THE 



PHILOSOPHICAL MAGAZINE 



AND 



ANNALS OF PHILOSOPHY. 



[NEW SERIES.] 



JANUARY 1828. 



I. On the Theory of Capillary Action, and the Depression of 

 the Mercury in the Tubes of Barometers, By J. Ivory, Esq. 

 M.A. F.R.S.* 



r | 1 HE elevation and depression of liquids in capillary tubes, 

 -*- that is, tubes of a very small bore resembling a hair, has 

 long occupied the attention of natural philosophers. If we 

 would acquire a precise notion of the present state of this 

 branch of science, we must consider it in two separate points 

 of view. In the first place we are in possession of a mathe- 

 matical theory which quadrates exactly with the phenomena ; 

 but, in the second place, when we direct our attention to the 

 physical foundation of this theory, we find as many opinions 

 as there are different inquirers, and no one account is entirely 

 free from difficulties. My present intention is to make some 

 observations on the first part of the subject, without touching 

 at all on the second, which is reserved for future discussion. 



The mathematical theory of the capillary phaenomena is 

 not complicated, being derived from two independent princi- 

 ples. The first of these is the fact, that the surface of the same 

 liquid always makes the same angle with the surfaces of solids 

 immersed in it, when the matter of the solids is the same. 

 In the case of glass and water, and generally whenever a solid 

 is wetted by a liquid, the two surfaces touch one another, or 

 make an infinitely small angle. In glass and mercury, the 

 two surfaces are inclined to one another in an angle of about 

 42°. 



* Communicated by the Author. 



New Series. Vol. 3. No. 13. Jan. 1828. B The 



