!■ 



94 Mr. II. Wilde's Experimental Researches 



47. Moreover the direction of the current in the electro- 

 helices, as shown by the galvanometer, was the same after as it 

 was before connexion with the electromotor was broken ; whereas 

 had the current, as shown by the spark obtained (38), been the 

 result of a static charge of the kind observed in insulated tele- 

 graph wires, the electricity would have discharged itself, when 

 the place of disjunction was at the electromotor, in the opposite 

 direction to that in which it entered the electrohelices. 



48. The conclusions drawn from a consideration of these ex- 

 periments are therefore opposed to the supposition that the 

 effects described are the consequence of a static charge of the 

 kind observed to be retained by insulated submarine and subter- 

 ranean telegraph wires ; but some of the phenomena described 

 — such as the retardation of the current when contact was made 

 with the magneto-electric machine (43, 45), and the exalted 

 electrical condition of the wire surrounding the electromagnet, 

 as shown by the voluminous spark seen and the severe shock 

 felt when contact with the machine was broken (37) — are iden- 

 tical with the phenomena of electric induction observed by Dr. 

 Henry* and investigated by Faraday with the aid of the voltaic 

 battery, and which form the subject of his Ninth Series of He- 

 searches in Electricity t- 



49. That an electromagnet possesses the power of retaining a 

 charge of electricity in a manner analogous to that in which it 

 is retained in insulated submarine cables and in the Ley den jar, 

 but not identical with it, is evident from the appearance of a 

 spark at the point of disjunction of the wires a considerable time 

 after all connexion with the electromotor has been cut off. The 

 production of this spark appears to me to arise from the compa- 

 ratively slow manner in which large masses of iron return to 

 their normal condition after having attained a highly exalted 

 degree of magnetism — the rate of decrease, however, being suffi- 

 ciently rapid to allow the induction-current to manifest itself in 

 the electrohelices, with a decreasing intensity, simultaneously 

 with the decreasing flux of magnetism in the iron itself. 



50. It is this important retentive property of the electromag- 

 net which maintains its attractive force unimpaired, notwith- 

 standing the intermittent character of the electricity transmitted 

 through the electrohelices; for, as is well known, no current 

 whatever is produced from the armature of the magneto-electric 

 machine when in certain positions during its revolution. These 

 positions correspond in some measure with the dead points 

 of the crank of a steam-engine, the fly-wheel of which performs 

 the same function dynamically as that which the electromag- 



* Silliman's American Journal of Science, 1832, vol. xxii. p. 408. 

 t Philosophical Transactions, 1 835, vol. cxxv. 



