Lightning Conductors to Powder Magazines. 437 



The objection based oh the possibility of a lateral discharge, may 

 at all times, Professor Daniell considers, be obviated by providing a con- 

 ductor sufficiently capacious to carry off all the electricity falling upon 

 it, and the standard size for this when made of copper, he states is 

 one inch in diameter, experience having proved that no rod of this 

 size was ever fused by an electrical discharge. He discusses the ques- 

 tion of the attractive power of conductors, and decides, that though " a 

 pointed conductor will draw off silently and safely a considerable portion 

 of electricity from a charged cloud, it can possess no power of deter- 

 mining a disruptive and destructive discharge when it wotild not other- 

 wise occur." In his comments on this passage, we conceive that Dr. 

 O'Shaughnessy has misapprehended Mr. Daniell's meaning entirely, 

 since this gentleman advances no such assertion as that a pointed bar 

 must cause a silent discharge without explosion. He could not but 

 know from historical records, that the whole range of our experience 

 contradicts this, and the indications his report^ itself gives us of his 

 close reasoning, convince us that Dr. O'Shaughnessy has here mis- 

 understood him. 



Mr. Daniell it appears to us means to state that a conductor directly 

 opposed to a charged thunder cloud will draw off silently a portion of 

 that cloud's electricity, but if the line of least resistance between the 

 cloud and the earth does not pass through it, no disruptive charge will 

 there take place. The conductor will diminish the quantity of electri- 

 city in the cloud, but it will not of its own attractive power determine 

 the entire charge to itself. In this manner we can account for the 

 circumstance stated by Mr. Faraday, that there is some evidence to 

 shew that the number of discharges in any given locality is dimi- 

 nished by the presence of conductors, since these may often operate 

 on charged clouds so as to diminish their electricity, and keep them 

 under " the point of discharge," if we may use such a term for that point 

 in the scale of electrical accumulation at which disruptive discharge 

 takes place. That the conductor is not so completely passive as the 

 water pipe which collects a portion of the falling rain, we think there 

 are grounds for believing, and some attractive influence appears to be 

 involved in the property possessed by copper conductors of " not 

 only conducting the shock better, but in the predetermination of the 

 stroke, or determining more of the electricity to themselves, than would 

 otherwise fall upon them." 



We cannot conceive such a property existing independent of some 

 power of attraction resident in the body possessing it, and if copper 

 attracts the electricity in some degree, as the above would imply, so 



