204 



PROCEEDINGS OF THE AMERICAN ACADEMY 



placed as armatures upon both poles of the electro-magnets, thus 

 making a magnet of a horse-shoe form. 'On charging the condenser, 

 I found a very great increase in quantity, which was manifested by the 

 swing of the galvanometer needle, the indications being entirely off 

 the scale. Table II. shows the results obtained by the use of iron 

 plates ^^ of an inch in thickness, twenty in number, constituting each 

 armature. 



TABLE II. 



Here a gain of four hundred per cent was manifested by the use of 

 the thin plates. 



The next step was to ascertain how many plates were necessary to 

 obtain the maximum effect. The difficulty of obtaining plates of the 

 same homogeneity made it impossible to obtain smooth curves. To 

 this diificulty was added that of breaking the primary circuit in a 

 regular manner. 



If the results of Table HI. are plotted, it will be seen that the 

 increase within small limits is very nearly proportional to the number 

 of thin plates, which were i^^ of an inch in thickness. 



TABLE IIL 



