FOLYTECRKIC ASSOCIATION PROCEEDINGS. 99 j^ 



for obtaining shocks and sparks from the Calorimotor, by C. G. 

 Page, Salem, Mass." This apparatus (Fig. 1) was so graduated 

 that the strength of the induced current could be varied at pleasure; 

 was furnished with mechanical and automatic circuit-breakers, and 

 the now celebrated spark-arrestmg circuit-breaker, and produced 

 secondary or induced currents from coils outside of the battery or 

 primary circuit, and of sufficient intensity to charge a Leyden jar. 

 The communication closes with this remark: "We have, then, in 

 this instrument a battery by itself, from which shocks of all grades 

 can be obtained; and, in cases of the medical application of gal- 

 vanism, it must prove far more convenient than the ordinary 

 methods." The " ordinary methods " at that time were the cum- 

 liersome galvanic batteries, the frictional electric machine, and the 

 magneto-electric machine. The description of Prof. Henry's appa- 

 ratus, hereafter noticed, and that of Prof Page, were both received 

 in London by Mr. Sturgeon, the editor of The Annals of Elec- 

 tricity and Magnetism^ at the same time, and pulilished side by side, 

 and with the following comment by the editor: " Mr. Page's varia- 

 tions of Prof. Henry's experiments are Yerj important." [Sturgfeon's 

 Annals, May, 1837.) They have proved to be important, inasmuch 

 as the principle of construction adopted in the Page coil is that of 

 an economical use of battery power, which has been applied since 

 that time in every form of induction apparatus, whether for reme- 

 dial or philosophical use and research. The principle is simply 

 this: In order to obtain induced currents of high intensity from a 

 battery of a single or only a few pairs of plates, an extra and much 

 longer circuit must be employed for the induced current than that 

 used to transmit the battery current; or, more briefly, the induced 

 or secondary circuit must be much longer than the inducing or pri- 

 mary circuit. In Prof Henry's experiments, only a primary circuit 

 was used. In Faraday's celebrated experiments on induction, the 

 primary and secondary circuits were of nearly equal length — the 

 secondary circuit being actually a little shorter than the primary by 

 a foot and one-half. The current he obtained from his secondary 

 circuit had less intensity than the terminal secondary or induced 

 current from his primary circuit. Hence he makes no mention of 

 shocks received from the secondary circuit, while he obtained them 

 freely from his primary circuit. In Faraday's first experiments, in 

 1831, and in his experiments in 1834, both relating to the subject 

 of induction, he used the same arrangement of his coils; and it is 

 somewhat remarkable that, in the multitude of his experiments," it 



