438 Exferimtnt! en the Chargt ef a P'ate of Air, i^c. 



Therefore the metaHio rod, which reprefents the conduftor, remaining as in the laft cafe; 

 the metallic ball which was connected with tlie comniur.icatlon between the interior cylin- 

 ders has now a fcparate communication with the earth only. 



RESULT. 



WHEN the condu(^or was terminated by a point, and the cloud pafTcd near it ; fome 

 weak fparks paflcd from it to the point on the conductor. If the cloud paflid at a greater 

 diftance, no fparks appeared, but the electricity on the tinfoiled cylinders was dLniiniflied 

 as in the former cafes. 



When the conduftor was terminated by a ball, weak fparks palTcd between the cloud and 

 the ball, and the cleftricity of the tinfoiled cylinders decrcafed ; but when the cloud pafled 

 at a diftance above the point at which no fparks paflcd, there was no variation to be obferved 

 in the eleflrlcity of the charged air. 



In this cafe no' fparks pafled in the interval between the balls where the rofin was placed. 



To the three cafes already eihlbited, a fourth may be added, to (hew that the lightning 

 may have pafled to the damaged part of the building without having ftruck the condudor. 



Ahhough a conductor may be extended to a confiderable diftance above the building, yet 

 fome part of the Bpper furface of the body of charged air may approach as near to fome of 

 the metallic fubftances belonging to the building as to the condudor ; and which may be ex- 

 hibited in this cafe in two parts. 



CASE IV.— Part I. 



THE metallic rod, which reprefents the conductor, has a perfect communication with the 

 earth only -, the glafs tube fifled with water, which connefted it with one of the infulated 

 balls, being removed. The other metallic rod, which is to reprefent any pointed metallic 

 fubftance, is placed upon an infulated ftand, and isconnedled by a metallic communication 

 with the infulated ball to which the tube of water had been attached; the other infulated 

 ball remaining conneded with the communication between the interior cylinders as before. 



The lower furface of the body of charged air is here fuppoled not to extend over the 

 conductor, or over the' other metallic body, but to extend over fome fubftance within ftrik- 

 ing diftance of it. 



That the cloud might pafs at nearly the fame diftance from the point on tho metallic rod 

 as from the conductor, the point on the metallic rod was fixed nearly at the fame height as 

 the upper extremity of the conduftor. 



RESULT. 



WHETHER the condu£Vor was terminated by a point or by a balJ, and the cloud paflfed 

 near to it as well as to the point upon the metallic rod, fometimes the conductor was ftruck, 

 fometimes the point upon the metallic rod was ftruck, and which inftantly fet fire to the 

 rofin betv/ecn the balls. 



Sometimes, when a fpark paflTed between the cloud and conductor, and no fpark upon (he 

 point of the other metallic rod ; fparks would appear between the infulated balls, and of fuf- 

 ficient fticngth fometimes to light the rofin. 



Thefc 



