252 MEMORIAL OF JOSEPH HENRY. 



as much as the terminal induction,) most of the results previously 

 obtained (.such as the detection of successive orders of currents) were 

 derived from the strong inductions at the moment of breaking the 

 circuit. It became therefore important to endeavor to intensify the 

 initial induction for its more especial examination : and this it was 

 found could be effected in two ways, — by increasing the "intensity" 

 of the battery, and by diminishing within certain limits the length 

 of the primary coil. 



"With the current from one element, the shock at breaking the 

 circuit was quite severe, but at making the same it was very feeble, 

 and could be perceived in the fingers oidy or through the tongue. 

 With two elements in the circuit the shock at the beginning was 

 slightly increased : with three elements the increase w^as more decided, 

 while the shock at breaking the circuit remained nearly of the same 

 intensity as at first, or was comjiaratively but little increased. 

 When the number of elements was increased to ten, the shock at 

 making contact was found fully equal to that at breaking, and by 

 employing a still greater number, the former was decidedly greater 

 than the latter, the difference continually increasing until all the 

 thirty elements were introduced into the circuit. - - - Experi- 

 ments Avere next made to determine the influence of a variation in 

 the length of the coil, the intensity of the battery remaining the 

 same." For this purpose the battery consisting of a single element 

 " was employed ; and the length of the copper ribbon coil was suc- 

 cessively reduced from 60 feet, by measures of 15 feet. With 45 

 feet, the initial induction was stronger than with 60 feet: w^ith the 

 next shorter length it was more perceptible, and increased in 

 intensity with each diminution of the coil, until a length of about 

 fifteen feet appeared to give a maximum result." At the same time 

 it was found that "tlie intensity of the sliock at the ending of the 

 battery current diminishes with each diminution of the length of 

 the coil. - - - By the foregoing results we are evidently fur- 

 nished with two methods of increasing at pleasure the intensity of 

 the induction at the beginning of a battery current, the one con- 

 sisting in increasing the intensity of the source of the electricity, 

 and the other in diminishing the resistance to conduction of the 

 circuit while its intensity remains the same." 



