CAPILLARY TUBES. 255 



'* follow: If two plane polished plates of glass (suppose two Laplace's theo- 



'* pieces of a polished looking-glass) be laid together, so that'^y^^^f ^^®^^" 



** their sides be parallel and at a very small distance from one pression of 



** another, and their lower edges be dipped into water, the*^"'*^!^^*if'"' 



' » ff > eftectofattrac- 



*' water will rise up between them. And the less the distance tion which is 



" of the glasses is, the greater will be the height to which the j^"®^ *^^P^* 



" water will rise. If the distance be about the hundredth part 



*' of an inch, the water will rise to the height of about an inch ; 



** and if the distance be greater or less in any proportion, the 



** height will be reciprocally proportional to the distance very 



" nearly. «****. And if slender pipes of glass be dip- 



** ped at one end into stagnating water, the water will rise up 



** within the pipe, and the height to which u rises will he re- 



*' ciprocally proportional to the diameter of the cavity of the 



*' pipe, and will equal the height to which it rises between two 



" panes of glass, if the semi-diameter of the cavity of the pipe be 



** equal to the distance between the planes or thereabouts. And 



^* these ex}>eriments succeed after the same manner in vacuo as 



*' in the open air, (as hath been tried before the Royal Socie- 



" ty), and therefore are not influenced by the weight or pres-e, 



*' sure of the atmosphere." 



The capillary phenomena of inclined planes and of conical 

 and prismatic tubes are so many corollaries of my analysis. 

 Thus it is observed that a short column of water in a conical 

 tube, open at both ends and kept horizontal, is moved towards 

 the summit of the tube ; and from what has been explained, it is 

 clear that this must be the event. In fact, the surface of the fluid 

 column is concave at its two extremities ; but the radius of its 

 surface is smaller at the end next the summit than at the end 

 next the base ; the action of the fluid on itself is therefore less 

 on tlie side next the summit, and consequently the column must 

 tend that way. But if the column of fluid be mercury, its surfac6 

 will then be convex , and its radius also less towards the sum- 

 mit than towards tlie base ; but on account of its convexity, 

 the action of the fluid on itself is greater towards the summit, 

 and the column must be carried towaiMs the base of the 

 tube. 



' We may balance this action by the proper weight of the co- 

 lumn, and keep it suspended in equilibrio, by inclining the axis 

 of the tube to the horizon. A very simple calculation shews 



that 



