600 WINTER'S ELECTRICAL MACHINE. 



The quantity of electricity which may be accumu- 

 lated on a conductor depends on its size; more electri- 

 city is clearly required to produce a given electrical ten- 

 sion at any point of the surface of a large conductor than 

 to produce the same tension on a small conductor. For a 

 long spark, quantity as well as high tension is requisite, 

 hence the sparks from a large conductor follow each 

 other at longer intervals of time than those from a small 

 one ; but as each spark is due to a much larger quantity 

 of electricity, they are louder and much more power- 

 ful. 



The surface of the conductor may be increased by 

 inserting in its upper opening a large wooden ring, 

 shown in fig. 317, provided with a short handle. Wood 

 is not a good conductor; the ring contains, therefore, a 

 core of iron wire, which communicates at the end of 

 the handle with the conductor. The wooden ring con- 

 sists of two halves, with a groove in each; the iron ring 

 is placed in the groove of one half of the ring, and the 

 other half is glued upon it. 



When the ring is placed upon the conductor, the 

 sparks follow each other much more slowly than 

 without the ring, but not only is their length and 

 brilliancy considerably greater, but they are also louder 

 and brighter and produce a stronger shock. 



The forms of electrical sparks are best observed at 

 night in a perfectly dark room. The bright, loud- 

 cracking sparks from the large ball form always a 

 single line, white or light blue, and mostly straight. 

 The sparks from the small ball are usually of a reddish 

 or violet colour, and have the form of a bush without 

 leaves, with a short single trunk, branches, and twigs. 



