WICKSTEED'S AUTOGRAPHIC APPARATUS. 225 



The existence of the spring-piece adds to the complica- 

 tion of the testing apparatus, and a second holding device 

 has to be provided at the end of the spring-piece nearest 

 the specimen. Any slip or yielding of the specimen in 

 the grips would, under ordinary conditions, be included 

 in the movement representing the stretch of the specimen, 

 but this difficulty is obviated by the use of the differential 

 arrangement of the pulleys which serve to transmit the 

 elongation. So far as the writer is aware, this apparatus 

 has only been used with specimens having specially turned 

 heads, and no attempts have been made to use it with 

 ordinary wedge grips.* 



125. Wicksteed's Autographic Recorder. In order to 

 produce workable autographic diagrams without the employ- 

 ment of so delicate an instrument as that of Dr. Kennedy, 

 Mr. Wicksteed has designed an apparatus on very different 

 lines. A very good idea of the general appearance of this 

 instrument will be obtained from the illustration on Figs. 

 21 and 22. Here the autographic apparatus will be 

 seen standing in the space below the beam of the machine, 

 and having somewhat of the appearance of a small lathe. 

 An enlarged view of the more important details is given 

 in plan and longitudinal section in Fig. 107. The diagram 

 itself is drawn upon a sheet of paper fixed upon the 

 surface of a drum, D. The rotational movement of this 

 drum is produced by the stretch of the specimen, the 

 motion being transmitted by means of a fine wire, one end 

 of which is attached to the lower end of the specimen, 

 after passing over a small pulley fixed to a clip on the 

 upper end, so that, as the bar stretches, the wire is drawn 

 over the pulley to an equal extent, and the drum is in this 

 way rotated. It will be seen that the wire, before reaching 

 the instrument, passes over two other guide pulleys, placed 

 at the joints of a light wooden knee-frame. This arrange- 

 ment has been adopted in order to prevent any movement 

 of the specimen, due to the slipping of the holding wedges 

 or the swing of the beam, being recorded as a part of the 

 strain. The wire, after passing round the drum pulley, is 

 kept tight by means of a small weight. 



It is in his method of recording the load upon the 

 specimen that Mr. Wicksteed makes use of a somewhat 

 novel arrangement. In most testing machines the strain 



* This instrument will be found to be fully described in the Proc. 

 Inst. Mech. Eng., 1886, p. 65. 



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