1888.] on Electrical Influence Machines. 301 



double cLargc in plato No. 2. This process was continued until the 

 desired degree of increase was obtained. I will not go through the 

 l^rocess of actually building up a charge by such means, for it would 

 take more time than I can spare. 



In 1787 Carvallo discovered the very important fact, that metal 

 plates when insulated, always acquire slight charges of electricity ; 

 folio wiDg up those two imj^ortant discoveries of Bennet and Carvallo, 

 Nicholson in 1788 constructed an apparatus, having two discs of metal 

 insulated and fixed in the same plane. Then by means of a spindle 

 aud handle, a third disc, also insulated, was made to revolve near to 

 the two fixed discs, metallic touches being fixed in suitable positions. 

 With this api^aratus he found that small residual charges might 

 readily be increased. It is in this simple aj^paratus that we have the 

 parent of influence machines (Diagram 1), and as it is now a hundred 

 years since Nicholson described this machine in the Phil. Trans., I 

 think it well worth showing a large sized Nicholson machine at work 

 to-night. 



In 1823 Eonalds described a machine in which the moving disc was 

 attached to and worked by the pendulum of a clock. It was a modi- 

 fication of Nicholson's doubler, and he used it to supply electricity for 

 telegraph working. For some years after these machines were 

 invented no important advance appears to have been made, and I think 

 this may be attributed to the great discoveries in galvanic electricity 

 which were made about the commencement of this century by Galvani 

 and Volta, followed in 1831 to 1857 by the magnificent discoveries of 

 Faraday in electro-magnetism, electro-chemistry, and electro-optics, 

 aud no real improvement was made in influence machines till 1860, 

 in which year Varley patented a form of machine shown in Diagram 2. 

 It also was designed for telegraj^h working. 



In 1865 the subject was taken up with vigour in Germany by 

 Toei^ler, Holtz, and other eminent men. The most prominent of the 

 machines made by them are figured in the Diagrams 3 to 6, but time 

 will not admit of my giving an explanation of the many points of 

 interest in them ; it being my wish to show you at work such of the 

 machines as 1 may be able, and to make some observations upon 

 them. 



In 1866 Bertsch invented a machine, but not of the multiplying 

 type ; and in 1867 Sir William Thomson invented the form of 

 machine shown in Diagram 7, which, for the purpose of maintaining 

 a constant potential in a Leyden jar, is exceedingly useful. 



The Carre machine was invented in 1868, and in 1880 the Voss 

 machine was introduced, since which time the latter has found a place 

 in many laboratories. It closely resembles the Varley machine in 

 appearance, and the Toepler machine in construction. 



In condensing this part of my subject, I have had to omit many 

 prominent names and much interesting subject matter, but I must 

 state that in placing what I have before you, many of my scientific 

 friends have been ready to help and to contribute, and, as an instance 



