2GS 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



errors 



of reading. The total displacement 

 at 6500 kgm. was about 0.35 mm. 

 in the form above. 



Among possible sources of error 

 we have here again a maximum 

 uncertainty in the effective length 

 of the glass tube of \ the width of 

 the ring D. In the form used the 

 total length was about 8 cm., and 

 the width of the ring 2 mm. The 



placed in the pressure chamber, and subjected to hydrostatic pressure 

 all over. Both glass and steel shrink, the glass shrinking the more, and 

 hence the ring D is pushed up on 

 the tube. When pressure is re- 

 leased, D comes back with the 

 tube, and the increased distance be- 

 tween the scratches, measured with 

 two microscopes, gives the relative 

 change of length for the highest 

 pressure reached. The glass tube 

 was taken out of the steel jacket 

 and everything washed carefully 

 after each application of pressure, 

 in order to insure freedom from 

 small particles of grit. It is an 

 advantage of this method over the 

 first, that because of the greater 

 accessibility of the parts, complete 

 freedom from grit is secured by 

 washing after each application of 

 pressure. Repeated measurements 

 of the zero position of the ring 

 gave results agreeing within 0.001 

 mm., which in this case was about 

 the magnitude of possible 



Fi 



G 



Figure 6. Apparatus for compar- 

 ing the linear compressibility of glass 

 and steel. The glass tube C is com- 

 pared with the enveloping steel tube 

 A. The relative change of length is 

 measured by measuring the displace- 

 ment of the ring at D, sliding on the 

 glass tube. The glass tube is kept in 

 contact with the shoulder B by the 

 spring G, acting on the nut F through 



results may, therefore, be in error 



b .Y bV> but probably by less than the tie rod H, which in turn presses 

 this. This source of error may ob- on the glass tube by the nut E. 

 viously be decreased at pleasure by 



increasing the length of the tube. Another possible source of error 

 is temperature change. Error from heat of compression was avoided 

 by operating slowly, applying pressure nearly to the maximum, waiting 



