528 Proceedings of the Royal Irish Acadetny. 



ten divisions, so that ten contacts were made with the brnsli every 

 revolution of the cylinder. The intervals of these makes and breaks 

 were equal. This cylinder rotated between two screws with conical 

 points, and by varying the pressure on the coned surfaces, as was 

 required, the effects of the inertia of the cylinder could be easily got 

 rid of. A brush in contact with the commutator made the electrical 

 connections as the cylinder revolved. 



Round the cylinder a string was wound which was attached to 

 the walker, and was unwound by him when walking away from the 

 apparatus. An electro-magnet, in circuit with the commutator, 

 recorded the velocity of the cylinder by attracting a soft iron armature 

 controlled by a spring. When the circuit was closed the armature, or 

 rather a lever projecting from the armature, was so arranged that it 

 made a stroke on the smoked paper. When the current was open the 

 armature being pulled back by the spring, a blank was left. This 

 little instrument worked rather like a Morse instrument, and the 

 recording was also similar to that of a Morse instrument, as may be 

 seen in the diagram (fig. 2, p. 532). If now a man walked uniformly 

 the number of strokes between each wave-length would be equal. 



By the use of this apparatus the velocity could be obtained during 

 a single step about 40 times, if the length of the strokes were measured. 

 This I found difficult and unnecessay, and it was sufficient to take 

 the velocity at the end of each wave-length, and plot it to obtain the 

 curves. This was done by simply counting the number of strokes in 

 each wave-length and plotting this number to scale. From the begin- 

 ning of one scratch to the beginning of the next is counted as one 

 " stroke." 



The steps of the walker were recorded on the drum by another 

 electro-magnet in circuit with the instrument shown in figure 1 . 



c I 



Fig. 1. 

 This instrument was fastened by straps under the instep up against 

 the heel of the boot and consisted of a piece of fibre cut so as to fit 

 the curred part of the boot under the instep and next the heel. To 



