Emily. And are not fountains, of the nature of springs?
Mrs. B. Exactly. A fountain is conducted perpendicularly upwards, by the spout or adjutage A, through which it flows; and it will rise nearly as high as the reservoir B, from whence it proceeds. ([Plate 14. fig. 2.])
Caroline. Why not quite as high?
Mrs. B. Because it meets with resistance from the air, in its ascent; and its motion is impeded by friction against the spout, where it rushes out.
Emily. But if the tube through which the water rises be smooth, can there be any friction? especially with a fluid, whose particles yield to the slightest impression.
Mrs. B. Friction, (as we observed in a former lesson,) may be diminished by polishing, but can never be entirely destroyed; and though fluids, are less susceptible of friction, than solid bodies, they are still affected by it. Another reason why a fountain will not rise so high as its reservoir, is, that as all the water which spouts up, has to descend again, it in doing so, presses, or strikes against the under parts, and forces them sideways, spreading the column into a head, and rendering it both wider, and shorter, than it otherwise would be.
At our next meeting, we shall examine the mechanical properties of the air, which being an elastic fluid, differs in many respects, from liquids.
Questions
1.(Pg. [129]) Why do not the frequent rains, fill the earth with water?
2.(Pg. [129]) Why will vapour rise? to what height will it ascend, and what will it form?