I. On the expansion of wood by heat

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 investigating 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, ⅜ths of an inch in diameter, and exposed to the tension of 26 lbs., gave an expansion of ·461 per degree Centigrade, but when a weight of 426 lbs. was hung to it, its coefficient of expansion was increased to ·566. In conformity with this result, it was found that the elasticity of the rod was considerably diminished by an increase of its temperature. On investigating 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 lbs. was found to be only ·436. Experiments with a rod of deal 33 inches long, and weighing when dried 425 grs., gave similar results. Its expansion when dry, with 26 lbs. tension, was ·428, and with 226 lbs. ·438; 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 beat ceased altogether, and, on the contrary, acontraction by heat equal to ·636 was experienced.