May 3) 1883] 



NA TURE 



*3 



On arriving at the left side it will therefore give up a 

 small positive charge to the left armature, thus charging 

 it more highly than before. Every button as it goes 

 round thus conveys the charges induced in it to the 

 appropriate armatures, and exalts their charge. A very 

 few turns given to the handle suffice to charge those 

 armatures to their fullest extent, so that they begin to 

 discharge pale sparks over the disks. But now begins 

 another action. From right to left in front of the front 

 disk lies an insulating bar of ebonite, holding at each 

 end another brass comb, each connected by a crossbar 

 of brass to the knob of a small Leyden jar. As the 

 charges in the armature rise they act again upon these 

 conductors fixed in front of them, and charge the jars, 

 one positively, the other negatively. A pair of dischargers 

 with ebonite handles serve to discharge the jars when 

 full, and with every turn of the winch, when the knobs of 

 the dischargers are separated bya few centimetres'distance 



a torrent of sparks is generated. If the machine is kept 

 free from damp and dust, no initial charge is necessary, 

 as the slight friction of the brushes suffices to give and 

 sustain the requisite preliminary electrification. 



Wimshurst's influence-machine is even simpler, and if 

 anything, more efficient. It is the result of a long experi- 

 mental research carried out with great care and skill by 

 Mr. J. Wimshurst, who is well known as an accomplished 

 amateur electrician. The latest of the many combina- 

 tions which Mr. Wimshurst has designed is depicted in 

 Fig. 2. It consists of two disks of common window glass 

 mounted upon a common spindle, and provided with driv- 

 ing gear by which an equal speed is given to each, but in 

 opposite directions. Each disk (about fourteen inches in 

 diameter in the smallest size) is well varnished with 

 shellac varnish, and carries twelve narrow strips of thin 

 sheet metal cemented at regular intervals apart. In front, 

 at about 45°, is fixed a diagonal conductor armed at each 



Fig. 2. — Wimshurst's Influence-Machine. 



end with a small brush of metallic bristles, which touch 

 the metal strips as they rotate. At the back a similar 

 diagonal conductor is fixed, exactly at right angles to that : 

 in front. Right and left are two upright pillars of glass ; 

 or ebonite which carry each a pair of metallic combs, 

 and serve also to support the dischargers which are 

 carried in an arch over the disks. It appears that in this 

 machine the metal strips affixed to the plates act both as 

 inductors and as carriers. Suppose, for example, that the 

 front plate is rotating clockwise, and the back plate 

 counter-clockwise. If the metal strips descending from 

 the summit on the left on the back disk are charged posi- 

 tively, the metal strips ascending on the front disk from 

 the left will, as they pass under the momentary touch of 

 the brush, acquire a negative charge. As these negatively 

 charged strips of the front plate advance towards the 

 right they will come to a point where they are opposite 

 the upper end of the hinder diacoral conductor, and 



here, whilst still acting as carriers to bring the negative 

 charge round to the right side, they will act as inductors, 

 and will influence the strips of the back disk, which will, 

 as they are in turn touched by the hinder brush, acquire 

 positive charges. The strips on the front disk will there- 

 fore constantly carry a negative charge as they move 

 over the top from left to right, and those of the back disk 

 will carry a positive charge from right to left. In the 

 lower halves of their respective rotations the inverse of 

 these actions will hold good, the front carriers conveying 

 positive charges from right to left, the back ones convey- 

 ing negative charges from left to right. The result will 

 of course be that the two main conductors on the left and 

 right will become respectively positively and negatively 

 charged. Theoretically, a small initial charge must be im- 

 parted to some one or more of the carriers or to one of the 

 two main conductors. Practically, if dry and free from 

 dust, the machine excites itself, and after a couple of turns 



