206 On the Fraciure~qf.JElectrieal Jars 



prime conductor of the electrical machine, one end of a chain 

 being annexed to the wire, while the other end of it descended 

 into the jar and caine in contact with the middle of its bottom, 

 so that the suspended part of the chain was at equal distances 

 from the opposite sides of the jar. The cliain was tlins con- 

 nected with tiie bottom only of the inside coating, in order that the 

 jar might be charged and discharged as nearly as possible under 

 the same circumstances as when it was in the battery; the jars 

 of which have their charging wires in communication with the 

 interior coating at the bottom of each, and nowhere else. The 

 jar being disposed as described above, the object of the first ex- 

 periment was to ascertain how many turns of the wheel were 

 necessary to make it explode spontaneously through the per- 

 foration in its side. 



Exp. 1. — The wheel being turned, on completing its eighth 

 revolution an explosion took place through the perforation in 

 the jar. The charge with which the jar exploded through the 

 perforation being thus known, I now wished to communicate to 

 it the greatest charge it would bear without so exploding ; in 

 order that the jar might be discharged in the usual wav, and 

 that I might observe at the moment of its discharge whether 

 any appearance worthy of notice would occur at the perfora- 

 tion. 



Exp. 2. — The jar was next charged by something more than 

 seven turns of the wheel ; one ball of an insulated discharging 

 rod was then put in contact with its exterior coating at the 

 same height as the perforation, and at about three inches di- 

 stance from it : on making the other ball of the rod approach 

 the ball communicating with the inside of the jar, a vivid spark 

 was seen to pass between the two balls, and at the same mo- 

 ment a similar spark with respect to brilliancy and strength was 

 likewise seen to pass between the interior and exterior coatings 

 of the jar through the perforation in its side. Although the re- 

 sult of this experiment seemed to confirm my conjecture as to 

 the cause of the bursting of the jars before related, yet it oc- 

 curred to me that possibly the spark througli the perforation 

 might have been occasioned by the mode in which the jar had 

 been discharged : to ascertain this, the jar was repeatedly 

 charged as in Exp. 2, and was afterwards discharged by putting 

 one ball of the discharging rod in contact at different times with 

 diiferent parts of its exterior coating, more or less distant from 

 the perforation ; and by bringing the other ball either more 

 slowly or more quickly towards the ball commuiiicating with the 

 inside of the jar ; but in all these instances the same phaeno- 

 niena occurred. Two sparks were always seen to pass simulta- 

 neously ; one between the two balls, and the other between the 



two 



