II //././ AM S/ EM ENS, F.R.S. 211 



In order [ carry out such a system of supply, it would IKJ 

 -ary i<> have the moans of so regulating the current in each 

 hrauch circuit, that only a predetermined amount should be allowed 

 to flow through the same ; it would be desirable also to furnish each 

 circuit with the means of measuring and recording the amount of 

 ;nc current passed through the same in any period of time. 



It is my special purpose to bring before you an instrument by 

 \\hich these two purposes can be accomplished. The current- 

 ivuulator (as represented in Plate 19) consists principally of 

 a strip of metal (of mild steel or fused iron by preference), 

 which by its expansion and contraction regulates the current 

 parsing through it. This strip is rolled down to a thickness 

 not exceeding 0'05 millim., and is of such a breadth that the 

 current intended to be passed through the regulated branch circuit 

 would raise the temperature of the strip to say 50 C. 



This strip of metal (A) is stretched horizontally between a fixed 

 support and a regulating-screw (B), at which latter the current 

 enters, passing through the strip, and thence through a coil of 

 German-silver wire (C) laid in the form of a collar round the 

 centre, and connected at its other extremity with a binding-screw 

 (D), whence the current flows on towards the lights or other 

 .Apparatus to be worked by electricity. Upon its middle the strip 

 carries a saddle of insulating material, such as ebonite, upon which 

 rests a vertical spindle, supporting a circular metallic disk (E), 

 witli platinum contacts arranged on its upper surface. Ten or 

 any other number of short stout wires connect the helical rheostat 

 at equidistant points with adjustable contact-screws (F), standing 

 above the platinum contacts on the surface of the metallic disk. 

 These wires are supported upon the circular frame (G) of wood or 

 other insulating material, but are free to be lifted off their support 

 if the metallic disk should rise sufficiently to be brought into 

 contact with the screws. These latter are so adjusted that none 

 of them touches the metallic disk when it is in its lowest position, 

 but that they are brought one after another into contact with 

 the same as the disk rises ; and it will be easily seen that for every 

 additional contact-screw that is raised seriatim by the disk, a 

 section of the helical rheostat between attachment and attachment 

 is short-circuited by the metallic disk, and thus excluded from the 

 circuit. AVIien the disk is in its uppermost position the whole of 



P 2 



