30 On t)cal Pendulum Rods* 



ceived into circulation without fatal effects. If ihese should 

 be found unsuccessful, to expose the patient for a certain 

 length of time to one or other of the mephitic gases. 



V. On Deal Pendulum Rods. 



Lynn, Dec. 17th, 1808. 



SIR) - To Mr. Tilloch. 



XT has been frequently observed, that clocks with wooden 

 pendulum rods vary considerably in their rates of going, at 

 different seasons t of the year ; but the cause of this irregula- 

 rity still remains in some obscurity, for want of a greater 

 number of observations. 



Mr. Ludlam says, " That such a pendulum rather loses 

 in cold and gains in warmer weather*." Mr. Wollaston had 

 a clock with a pendulum rod of deal, and he says, " It ap- 

 pears as if the clock gained in warm and lost in cooler 

 weather : but this is not clear. It began to gain before 

 the weather grew warm. Whether this be owing to damp, 

 or any other causes, longer experience and abler observers 

 may discover f." 



My clock, of the rate of which the following table contains 

 a short abstract from 1798 to 1807, has a deal pendulum 

 rod, a dead escapement, and goes when winding up. The 

 daily rate was ascertained by a transit instrument which 

 stands in the same room with the clock, and the observations 

 were taken at all convenient opportunities, as an exact rate 

 cannot be found from observations taken only once in a fort- 

 night or three weeks. 



It appears from this table, that pendulums with wooden 

 rods gain most in the driest, and lose most in the dampest 

 weather. I could never discover that heat or cold had any 

 effect upon my clock, further than that it went very regularly 

 during hard frosty weather, which I suppose was owing to 

 the moisture in the pendulum being frozen. And it also ap- 

 pears, that moisture does not affect the wood so much ai 



* Ludlam's Observatioas, p. 40. + Phil. Trans, abridged, No. 50, p. 216. 



the 



