1891.J the Discharge of Ley den Jars. 19 



overflow discharge prefers. It takes it in preference to a metal rod 

 of twice the apparent elevation, and strikes down right through the 

 flame. 



But though it thus readily smashes a weak dielectric, it will not 

 take a bad conductor. A wet string or water tube may, in fact, 

 reach right up till it touches the top plate, and yet receive no flash, 

 while the other things shall be getting struck all the time. 



When the striking distance is too great for a noisy flash, a crowd 

 of violet brushes spit between the top plate and protuberances on the 

 lower plate : reminding one of some lightning photographs. The 

 effect is still more marked if the top plate is a reservoir of water with 

 a perforated bottom. The rain shower increases the length of these 

 multiple gentle high-resistance purple discharges. Adding salt to the 

 water tends to bring about the ordinary noisy white flash of great 

 length. 



Contrast "between Path of Discharge under circumstances of Hurry and 



Leisure. 



21. "When the plates are arranged as in fig. 9, so that until an A 

 spark occurs they are at the same potential and are then filled by a 

 sudden and overflowing rush of electricity, all good-conducting 

 things of the same height struck equally well, independently of their 

 shape. 



But when, on the other hand, the difference of potential between 

 the plates was established gradually, as in fig. 10, so that the strain 



FIG. 10. 



in the dielectric had time to pre-arrange a path of least resistance, then 

 small knobs got struck in great preference to big ones, and points 

 could not be struck at all, because they take the discharge quietly. 



An intermediate case is when the charge and discharge of the top 

 plate is brought about by pulling a lever over with string, so as to 

 connect it with the jar, as in fig. 11. 



c 2 



