On the Thermal Effect of drawing out a Film of Liquid. 61 



mountaiu must nevertheless be referred, geologically, to the more 

 modem part of the latest Tertiary epoch. 



" On some Thermo-dynamic Properties of Solids." By J. P. 

 Joule, LL.D., F.R.S. &c. 



A resume of the greater part of this paper has already appeared 

 in the 'Proceedings' for January 29, June 18, and November 26, 

 1857. The author has since examined the expansion by heat of 

 wood cut across the grain, which, as well as that cut in the direction 

 of the fibre, he finds to be increased by tension and decreased by 

 moisture. When a sufficient quantity of water has been absorbed 

 the expansibility by heat ceases, and wood is contracted in each di- 

 rection by rise of temperature. Nevertheless, when wood, saturated 

 with water, is weighed in water of different temperatures, the result 

 shows cubical expansion of the substance of the wood by heat. The 

 inference drawn by the author from these facts is, that the contraction 

 of the dimensions of wet wood is owing to the action of heat in di- 

 minishing the force of capillary attraction, and that thus the walls of 

 the minute cells and tubes of the woody structure are partially re- 

 lieved from a force which thrusts them asunder, a small quantity of 

 water exuding at the same time. In the case of wet wood which 

 contracts by heat, he finds, in accordance with Professor Thomson's 

 formula, that a rise of temperature is produced by the application of 

 tension. In conformity with the deductions of the same philosopher, 

 the author has also been able to detect experimentally the minute 

 quantity of heat absorbed, in bending or twisting an elastic spring, 

 arising from the diminution of the elastic force of metals with a rise 

 of temperature. 



"On the Thermal Effect of drawing out a Film of Liquid." By 

 Professor William Thomson, F.R.S. 



A very novel application of Carnot's cycle has just occurred to 

 me in consequence of looking this morning into Waterston's paper 

 on Capillary Attraction, in the January Number of the Philosophical 

 Magazine. Let T be the contractile force of the surface (by which 

 in Dr. Thomas Young's theory the resultant effect of cohesion ou 

 a liquid mass of varying form is represented), so that, if II be the 

 atmospheric pressure, the pressure of air within a bubble of the 



liquid of radius r, shall be — + H. Then if a bubble be blown 



r 

 from the end of a tube (as in blowing soap-bubbles), the work spent, 

 per unit of augmentation of the area of one side of the film, will be 

 equal to 2T. 



Now since liquids stand to different heights in capillary tubes at 

 different temperatures, and generally to less heights at the higher 

 temperatures, T must vary, and in general decrease, as the tempe- 

 rature rises, for one and the same litpiid. If T and T' denote the 

 values of the capillary tension at temperatures t and t' of our abso- 

 lute scale, we shall have 2(T— T') of mechanical work gained, iu 

 allowing a bubble ou the end of a tube to collapse so as to lose a 



