COMPENSATION PENDULUM. 55 



perty of zinc renders it in theory extremely fit for the p«rr 

 pose of compensation in a pendulum, and I was desirous of 

 knowing if it would answer in practice, and likewise the 

 exact proportion, that was requisite to answer the intended 

 purpose. 



I made two regulators, the pendulums of wliich were Two regulators 

 composed of iron and zinc, as above described ; with this ™^ ^ "^^ ^"'^ ' 

 difference, however, that one had a detached scapement of 

 a particular construction ; the zinc rod was not hammered, 

 the ball of a lenticular form, and weighed twenty pounds, 

 its arc of vibration nearly five degrees. The other had a 

 simple remontoiring scapement, the zinc rod was hammered 

 half an inch per foot, the ball, of a spherical form, weighed 

 forty-six pounds, and vibrated two degrees and three quar- 

 ters. 



These regulators were both placed in the same room, and 

 their cases firmly fixed to the wall; the pendulums were 

 suspended from a stout brass cock, screwed to the back of 

 their respective cases. In the inside of each case, and im- 

 mediately behind the pendulum rod, was hung a thermo- 

 meter, for the purpose of comparing the degrees of heat. 

 1 adjusted them to mean time nearly by corresponding alti- 

 tudes of the sun. After having compared them together Difference of 

 for several days, I found, that the one which had the ham- Ser^g'^Xr 

 mered zinc rod went somewhat faster when the air of than Mr. 

 the room was heated by a fire in the grate than the other ^^"J^^'o"'^ ^^" 

 did. Hence I concluded, that the difference of expan- 

 sion of hammered and unhammered zinc was greater 

 than Mr. Smeaton made it, at least it appeared so in this 

 instance. 



But to determine whether the length of the hammered Contrivance 



zinc rod was accurately proportioned to that of the iron ^'^'' '^'^*^'?S J^® 



11- J • L I 1 air round the 



ones, without being obliged to wait that length of time hammeped zinc 



that nature would require to produce a sufficient alter- '^"'^• 



ation in the temperature of the air, I proceeded to make the 



following experiment: I caused to be made a tin tube six 



feet long, and two inches and a half diameter at its larger 



end, from which it gradually tapered to the other, which 



was only half an inch diameter. Within the case, and as 



far from the pendulum as possible, I placed this tube; the 



smaller 



