Mr Hart's Improvement on the Galvanic Battery. 1 9 



experiments relative to the law of the force. Mr Christie 

 found, that, when a thick copper plate was made to revolve 

 under a small magnet, the force tending to deflect the needle, 

 varied inversely as the fourth power of the distance ; but 

 when the magnets were large, and the copper discs small, the 

 power varied as stated in the preceding paper, according to 

 some power of the distance between the square and the cube, 

 and for plates of different weights, the force was very nearly 

 in the ratio of the weights. 



Art. III. — Account of an Improvement on the Galvanic Bat- 

 tery. By Mr John Hart, Civil Engineer, Glasgow. In 

 a Letter to the Editor. 



Dear Sir, 



Allow me, through the medium of your valuable Journal, 

 to describe an improvement on the galvanic battery, which I 

 have recently made, and the advantages of which have been 

 ascertained by actual experience. Before I proceed, how- 

 ever, to give a description of it, it may be proper to notice 

 the prominent defects of those which are in common use. 



The pile of Volta is very troublesome to put in action, and 

 as the moisture is liable to be pressed out of the discs of 

 cloth by the weight of the plates, it frequently runs over the 

 edges and destroys their insulation. 



A capital improvement was made on this apparatus by the 

 invention of the trough, by the ingenious Mr Cruikshanks 

 of Woolwich. This trough, though extremely convenient 

 and powerful, is subject to some disadvantages, the principal 

 of which is, that the exciting liquid causes the wood to warp. 

 The cement into which the plates are fixed, is thus cracked, 

 and the liquid, insinuating itself into the fissures, soon de- 

 stroys the insulation. For the purpose of keeping them in 

 order, the cement must therefore be occasionally run over 

 with a hot iron, which is a tedious and very troublesome pro- 

 cess. In Mr Children's battery, (which was a combination of 

 Volta's couronne des tasses and the trough of Cruikshanks,) 



