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LL.D. ; John Percy, M.D. ; Lyon Play fair, Ph.D. ; The Rev. Bar- 

 tholomew Price, M.A. ; Archibald Smith, Esq., M.A. ; Charles 

 Wheatstone, Esq. 



Mr. Henry Clifton Sorby was admitted into the Society. 

 The following communications were read : 



I. " On the Expansion of Wood by Heat." By J. P. JOULE, 

 LL.D., F.R.S. &c. Received November 5, 1857. 



In pursuing the researches of which abstracts have been given in 

 the * Proceedings' for January 29 and June 18, the author found that 

 the heat evolved by compressing wood, cut either in or across the 

 direction of the grain, was nearly that due to the application to the 

 particular case of Professor Thomson's formula. Exact agreement 

 could not be expected, on account of the discordant results arrived at 

 by different experimenters on the expansion of wood. On investi- 

 gating the subject, the author finds that the expansion of wood cut 

 in the direction of the grain, is greatly influenced by the tension to 

 which it is exposed, as well as by its humidity. A rod of well- 

 seasoned and dried bay-wood, |ths of an inch in diameter, and exposed 

 to the tension of 261bs., gave an expansion of -00000461 per degree 

 Centigrade, but when a weight of 426 Ibs. was hung to it, its co- 

 efficient of expansion was increased to '00000566. In conformity 

 with this result, it was found that the elasticity of the rod was con- 

 siderably diminished by an increase of its temperature. On inves- 

 tigating the effect of humidity, the author found that it occasioned 

 a diminution in the expansibility by heat. After the rod of bay-wood 

 with which the above experiments were made had been immersed in 

 water until it had taken up 150 grains, making its total weight 

 882 grs., its expansion with a tension of 26 Ibs. was found to be 

 only -000000436. Experiments with a rod of deal 33 inches long, 

 and weighing when dried 425 grs., gave similar results. Its expan- 

 sion when dry, with 26 Ibs. tension, was -00000428, and with 226 Ibs. 

 00000438 ; but when made to absorb water, its coefficient of 

 expansion gradually decreased, until, when it weighed 874 grs., 

 indicating an absorption of 449 grs. of water, expansion by heat 

 ceased altogether, and, on the contrary, a contraction by heat equal 

 to -000000636 was experienced. 



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