On a Case of Work produced by the Electric Current. 469 



coil is more than doubled in length. An application of this 

 fact to the induction-coil is suggested. 



2. The results by the different methods used all show an in- 

 crease of electromotive force when the circuit is broken in a 

 magnetic field, and that the effect cannot be purely a mecha- 

 nical phenomenon as M. Becquerel affirms. 



3. By breaking the circuit between mercury and copper in 

 the magnetic field, a remarkable change of polarity was ob- 

 served with the electrometer. 



4. An explanation is offered of the fact noticed by Sir Wil- 

 liam Thomson, that a greater electromotive force per unit of 

 length is needed to produce a spark at a short distance than at 

 a long one. 



The subject of this paper was suggested to me by Professor 

 Trowbridge ; and throughout all my work he has kindly given 

 me his advice and help. 



Physical Laboratory, Harvard College, 

 Cambridge, U. S. 



LV. On a Case of Work produced by the Electric Current. 

 By B. Colley, of Moscow*. 



THE notice which I have the honour to place before the 

 readers of the ' Philosophical Magazine ' is a succinct 

 rfeume of two articles which I have recently published in the 

 (Bussian) ' Journal of the Physical and Chemical Societies of 

 St. Petersburg ' (vol. vii. December 1875, and vol. viii. April 

 1876) f. For more ample details I refer the reader to the 

 articles themselves, where he will find all the developments 

 and numerical calculations, which I have omitted in the pre- 

 sent notice. 



The total quantity of energy which becomes free in a deter- 

 mined galvanic element (for instance a Daniell element) by 

 the solution of a gramme of zinc is a constant quantity, in- 

 dependent of the time spent in dissolving the zinc. It is the 

 mechanical equivalent of the chemical reactions that take 

 place in the pile. A portion of this energy always manifests 

 itself under the form of heat in the circuit ; another may ap- 

 pear as mechanical work produced by the current. A direct 

 consequence of the principle of the conservation of energy is, 

 that this second portion can only exist and increase at the 

 expense of the first, their sum being constant. 



* Translated from the MS. (in French) communicated by the Author. 



t An abridged German translation of the first of these articles will be 

 found in Poggendorff's Annalen, vol. clvii. p. 370 ; that of the second will 

 shortly appear in the same journal. 



