Intelligence and Miscellaneous Articles. 

 Table I. 



565 



Without armatures. 



With armatures. 



80 

 70 

 90 



60 

 70 

 80 



90 



80 



100 



70 



85 

 90 



Mean ...75 



86 



In this Table the numbers are the deflections of the reflecting 

 galvanometer expressed in millimetres. In this case the gain by 

 the use of the armatures was trifling, being only about 14 per cent. 

 These results were obtained by charging the condenser of ^ of a 

 farad by sparks one millimetre in length. 



On a closed secondary circuit, however, a gain of one hundred 

 per cent, was clearly shown in the strength of the induced current 

 produced by breaking the primary circuit. The question of how 

 to make this great increase in the strength of the induced current 

 by the employment of armatures manifest in the spark became an 

 interesting one. It seemed at first as if the application of arma- 

 tures, by maintaining the temporary magnetization of the iron cores, 

 would be detrimental rather than otherwise. 



I next tried the effect of bundles of thin iron plates, which were 

 placed as armatures upon both poles of the electromagnets, thus 

 making a magnet of a horseshoe 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 en- 

 tirely off the scale. Table II. shows the results obtained by the 

 use of iron plates -fa of an inch in thickness, twenty in number, 

 constituting each armature. 



Table II. 



Without plates. 



With plates. 



80 

 70 

 90 

 60 

 70 

 80 



400 

 380 

 370 

 400 

 370 

 400 



Mean ... 75 



3866 



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 



