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Jii Account of S0711C E.rpenmeirts made to determine fJic T7ier- 

 mrd Expansion of MarUeJ^ By Mr John Dunn and Mr 

 Edward Sang. Couinumicated by the Authors. 



In the construction of clock movements and of metrical stantl- 

 ards, we are constantly harassed by the expansion and contrac- 

 tion of the parts. 



As soon as the fact that bodies expand by heat became known, 

 the question must have arisen, " Does any substance exist which 

 is not liable to this change of volume T'' Many have been the 

 experiments made to determine the rates of expansion of dif- 

 ferent bodies ; but although some bodies have been found of 

 •which the elongation is exceedingly small, in none, as yet, has 

 it been discovered to be awanting. 



The construction, on the supposition that marble is inexpan- 

 sile, of a marble clock pendulum for the Royal Society of Edin- 

 burgh, a description of which was read at our last meeting, 

 and previously, we understand, before the Royal Society itself, 

 can hardly have failed to have excited a considerable sensation 

 among those who are practically acquainted with the many in- 

 conveniences which attend a change of temperature, or to have 

 created some curiosity about the manner in which such a singu- 

 lar fact was arrived at. 



The analogy from which the inexpansibility of marble was 

 deduced, at first sight plausible, will not bear a rigid examina- 

 tion. Granting, though it has not been confirmed, that a re- 

 gularly crystallized piece of calcareous spar changes its shape 

 but not its volume on being subjected to a change of tempera- 

 ture ; this only shows that, when disposed in a peculiar man- 

 ner, the particles of carbonate of lime approach in one direc- 

 tion, and recede in others, so as to retain the same aggregate 

 volume. We are by no means at liberty to infer, that irregu- 

 larly disposed particles, or even crystals of this substance, are 

 acted on in the same way ; the very fact of their accidental dis- 

 tribution destroys of iiself the force of tiie analogy. Particles 

 of carbonate of lime, when regularly arranged, may obey one 

 law, while, for any thing that we know, the intimate consti- 



* R?ad before the Societv of Arts for Scotland, IVrarch 30. IfWI. 



