Proceedings of the Albany Institute. 267 



every degree of temperature lying between the two ex- 

 tremes. In case the pendulum moves with an uniformly 

 accelerated velocity in the process of heating, the chrono- 

 graph record will exhibit a curve bending towards the 

 left. By means of an angular micrometer, the difference 

 between the rates of the two pendulums down to the 

 hundredth of a second may be measured. 



By this method, the compensation of any pendulum be- 

 comes an easy matter and susceptibl e of very accurate results . 

 After having computed the amount of mercury necessary, 

 the oscillations of an experimental pendulum are recorded 

 in the chronograph for half an hour or more, when com- 

 paring it with the standard pendulum which is also re- 

 corded at the same time, and the difference of rate between 

 the two pendulums is determined. On subjecting our expe- 

 rimental pendulum to a higher temperature and again mak- 

 ing the record, any change of rate is immediately detected. 

 Having determined the amount of this change, any con- 

 venient amount of mercury may be added or subtracted, 

 and repeating the same process, the effect of the amount 

 of mercury in compensating may be found. Now without 

 going into a rigid mathematical discussion to determine 

 what amount of mercury should be added or subtracted, 

 the simple proportional part corresponding to the change 

 of rate may be taken. In case a pendulum is nearly com- 

 pensated at the start, two repetitions of this process will 

 give an excellent pendulum. 



Prof. Hough mentioned some other influences which 

 disturb the regular vibrations of the pendulum, among 

 which is the effect of the attraction of the moon, which acts 

 in two ways to affect the vibrations, by modifying the in- 

 fluence of the earth's attraction. 



Changes in the atmosphere, giving at different times a' 

 medium of varying density to resist the motion of the 

 pendulum, were also mentioned. The amount of this varia- 



