VOL. 1.X1II.] PHILOSOPHICAL TRANSACTIONS. 375 



Experience, which is our best guide in all physical inquiries, but particularly 

 in electrical ones, every day convinces me, that we know but little of that subtile 

 fluid, which operates so secretly, and at the same time so powerfully, on the 

 earth, and its atmosphere I confess that I am even now less acquainted with the 

 principle of its action, than I thought I was 20 years ago; the smallest 

 differences in the circumstances of our experiments, frequently causing very 

 material differences in their results. And perhaps no one, who has not applied 

 his mind closely to inquiries of this kind, could conceive how the pointing a 

 piece of metal, or not, should make any material difference in the experiment. 

 The electrician has it always in his power to convince any one of the fact, who,, 

 through inexperience, may be inclined to entertain the least scruple about it: 

 for even from those experiments to which it was thought proper to appeal qt the 

 committee, it appeared, that the difference in the effects on this fluid, between 

 pointed and blunted metal, is as 12 to 1 . 



A thunder cloud therefore, according to that reasoning, (the circumstances of 

 it being supposai to be nearly similar to what is called the prime conductor in 

 those experiments), if it acted at 1200 yards distance on a point, would require 

 a blunted end to be brought within the distance of 100 yards; and beyond those 

 limits, would pass over it, without affecting it at all. On this occasion permit 

 me to observe, that the longer the conductors are above any building, the more 

 danger is to be apprehended from them ; as they will in that case approximate 

 nearer in their effects to those that are pointed. And that is one reason why I 

 was not for advising the proposed conductors at Purfleet, to be so high as 10 feet 

 above the magazines, and more particularly on that building called the board- 

 house, which stands considerably higher than the magazines themselves. 



But, before we advance further into this subject, it may be proper to show the 

 reasons for introducing a pointed apparatus, when the experiment on lightning 

 was first proposed: what good consequences were derived from that experiment: 

 and why, on further experiments and observations, such points ought now to be 

 laid aside, when our intention is not to make electrical experiments, but by the 

 means of conductors, to preserve buildings from the dangerous effects of 

 lightning. 



Dr. Franklin, in his conjectures, that lightning and electricity were one and 

 the same fluid, considered how he should invite, or bring down and collect the 

 lightning, so as to make experiments on it. And he concluded, from observation, 

 that the likeliest method would be, to make use of such an apparatus for the 

 purpose, as was most susceptible of electric effects; or, in other words, such an 

 apparatus as would receive the electric fluid with the greatest ease. Repeated 

 experiments taught him, that metals had the property of receiving that fluid, 

 with more ease than other substances. He also learnt, from the like experience. 



