XXXIV.] 



THE GRAPHIC METHOD. 



195 



recording drum is used, provided it moves smoothly and evenly, 

 and is capable of being made to move at different speeds as required. 

 In Hawksley's form of drum this is accomplished by placing the 

 drum on different axles, moving at different velocities. In Lud wig's 

 form (fig. 115) this is done by moving a small wheel, w, on a large 

 brass disc, D. Where a number of men have to be taught at 

 once, one must have recourse to an arrangement of shafting, 

 moved, say, by a water-motor or turbine, from- which several 

 drums can be driven by cords. Or one may use a small gas- 

 engine as the motive power, and cords passing over pulleys to 



v 



FIG. 115. Ludwig's Revolving Cylinder, R, moved by the clockwork in the box A, and 

 regulated by a Foucault's regulator on the. top of the box. The disc D, moved by 

 the clockwork, presses upon the wheel n, which can be raised or lowered by the 

 screw L, thus altering the position of n on D, so as to cause the cylinder to rotate 

 at different rates. The cylinder itself can be raised by the handle U. On the left 

 side of the figure is a mercurial manometer. 



move the drums. This is the arrangement adopted in the Physio- 

 logical Department of Owens College, so that a number of men 

 can work at the same time, each being provided with recording 

 apparatus for himself. The Thirlemere water-motor may also 

 be used for actuating a number of recording cylinders. 



2. Fixing and Smoking the Paper. The paper is glazed on 

 one surface, and is cut to the necessary size to suit the drum. 

 The drum can be removed from the clockwork or other motor 



