PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 601 



power of the electro-magnet to be t-\vo, and of the permanent mag- 

 net to be four, it would seem that the power of the two combined 

 should be six ; but instead of that we find it to be sixteen. It 

 would seem from Faraday's law, that the decomposition of a cer- 

 tain amount of zinc will generate a certain force, that with the 

 combination there should be a greater consumption of zinc ; but 

 while, he had, by trying it over and over again, ascertained be- 

 yond all possible doubt, that the power was thus increased, he 

 had been unable to determine whether there was really any more 

 zinc used, 



Mr. Johnson stated that by placing a galvanometer between 

 the battery and the magnet, it appeared that the magnet did not 

 act apon the battery at all. 



Mr. Dibben said that it might be that the rosiistance at the end 

 was overcome, and that there was a faster current although no 

 stronger. He could not conceive of any other rational explana- 

 tion of the increased power than an increased consumption of the 

 zinc. 



Mr. Holcomb exhibited specimens of chemical electro-magnet 

 printing, a mode which has now nearly gone out of use. As the 

 time required for the printing is less than that required for ma- 

 nipulation, perforated paper is used to complete and break the 

 circuit, the paper being prepared by operators, and passed rap- 

 idly through the instrument. He had devised a new method of 

 preparing chemical paper, by freeing it from glutinous matter 

 and then wetting it with a solution of the nitrate of silver, which 

 is much more sensitive than the prussiate of potash. The im- 

 pression is fixed by dipping the paper into the iodine of potassium, 

 which changes the nitrate of silver into an iodide of silver. As 

 to his invention, now before the Committee, he had been for some 

 time very doubtful of the fact of the increase of power, for the 

 reason that there were no known laws to account for it. The 

 nearest experiment made by others, was that of Prof. Faraday, of 

 placing a permanent magnet in a coil, and endeavoring so ascer- 

 tain whether it produced any effect upon the current. Professor 

 Faraday thought it did not. 



Mr. Johnson said that it was Oerfted who discovered that 

 when a needle was brought into proximity to the wire, it was 

 deflected to the east or west, depending upon its position above 

 or below the wire. Ampere afterwards increased the number of 

 turns and made it available as a multiplier. He proceeded to 



