On Electro- Dynamic Induction. 119 



per and zinc as usual are separated by a membrane, on both sides 

 of which is placed a sohition of one part of sulphuric acid in ten 

 parts of water ; and to this is added, on the side next the copper, 

 as much sulphate of copper, as will saturate the solution. The 

 battery was sometimes used as a single series, with all its ele- 

 ments placed consecutively, and at others in two or three series, 

 arranged collaterally, so as to vary the quantity and intensity of 

 the electricity as the occasion might require. 



4. The galvanometers mentioned in this paper, and referred to 

 in the last, are of two kinds; one, which is used with a helix, to 

 indicate the action of an induced current of intensity, consists of 

 about five hundred turns of fine copper wire, covered with cotton 

 thread, and more efTectually insulated by steeinng the instrument 

 in melted cement, which was drawn into the spaces between the 

 spires by capillary attraction. The other galvanometer is formed 

 of about forty turns of a shorter and thicker wire, and is always 

 used to indicate an induced current, of considerable quantity, but 

 of feeble intensity. The needle of both these instruments is 

 suspended by a single fibre of raw silk. 



5. I should also state, that in all cases where a magnetizing 

 spiral is mentioned in connection with a helix, the article is 

 formed of a long, fine wire, making about one hundred turns 

 around the axis of a hollow piece of straw, of about two inches 

 and a half long: also the spiral mentioned in connection with a 

 coil, is formed of a short wire, which makes about twenty turns 

 around a similar piece of straw. The reason of the use of the 

 two instruments in these two cases is the same as that for the 

 galvanometers, under similar circumstances, namely, the helix 

 gives a current of intensity, but of small quantity, while the coil 

 produces one of considerable quantity, but of feeble intensity. 



Skction I. 



On the Induction produced at the moment of the Beginning of a 

 Galvanic Current, 4*c. 



6. It will be recollected that the arrangement of apparatus em- 

 ployed in my last series of experiments gave a powerful induction 

 at the moment of breaking the galvanic circuit, but the effect at 

 making the same was so feeble as scarcely to be perceptible. I 

 was unable in any case to get indications of currents of the third 



