

MR. A. E. TUTTON ON A COMPENSATED INTERFERENCE DILATOMETER. 335 



for the purpose, this spring presses lightly against the drum and maintains it in 

 position. The tape comes up through a slot in the top of the box, and passes over a 

 small roller raised on supporting bearings about half an inch above the surface. 

 From this roller the tape passes horizontally through the punch and thence between 

 a pair of caoutchouc rollers, which compress it sufficiently to be able to determine its 

 movement when the lower driving roller is rotated. The upper roller is free to rotate 

 on its axle simultaneously with the lower one, but in the opposite direction, by simple 

 contact with the latter ; its axle is adjustable for height in order to obtain the 

 necessary amount of pressure between the two rollers, by means of two little milled- 

 headed screws carried on the top of these supports ; the screws press down upon 

 rectangular sliders carrying the axle and sliding in slots cut in the upright supports. 

 The axle of the lower roller is continued backwards just beyond the back of the box, 

 where it carries, rigidly attached to it, a ratchet wheel. The movement of the latter 

 is determined by a click, maintained in position against the teeth by a spring ; the 

 click is pivoted to and in front of a short lever, the fulcrum of which is the end of 

 the roller axle, upon which it freely turns. The teeth of the ratchet are so arranged 

 that upward movement of the lever and click causes the latter merely to pass round 

 the tooth, while downward movement causes the click to force the ratchet round 

 by one tooth. The lever is connected with a longer one by a short vertical link ; the 

 longer one is pivoted at the end of a prolongation of the drum axle, and its move- 

 ment is directed by another vertical link, which is hinged to the back end of the 

 punch lever. .This latter is supported by two fulcrum upright supports, which form 

 the bearings of the horizontal axle about which it is capable of movement. The 

 longer front end terminates in a knob above and a cylindrical rod beneath ; the latter 

 passes slightly through a hole in the top of the box when the lever end is up at its 

 normal height. The lever is kept up by a strong spiral spring wound round the rod 

 and slightly compressed between the lever end and the top of the box. Between 

 the knob and the fulcrum the lever carries below a thickening, directly over the 

 punch head, not in contact with the latter, but separated from it by about 4 millims. 

 The small cylindrical punch is provided at the top with a circular head carrying an 

 annular groove, in which gear the two prongs of the forked end of a strong strip of 

 steel spring. The spring is fastened at its other end to a suitable raised support, and 

 the punch passes down, but not quite so far as the tape, through a guiding block 

 provided with a corresponding vertical bore and fixed to the upper plate of the punch 

 bed. Underneath this, leaving a space sufficiently thick for the passage of the tape, 

 is the steel plate of the punch bed, whose sharp-edged circular aperture corresponds 

 to the punch, which fits it sufficiently tightly. It will be at once evident that on 

 pressing down the knob of the lever and thus compressing the spiral spring round 

 the rod, after traversing the 4 millims. space the punch will be pressed through the 

 tape, and the click of the ratchet will be slipped upwards round one tooth ; on 

 releasing the knob, the spring pushes it upwards again, but the click now drives the 



