256 Capillary tubes. 



Laplace's theo- that if tlic len£[tli of ihe column be very small, the sine of the 

 tion and de-^*^ inclination of the axis will then be very nearly in the inverse 

 pression of ratio of the square of the distance of the middle of the column 

 fffectofattrac ^^"^^ ^^^ summit of the cone; and this also takes place, if 

 tion which is instead of causing a drop of the tluid to move in a conical tube 



called capil 

 laiy. 



it be made to move between two planes forming a very small 

 angle between them. These results are entirely conformable 

 fo experience, as may be seen in the Optics of New ton (query 



31.). 



Calculation also teaches us, that the sine of the inclination of 

 the axis of the cone to the horizon, is then, very nearly, equal 

 to a fraction, of which the denominator is the distance of the 

 middle of the drop from the summit of the cone, and its nu- 

 merator the height to which the fluid would rise in a cylindri- 

 cal tube, having for its diameter that of the cone at the middle 

 of the column. If two planes which include a drop of the 

 same fluid form between them an angle equal to double the 

 angle formed by the axis of the cone and its sides, the incli- 

 nation to the horizon of a line which equally divides the angltf 

 formed by the planes, need be only half that required in the 

 axis of t}ie cone, in order that the drop should remain in equi- 

 11 brio. 



The precceding theory likewise gives the explanation and 

 measure of a singular phenomenon, presented by experiment. 

 Whether the fluid be elevated or depressed between two verti- 

 cal planes, parallel to each other, and plunged in the fluid at 

 their lower extremities, their planes tend to come together. 

 Analysis shews us that if the fluid be raised between them, 

 each plane will undergo, from without, inwards, a pressure 

 (equal to that of a column of the same fluid, of which the 

 height would be half the sum of the elevations, above the 

 level, of the points of contact of the interior and exterior sur- 

 faces of the fluid with the plane, and of which the base should 

 be the parts of the plane comprised between the two horizon- 

 tal lines drawn through those points. If the fluid be depress- 

 ed between the planes, each of them will in like manner un- 

 dergo from without, inwards, a pressure equal to that of a co- 

 lumn of the same fluid, of which the height would be half the 

 sum of the depressions below the level of the points of contact 

 of the interior and exterior surfaces of the fluid with the viane, 



and 



