GENERALITIES OF THE OAITS. 



481 



Finally, the two drums are connected with each other by means of a rubber 

 tube, T, T, T. The apparatus being closed and full of air, it is apparent that all 

 pressure exercised upon the drum A, for example, will force the air through the 

 tube TT into the drum B, whose membrane, as well as its lever, it will elevate. 

 As soon as the pressure ceases, the two levers will naturally return to their initial 

 position. From this unity of action of the 

 two drums any movement whatever can 

 therefore be transmitted from a distance, and 

 even amplify itself if the length of the lever 

 be augmented. 



Moreover, let us imagine a cylinder (Fig. 

 174) covered by a layer of smoked paper, 

 turning circularly in a uniform movement, by 

 a sort of clock-work, opposite to one of the 

 levers transformed into a registering needle. 



Fig. 175.— Chaussure exptoratrice, or pneu- 

 matic foot-bulb of Marey, for the registra- 

 tion of the gaits by compressed air. 



Fig. 176.— Bracelet explorateur, or pneu- 

 matic bracelet of Marey, for the registra- 

 tion of the gaits by compressed air. 



It is easy to understand that the least displacement of the latter will leave its 

 trace upon the paper. All pressure will produce a more or less marked deviation 

 of the point of the needle; if there is no pressure the line traced will be straight 

 from the point of its oi'igin to its termination. 



The figure of the tracing of a gait (Fig. 174) is therefore a curve offering a series of vertical 

 undulations, a, a, which correspond to the pressure transmitted to the registering apparatus by 

 the concussion and the contact of the hoofs upon the ground. 



The tracing reads from left to right. The ascent, b, b, b, of each undulation indicates an 

 increase of pressure, a contact of the member; the descent, c, c, c, signifies, on the contrary, a 

 •diminution, an elevation of the member. For the same velocity of the revolving cylinder, the 

 more vertical the ascent is the more sudden the percussion with the soil has been ; the higher it 

 is, e, the stronger the percussion has been. When the curve,/, at the summit of the undulation 

 becomes parallel to the horizontal, it is a sign that the pressure is uniform ; when it is parallel . 



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