120 



DISPLACEMENT INTERFEROMETRY APPLIED TO 



In figure 151 the last three scale-rates of the lines prolonged have the mean 

 value 2.17 cm. per five minutes, for the scale-distance of 265 cm. Hence co = 

 2.17/300X530 = 0.00001364 radian per second. Inserting these data, 7 = 

 io~ 8 X6.2, which is much closer to the standard value than from the inade- 

 quate theory and improvised apparatus (straw shaft) I had expected to get. 

 It sufficiently substantiates, I think, the assumed viscous character of the 

 resistance, and moreover shows that the Newtonian constant may be found 

 with precision, in terms of the resistance to the uniform motion, broad-side on, 

 of a cylinder with hemispherical ends, in air. 



TABLE 5. -Apparatus II. Values of co. 



Mean total: co =0.000,012,53 8 cm. to 76 cm. 



95. Angular velocity at different pressures. The favorable result obtained 

 in the preceding tentative computation of 7 induced me to make a summary 

 of the values of co occurring in the different experiments of figures 143, 150, 

 151, 152, 153, for the needle of apparatus II. They were obtained graphically, 

 by prolonging the lines of the triplets as shown in the figures and dividing the 

 scale-rate (y) per minute by 60X2X265, the scale being at 265 cm. from the 

 mirror. These results with their mean values are given in table 5. 



Except in case of the last series (p = 8 cm), the rate-lines pass through three 

 consecutive points after turning. In the case of p = 8 cm., figure 1 53, they pass 

 through but two, the curve being sinuous. The variation of co can not be 

 ascribed to insufficiently rapid turning of M, though this was done by hand. 

 The individual values of co are rather more variable than I hoped to find them, 

 and this is also true to the mean values. The data do not, however, show any 

 systematic relation to pressure, the differences being clearly referable to other 

 incidental causes. 



96. Water-bath. The next step in the pursuance of this subject consisted 

 in putting the apparatus II in a capacious water-bath of copper, sufficiently 

 large to contain the movable weight M. An additional object to be gained was 



