EXPERIMENTS WITH THE DISPLACEMENT INTERFEROMETER. 47 



The results with the aluminum pendulum are constructed in fig. 27, the 

 curves showing the variation of inclination in seconds of arc in the lapse of 

 time, here a = 8.6Xio- 3 radian. Since = A/V/2 R=&N/222, 



= 3 -9 X io~ 6 radian = 8AAT seconds of arc, 



the present factor 8 replacing the above value 10. As in the case of 17, 

 Part I, above, the present results are intended to test the variations from fall 

 to winter conditions, and during the introduction of steam heat into the labo- 

 ratory. The temperature observations are therefore also inserted in the dia- 

 gram, so far as necessary. No difficulty whatever was experienced with the 

 film grating throughout the whole of the work. 



ft 



AT 



AA 



-: 



a 



KT~iZ It- Y3 



Zl 25 



2) 



za 



\ 



- 



x_/ 



WTtft? 



r 



aftttte 



&j' 



B 50"Ctf 2 



23 25 27 2J?e/fcb/ 8 5 



sr 



10 



FIG. 27. 



In the first half of the observations (upper curve) , between August 1 7 and 

 September 28, the curve shows a persistent upward trend. Gaps occur in the 

 curve at a. and b, owing to the absence of the observer, and these places happen 

 to be associated with variations in the curve; but this is purely incidental. 

 The curve fails to get back to its original reading. It seems probable, there- 

 fore, that the cause of this uniformly progressive march is the viscosity of the 

 aluminum tubing out of which the pendulum was built, and what is observed 

 is in the main a continuous viscous yield of the pendulum to the load of its 

 own weight. 



The lower curve shows the results between September 28, when the steam 

 heat was turned on, and November 4. The effect of the sudden appearance 

 of steam heat is sufficiently startling, as the curve on October i runs off of 

 the scale at c. It was then necessary to displace the micrometer; but this 

 was done so as to change the fiducial zero as little as possible. Afterwards, 

 however, contrary to expectations, the curve again approaches its old value, 

 so that the displacement would not really have been necessary. What took 



