«68 



M. Wartmann's First Memoir 



e. A small helix for magnetizing^ formed of a wire of plated 

 copper (cuivre argente) of 0"^'00065 in diameter, making 9^ 

 revolutions around a lube of reed. 



6. The pile employed is constructed of separate elements 

 and has a constant force. The zincs are amalgamated solid 

 cylinders, of G^'\5 long and Qi^'Q^B in diameter; they are 

 immersed in a solution of chloride of sodium, inclosed in mem- 

 brane. The coppers are hollow cylinders of 0™'06 in dia- 

 meter, immersed in a saturated solution of sulphate of copper. 

 The energy of this apparatus is sustained during more than 

 five hours without very perceptible variations*. 



7. The additional wires of which we shall treat were all 

 carefully annealed; they are of the following dimensions. 

 (See the annexed Table.) 



8. In all the experiments related in this memoir we shall 

 only treat of currents induced by the completion of the voltaic 

 circuit, unless the contrary be expressly indicated. 



9. The numbers stated in the tables are the mean of several 

 readings according well with each other. To obtain this mean 

 was essential, whether as a guarantee against the variations of 

 intensity of the pile, or especially on account of the difficulty 

 of the readings when the needles, yielding to an instantaneous 

 deviating action, traverse an arc, the precise amplitude of which 

 it is necessary to appreciate. 



10. The needles of the rheometers generally coincided with 

 the seventh degree to the right or left of the zero of gradua- 

 tion; when they were in equilibrium, having no compass with 

 sines at my disposal, I strove to leave to the most intense cur- 

 rents an energy which would cause the index to deviate not 

 more than from thirty to forty degrees, so that I might con- 

 sider the angle described as sensibly proportional to the force 

 which acted on the needle. 



§ II. Induction of a constant "joire by a variable wire. 



11. The circuit of the induced wire of the great helix with 



* Archives de PElectricite, vol. ii. p. 597. 



