MACHINE, ELECTRIC. 



pressure to be employed, by diminishing 

 the friction, and prevents both the glass 

 and silk from being soiled by the amal- 

 gam, so that the excitement is more 

 powerful, and the amalgam requires to 

 be renewed less frequently. As the semi- 

 circular branch of the prime conductor 

 is moveable, it may be made to exhibit 

 the electricity of the rubber at any time, 

 by placing the cylindrical ends in contact 

 with the cushions, the semicircular wire, 

 I, being at the same time turned so as to 

 cross it at right angles, which insulates 

 the cushions. When the conductor is re- 

 quired to give electricity from the glass, 

 the arc I must be in contact with the 

 cushions, and the arc EE perpendicular 

 to the horizon. 



If the insulated prime conductor of a 

 machine be well polished, and without 

 corners or angles, it will retain its electric 

 state very well, and will emit strong 

 sparks upon the approach of any uninsu- 

 lated conductor. If the uninsulated con- 

 ductor be broad, round, and polished at 

 the end, the sparks will be short and 

 dense, and will produce a considerable 

 sound ; if less broad, the spark will be 

 long, crooked, and less sounding ; if the 

 breadth be still more diminished, the con- 

 ductor begins to come under the deno- 

 mination of a pointed body, the electric 

 matter passes to it from the prime con- 

 ductor, through a great space of air, with 

 a hissing or rustling noise, and in a con- 

 tinual stream : a still greater sharpness 

 enables the electricity to pass over a 

 greater space, but silently, and nothing is 

 seen but a small light upon the point. If 

 a similar point issue from the prime con- 

 ductor, and the uninsulated conductor be 

 round and polished, the same effects hap- 

 pen in like situations; but if both be 

 pointed, the electricity is more readily 

 discharged: and in all these cases the ap- 

 pearance of the electric matter at the 

 point of the prime conductor will be that 

 which is peculiar to its electricity, a large 

 divergent cone, if positive, or a small 

 globular light or cone, if negative, and 

 the light at the point presented to the 

 prime conductor will be distinctive of the 

 contrary electricity. Whether a pointed 

 conductor be electrified positively or ne- 

 gatively, if the nose be brought near the 

 point during the electrixation, a wind will 

 be felt blowing from the point, and the 

 sense will be affected with a sulphureous 

 or phosphoreal smell. 



The reaction of the force by which the 

 air is put into motion, is exerted on the 

 pointed body. This is shewn by a pleas- 



ing experiment with an electrified wire ; 

 thus, to the middle of the wire, or rather 

 between two wires that lie in the same 

 line, is affixed a centre-cap like those 

 used in sea-compasses, so that the wire 

 may easily be moved on a point in a hori- 

 zontal direction, as magnetical needles 

 are : and the ends of the wire are pointed 

 and bent contrary ways, to point in the 

 direction of the tangent to the circle de- 

 scribed by them. Now if this wire, thus 

 suspended on a point, be insulated and 

 electrified, its sharp ends will become lu- 

 minous, and it will revolve in a direction 

 contrary to that in which its ends are bent ; 

 or if it be suspended on an uninsulated 

 point, and brought near the electrified 

 prime conductor, the same effect will fol- 

 low. 



It may be thought strange that the air 

 should issue from an electrified point, 

 whether its electricity be positive or ne- 

 gative. It is easy to conceive that the is. 

 suing out of the electric matter may cause 

 the air to move in the same direction ; but 

 it appears odd, that the electric matter 

 rushing towards a point should cause the 

 air to move directly contrary, that is to 

 say, likewise from the point. If, however, 

 the circumstance be examined more nar- 

 rowly, the difficulty will vanish. For it 

 is highly probable that the electric mat- 

 ter passes too swiftly to excite any mo- 

 tion in the air, but that undulation where- 

 in sound consists ; to which may be add- 

 ed, that if the electric matter do act on 

 the air to put it in motion, the air must 

 react with an equal force ; and, therefore, 

 that a current of air blown against the 

 course of the electric matter must affect 

 its appearance, by retarding the rays and 

 deflecting those against which it struck 

 obliquely : the contrary to which is, by 

 experience, known to obtain ; for the lu- 

 minous cones are not sensibly affected by 

 such treatment. The air being thus in- 

 different as to the motion of the electric 

 matter, its motion may be shewn to depend 

 on the established principles of electrici- 

 ty. The point is electrified either posi- 

 tively or negatively, and the air imme- 

 diately opposite and contiguous to the 

 point, must, by the emission or exhaus- 

 tion of the electric matter, become strong- 

 ly possessed of an electric state of the 

 same kind with that of the point : it 

 is therefore, repelled and replaced by 

 other air which is also electrified and 

 repelled, by which means a constant 

 stream is produced blowing from the 

 point, and that equally, whether the elec- 

 trization be positive or negative. And the 



