DefcAption of the Revohwg DoubUir. ^g 



XI. 



Dtfcription of the Revolving Doubter. W. N. 



A. 



1.S the doubler of Bennet, to which I adapted the following machinery in the year 

 1788, is not yet generally noticed in elementary works, and, confequently, little known, 

 I have thought it might be acceptable to copy the fhort Defcription and Plate from my 

 paper in the LXXVIIIth volume of the Philofophical Tranfaftions. 



Plate IV. reprefents the apparatus of the doubler fupported on a glafs pillar 6i inches 

 long. It confifts of the following parts. Two fixed plates of brafs, A and C, are fepa- 

 rately infulated and difpofed in the fame plane, fo that a revolving plate B may pafs very 

 near them, without touching. Each of thefe plates is two inches in diameter ; and they 

 have adjufting pieces behind, which ferve to place them accurately in the required pofition,. 

 D is a brafs ball, likewife of two inches diameter, fixed on the extremity of an axis-that 

 carries the plate B. Befides the more eflential purpofe this ball is intended to anfwer, it 

 is fo loaded within on one fide, that it ferves as a counterpoife to the revolving plate, and 

 enables the axis to remain at reft in any pofition. The other parts may be diftindlly feen 

 in fig. 2. The (haded parts reprefcnt metal and the white reprefent varniflied glafs. ON 

 is a brafs axis, pafling through the piece M, which laft fuftains the plates A and C. At 

 one extremity is the ball D already mentioned ; and the other is prolonged by the addition 

 of a glafs ftick, which fuftains the handle L and the piece GH feparately infulated. E, F, 

 are pins rifing out of the fixed plates A and C,'at unequal diftances from the axis. The 

 crofs-piece GH, and the piece K, lie in one plane, and have their ends armed with fmall 

 pieces of harpfichord-wire, that they may perfeftly , touch the pins EF in certain points 

 of the revolution. There is likewife a pin I, in the piece M, which intercept a fmall 

 wire proceeding from the revolving plate B. 



The touching wires are fo adjufted, by bending, that when the revolving plate B is im- 

 mediately oppofite the fixed plate A, the crofs piece GH connefls the two fixed plates, at 

 the fame time that the wire and pin at I form a communication between the revolving 

 plate and the ball. On the other hand, when the revolving plate is immediately oppofite 

 the fixed plate C, the ball becomes conneded with this laft plate, by the touching of the 

 piece K againft F; the two plates, A and B, having then no connedion with any part of 

 the apparatus. In every other pofition the three plates and the ball will be perfedly un- 

 Gonnefled with each other. 



Mr. Cavallo's difcovery, fo well explained in the laft Bakerian Ledure, that the minute 

 differences of the eledrization in bodies, whether occafioned by art or nature, cannot be 

 completely deftroyed in any definite time, may be applied to explain the a£lion of the 

 prefent inftrument. When the plates A and B are oppofite each other, two fixed plates 

 A and C may be confidered as one mafs ; and the revolving plate B, together with the ball 



