$4 Description of anew Compensation Pendulum* 



But to determine whether the length of the hammered 

 zinc bar was accurately proportioned to that of the iron ones 

 I wished next to prove, without waiting that length of time 

 that Nature would require to produce a sufficient alteration 

 in the temperature of the air, I proceeded to make the fol- 

 lowing experiment : I caused to be made a tin tube six feet 

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

 from whence 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; tfee 

 smaller end was carried through a hole in the top of the case, 

 and projected a few inches above it. In the lower end of 

 the tube was inserted the nozzle of a lamp, and immediately 

 under it, in the bottom of the case, was a hole of an inch 

 diameter to supply the lamp with air. By this means the 

 tube wouljd communicate as much heat to the internal air, 

 as to raise the thermometer about thirty-five degrees. 



Previous to the lamp being put in the case, I made both 

 pendulums vibrate exactly together; and after an interval of 

 twenty-four hours, the one with the hammered zinc bar 

 had gained, as near as I could judge, one tenth of a second. 

 The mean height of the thermometer was fifty-three de- 

 grees. I now lighted the lamp, and in about four hours 

 every part appeared to be thoroughly heated, and the ther- 

 mometer arrived at its maximum, which was eighty-eight 

 degrees; at this point it continued with little variation. 

 While the heat was increasing I found the motion of the 

 pendulum was accelerated. 1 again made them beat exactly 

 together, and in about ten hours after, the heated pendulum 

 had gained one second ; the thermometer in the other case 

 continuing nearly the same. The lamp was then taken out, 

 and as soon as the parts were cooled, and both thermome- 

 ters showed the same degree, I adjusted the beat of the pen- 

 dulums as before, and at the end of twenty-four hours I 

 found the pendulum that had been heated kept precisely the 

 same rate as it did before the experiment was made. 



By this experiment it appeared evident that the zinc bar 

 was considerably too long. The pendulum was then taken 

 down, to have more holes made for the adjusting screw ; 



and 



