ELECTRICITY. 369 



not very strong, may occasion several disagreeable 

 accidents. In making the discharge, care must be 

 taken that the discharging-rod be not placed on 

 the thinnest part of the glass; for that may cause 

 the bursting of the jar. 



When a large battery is discharged, jars will be 

 often found broken in it, which burst at the time 

 of the discharge. To avoid this inconvenience, 

 never discharge the battery through a good con- 

 ductor, except the circuit be at least five feet long. 

 Mr. Nairne says, that ever since he made use 

 of this precaution, he discharged a very large 

 battery near 100 times, without ever breaking a 

 single jar ; whereas, before he was continually 

 breaking them. But here it must be considered, 

 that the length of the circuit weakens the force of 

 the shock proportionably ; the highest degree of 

 which is in many experiments required. 



It is advisable, when a jar, and especially a bat- 

 tery, has been discharged, not to touch its wires 

 with the hand before the discharging-rod be applied 

 to its sides a second, and even a third time; as 

 there generally remains a residuum of the charge: 

 this residuum is occasioned by the electricity, 

 which, when the jar is charging, spreads itself over 

 the uncoated part of the glass near the coating, 

 which will not be discharged at first, but gradually 

 returns to the coating after the first discharge, 

 which is sometimes very considerable. 



When any experiment is to be performed, which 

 requires but a small part of the apparatus, the re- 

 maining part of it should be placed at a distance 

 from the machine, the prime conductor, and even 

 from the table, if that is not very large. Candles, 

 particularly, should be placed at a considerable dis- 

 tance from the prime conductor; for the attraction 



VOL. I. B K 



