334 Burhank — Apparent Variations of the Vertical. 



hours. Tlic total displacoineiit was about 3-00" of arc toward 

 the east and O'O" toward the north, and this condition remained 

 ])ractically unchanged for over 2 days. It would appear from 

 this that the drying out of the ground had caused the pier to 

 tip toward the southwest and the return of moisture caused a 

 reverse movement. 



Again on Aug. 25th about midnight there was a heavy rainfall 

 the effect of which was superposed on a tilting due to tlie tem- 

 perature change. This temperature change was such that the 

 pier was moving toward the northwest and the rain caused mo- 

 tion toward the northeast, accentuating tlie motion in the north 

 component and decreasing and reversing that in the E-W com- 

 ponent. In this case there appears to have been a partial 

 recovery due possibly to the fact that the soil had received, from 

 recent rains, nearly its normal moisture content, and the excess 

 soon ran through. 



On September 6th during the early morning hours a heavy 

 downpour of rain (2'34: inches) occurred. This produced a tilt- 

 ing of the pier toward the northeast, but the effect was super- 

 posed on a gradual temperature change and was much less than 

 on Aug. 5th. Partial recovery appears to have occurred during 

 the next two days. August f)th,7th, and 8th were cloudy, as was 

 August 25th also. September 6th was cloudy during the morn- 

 ing while September 7th was clear. The solar diurnal tilting 

 occurred on September 7th, and it would appear that a saturated 

 soil may modify but apparently does not prevent this effect. 



The return of the pier to its former position appears quite 

 marked on September 7th, and it is possible that its failure to 

 return in the iirst two cases was due to the cloudy weather, 

 which prevented the ground from being dried out. 



