204 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



A 



c 



^y 



E 



\r 



Figure 1. The direct 

 reading gauge. P, piston ; 

 E, cylinder; A, larger 

 steel rod through wliich 

 the pressure of the equi- 

 librating weights is trans- 

 mitted to the piston; B, 

 hardened steel point on 

 which the stirrup carrying 

 the weight pan is hung; 

 C, stop (see Figure 2) ; D, 

 groove by which the rubber 

 tube containingthe viscous 

 mixture of molasses and 

 glycerine is attached. 



cylinder to pressure. By suitably changing 

 the area subjected to pressure, the shrinkage 

 of the interior may be controlled. This is 

 the method adopted with the present gauge. 



The leak may be further "decreased by 

 decreasing as far as possible the dimensions 

 of the piston and cylinder, thus decreasing 

 the circumference of the crack through which 

 leak occurs. Decreasing the size has the 

 additional advantage of making the whole 

 gauge more compact and manageable. In 

 particular, the total thrust becomes small 

 enough to be balanced directly by hanging 

 weights on the free end of the piston. Where 

 the magnitude of the weights is not so great 

 as to make this infeasible, the direct applica- 

 tion of weights seems preferable to the usual 

 indirect methods of measuring the thrust. 

 In the gauge adopted in this w r ork, the piston 

 is only tV in. (0.159 cm.) in diameter, requir- 

 ing at the maximum pressure of 6800 kgm. 

 an equilibrating weight of about 130 kgm. 



The cylinder and piston are shown in 

 Figure 1. In Figure 2 they are shown in 

 place in a large steel block which serves as 

 a reservoir between the gauge and the pres- 

 sure pump. The dimensions of the impor- 

 tant parts are indicated in Figure 3. The 

 thrust on the piston P (Figure 1) is taken 

 by the large cylindrical rod A joined to the 

 piston by a forced fit. A terminates in a 

 hardened point B, on which the weights 

 are hung by a stirrup supporting the scale 

 pan underneath the large steel block. The 

 upper end of the cylinder acts as a guide 

 for the rod A, as does also the attachment 

 screwed onto the top of the cylinder shown 

 in Figure 2. It is essential that fitting here 

 should be accurate, so that the small piston 

 may move freely in a vertical line without 

 danger of any bending of the top end when 

 projecting some distance from the cylinder. 



