266 Prori, dings of the . 1 JJbany TnsdtuU . 



members and contributors to tl who w . 



sent, which wa ed to. 



Adjourned. / 



February LOth, L864, 



Ten members present. In the absence of the president, 

 on motion of Dr. Hough,Dr. Vanderpoel took the chair. 



Prof. G. W. Hough presented an account of a series of 

 experiments with which he hasbeeu engaged during the 

 last year, in reference to the compensation of pendulums 

 for changes in temperature. 



Prof. Hough prefaced his account with some general 

 remarks on the various kinds of pendulums. 



Wooden pendulum rods expand one-fifth as much 

 steel, and steel expands B |, of its length, for a change of 

 180° in the temperature. In the mercural pendulum, the 

 expansion of the mercury varies the point of oscillation as 

 much as the expansion of the rod Lowers it. Mercury ex- 

 pands ^ of its length at the sunn' time thai steel expands 

 5 J , and the length of the column of mercury is to the 

 length of the rod as 55 : 833. So much having been de- 

 termined by calculation, the pendulum is compared with 

 another, and they arc closely watched to see if their vibra- 

 tions are alike. If the pendulum thus prepared vibrates too 

 rapidly, the point of oscillation is too high and some of the 

 mercury musl be taken out — if too slow more mercury 

 is to he added. The amount of mereury cannot be accu- 

 rately 'computed beforehand. 



Prof. Hough has made use of a new method ^A' com- 

 pensating, by which it can he done to a greater degree 

 of accuracy than by any process previously used. This 

 method of compensating a pendulum is another appli- 

 cation of electricity in connection with a chronograph. 

 By it we are enabled to know from Becond to second and 

 minute to minute exactly how our pendulum is performing. 

 We are aide to determine the late of the pendulum for 



