GENERAL ACCOUNT OF COMMON PHENOMENA '19 



velocities in opposite directions on the same axes. On the outer 

 faces of the plates are equal numbers of thin brass sectors arranged 

 radially at equal intervals. On the horizontal diameter are the 

 collecting combs connected with the discharging knobs which are 

 placed above the plates. Two small Leyden jars have their inside 

 coatings connected one to each of the collecting combs, while their 

 outside coatings are connected with each other. At 45 or there- 

 abouts to the horizontal, the best position being found by trial, 

 are two neutralising rods, one opposite each face, and nearly at 

 right angles to each other. These terminate in wire brushes which 

 touch the sectors as they revolve. To start the machine most 

 easily, the discharging knobs are placed nearly in contact and the 

 handle is turned. After a few revolutions of the plates, if the 



FIG. 16. 



machine is fairly dry and dust-free, sparks will pass. The knobs 

 may now be separated gradually, and the sparks will continue to pass 

 till the limiting length is passed. Even when the machine will not 

 excite itself it may readily be set iii action by holding an electrified 

 body near one of the brushes on the far side of the plates from it, 

 and then rotating the plates. The Wimshurst is one of the most 

 easily worked and most regular of the influence machines. The 

 explanation of its working can be given most readily by aid of a 

 diagram in which, as represented in Fig. 16, the plates are re- 

 placed by co-axial cylinders. We may then distinguish them as 

 inner and outer. Let us first leave out of account the discharging 

 circuit and suppose only that we have the two neutralising rods 

 m^m v ?t 1 ;? 2 . I,et the plates revolve as in the figure, and let us 

 suppose that in some way, say by friction as it passes the brush n 19 

 a sector at the highest part of the inner plate is slightly positively 

 electrified. As this comes opposite m l it induces on the 

 sectors of the outer plate under m v and sends -+- on to the 



