348 Froceedings of the Royal Physical Society. 



When the pin is withdrawn, the spindle and drum can be 

 rotated in any direction without affecting the clock. The 

 convenience of this arrangement will be apparent when the 

 continuous paper apparatus is described (PL XII., Fig. 3). 

 The slow speed gives one revolution in 35 seconds, and the 

 quick one in 8 seconds. The clock is stopped by a simple 

 brake, which acts on a disc carried by the governor spindle. 

 There is also provided a more rigid check, which is useful 

 when the instrument is being moved about. Under such 

 conditions, the light brake referred to might be shaken off, 

 and permit the clock to start. This extra check is of course 

 not required when the clock is being stopped in working, as 

 the brake referred to is amply secure and very convenient. 



For smoked tracing requiring such speed as that mentioned, 

 this apparatus will be found quite efficient. It would serve 

 well for demonstrating such experiments as those on 

 muscular contraction, etc. It is compact, works with re- 

 markable regularity, and can be employed in either a vertical 

 or horizontal position. 



When, however, a slower rate of motion is required, the 

 apparatus, as described, is of no use ; and in order to provide 

 in a simple and economical fashion such a variety of speeds 

 as may be necessary, I have made the arrangement shown in 

 PL XIII. 



The clockwork already described, from which the drum 

 has been removed, is again employed as the motor. It is 

 now placed on a bracket fixed to the end of the table, and 

 placed about 3 in. lower than the top of the latter. The 

 steel pins in the disc on the second wheel are unscrewed, 

 and the disc itself reversed on the arbor. The disc, which 

 is cut with a groove on its edge, thus forms a pulley. A 

 much smaller disc, also grooved and \ in. in diameter, is 

 fixed on what is now its upper surface. We have thus a 

 compound pulley, the larger portion 1| in., and the smaller 

 \ in., in diameter, turning once in 35 or 8 seconds according 

 as the clock is running at its slow or quick speed. 



The drum is now arranged on a steel spindle of the same 

 thickness as the former one, but 16 in. in length. This 

 spindle carries near its lower end a compound pulley of three 



