1000 Transactions of the American Institute. 



metres iu length, and two and a half millimetres in diameter, 

 divided into two equal lengths, which were wound in juxtaposition 

 into a bobbin or coil, of such proportions that the central or core 

 opening was over six inches in diameter. ' 



In 1850 some remarkable experiments with induction coils were 

 made by Prof. Page, and published in SiUimanJs Journal. Three 

 reports on the subject may be found in vol. 10, No. 80, November, 

 1850, page 349; vol. 11, No. 31, January, 1851, page 88; and vol. 

 11, No. 32, March, 1851, page 191. The coils and magnetic bars 

 ■svere on a grand scale, and by far the most powerful magnets ever 

 produced. One of the helices raised within its central opening " a 

 bar of iron one thousand and forty pounds in weight, vibrating iu 

 the air without visible support." .These helices have been described 

 elsewhere as made of square wire one-quarter inch thick, of very 

 fiire copper, and the battery used from fifty to one hundred pairs 

 Cirroves, with platinum plates one hundred square inches immersed. 

 Very interesting experiments were performed, showing that the 

 time required to raise the current to its maximum in the coils varied, 

 according to circumstances, from one-sixth of a second to two 

 SBConds, and that^the subsidence of the current was in the same 

 time. Coils were closed after the battery current had been with- 

 drawn, and afterwards opened within a half second, and a current 

 still found to be flowing. The time recfuired was much less when 

 11.0 magnetic bar was inclosed in the helices, from one-third to one- 

 half less. The most striking results, however, from these coils, was 

 the immense length of the terminal secondary or separation spark. 

 When the current was allowed to attain its full power, the sudden 

 separation of the wires produced sparks eight inches in length. 

 When the separation was slow, the sparks were short, and spread 

 out more like a flame. An extraordinary change was jjroduced in 

 the character of this secondary spark by magnetic action. When 

 the circuit was broken at a distance of several feet from the magnet, 

 the spark was attended with very little noise. But as the point 

 of separation approached the magnet, the noise increased, until, 

 when the circuit was broken on the pole of the magnet, the report 

 was as loud as a pistol, and the spark diminished in length, and 

 spreading out as large as the palm of the hand. The secondary 

 spark was found also to obey the same rotative or tangential action 

 as the conductor itself. (Vol. 11, No. 33, page 191. March, 1851.) 



Soon after the publication of tlicse interesting results, M. Ruhm- 

 korflf, an instrument-maker in Paris, took up the induction apparatus 



