Alternating and Experimental Influence- Machine. 507 



form has four pairs of half-disks. The Blondlot and Curie 

 form also reads power directly, but the needle is made in two 

 insulated portions, and needs two metallic connexions, and 

 this gives rise to mechanical troubles and loss of sensitiveness. 

 The instrument shown in fig. 3 has the needle all in one 

 piece, and the disks can be so far apart that errors from varia- 

 tions of height of the needle due to variations of the length of 

 the fibre do not become serious. A long suspension of phos- 

 phor-bronze wire is, however, preferable for most purposes. 



LXIII. Alternating and Experimental Influence-Machine. By 

 Mr. James Wimshurst, Member of Council*. 



I HAVE pleasure in bringing to your notice a new form of 

 influence-machine which is self-exciting, notwithstanding 

 that when at work its electrical charges alternate during each 

 revolution. 



In order that you may readily follow the action of the 

 machine when at work I will first describe its construction in 

 all its details. 



It consists of a base or frame, from the sides of which rise 

 the standards to carry the spindle and boss for the rotating 

 disk, suitable driving gear being fixed thereto. 



In the same plane as the rotating disk is fixed a square 

 wooden frame having the necessary holes, plugs, and clamps, 

 by means of which the inductor-plates are held in position. 



The rotating disks are cut from ordinary window glass, and 

 are coated with shellac ; they are 16 inches in diameter ; one of 

 them has no metal upon it, the next has four medium-sized 

 tin-foil sectors upon each of its sides, the last of this series has 

 16 sectors upon each side ; other disks have from 2 to 4 sectors 

 of large size upon them ; another disk has four large 

 sectors upon each side, so placed that the sectors upon 

 one side cover those upon the other side ; another has four 

 very narrow sectors upon each side, and another has 16 sectors 

 all upon the one side. 



The inductor-plates are squares of glass measuring 9 j inches; 

 one corner of the plate is cut away to admit the spindle and 

 the boss. They are coated with shellac, and upon one side of 

 each of them is a tin-foil patch, and a suitable device for hold- 

 ing the rod and the brush. 



Two of these inductor-plates are mounted at the diagonal 

 corners, upou one side of the wooden frame, and two upon the 

 other side of the frame ; those at the front of the machine are 

 at the lower right-hand corner and the upper left-hand corner ; 

 those at the back of the machine are at the upper right-hand 

 * Communicated by the Physical Society: read April 17, 1891. 



