NEW COMPENSATION PENDULUM. 



Q17 



Previous to its being reduced to the exact dimensions, jt is to Pendulum do 

 he baked in an oven, till the surface appears a little charred; scribed. 

 ^nd as it is of the utmost importance, tiiat it should be ren- 

 dered perfectly impervious to moisture, the ends are soaked 

 in melted sealing wax, and the rod, being cleaned, is coated 

 several times with copal varnish. 



The top of the rod is to be divided with a very fine saw> 

 to admit the spring of the pendulum, where it is secured by 

 two or three small pins passing through it and the spring, 

 and rivetted on each side. 



The weight of the pendulum is of the usual form, and. 

 pierced to receive the rod, which is immovably fixed to the 

 centre by means of a screw, passing through it and the 

 weight. 



The length of the pendulum is regulated by the screw 

 and nut at the top ; but there is also a screw with a less 

 weight at the lower extremity of the pendulum, in order to 

 adjust it with greater accaracy*in the usual manner. 



Now it is evident, that, if the part which is made of zinc 

 be so proportioned to the other materials of which the pen- 

 dulum is composed, as to undergo an equal expansion with 

 any increase of temperature, the pendulum will always 

 maintain the same length, and its oscillations, as far as tem- 

 perature is concerned, will be performed in equal times. 



In order to discover the length of zinc necessary to effect Calculation of 



this, let the steel screw, g, h, be 9-5 inches long'; and the '^^ '''"S^*' °^ 

 , . , . , J?' z-nc necessary- 



spring 3 inches, making together I'i'S niches. 1 hen, as the for the corn- 

 expansion of ginc to steel is as 353 to 147, we shall have l^^""^'^*^"' 



p-^— — 5*2 inches nearly, for the length of zinc re- 

 quired to correct the expansion of the steel employed in the 

 pendulum. Next, as the spring will extend about two 

 inches below the plate of the cock of the time-piece, whence 

 the lengtli of the pendulum is measured, there will remain 

 about 37 inches of deal, and the expansion of deal being to 



49 X 37 

 that cfzinc as 49 to 353, we have — 5-\ inches nearly; 



which, being added to 5'2 before found, gives 10"3 inches, 

 the length of zinc which will counteract the expansion of 

 the whole pendulum. 



The 



