350 I'JIII.OSOPHICAL TRANSACTIONS. ' j^ANNO 1778. 



length than the great cylinder: I therefore made use occasionally of the long wire 

 which has been already described. 



Exp. 37. On connecting one end of this long wire with the further end of 

 the great cylinder, and the other with one end of the brass drums; I found, that 

 about 6 uniform turns of the wheels, with a moderate velocity, were required 

 to cause the appearance of a small stream of light at the top of the spout 

 described in the first experiment, when the model, with the pointed conductor 

 on it, stood directly under the great cylinder, but at the distance of 5 inches. 

 Exp. 38. When the great cylinder was unconnected with the long wire and 

 brass drums, and while the model, with the same conductor on it, remained in 

 its place; about 2 turns, with the same velocity, were sufficient to charge the 

 great cylinder, so as to cause a similar appearance at the spout. — Exp. 3g. On 

 separating the great cylinder from a ]4th part of it, the model and machine 

 continuing in their places, it was found, that half a turn of the wheel was 

 sufficient to charge the little cylinder, so as to cause the like appearance at the 

 spout. • ''■■'- '■:.:>:;..<'.■ .■:-■■ ■- 



1 5th Observation. — Now these differences in the numbers of turns required for 

 causing similar appearances, when the several charges were given in the 37th 

 and 38th experiments, could not arise from a ditl'erence in the quantity of 

 metallic matter contained in the respective substitutes; because the tin-foil 

 which covered the great cylinder was found to be nearly 3 times heavier than the 

 weight of the whole wire. Neither could these difterences be owing to a 

 difference in the quantity of surface of the respective substitutes; because the 

 surface of the great cylinder was found to be 10 times greater than the surface of 

 the wire. Those several differences must therefore depend on some other cause; 

 and, as a true knowledge of this cause may be ot some moment in the present 

 inquiry, we must endeavour to find it out by experiments and observations. 



Exp. 40. When the great cylinder, with the wire and brass drums, were 

 charged with a very small quantity of this fluid, by the wheel being turned something 

 less than a quarter round, there was the moment after, a visible explosion, and a 

 sensible effect perceived at the remote end of the wire. When half a turn was 

 given, these effects were greater; and, after a whole turn, the quantity of the fluid 

 accumulated in this great apparatus was increased considerably. 



\6lh Observation. — Now, something must have hindered the fluid from 

 getting out of the cylinder and wire all the time they were charging, otherwise 

 we should not have been able to have caused the least accumulation; for, from 

 the nature of this fluid, there cannot be any accumulation without soine 

 resistance to occasion it. And whatever the nature of that resistance may be, 

 experiments show, that there are certain bounds prescribed to its power of 

 acting, and which in particular circumstances seem to be very easily surniounlcd. 



