ELECTRICITY. 481 



accumulated upon the glass, and the resinous upon the 

 rubber. It is plain, that the form of the glass is not ma- 

 terial, excepting that one form may more easily be mount- 

 ed than another. The most common form is a cylinder 

 or a jar. Any common open mouthed jar will answer 

 for this purpose. Sometimes plate glass is used. The 

 advantage of this is that a rubber may be applied to each 

 side of the glass, which increases the effect. A plate ma- 

 chine is however much more liable to be broken, and is 

 consequently less frequently used. The axis upon which 

 the glass turns may rest upon wooden supports. It is 

 desirable however that the rubber should be supported 

 by a glass pillar, for reasons which will hereafter be ex- 

 plained. The forms which the electrical machine has 

 assumed are very various. Different artists have arrang- 

 ed the parts to suit their own fancy, or the particular 

 purpose for which each machine is intended. Almost 

 all electrical machines, however, consist essentially of 

 glass cylinders or plates, put into rapid motions by means 

 of a crank, so that a great amount of friction may be se- 

 cured with as little labor as possible to the operator. 

 This is all that is essential, and by understanding this 

 general principle, the reader can, by inspection, clearly 

 comprehend the details of any particular machine which 

 he may have the opportunity of examining. 



The electricity thus accumulated upon the glass of the 

 electric machine is received usually upon a metallic cy- 

 linder, which is a sort of reservoir, where the fluid is pre- 

 served for use. From this cylinder which is called the 

 prluK: conductor, there proceed a number of sharp metal' 

 lie points, by which the electricity passes off from the 

 glass cylinder to the conductor. The reason why these 

 points are used will be hereafter explained. The prime 

 conductor may be made of any substance, provided that 

 it has an external surface of metal. Sometimes it is 

 made of wood, and coated with sheet lead or tin foil. 

 Sometimes it is of tin or brass plate, and hollow. The 

 writer of this tract once constructed a large one, five 

 feet long, and eight or ten inches in diameter, of thin 

 pine boards, put together like the staves of a barrel, 

 and coated with sheet lead. The prime conductor may 



