 motive force of the battery of seventy-one elements ; then if 

 the pole C of the battery and the end B of the cable are con- 

 nected to earth, the tension at A will be A L= half C Q. But 

 if the circuit is formed by joining the end B of the cable to the 

 pole C previously to any charge existing in the cable, and when 

 the battery is also carefully insulated, the tension at A will be 



A H ( = -jr \ : supposing this the zinc plate or negative pole, 



the tension A H will be negative, and the tension at C and at B, 

 which is now joined to C, will rise to C K and B D equal and 

 opposite in name to A H. 



The line of tension throughout the circuit is represented, 

 therefore, by the step-like line K H in the battery, and by the 

 line H D in the cable. The quantity of electricity in the cable 

 and its distribution is represented by the equal triangles A H 

 and D B, the first negative, the second positive. The distri- 

 bution of the electricity on the surface of the battery is repre- 

 sented by the triangles (with step-like hypothenuses) C K P and 

 PAH; but the equality of these triangles with those represent- 

 ing the quantity in the cable does not show equality in the 

 quantity on the battery with that in the cable, on account of the 

 minute inductive capacity of the former as compared with that 



