APPARATUS FOE PHYSIOLOGICAL USE. 243 



communication by a long flexible tube. You observe that 

 the lever of the recording tympanum and the lever on 

 which the cam acts directly, are so arranged that they 

 move in the same vertical plane, that their writing points 

 are directly one above the other, and that both points are 

 in contact with the surface of a blackened sheet of paper 

 with which this cylinder is covered. By this arrangement 

 two records are obtained simultaneously of the same motion 

 one by immediate transmission by the lower lever, the 

 other mediately by the two tympana. If you compare 

 them you will be unable to detect any difference between 

 them. In fact, for practical purposes they are identical : 

 there are, however, certain slight differences which have 

 been investigated by Prof. Donders. 



I will now proceed to describe to you various applications 

 of this method to the investigation of physiological motions, 

 and will first refer to the remarkable researches of M. 

 Marey on locomotion. The principal purpose of these re- 

 searches was to determine with much greater precision than 

 was before possible the time relations between the various 

 motions which are executed by the body and limbs in 

 different kinds of locomotion, as, for example, in walking, 

 running, or flying. I can best illustrate this by asking you 

 to look at this large diagram, in which a man is represented 

 running and carrying with him a recording apparatus, con- 

 sisting of clockwork and tympana, by which his motions 

 are faithfully transmitted to paper. You will observe that 

 there are three pairs of tympana, viz., three recording ones 

 which inscribe their records one above the other on the 

 small revolving cylinder which he carries in his hand, and 

 three contrivances which correspond in function to receiving 

 tympana. Of these two are for recording the time during 

 which, and the degree in which, the ground is pressed upon 

 by each foot in the act of running. You will readily under- 

 stand this if I show you one of the shoes which the runner 

 wears. In the sole, which is made of vulcanised indiarubber, 

 there is a flattened cavity, which communicates with that of 

 the recording tympanum. You will readily understand that 

 the air it contains is compressed by the foot, just so long as 

 the weight of the body rests on it. The third receiving 

 apparatus rests on the top of the head and communicates 

 to the tympanum, with which it is connected, the up and 



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