360 Mr. T. Gray on an Improved 



made to pass at regular intervals by a clockwork circuit- 

 closing arrangement ; and, by the perforations they leave, a 

 record both of their position and the corresponding time is 

 obtained*. This method is absolutely frictionless so far as the 

 recording-point is concerned, and has the advantage that the 

 sheet can afterwards be used as a stencil-plate for printing 

 copies of the record. An ordinary simple pendulum, furnished 

 with a very light vertical index of thin aluminum tube giving 

 a multiplication of 200, has been for some time in use. The 

 record of the position of the end of the index is taken on two 

 strips of paper which are being slowly pulled along, in direc- 

 tions at right angles to each other, under it. The sparks per- 

 forate both sheets simultaneously, thus automatically breaking 

 up the motion into two rectangular components. The details ot 

 some forms of apparatus for this purpose will form the subject 

 of a separate communication. 



Mechanical Details, 



The record-receiver consists of a long ribbon of thin paper, 

 about five inches broad, which is slowly wound from the 

 drum A, situated behind the drum C (Plate IV. fig. 1), on 

 to the drum, B, by means of a train of clockwork driven 

 by a spring or a weight of sufficient power to keep the 

 ribbon taut. The rate at which the paper is fed forward 

 is governed by a second train of clockwork, driven by a 

 separate weight and governed by means of two Thomson 

 spring-governors. In gear with this train of wheelwork 

 there is a third drum, C, round which the paper is taken as 

 it passes from the drum A to the drum B. This drum is 

 kept moving at a uniform rate, and serves to regulate the 

 motion of the paper. The object of the double set of clock- 

 work mechanism is to render the rate at which the paper is 

 fed forward independent of the size of the coil on the drums 

 A and B. The surface of the drum C is covered with several 

 thicknesses of blotting-paper for the purpose of giving a soft 

 surface for the siphons to write upon, and of preventing the 

 ribbon blotting or adhering to the drum in consequence of ink 

 passing through the paper. This blotting-pad is of some 

 importance, because a cheap kind of thin paper is found to 

 answer perfectly for the siphons to write upon. They move 

 with less friction on a moderately rough surface and on paper 

 which rapidly absoros the ink. Under ordinary circumstances 

 the paper is fed forward from a quarter of an inch to an inch 



* This method of recording the motions of an index was used by 

 Sir William Thomson in his "Spark Recorder." 'Mathematical and 

 Physical Papers/ vol. ii. p. 168. 





