214 



NEW COMPENSATION PENDULUM. 



nzz r32, » implying here the mean density of the earth 

 compared with the mean density of the elevated portion of 

 the spheroid, which hence appears to be about three fourths 

 of that of the whole earth. It is obvious that, in this 

 case as well as in the'former, if the density of the sea were 

 two thirds greater than that of the earth, the slightest dis- 

 turbing for.e would completely desti-oy the equilibrium, 

 and the whole ocean would be collected on one side of the 

 earth, 



I am, Sir, 



Your very humble servant, 



A. B. C. D. 



X. 



Description of a new Compensation Pertdulum; hj Lieute- 

 nant Henry Kater. Communicated by the Author. 



Manyattempts OiNCE the first application of the pendulum to clocks, 

 irre<^uianty of numerous attempts have been made, to correct the errour 

 clocks fi jm arising from a variation of temperature, which, by contract- 

 heat an CO . -^g ^^ dilating the substance of which the pendulum rod is 

 composed, occasions the clock to go faster in cold than iu 

 warm weather, and consequently to vary considerably in its 

 rate at different seasons of the year. 

 Defe-ts of the The gridiron pendulum, now used in almost all regular 

 gridtron pen- obsei'vatories, though generally supposed to be the best cal- 

 culated to remedy this inconvenience, is complex, and re- 

 quires the greatest nicety in proportioning the brass and 

 steel rods (of which it is composed) to each other; it is very 

 expensive; and, if it should be badly constructed at first, is 

 and of the mer- incapable of adjustment. The mercurial pendulum is not 

 "^"" so liable to the last of these objections, for, if the quantity 



of mercury should not be found exactly to compensate for 

 the expansion of the metallic rod, a little may be added or 

 taken away ; but then it must require very numerous trials, 

 before an accurate result can be obtained. - 



A siirple, These considerations induced me, to turn my attention to 



the 



