On Deal Pendulum Reds. 5 



ought always to be avoided in any compensation applied lo 

 time-keepers : and moreover, the length of tlie pendulum 

 may be increased by its own weight ; indeed, the great num- 

 ber of times that the bob of the transit clock at the Royal 

 Observatory has been raised, renders this supposition more 

 than probable. 



In a pendulum with a wooden rod there is no friction ; and 

 as my pendulum was not altered during six successive years, 

 except by the vicissitudes of dryness and moisture, the 

 weight of the bob or lens had no tendency to increase the 

 length of the rod. And it may be further observed, that, 

 as the cleaning of the clock made no alteration in its daily 

 rate, it seems probable that the pendulum is the only part of 

 it which measures the time into equal portions. 



It may not be foreign to my subject to explain the hy- 

 grometer which I made use of to determine that the length 

 of this pendulum was altered by dryness and moisture, not 

 by heat and cold. 



It is not necessary tlut we should always have recourse to 

 philosophical instruments to investigate the operations of 

 Nature; for instruments made for ordinary purposes may 

 sometimes, bv common observation, lead us to new truths. 



My clock stands in a room in which there has been no 

 fire for many years. In this situation the clock case, which 

 is made of mahogany, acts as a hygrometer, -For in the 

 driest season of the year t!ie door is so contracted as not 

 to touch one side of the case ; but when the atmosphere i% 

 very moist the door is so. much increased in breadtli that it 

 cannot be opened, without using a force which might alter 

 the rate of the clock. 



When the door was too little for the clock case, the clock 

 always gained of true time, but it always lost when the door 

 could not be opened. Hence it is evident, that a damp ax- 

 ino:-phere, which increased the breadth of the clock case 

 door, increased the length of the pendulum rod ; and a dry 

 .ilmospherc, which contracted the breadth of the door, con- 

 tracted, at the same time, the deal rod of-the j)endulum. 

 I am, sir, your very humble servant, 



Lynn, July 5, 1809. E. WaLKRI?. 



A3 II. The 



