BRroGMAN. — MEASUREMENT OF HYDROSTATIC PRESSURES. 



323 



Nm 



rv-^ 



N/^ 



B 



A 



gains at three points. The soft steel packing, which takes the place 



of the rubber, does not transmit pressure hydrostatically and so exerts 



a smaller pinching-off effect ; the cylinder is made of hardened nickel 



steel instead of tool steel, so that it has a higher yield point and more 



etfectively resists what pinching-off 



eft'ect there is ; and the cylinder itself, 



which is the only vital part, is placed 



entirely beyond the reach of this effect. 



Even in this form, however, the soft 



steel packing does flow sufiiciently to 



produce the beginning of the effect. 



After the application of the maximum 



pressure the bore at C showed a very 



marked decrease. But since nothing 



depends on the size of the bore at C, 



no inaccuracy is introduced. 



This form gives up one advantage 

 claimed for the former gauge, namely, 

 that by changing the area over which 

 the packing is distributed it becomes 

 possible to some extent to control the 

 distortion of the cylinder and so the 

 leak. But this question of leak proved 

 of much less importance than was an- 

 ticipated, it being possible to range 

 from to 13,500 kgm. without incon- 

 venient leak at any point. The leak YiGvn^2. The absolute gauge; 

 does, however, as anticipated, become shows enlarged detaU of the cyhn- 

 less at higher pressures, partly because der and the piston, 

 of closing up of the crack, so that some 



sort of control of the leak would become necessary if the crack should 

 ever close up completely. But it has been found possible with the 

 present form of gauge to provide an effective control of leak by provid- 

 ing for the highest pressures a piston slightly smaller than normal. 

 This is evidently easier than to attempt so to design the gauge that 

 the adaptability for different pressures should be secured by changing 

 the packing. The need for even this procedure of changing the piston 

 would probably be slight in practise, for as already stated, one piston 

 sufficed up to 13,500 kgm., and the gauge itself would probably not 

 stand much more. 



It is evident that the new form given the gauge makes necessary a 

 recomputation of the correction for distortion. The effect of this distor- 



