2 CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. 



subject of my last paper, namely, the induction at the beginning and ending 

 of a galvanic current, and to present them as a continuation, and, in a measure, 

 as the completion, of this part of my researches. The other results of ray 

 labours in this line will be arranged for publication as soon as my duties will 

 permit me to give them a more careful examination. 



2. In the course of the experiments I am about to describe, I have had occa- 

 sion to repeat and vary those given in my last paper, and I am happy to be 

 able to state, in reference to the results, that, except in some minor particulars, 

 which will be noticed in the course of this paper, I have found no cause to 

 desire a change in the accounts before published. My views, however, of the 

 connexion of the phenomena have been considerably modified, and I think 

 rendered much more definite by the additional light which the new facts have 

 afforded. 



3. The principal articles of apparatus used in these experiments are nearly 

 the same as those described in my last paper, namely, several flat coils and a 

 number of long wire helices. (III. 6, 7, 8.*) I have, however, added to these 

 a constant battery, on Professor Daniell's plan, the performance of which has 

 fully answered my expectations, and confirmed the accounts given of this form 

 of the instrument by its author. It consists of thirty elements, formed of as 

 many copper cylinders, open at the bottom, each five inches and a half in height, 

 three inches and a half in diameter, and placed in earthen cups. A zinc rod 

 is suspended in each of these, of the same length as the cylinders, and about 

 one inch in diameter. The several elements are connected by a thick copper 

 wire, soldered to the copper cylinder of one element, and dipping into a cup of 

 mercury on the zinc of the next. The copper and zinc as usual are separated 

 by a membrane, on both sides of which is placed a solution 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 elements 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 



* "When the numerals II. or III. are included in the parei^esis, reference is made to the corre- 

 sponding Nos. of my contributions. 



