444 PHILOSOPHICAL TRANSACTIONS. [aNNO 1778. 



is small, will draw it off silently. This then is the whole amount of his ex- 

 periments ; the only one of them in which the electric fluid had time to accumu- 

 late, being attended with a different event from the rest, and producing, as 

 might reasonably be expected, a strong explosion. 



It is not however this single property of sharp-pointed conductors, which 

 must decide the question. We have already seen, that there are two properties 

 inseparable from them, both of which must be taken into the account, before 

 we can determine the propriety of affixing them to buildings, particularly 

 powder magazines, as preservatives from lightning : first, their greater propensity 

 to admit the electric fluid, in consequence of which they act on electrified bodies 

 at a greater distance than rounded ends will ; and, 2dly, their incapacity to draw 

 away more than a certain quantity of electricity without an explosion. The first 

 quality enables them, when electricity is accumulated gradually, or when they 

 are brought gradually towards the electrified body, to steal away the fluid by 

 little, till there is not enough left to give an explosion. And hence, in common 

 experiments, the point, placed at a greater distance than the ball, will prevent 

 the electricity from exploding, as it otherwise would do, on the latter. But if 

 we combine this quality with the 2d, the superior propensity to admit, with the 

 incapacity in certain circumstances of discharging silently, it will be evident, 

 a priori, that the phenomena must in such cases be reversed, just as they appear 

 to be in Mr. Wilson's experiments ; that the point must strike at a greater dis- 

 tance, and the rounded end at a lesser. 



These phenomena, to persons who have not carefully considered them, must 

 appear so extraordinary, that unless the cause of the diversity is explained, they 

 will perhaps be led to suspect some unfairness in making the experiment. The 

 truth however is this ; that when the two conductors are set at the greater of 

 the two distances, the absolute quantity of electricity collected before the explo- 

 sion, is exactly the same in each experiment ; and therefore the distances of the 

 ball and point from the 2d conductor being equal, and the greatest at which 

 either of them will be struck, the explosion will go to the point, as being more 

 susceptible, and giving less resistance than the ball. But in the 2d supposed 

 case, when the 2d conductor is set considerably within the former distance, the 

 quantity of electricity which explodes on the point and the ball is not the same ; 

 the point in this case exerting its known property of stealing away the electricity 

 silently, which the ball from its greater resistance is incapable of doing. The 

 consequence is, that the quantity accumulated to give an explosion on the ball 

 is greater than that which explodes upon the point, and, being greater, will very 

 naturally explode to a greater distance. 



I come now to consider more particularly the practical question, whether the 

 sharp-pointed or the blunt conductors are most proper to be affixed to buildings, 



