543 Intelligence and Miscellaneous Articles. 



May,) states that he had prosecuted his experiments on the soap- 

 bubble to a greater extent, and had arrived at a nuihber of results 

 which appeared to him of some interest in reference to capillarity, 

 a subject which had given rise to a greater diversity of opinion than 

 any other part of natural philosophy. As an evidence of its present 

 unsettled state, he mentioned the fact that the last edition of the En- 

 cyclopaedia Britannica contained two articles on this subject, under 

 different names ; one by Dr. Young, and the other by Mr. Ivory, 

 which explain the phsenomena on entirely different physical prin- 

 ciples. 



According to the theory of Young and Poisson, many of the phse- 

 nomena of liquid cohesion, and all those of capillarity, are due to a 

 contractile force existing at the free surface of the liquid, and which 

 tends in all cases to urge the liquid in the direction of the radius of 

 curvature towards the centre, with a force inversely as this radius. 

 According to this theory, the spherical form of a dew-drop is not the 

 effect of the attraction of each molecule of the water on every other, 

 as in the action of gravitation in j^roducing the globular form of the 

 planets (since the attraction of cohesion only extends to an unappre- 

 ciable distance), but it is due to the contractile force which tends 

 constantly to enclose the given quantity of water within the smallest 

 surface, namely, that of a sphere. Prof. Henry finds a contractile 

 force perfectly similar to that assumed by this theory in the surface 

 of the soap-bubble ; indeed, the bubble may be considered a drop of 

 water with the internal liquid removed, and its place supplied by air. 

 The spherical force in the two cases is produced by the operation of 

 the same cause. The contractile force in the surface of the bubble 

 is easily shown by blowing a large bubble on the end of a wide tube, 

 say an inch in diameter ; as soon as the mouth is removed, the bubble 

 will be seen to diminish rapidly, and at the same time quite a forcible 

 current of air will be blown through the tube against the face. This 

 effect is not due to the ascent of the heated air from the lungs with 

 which the bubble was inflated, for the same effect is produced by in- 

 flating with cold air, and also when the bubble is held perpendicu- 

 larly above the face, so that the current is downwards. 



Many experiments were made to determine the amount of this 

 force, by blowing a bubble on the larger end of a glass tube in tlie 

 form of the letter U, and partially filled with water ; the contractile 

 force of the bubble, transmitted through the enclosed air, forced 

 down the W'ater in the larger leg of the tube, and caused it to rise 

 in the smaller. The difference of level observed by means of a mi- 

 croscope, gave the force in grains per square inch, derived fi*om the 

 known pressure of a given height of water. The thickness of the 

 film of soap water which formed the envelope of the bubble, was es- 

 timated as before by the colour exhibited just before bursting. The 

 results of these experiments agree with those of weighing the bubble, 

 in giving a great intensity to the molecular attraction of the liquid ; 

 equal at least to several hundred pounds to the square inch. Several 

 Other methods were employed to measure the tenacity of the film, the 



