VOL. LXVIII.] PHILOSOPHICAL TBANSACTIONS. 347 



parapet, nearest to the cramps, darting, as it seemed, from tlie gutter up to the 

 cramps. — Exp. 28. On pasting tin foil on the top of the parapet quite round the 

 model, as had been done before, and moistening the inner part of the parapet 

 down to the gutter, tlie stroke was again received by the point, when the same 

 appearances were observed as in the last experiment. — Exp. 29. I then made a 

 metallic communication between the top of the parapet down to the gutter : after 

 this the experiment was repeated. And though the point was struck at 5 inches 

 distance, there was no spark, either between the cramps or at the inner corner 

 next to the gutter. 



Villi Observation. — From these last experiments it ap])eared, that rain contri- 

 buted to make the lateral effect greater at the corner, by forming a Letter com- 

 munication between the cramps and the gutter, than the dry materials of brick 

 and stone admitted of. But it also appeared that, when the communication 

 between the gutter and cramps was rendered more perfect by a slip of tin foil that 

 was interposed between them, that lateral effect ceased at the cramps ; because 

 a still freer passage was made for the fluid to discharge itself through ; not only 

 along the slip of metal comnmnicating with the gutters and the tin foil quite 

 round the parapet, but also along the tin foil down the side of the model, from 

 which it was conveyed by the wire to the well. — Exp. 30. An objection having 

 been made, that the wire communicating from the bottom of the model to the 

 well, as it consisted of several distinct parts, occasioned a resistance at each of 

 the junctions, and therefore constituted only an imperfect conductor; in order 

 to try the validity of this objection, a new communication was now made from 

 the model to the well, consisting of one entire wire, pointed at the end, with 

 which I repeated the experiment of passing the model ; and finding no sensible 

 difference from the former results, I then, in order to apply a rounded end to 

 this perfect communication, had the pointed conductor, which was previously 

 made use of, soldered on to the end of the wire instead of the other point ; and 

 to this conductor so soldered I occasionally applied the small ball which was used 

 in the former experiments, and which has hitherto been called the rounded end. 

 With these different terminations, and thus circumstanced, all the experiments 

 were repeated ; and it was found, that the results were rather more in favour of 

 the doctrine hitherto advanced, than before the communication was made so 

 perfect. It having been farther objected, that the motion of the model em- 

 ployed in these experiments was considerably greater than the motion of a thun- 

 der-cloud, I made tlie following experiment. — Exp. 31. The weight which 

 moved the model in the preceding experiment was gradually reduced till it was 

 nearly balanced by the friction ; and when the motion was rendered so slow as 7 

 feet 7 inches in 7 seconds, it was very little iaccelerated ; and in this state the 



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