ELECTRICITY. 379 



_, ^ , . The receiver of electricitv from an electrical machine is 



What Is the 



conductor i.f Called the prime conductor. It usually consists of a thin brass 



machin^*'"'^ cylinder, or a brass rod, mounted on a glass pillar, or some 



other insulating material. 



To put the electrical machine in good order, every part must be dry and 



clean, because dust or moisture would, by their conducting power, diSiise the 



electric fluid as fast as accumulated. As a general rule, it is highly essential 



that the atmosphere should be in a dry state when electrical experiments are 



made, as the conducting property of moist air prevents the collection of a sui^ 



ficient amount of electricity for the production of striking effects. In tliO 



winter, the experiments succeed best when performed in the vicinity of a 



fire ; and it is advisable to place the apparatus in front of the fire for some 



lime before it is employed. 



^ . . . Electricitv is developed bv the action of an electrical ma- 



Explam the , . . " . „ , ' ... • , , 



method in chine m essentially tue same manner as it is m a simple glass 



which an elec- j^j^g jjy fi-iction. When the glass cvlinder or plate is turned 

 tncil machine ■' c . r 



develops elec- round by the handle, the friction between the glass and- the 

 tricityf rubber excites electricity; positive electricity being developed 



upon the glass, and negative upon the rubber. When the points of the prime 

 conductor are presented to the revolving glass plafe or cylinder, the positive 

 electricity is immediately transferred to it, and it emits sparks to any conduct- 

 ing substance brought near. The electricity thus abundantly excited is sup- 

 plied from the earth to the rubber (by means of a chain extending to the 

 ground), and the rubber is continually having its supply drawn from it by the 

 force called into action by friction with the glass. That the electricity is de- 

 rived from this source is evident from tlie fact that but a small quantity of 

 electricity can be excited when the metallic connection between the rubber 

 and the ground is removed. For this reason the chain must always bo 

 attached to the rubber when it is desired to develop positive electricity, and 

 to the prime conductor when negative electricity is required. 



According to the theory of a single fluid, the excitement of electricity is as 

 follows : — the friction of the glass and silk, by disturbing the electrical equi- 

 librium deprives the rubber of its natural quantity of electricity, and it is 

 therefore left in a negative state, unless a fresh quantity be continually drawn 

 from the earth to supply its place. The surplus quantity is collected on the 

 prime conductor, which thereby becomes charged with positive electricity. 

 On the hypothesis of two electric fluids, the same frictional action causes 

 the separation of the vitreous from the resinous electricity in the nibber, which 

 therefore remains rosinously charged, unless there be a connection with the 

 earth to restore the proportion of vitreous electricity of which the rubber has 

 been deprived. 



Various other arrangements have been devised for the pro- 



boUer'be'uspd duction and accumulation of electricity. High-pressure steam 



as an electrical escaping from a steam-boiler carries with it minute particles 



of water, and the friction of these against the surface of the 



jet from which the steam issues produces electricity in great abundance. A 



