300 Mr. James Wimsliurst [April 27. 



WEEKLY EVENING MEETING, 



Friday, April 27, 1888. 



William Huggins, Esq. D.C.L. LL.D. F.R.S. Vice-President, 

 in the Chair. 



James Wimshurst, Esq. M.B.L 



Electrical Influence Machines. 



I HAVE the honour this evening of addressing a few remarks to you upon 

 the subject of influence machines, and the manner in which I ju-oposc 

 to treat the subject is to state as shortly as possible, first, the histori- 

 cal portion, and afterwards to point out the prominent characteristics 

 of the later and more commonly known machines. The diagrams 

 upon the screen will assist the eye to the general form of the typical 

 machines, but I fear that want of time will prevent me from explaining 

 each of them. 



In 1762 Wilcke described a simple apparatus which produced 

 electrical charges by influence, or induction, and following this the 

 great Italian scientist, Alexander Volta, in 1775 gave the elcctro- 

 phorus the form which it retains to the ju'esent day. This apparatus 

 may be viewed as containing the germ of the principle of all influence 

 machines yet constructed. 



Another step in the development was the invention of the doubler 

 by Bennet in 1786. He constructed metal plates which were thickly 

 varnished, and were supported by insulating handles, and which were 

 manipulated so as to increase a small initial charge. It may be 

 better for me to here explain the process of building up an increased 

 charge by electrical influence, for the same principle holds in all of 

 the mauy forms of influence machines. 



This Volta electrophorus, and these three blackboards, will serve 

 for the purpose. I first excite the electrophorus in the usual manner, 

 and you see that it then influences a charge in its top plate ; the 

 charge in the resinous compound is known as negative, while the 

 charge induced in its top plate is known as positive. I now show you 

 by this electroscope that these charges are unlike in character. Both 

 charges are, however, small, and Bennet used the following system to 

 increase them. 



Let these three boards represent Bennet's three j^lates. To plate 

 No. 1 he imparted a positive charge, and with it he induced a negative 

 charge in plate No. 2. Then with plate No. 2 he induced a positive 

 charge in plate No. 3. He then placed the plates Nos. 1 and 3 

 together, by which combination he had two positive charges within 

 practically the same space, and with these two charges he induced a 



