14 EXPERIMENTS WITH THE DISPLACEMENT INTERFEROMETER. 



There is another point of view from which the question may be approached : 

 Any variation of buoyancy B, if B is eccentric, is virtually equivalent to a 

 displacement of the center of gravity of the pendulum. This occurs when 

 the temperature of the water, in which the float is submerged, changes. Let 

 AG be the plane through the axis of the center of gravity of the pendulum when 

 the float is not submerged, k the perpendicular distance of B from this plane. 

 The center of gravity after the submergence of the float will be displaced 

 laterally (if Vp is the mass of liquid displaced by the float) 



A' _ / *" v _ ULlm 



rv , , . f *C 



M M 



Since the center of gravity must lie in the same vertical plane with the line 

 of pivots AF, the pendulum will have to rotate over an angle 



The observed angle is thus to be divided by 0' to obtain the amount due to 

 simultaneous changes of inclination only. Of course, e may be either positive 

 or negative. Hence, the apparent change of inclination from a to a' is to be 

 interpreted 



Before discussing the question, however, it is preferable to obtain data 

 with a more perfect pivot adjustment; in other words, to use pivots inclined 

 toward the center of gravity and provided with jeweled bearings. 



a 



a 



c 



FIG. ii. 



8. Second apparatus, with float. Jeweled bearings. The anomalous 

 results for a obtained in the last experiments were in the first place to be 

 associated with the unsatisfactory pivots. Hence, these were readjusted so 

 as to point toward the center of gravity of the pendulum. Moreover, the 

 steel cup was inadequately smooth and could not be polished. It was there- 

 fore replaced by a conical hollow of polished sapphire, placed so that its axis 

 prolonged passed through the center of gravity of the horizontal pendulum. 



