508 Mr. J. Wimshurst on an Alternating and 



corner and the lower left-hand corner : the rotating disk is 

 therefore covered for one half of its surface upon both of its sides. 



The brushes are made of fine brass wire, and the brush- 

 holders are brass rods^ bent to a form to admit of the brushes 

 touching the rotating disk at a point opposite to the middle of 

 the next following induction-plate ; this arrangement supplies 

 two brushes to each side of the disk, and the brushes when 

 in place are situated 180° asunder. 



The several parts of the machine are interchangeable, and 

 by means of the varied combinations many experiments can 

 be made ; in fact its combinations include nearly every type of 

 electrical influence-machine. 



The prominent results obtained from it are : — (1) That glass 

 disks which have no metal upon them are freely self-exciting. 

 (2) That the freedom to self-excitement increases about pro- 

 portionally to the number of sectors. (3) That the quantity 

 of electricity decreases with the amount of metal upon the 

 disk — whether the amount be in the greater number of 

 sectors, or the increased size of sector (chiefly the latter). 



The only tests as to when the alternations occur which I 

 have been able to make were made by means of a sensitive 

 arrangement of light paper disks, suspended by fine wire. 

 When this apparatus is connected to one of the inductors, and 

 the glass disk turned very slowly, the alternations are seen to 

 occur with each f revolution of the disk ; when the disk is 

 turned much faster, then the alternations occur too rapidly for 

 the paper disks to respond, and they hang motionless and 

 nearly together. 



It is not possible to obtain any sensible charge in a Leyden 

 jar, although the electricity may be clearly seen as a stream 

 between the jar and the inductor. 



Another series of combinations may be made by removing 

 the two inductor-plates from the back of the machine and 

 substituting an insulating arm extending across the disk, it 

 having wire brushes at its ends, the brushes being connected 

 metallically with terminal balls. When this combination is in 

 use the charges no longer alternate unless the terminal balls 

 are separated beyond the sparking distance. The plain glass 

 disk without metal sectors, and also the disks having large 

 sectors upon them, are no longer self -exciting. The glass disk 

 having 16 sectors upon one side is not self-exciting when 

 placed so that the sectors touch the brushes of the inductors, but 

 when placed so that the sectors touch the brushes of the insula- 

 ting arm it then becomes freely self-exciting. All disks having 

 medium-sized sectors :upon each side are freely self-exciting. 



I have noted many of these results in tabular form. 



