48 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. 



peared at G or E, the extra current forcing its way through the electromotor itself. 

 The same results were obtained by the use of the helix or the extended wire at D in 

 place of the electro-magnet. 



1081. On introducing a fine platina wire at <r, and employing the electro-magnet 

 at D, no visible effects occurred as long as contact was continued ; but on breaking 

 contact at G or E, the fine wire was instantly ignited and fused. A longer or thicker 

 wire could be so adjusted at x as to show ignition, without fusion, every time the 

 contact was broken at G or E. 



1082. It is rather difficult to obtain this effect with helices or wires, and for very 

 simple reasons : with the helices i, ii, or iii, there was such retardation of the elec- 

 tric current, from the length of wire used, that a full inch of platina wire one fiftieth 

 of an inch in diameter could be retained ignited at the cross wires during the con- 

 tinuance of contact, by the portion of electricity passing through it. Hence it was 

 impossible to distinguish the particular effects at the moments of making or breaking 

 contact from this constant eff^ect. 



1083. On using the thick wire helix (1055.), the same results ensued. Proceeding, 

 however, upon the known fact that electric currents of great quantity but low inten- 

 sity, though able to ignite thick wires, cannot produce that effect upon thin ones, I 

 used a very fine platina wire at a?, reducing its diameter until a spark appeared at G 

 or E, when contact was broken there. A quarter of an inch of such wire might be 

 introduced at x without being ignited by the continuance of contact at G or E ; but 

 when contact was broken at either place, this wire became red hot ; proving, by this 

 method, the production of the induced current at that moment. 



1084. Chemical decomposition was next eff'ected by the cross-wire current, an elec- 

 tro-magnet being used at D, and a decomposing apparatus, with solution of iodide of 

 potassium in paper (1079.), employed at .r. The conducting power of the connecting 

 system A B D was sufficient to carry all the primary current, and consequently no 

 chemical action took place at x during the continuance of contact at G and E ; but 

 when contact was broken, there was instantly decomposition at x. The iodine 

 appeared against the wire N, and not against the wire P ; thus demonstrating that 

 the current through the cross-wires, when contact was broken, was in the reverse 

 direction to that marked by the arrow, or that which the electromotor would have 

 sent through it. 



1085. In this experiment a bright spark occurs at the place of disjunction, indi- 

 cating that only a small part of the extra current passed the apparatus at x, because 

 of the small conducting power of the latter. 



1086. I found it difficult to obtain the chemical effects with the simple helices and 

 wires, in consequence of the diminished inductive power of these arrangements, and 

 because of the passage of a strong constant current at x whenever a very active 

 electromotor was used (1082.). 



1087. The most instructive set of results was obtained, however, when the galvano- 



