No. 8. 



Lightning Rods, — JVo. 1. 



251 



cause it to approach the electrified ball a., 

 so as just to come within the influence of 

 its atmosphere, the electricity of «, will re- 

 pel the natural quanlily possessed by i, to 

 the opposite side, where it will form a local 

 atmosphere, c. If the finger be approached 

 to this part, a spark will be received without 

 diminishing the charge of a., but on remov- 

 ing b, it will be found negatively charged, 

 and will more readily receive a spark from 

 a, than before. 



29. If instead of the ball we now present 

 a pointed body, d, fig. 12, the same thing 



Fig. 12. 



^^.A ^^^m 





will take place. But the point immediately 

 receives more electricity from a, — another 

 spark is given, and another, and another, 

 until a, is completely discharged. But if 

 instead of applying the finger to d, we at- 

 tach a conducting wire e, to it, so as to com- 

 municate with the earth, we have all the 

 conditions mentioned (21) and a, is silently 

 discharged. 



30. Instead of the point d, we may next 

 substitute a double point, as e, fig. 13, and 



Fig. 13. 





-//i/ii'ji'W 



I 



it will discharge a, without the intervention 

 of a conducting rod. The nearest point 

 will receive the fluid from a, (21) and the 

 more distant one will disperse it, (26.) 



31. If we insulate and electrify a thin, 

 narrow, metallic tube, a, fig. 14, it will bo 



Fig. 14. 



found that the charge does not enter the 

 tube, but occupies the outside only. This 

 is owing to the mutual repulsion of the por- 

 tions of the fluid on opposing sides of the 

 instrument. As the tube is increased in 

 width proportioned to its length, as at 6, a 

 portion of the charge will enter upon its 

 inner surface, and still more as it approaches 

 nearer to the form of a ring, c. 



32. As the quantity and intensity of the 

 charge which any body is capable of receiv- 

 ing — other circumstances equal — are in pro- 

 portion to the quantity of matter which it 

 contains, (16); Hence if a, and 6, fig. 15, 

 Fig. 15. 









\\\\\t- 







represent cross sections of two charged bo- 

 dies, one tubular and the other solid, it must 

 be evident that the latter will hold a charge 

 of many times greater intensity than the 

 former. 



33. Take two similar balls, fig. 16, and 

 electrify them, one positively and the other 

 negatively. Each one alone will present 

 electrical phenomena, but when brought 

 near together, their atmospheres will sud- 



