and 071 certaiii Principles in Electrical Science. 467 



12. These experiments are conclusive of the nature of Mr. 

 Sturgeon's experiments. 



Exp. {k) {I) — show, that the electricity of the spark varies 

 with that of the coatings. 



Exp. {m) —proves that the spark is readily obtained after 

 the discharge has taken place ; it is not therefore any lateral 

 explosion caused by the discharging rod. 



Exp. (o) — proves that the spark is merely a residuary ac- 

 cumulation. 



Exp. (j)) (q) — prove that the spark is of different degrees 

 of force, when the electricity is discharged from a greater or 

 less extent of surface, whilst double, treble, &c., quantities, 

 when discharged from double, treble, &c., surfaces, give the 

 same spark. Now as no one can doubt but that the effect of 

 a double, &c. quantity should be greater than a single, &c. 

 quantity, it is again evident that the spark is not caused by 

 any lateral explosion from the discharging rod ; it being a 

 well-established law, that the same quantity has the same 

 heating effect on wires, whether discharged from a great 

 surface or a small one, from thick glass or thin ; some little 

 allowance being made for the greater number of rods, &c., 

 when the surface is increased by an additional number of 

 jars ■*. The effect therefore depending on the jar, Mr. Stur- 

 geon had a greater chance with a small jar than with a large 

 one. 



Exp. (f) — proves that the degree of tension in the rod is 

 not of any consequence. 



Exp. (s) (t) — show, that no kind of lateral action arises 

 during the passage of the charge. 



13. Mr Sturgeon confounds this residuary spark, with the 

 Earl of Stanhope's experiments on induction : he observes, 

 p. 176, "Viscount Mahon studied this kind of lateral dis- 

 charge very extensively." But any one who considers His 

 Lordship's work, will soon detect the fallacy of such a conclu- 

 sion. Lord Mahon shows, that when an electrical charge is 

 about to pass from a body M, fig. 7, in the direction C L, 

 the action upon a near body N will displace some of its elec- 

 tricity ; hence a spark will take place at E between that body 

 and another connected with the ground whenever the discharge 

 takes place from M, in consequence of the return of the dis- 

 placed electricity. This effect His Lordship termed the *' re- 

 turning stroke." Now to apply thij to the operation of a 

 thunder-cloud. Let M, fig. 6, represent a mass of cloud 



* Philosophical Transactions for 1834. Part II. p. 225, and Faraday's 

 Researches. 



2 H2 



