MACHINE, ELECTRIC. 



which communicated with the prime con- 

 ductor, during the electrization, will have 

 a like electricity, and the other the con- 

 trary. Take off the electricity of the 

 plates of metal, and carefully replace the 

 glass on the lower, without destroying 

 the insulation, and also replace the upper 

 plate with ti.e same precaution. Then, 

 with one end of an insulated wire, not 

 pointed, but knobbed ai the ends, touch 

 one of the plates, and bring the other end 

 near the other plate: the consequence 

 will be, that a strong and loud spark will 

 pass between it and the wire, the electri- 

 ty ot" the giuss will be discharged, and 

 the plates and the wire will exhibit tew 

 or no signs of electricity. 



An electric body, the surfaces of which 

 are thus possessed of the contrary elec- 

 tricities, is said to be charged. The insu- 

 lation of the lower metallic plate, and of 

 the dischaiging wire is not necessary, ex- 

 cept for ihe purpose of drawing inferen- 

 ces, respecting the manner of charging 

 the electric plate. If the electricity of the 

 prime conductor be strong, and the glass 

 thick, the discharge wilt often be made by 

 a spark from the one metallic plate to the 

 other, over the surface of the glass winch 

 projects on every side ; but if the glass 

 plate be thin, in which case, at an equal 

 intensity, it admits of a much greater 

 charge, the discharge will be made 

 through its substance. Glass, as thick 

 as one eighth of an inch, may be pene- 

 trated by this means, one or more holes 

 being made where the electric matter 

 lias passed, in which holes the glass is 

 pulverised, and may be picked out with 

 a pin. 



It is not possible to charge an electric 

 plate by inducing an electric state on one 

 of its surfaces, unless the other be at the 

 same time sufficiently near to a non-elec- 

 tric to assume the contrary state, by emit- 

 ting or receiving the electric matter. 



If a plate of glass be laid upon an un- 

 insulated plate of metal, the upper sur- 

 face may be rendered electric by friction, 

 or by applying an electrified body succes- 

 sively to its parts. This electricity may 

 be taken off by touching the upper sur- 

 face with an uninsulated metallic plate of 

 the same dimensions as that upon which 

 the glass is placed, but will not be entire- 

 ly taken off, because the communication 

 between the two surfaces in this method 

 is not perfect, and because the metal can- 

 not by ordinary means be brought into 

 actual contact with the glass. The small 

 quantity which remains, produces an ef- 

 fect which has been mistaken for a per- 



petual electricity. For if a plate of me. 

 tal, to which a glass handle is affixed, be 

 laid upon the glass, this small quantity of 

 electricity will influence the melal, and, 

 without actually communicating the elec- 

 tric matter, will cause it to exhibit a simi- 

 lar state. If this be taken off, by drawing 

 the spark, and the metal then removed, 

 by means of the glass handle, it will be 

 found possessed of the contrary state of 

 electricity, and another spark may be ob- 

 tained. The metallic plate may be then 

 again applied to the surface of the glass, 

 and the process again repeated, and so on 

 for a prodigious number of thncs, with- 

 out any sensible difference in the event. 

 For the electricity at the surface of the 

 glass being almost in the natural state, as 

 to condensation, docs not disappear for a 

 very long time, and the very near ap- 

 proach of the metal enables it to produce 

 the same effect as would be obtained at a 

 greater distance from a stronger electri- 

 city. This is made obvious, by bringing 

 the metallic plate near the surface of the 

 glass before its first strong electricity is 

 taken off, for the same event is then per- 

 ceived at the distance of four, five, or six 

 inches, as in the former case is produced 

 by contact. 



The vapours of the atmosphere are con- 

 tinually attaching themselves to the sur- 

 face of cold glass, and by that means de- 

 stroy the electricity. Sulphur, wax, or 

 resin, being less subject to this, retain 

 their electric state much longer. A plate 

 of glass or wood, coated over with any 

 substance of this nature, may be excited 

 by friction, and will produce electricity 

 in a metallic plate, in the manner above 

 described, for a very great length of 

 time. Such a plate, together with its me- 

 tal, has been named the electropho- 

 phorus, fig. 3. 



If the discharge of an electrified plate 

 be made by the parts of a living animal, a 

 considerable pain will be felt, chiefly at 

 the extremities of the muscles. For ex- 

 ample, if the lower mt.JJic plate be 

 touched with one hand, and the other 

 brought to the upper plate, at the instant 

 of the emission, a pain will be felt at the 

 wrist and elbows, which as instantly va- 

 nishes. If a larger glass plate be used, 

 the pain will be felt on the breast ; if yet 

 larger, the sensation will be that of a uni- 

 versal blow. This sensation has obtained 

 the name of the shock, and will deprive 

 animals of life, if sufficiently strong. The 

 shock from thirty square inches of glass, 

 well charged, will instantly kill mice, 

 sparrows, or other small animals. Six 



