7Q DEGREES OF FACILITY WITH WHICH BODIES 



II. 



Observations on the different Degrees of Facility with which 

 MaJJes of the fame Material admit of Changes in their Tem- 

 perature; with Applications of the Fuels to the Conjlruclion of 

 Pendulums, and Speculations upon various new Forms of pen- 

 dulous Regulators of Time. In a Letter from]. Whitley 

 Boswell, Efq. 



To Mr. NICHOLSON. 

 SIR, 



Compound pen- 1 HE fatisfa&ory communication on an ingenious improve^ 

 dulums. ment of the compound pendulum, in your Journal for De- 



cember, has reminded me of fome ideas which occurred to me 

 on fimilar fubjects. In hopes that they may be of fome ufe in 

 a matter fo interefting in itfelf, and fo important in its appli- 

 cation, I fend them for your opinion. 



A very material point feems to have been omitted in all the 

 confederations I have met with on the expanfion of bodies by 

 heat; pyrometrical experiments being directed to that merely 

 of different fubftances of the fame fize, but none being made 

 on bodies differing in bulk. 

 Bodies are more Though various bodies differ in their degree of expanfion 

 or lefs fpeedily by heat according to their materials, yet all are fubject to 

 sccordineto " cerla ' n laws on this point, depending on their dimenfions ; 

 their dimenfions for as bodies receive or communicate heat by their furfaces, 

 and figure. anc j reta ; n j^ j n proportion to their bulk, it follows, that their 

 mutability of temperature muft depend on the ratio of their 

 folid contents to their furfaces ; and that the greater the fur- 

 face in proportion to the bulk, the more readily will a body 

 change its temperature; and on the contrary, the greater the 

 bulk in proportion to the furface, the lefs will it be affected 

 by the fluctuating heat of the furrounding medium. 

 Dedudionof the T^e proportion which the furfaces of bodies bear to their 

 effects, bulk may be varied, either by altering their fhape or changing 



their fize. In the firft refpecl it is fufficient to note, that the 

 flatter and longer any body is, the greater will be its furface 

 in proportion to its mafs of matter, and viceterfa: the dif- 

 ference caufed by the variation of bulk can be more eafily 

 calculated, as in bodies of fimilar figures their furfaces are 



exactly 



