Polytechnic Association Proceedings. 999 



matic device for breaking the circuit, which is effected by the 

 attractiou of a small piece of iron, G, by one end of the magnet, 

 the iron being attached to a wire, E, suspended over a glass mer- 

 cury cup, M, in such manner that the motion of the u'on lifts the 

 wire from the mercury and breaks the circuit. The distance 

 between the iron and magnet is easily adjusted, as also the force 

 with which- it is held, and pulled back by means of the adjustable 

 weight, F, so that the length and rapidity of the vibration may be » 

 regulated at pleasure. It was the first circuit-breaker in which the 

 resistance was adjustable without altering the attractive force. 



We may form some idea of the importance attached to this 

 induction apparatus, from the fact that, in a supplementary letter- 

 sheet catalogue issued the next year, Mr. Davis advertises three 

 different sizes of the same — one with 3,000 feet of fine wire, one 

 with 2,000 feet, and one jvith 1,000 feet, the prices being $29, $15 

 and $10. He also described an interesting modification of his own. 

 invention of the spark-arresting circuit-breaker, causing the wire to 

 vibrate in the mercury cup by means of clock-work. (See Fig. 3.) 

 In connection with this, the coils were placed in a vertical position. 

 There was also attached to the base-board the steel-Tasp, the original ^ 

 circuit-breaker adopted by Prof. Page in 1836. 



The first practical magneto-electric machine was made by Mr. 

 Saxton, of Philadelphia, but the way was first opened for unlim- 

 ited increase of the magneto-electric current, by increasing the • 

 number of magnets and armatures, instead of increasing the size of 

 the magnet and coils, to which, of course, there would have soon 

 been found a limit. 



In Silliman^s Journal (July, 1840), is found a lengthy account 

 of the experiments of Prof. Henry upon induction, communicated 

 to the American Philosophical Society November 2d, 1838, in 

 which he discovered the different orders of currents produced by 

 induced currents. The paper is full of scientific interest, but 

 nothing novel is presented in the construction of apparatus. 



In the year 1842, according to Becquerel, or according to Du 

 Moucel, about or towards the year 1842 (" vers I'annee "), M. M. 

 Masson and Breguet also undertook to verify the identity of 

 dynamic and static electricity by the operations of the secondary 

 current. Their memoir is found in the Annates des Chimie, vol. 4, 

 1842, page 129. It is there stated that the memoir was presented 

 to the Academy of Sciences .23d August, 1841. They employed 

 powerful batteries, forty pairs Daniell's, and a coil of wire 1,300 



