138 On ttlectro-magiietic Experiments. [pEis. 



80°. On removing the larger wire, the deviation under the 

 smaller increased, &c. 



When the circuit was made by a glass tube filled with mer- 

 cury, the deviation was the same as with a wire of the same 

 thickness ; but on removing the mercury, and coating the tube 

 with silver leaf, the deviation was not more than between 5° 

 and 10°. 



The electro-magnetic influence was not diminished by raising 

 the connecting wire to a red heat; but on interrupting the circuit 

 by water, it was destroyed, though the connectmg wire placed 

 immediately over the compass decomposed water at each end. 



If the connecting wire were bent alternately from N. to S. and 

 from S. to N. the magnetic needle deviated to the W. of the N, 

 in all the former, and to the E. of N. in all the latter bendings, 

 whatever were their number, and in whatever part of the wire 

 they were placed. 



when the connecting wire was made to pass from N. to S. 

 over the needle, and from S. to ^. under it, the electro-magnetic 

 influence was doubled. 



A single pair of rather large plates was found, as in Oersted's 

 experiments, to be more efficacious than a number of plates with 

 the usual arrangement ; but when wires from all the zinc plates 

 were connected on one side, and from all the copper plates, on 

 the other, the electro-magnetic influence increased with the num- 

 ber of plates. 



It was found that the relative quantities of galvanism generated 

 in different experiments might be estimated with great readiness 

 and accuracy by using a graduated shde cariyingthat connecting 

 wire over a fixed compass with a standard deviation. 



I am. Sir, respectfully yours, J. C. 



Article XIV. 



Analyses of Books. 



Vntersuchungen uher den Magnetismus der Erde, Von Christo- 

 pher Hansteen, Professor der Angewandten Mathematik an 

 den Norwegischen Universitat. Christiania, 1819. 



Researches on the Magnetism of the Earth, By Professor Han- 

 steen, of Christiania. 1 vol. 4to. 650 pages. 



I HAVE just received a copy of the first volume of this cele- 

 brated work, which I have been very anxious to see. I am 

 unwilling to peruse it till I recover the Atlas, which ought to 

 have accompanied it, and which has been unfortunately lost on 

 the way between Christiania and London ; but I cannot avoid 



