ELECTRICITY AND GALVANISM. 61 



to describe minutely. The principal article of the elec- 

 trical apparatus is that which is usually called the Elec- 

 trical Machine. A brief description of that used at the 

 present day is here subjoined. 



An Electric Machine consists of a glass cylinder or 

 plate, turned by a winch, and so contrived, that as it is 

 made to revolve, it rubs against a cushion, by which 

 means the glass is excited. An instrument called the 

 prime conductor, generally made of metal, and without 

 points or corners in itself, but having a piece of iron, of 

 several points, inserted at one end (points attracting the 

 fluid much more readily than knobs), and the whole be- 

 ing insulated by means of a glass stand, is placed very 

 near the cylinder or plate, and attracts the electricity to 

 itself as it is excited. On presenting a knob of brass, 

 the knuckle, or any other round conductor, to the prime 

 conductor, at the distance of about an inch, a spark will 

 issue, accompanied with a snapping noise ; if a point be 

 presented, the electricity will be abstracted silently, and 

 the point will in the dark have the appearance of a star. 

 A glass jar, coated on both sides with tinfoil to within 

 about two inches of its top, called the Leyden Jar, is con- 

 nected to the prime conductor by means of a chain com- 

 municating with a wire or chain which passes to the 

 bottom of the jar. The use of the Leyden jar is to col- 

 lect the fluid which is conducted into it through the prime 

 conductor, as it is excited by the friction of the cylinder. 

 A jar charged in this manner has a redundancy of the 

 fluid in the inside ;* then if a knuckle or any other round 

 conductor not insulated be presented to the tinfoil coating 

 on the outside, and a knuckle of the other hand, or any 

 other un-insulated conductor be presented to the knob of 

 the wire at the top of the jar which communicates with the 

 tinfoil coating in the inside, a sudden contraction of the 

 muscles, called a shock, will be experienced, accompanied 

 with a flash of light. The cause of the shock is the sud- 

 den rush of the electricity from the inside to the outside 

 of the jar, in order to obtain its equilibrium. Jf the jar 



* According to the Franklinian theory, electrics always contain an 

 equal quantity of this fluid ; so that there can be no surcharge on one 

 side without a proportional decrease on the other. 



