A. deF. Palmer, Jr. — Apparatus for Measuring, etc. 451 



Aet. XLV. — On an Apparatus for Measuring very High 

 Pressures ; by A. deFokest Palmee, Je. 



Some time ago, while I was investigating the relation 

 between the electrical resistance and the pressure of pure mer- 

 cury, Prof. Barns remarked that the results might be used by 

 exterpolation in the calculation of very high pressures, and 

 suggested that I undertake the construction of an apparatus to 

 utilize this principle and determine the limit of pressure obtain- 

 able with a tinned screw. After several disappointing pre- 

 liminary trials the method described below was finally adopted 

 and found to give very satisfactory results. 



Figure 1 is a sectional diagram of the piezometer. A is a 

 Bessemer steel cylinder, two inches in diameter and seven 

 inches long, firmly keyed to a cast-iron collar having holes H H 

 for anchor bolts. D is a capillary glass tube, about one-tenth 

 millimeter in internal diameter and eight centimeters long, 

 filled with pure mercury electrically connected with A by 

 a globule of mercury E. A platinum electrode, sealed into the 

 top of D, is soldered to a silk-covered copper wire that passes 

 out of A through a marine glue plug in the tinned steel screw 

 C and forms the upper connection with a Wheatstone's bridge. 



