EKperimenti on the Charge of a Plate of Air, ^e. 4.39 



TTiefe fparks were the vveakeft when the condu£lor was terminated by a point, and 

 much ftronger when it was terminated by a ball. 



This circumftance feemed to (hew, that the paflage of the electrical fluid is not confined 

 to one circuit only. 



CASE IV.— Part II. 

 THE lower furface of the body of charged air is now fuppofed to extend over the con- 

 duftor ; the other metallic fubflances remaining in the fame ftate as before. 



The condu(Slor is now conneftcd with the communication between the interior cylinders. 



RESULT. 



WHEN the cloud pafled near to the conduflor, and alfo within ftriking diftance of the 



point upon the other metallic rod; no explofion or fpark appeared in any of the intervals; 



but the body of air was filently difcharged, as- was (hewn by the eleftrometer : and the fame 



effedl was produced, when, by lowering the point upon the conduftor, the cloud pafled 



.nearer to the point on the metallic rod than to the condu£tor. 



When the conduftor was terminated by a ball, the ball was ftruck when the cloud pafled 

 near to it ; and if the ball was fituated as the point was, fo that the cloud pafled nearer to the 

 point upon the metallic rod than to the ball on the condu6tor, the point on the metallic 

 rod was ftruck, and the rofin inftantly lighted. 



CONCLUSION. 



TROM this experiment it appears to be manifeft, that the advantages arifitig from me- 

 tallic conductors, eredled for the purpofes of fecuriftg buildings from [the efl^efts of light- 

 ning, depend more upon the lower furface of the body of charged air extending over them, 

 than upon their form or confl;ru£lion. 



It is not eafy to decide, from the refult of the experiment, whether they fhould be ter- 

 minated by /iwnr/ or by inZ/x. Probably, with refpe£t to the large operations of nature, 

 there may be no difference. The ball ufed in this experiment is three inches diameter ; 

 the largeft furface of charged air fcarcely exceeded 70 fquare feet': but if fome acres of 

 charged air were brought into aftion, the ball of three inches would foon be reduced to a 

 point. However, as the fubjeft has occafioned much controverfy, we may take the oppor- 

 tunity of invefligating it from the data afforded "by this experiment. 



If we reafon upon what is exhibited in the firft and third Cafes, it is obvious that pointed 

 conduiSlors are to be preferred to thofe terminated by balls. They have the property of afl- 

 ing at a much greater diftance than balls, and have the power of dcftroying, filently, the 

 cffeds of lightning, when balls c^n only accomplifii it by means of an explofion, which 

 muft always be attended with fome danger. 



But if we reafon upon the refult in the fecond Cafe, we fliall find that the power which 

 points have of ailing at a greater diftance than balls, will make them more liable to produce 

 the mlfchief (hewn in that experiment. 



I Under 



