462 NOTES. 



cast-iron tubbing is employed to support the sand or mud bed, and carry the water 

 down to the bottom of the pit. 



Water stands higher in narrow than in wide glass tubes, but quicksilver mounts 

 higher if the inside of the tube be lined with bees-wax or tallow. We can easily 

 conceive that the lateral action may yet cause the perpendicular ascent j for it is 

 a fundamental property in fluids, that any force impressed in one direction may be 

 propagated equally in every other direction. Hence the affinity of the fluid to the 

 internal surface producing the vertical ascent. A drop of water let fall on a clean 

 plate of glass spreads over the whole surface, in as far as there is liquid to cover 

 the glass, the remoter particles extending the film, yet adhering with the closest 

 union. The adhesiveness of fluids is still more clearly shown in their projection 

 through the pores of minerals, plants, animals, gravel, earth, and sand. Water 

 rises through successive strata of gravel, coarse sand, fine sand, loam, and even 

 clay : and hence, on the sea-coast, those quicksands, which have engulfed armies 

 and ships, the pressure and elevation of the ocean at flood tide sending its 

 advanced column up in the sand to a level with its surface far out at sea. Gravel 

 divided into spaces of the hundredth part of an inch, will allow water to ascend 

 above four inches ; it would mount up through a bed of sixteen inches of this 

 material, supposing sea gravel to be the 500th part of an inch. Fine sand, in 

 which the interstices are the 2,500th part of an inch, allow the humidity to 

 ascend seven feet through a new stratum; and if the pores of the loam were 

 only the 10,000th part of an inch, it would gain the further height of 25f feet 

 through the soft mass ; thence originate v astce syrtes. The clay would retain the 

 moisture at a greater altitude ; but the extreme subdivisions of the clay, which 

 enable it to carry water to almost any elevation, yet make it the most efficient 

 material in puddling or choking up the interstices of masonry. 



The ascent of water in a glass tube is due chiefly, we think, to the excess of the 

 attractive power of the glass above the cohesive power of the fluid mass over itself. 

 Were the attractive and cohesive forces equal, the fluid would remain balanced at 

 a common level. Mercury hence sinks, by reason of the strong cohesive power of 

 its own particles. Hence we account for mercury closing over a ball of crude 

 platinum, which nevertheless, being gently laid on the mercury, will float, although 

 its specific gravity is above that of mercury. 



It is however the province of chemistry, rather than of mechanics, to measure 

 the cohesive power possessed by different fluids, or by the same fluid under different 

 degrees of temperature. 



The suspension of water in any stratum through which it can percolate, must 

 depend entirely upon the smallness of the upper orifice, or superficial extent of 

 the deflection with which the stratum slopes off horizontally above ground, and 

 upon the relative elevation of the extremities of the impervious stratum. Thus, 

 suppose a and b to be two extremities of a stratum pervious to water ; the central 

 column of water at c is pressed with the whole weight of the space be, and this 

 pressure upon c a pushes the fluid out at a 

 by the excess of force in be above that in 

 a; and therefore, while the ground or 

 land at b is generally dry, that at a is per- 

 haps boggy; at all events it will exhibit 

 springs at its surface, be cold, damp, and 

 its inhabitants subject to rheumatism or 



