J25 ON THE TKEOEY OF CAPILLARY ATTRACTIOS. 



V. 



Ore tlie Theory of Capillary Attraction, By Thomas 

 Knight, Efq. In a Letter from the author. 



To Mr. NICHOLSON. 

 SIR, 



tion imperfect. 



Theory of i^ OTWITHSTANDING the attention, that has lately 

 capillary ac- been paid to the phenomena arising from capillary action, 

 the theory appears to be still in a very imperfect state. I 

 have endeavoured, in what follows, to throw some light on 

 th'c5t part, which is most defective. The insertion of it, in 

 your valuable Journal, will speedily bring my ideas before 

 competent j u d ges, 



And much oblige, Sir, 



Your most obedient Servant, 

 Papcastle, near Cockermouth, THOMAS KN IGHT. 



July2'2d, 1810. 



Thepheno- There are tv.'o ways of treating the subject of capillary 

 tnenaniay be action ; first, the measure of the other phenomena may be 

 the figure of estimated from the figure of the surface, which is a simvlla- 

 the aiirface, oi neous effect with the height of the fluid : or, secondly, in a 

 forces^^ ^ more natural manner, from the forces themselves which 



support the fluid, 

 Wistake of If, with Mr. La Place and Dr. Young, the first method 



Mr. la Place, y^^ made use of, we must take care not to mistake an effect 

 for the cause, as the former of these authors appears atjirst 

 to Lave done*. But, even if we do not fall into this errour, 

 a theory, which stops here, must appear, I think, to any 

 one, to be exceedingly defective. Let the hydrostatic prin- 

 ciple, of the perpendicularity of the force to the surface, 

 be used to explain what relates to the figure of that surface: 



♦ It is very remarkable, that Dr. Young, itj his observations on Mr. 

 la Place's theory, should not have noticed the chief circumstance in 

 M hich it differs from all others : viz. " Que I'eaii s'eleve, dans un tube 

 capillaire, par Peffet de la concavil6 de sa surface interieure." Sur 

 TAction capillaire p. 60. Whether Dr. Young himself be of this 

 opinion, I do not very clearly perceive, 



but. 



