80 Magnetic Galvanism. 



the coil). These plates were perforated at the centres, so as to al- 

 low the keeper to pass through, and then fastened by pins on the out- 

 side. The end of the coil {b h), connected with the magnet, must, 

 in no case, touch the keeper or the brass plates fastened to it, and, 

 in the figure, it is represented as preserving this intermediate position 

 by means of a string. It is equally necessary that no metallic com- 

 munication should exist permanently between the magnet and the 

 keeper, except through the coil. 



2nd. Wires, c and e, are firmly fastened to the keeper and magnet, 

 respectively. They serve as conductors of the galvanic fluid, for the 

 purpose of giving shocks, affecting the galvanometer, &;c. 



3rd. The keeper to touch the magnetic poles as usual, but instead 

 of being pulled, which is at all times an inconvenient process, is to 

 be pushed smoothly but quickly downwards off the magnet. TJ|is 

 movement is very easy, and, when well performed, increases aston- 

 ishingly the induced magnetism of the keeper, and, consequently, 

 the galvanic impulse, as is shown by the brilliant scintillations, and 

 the vivid flashes of light, shock, Stc. when the conducting wires c 

 and e are taken into the mouth. 



The magnet, made use of, consisted of seven plates and could not 

 easily sustain more than fifteen pounds. The poles were not much 

 over an inch apart, which is a great disadvantage, by preventing the 

 use of a sufiiciently large coil. The poles, it may be observed, should 

 be ground down until they become very smooth and lie, accurately, 

 iti the saine plane. As to the keeper, the best form seems to be that 

 which enables it to adhere most firmly to the magnet (a result pro- 

 moted by the smoothness of surface), for all the galvanic phenomena 

 seems to be in direct proportion to the degree of adhesion. A flat 

 bar of soft iron, about one quarter of an inch thick, and applied at its 

 edge, was found to answer remarkably well and seemed to receive 

 most rapidly, the induced magnetism, as it passed over the magnet. 

 Contrary to expectation a keeper of the highest tempered steel was 

 found to answer very well, even after it had obtained permanent and 

 powerful polarity. With a coil of about thirty yards, the instrument, 

 here described, gave sparks, shocks, flashes, in the eyes, the galva- 

 nic taste to the conducting wires, and some other results, but the ob- 

 servations, which follow, were made with, about one hundred and 

 ten yards of fine copper coil. Five times the quantity could, it is ob- 

 vious, be as easily managed and, by friction over a magnetic surface 

 of twenty plates, would produce very powerful effects. 



