268 Proceedings of ih* Albany Institute. 



tion has never been computed, but it is of considerable 

 importance. 



Tin- difference of temperature in the top and bottom of 

 the room is also a cause of disturbance, as it affects the 

 rod of the pendulum, and docs not compensate by expand- 

 ing the mercury. He Btated that it had been sup posed 

 that pendulums require some time after being disturbed 

 before they regain their regular vibrations. He has deter- 

 mined by accurate experiments with the chronograph, 

 that they will begin to vibrate regularly in about twenty 

 minutes. 



Prof. Hough made some remarks during the discussion 

 that followed, upon the subject of personal equation ; and 

 announced a future paper on that subject. 



The personal equation* of the eve may be divided. into 

 two classes. First: The recording of an instantaneous 

 phenomenon, as the sudden appearance of a meteor, and 

 Second : the recording of the transit of a star across the 

 wires of the telescope. 



In the first case, there is but little variation between 

 different persons, the average time for the mind and muscles 

 to act being about 0.14 of a second. 



In the second case, there is a wide range between differ- 

 ent persons, the different amounting in some instances to 

 nearly half a second of time. 



It has been supposed by some, thai this error of observ- 

 ing might be removed by cultivation, but investigations 

 thus far goto show, that in attempting to do this we intro- 

 duce other errors of greater magnitude and uncertainty 

 than those wo propose to remove. 



Dr. Willard offered the following report: 



The undersigned who were appointed a committee to 

 examine the treasurer's account, beg leave to report that 

 they have compared the vouchers with the statement of 



the treasurer, that they find his report correct and that 



