The London, Edinburgh and Dublin philosophical magazine and journal of science . the lateral pressure upon the wire is so great that it becomespermanently stretched, and is sometimes forced completely outof its groove. The wire, too, is necessarily thick; and the wholeapparatus must consequently be large and cumbersome if it isto work through any considerable range of resistance. A Wheatstones rheostat in good working order is rarelyseen, even in the shop of the instrument maker ; and in pointof fact it is little used except for the purpose of lecture-illustration. In the course of some experi
The London, Edinburgh and Dublin philosophical magazine and journal of science . the lateral pressure upon the wire is so great that it becomespermanently stretched, and is sometimes forced completely outof its groove. The wire, too, is necessarily thick; and the wholeapparatus must consequently be large and cumbersome if it isto work through any considerable range of resistance. A Wheatstones rheostat in good working order is rarelyseen, even in the shop of the instrument maker ; and in pointof fact it is little used except for the purpose of lecture-illustration. In the course of some experimental work the pressing needof some means of continuously varying a resistance led me todevise the modified rheostat, which is figured in the annexedwoodcut. As in the second form of Wheatstones instrument, a wire of Wheatstones Rheostat. 31 is coiled in a spiral groove upon an insulating cylinder. Thisis mounted upon the middle of a brass axle of rather morethan three times its length. Upon one of the projectingends of the axle a screw is cut, the pitch of which is equal to. the distance between the consecutive turns of the wire. Theaxle revolves in two brass bearings, fixed at a distance apartequal to twice the length of the cylinder ; one of the bearingshas an inside screw corresponding with that upon the flat spring is attached at one end to the base-board of theinstrument midway between the bearings ; to the other endis riveted a short copper pin, which is directed perpen-dicularly to the axis of the cylinder and bears upon the spiralwire, being kept in position by a shallow notch cut in its end of the spiral wire is electrically connected with thebrass axle, and thence through the screwed bearing and astrip of copper with a terminal upon the base-board. Thespring is directly connected with a second terminal. Whenthe cylinder is turned by means of a handle, it travels back-wards or forwards in the direction of its axis, the point of con-tact of the copper p
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
