ELECTRICITY. o c 23 



der ; but its power is vastly increased by laying 

 upon it a little amalgam of zinc. 



Globes of glass have also been used for electrical 

 machines; and sometimes multiplying-wheels have 

 been employed for producing a greater velocity of 

 rotation, but these have not been found to answer 

 so well as cylinders. 



Plates of glass are also used for t:r!s purpose ; 

 and when properly constructed, appear to be the 

 most powerful of any. They are more compact, 

 and are less liable to be affected by damp. The 

 simplest construction of the plate machine is re- 

 presented Plate 18. fig. 2. A B C D M is a wooden 

 frame, to which the four rubbers are affixed by 

 means of the screws g g, and may be made to bear 

 with proper pressure upon the circular glass-plate 

 H K. This plate has a hole through its middle, 

 to which an axis is firmly fixed, and is turned by 

 the winch L. The prime conductor I, which may 

 be fixed on the stand of the machine or not, as 

 thought proper, has a branched termination, which 

 points at the extremities, which collect the elec- 

 tric fluid from the forepart of the glass plate. 



Some plate machines have been made with two 

 glass plates and eight rubbers, and when they are 

 constructed in the best manner, as by Mr. Cuth- 

 bertson, their power is very great. Indeed, the 

 most powerful electrical machine now extant is 

 one of this construction made by the above-men- 

 tioned instrument-maker, at Haerlem. This ma- 

 chine consists of two circular plates, each 65 inches 

 in diameter, fixed on an axis parallel to each other, 

 and 7j inches asunder. Each plate is excited by 

 four rubbers : the prime conductor is divided into 

 two branches, which enter between the plates, and 



y 2 



