90 



THE INTERFEROMETRY OF 



45. Brass tube. A somewhat thinner seamless tube of soft brass was next 

 tested within 600 atmospheres. The dimensions were: length, 161 cm.; 

 diameter within, 0.485 cm.; diameter outside, 0.960 cm. Hence 



161X0.235 __ 18.36 



(0.9216 0.2352)3^ AL 



The ellipses were centered throughout and the yoke was given additional 

 stability by soft adhesive wax, as above. The tube showed extraordinary 

 variability, but during the trials under increasing and decreasing pressure 

 and in the lapse of time the viscous changes somewhat subsided, as will be 

 seen from table 19. 



TABLE 19. 



Disregarding the first series, which was preliminary, the remaining data 

 are consistent. Hence k from the mean io 6 AL=i5.2 is relative to atmos- 

 pheres 



15.2 



=i.2iXio 6 



Voigt's value for brass is but 0.61 X io 6 , i.e., but half this. Throughout these 

 experiments the reading for 100 atmospheres wandered continually, creeping 

 over 7 X io" 3 cm. during the time interval of the experiments. The following 

 individual data show this for the fourth series : 



Pressure ........... 100 200 300 400 500 600 600 500 400 300 200 100 atm. 



Micrometer reading 320 301 290 274 263 250 252 270 290 305 321 336 cm./io 4 



One would naturally refer this to the viscosity of the brass tube, but, curiously 

 enough, the march is a contraction. Apparently the tube continually con- 

 tracts in the lapse of time under internal pressure. The contraction occurs, 

 however, for the case of a tube which was not rigorously straight. 



Optically, apart from the tremor of the laboratory, one would have no 

 fault to find with the measurements, allowing a micrometer accuracy of a 

 few io- 4 cm. Interference rings could easily have been utilized, but this 

 would have required two observers. 



Two more series of experiments were made with the brass tube (table 20), 

 in one (5) of which it was supported only at the ends with its original curva- 



