57 



fralize the polarity of the molecules so as to give them perfect free- 

 dom of motion around every imaginable axis. The small amount of 

 cohesion (53 grains to the square inch), exhibited in the foregoing 

 experiment, is due, according to the theory of capillarity of Young 

 and Poisson, to the tension of the exterior film of the surface of water 

 drawn up by the elevation of the plate. This film gives way first, 

 and the strain is thrown on an inner film, which, in turn, is ruptured; 

 and so on until the plate is entirely separated; the whole effect 

 being similar to that of tearing the water apart atom by atom. 



Reflecting on this subject. Professor H. had thought that a more 

 correct idea of the magnitude of the molecular attraction might be 

 obtained by studying the tenacity of a more viscid liquid than water. 

 For this purpose he had recourse to soap water, and attempted to 

 measui'e the tenacity of this liquid by means of weighing the quan- 

 tity of water which adhered to a bubble of this substance just before 

 it burst, and by determining the thickness of the film from an obser- 

 vation of the colour it exhibited in comparison with Newton's scale 

 of thin plates. Although experiments of this kind could only fur- 

 nish approximate results, yet they showed that the molecular attrac- 

 tion of water for water, instead of being only about 53 grains to the 

 square inch, is really several hundred pounds, and is probably equal 

 to that of the attraction of ice for ice. The effect of dissolving the 

 soap in the water is not, as might at first appear, to increase the mole- 

 cular attraction, but to diminish the mobility of the molecules, and 

 thus to render the liquid more viscid. 



The communication of Professor Henry gave occasion to 

 further observations from him in reply to remarks made by 

 Dr. Patterson. 



Dr. Dunglison directed attention to the establishment of the 

 Sydenham Society of London, instituted with objects similar 

 to those of the Ray Club, — to facilitate the publication of medi- 

 cal works and the diffusion of medical literature; and detailed 

 the plan which the Society intends to pursue in order to carry 

 its objects into effect. 



These objects will consist of a succession of publications, embracing, 

 among others, 1. Reprints of standard English works, which are 

 rare and expensive. 2. Miscellaneous selections from the ancient 

 and from the earlier modern authors, reprinted or translated. 3. 

 Digests of the works of old and voluminous authors, British and Fo- 



