364 Mr. Saxton on his Magneto-electrical Machine ; 



nected with the dipping points, so that the current in both parts 

 of the coil is continuous in the same direction, it is obvious that 

 by the rotation of the spindle the circuit is alternately broken 

 and renewed, and a spark occurs every time either of the cop- 

 per points leaves the surface of the mercury, into which the 

 copper disc also dips, thus completing the metallic communi- 

 cation twice during the revolution of the spindle. In the ar- 

 rangement here described the successive transient currents 

 are in opposite directions; to obtain a series of currents in 

 the same direction, the double must be replaced by a single 

 point, but in this case one half of the effect is lost. 



The first electro-magnetic machine, that is, an instrument 

 by which a continuous and rapid succession of sparks could 

 be obtained from a magnet, was invented by M. Hypolite 

 Pixii of Paris, and was first made public at the meeting of the 

 ^cademie des Sciences on September 3, 1832. A description 

 of this invention will be found in the Aimales de Chimie for 

 July 1832 (that journal is always published several months 

 after its date), and a representation of it in Becquerel's Traite 

 de V Electricite^ vol. iii. It differs from mine principally in 

 two respects: first, in M. Pixii's instrument the magnet itself 

 revolves and not the armature; and secondly, the interrup- 

 tions, instead of being produced by the revolution of points, 

 were made by bringing one of the ends of the wire over a cup 

 of mercury, and depentling on the jerks given to the instru- 

 ment by its rotation for making and breaking the contact with 

 the mercury. With this machine, furnished with a coil about 

 3000 feet in length, sparks and strong shocks were obtained, a 

 gold-leaf electrometer was made to diverge, a Leyden jar was 

 weakly charged, and water was decomposed. 



My first complete magneto-electrical machine was exhibited 

 at the meeting of the British Association at Cambridge in June 

 1833, and that now in the Gallery of Practical Science in Ade- 

 laide-street was placed there in August of the same j'ear. 

 The effects first shown by my machine were the following : 1st, 

 the ignition and fusion of platina wire ; 2ndlyj the excitation 

 of an electro-magnet of soft iron (these were first shown 

 August 25th, 1833) ; and 3rdly, those of the double arma- 

 ture, producing at pleasure, either the most brilliant sparks 

 and strongest heating power, or the most violent shocks and 

 effective chemical decompositions ; this was added to the in- 

 strument in December 1835. 



I was led to furnish my magnet with the double arma- 

 ture from the following circumstances. In November 1833, 

 Count di Predevalli brought from Paris one of Mr. Pixii's 



