.v/A' WILLIAM SIEMENS, F.R.S, 



20 1 



ON CERTAIN MEANS OF MEASURING AND 

 REGULATING ELECTRIC CURRENTS. 



BY C. WILLIAM SIEMENS,* D.C.L., F.R.S. 



THK dynamo-electric machine furnishes us with a means of pro- 

 ducing electric currents of great magnitude, and it has become a 

 matter of importance to measure and regulate the proportionate 

 amount of current that shall be permitted to flow through any 

 bntnch circuit, especially in such applications as the distribution 

 of light and mechanical force. 



On the 19th of June last, upon the occasion of the Soiree of 

 the President of the Royal Society, I exhibited a first conception 

 of an arrangement for regulating such currents, which I have 

 since worked out into a practical form. At the same time, I have 

 been able to realize a method by which currents passing through a 

 circuit, or branch circuit, are measured, and graphically recorded. 



It is well known that when an electric current passes through a 

 conductor, heat is generated, which, according to Joule, is propor- 

 tionate in amount to the resistance of the conductor, and to the 

 square of the current which passes through it in a unit of tune, or 

 H = C 2 R. 



I propose to take advantage of this well-established law of 

 electro-dynamics, in order to limit and determine the amount of 

 current passing through a circuit, and the apparatus I employ for 

 this purpose is represented on Figs. 1 to 3, Plate 17. Letters of 

 reference to the principal parts of the instrument are given on 

 the foot-note of the drawing. 



The most essential part of the instrument is a strip (A) of 

 copper, iron, or other metal, rolled extremely thin, through which 

 the current to be regulated has to pass. One end of this thin 

 strip of metal is attached to a screw (B), by which its tension can 

 be regulated ; it then passes upwards over an elevated insulated 

 pulley (I), and down again to the end of a short lever, working on 

 an axis, armed with a counter-weight and with a lever (L), whose 

 angular position will be materially affected by any small elonga- 



' Excerpt Proceedings of the Royal Society, Vol. XXVIII. 1879, pp. 292-297. 



