Chap. 4.]

Raising Water with Open Tubes.

503

inade the extreme end of the tube 7.5 inches diameter. The tube as thusformed was secured to a straight strip of wood of nearly the same length,by means of three copper Straps, whieh were soldered to the tube andsorewed to the wood. (See the figure.) About a foot from each end, andacross the back of the strip, two pieces of wood, 3 inches long and ljwide, were secured. They projected half an inch over each side of thestrip, and were beveled at the ends, so as to fit into and slide readily upand down in a dovetailed groove formed on the face of the post F F.This post was secured in an inclined position, as represented. Whenlarge tubes are used they should always be inclined, that the water onceraised above the orifice may not fall into it again and run back. Thesurface of the water in the cask was 13 inches below the upper end of thetube, and upon working the latter the jet (.§ of an inch diameter) rose 22feet. A piece of pipe was next slipped on the end, which made the tubea foot longer, and reduced the orifice to half an inch, when the jet roselittle if any higher than before. Another tapered piece of pipe was addedto the last, making the orifice five-sixteenths of an inch, upon which thejet did not ascend over six or eight feet. An air-pipe, figured at No. 232,was now added, that the water might be fully depressed in the tube on itsascent, but the jet was so pinched at the orifice that no obvious changewas perceived.

The upward stroke ought to be so regulated, that the air in rushingdown should push nearly all the water out of the tube, that the wave inrising may be urged up with the full pressure of that above it in the re-servoir : hence the elevation of the jet produced by the upward stroke ofa spouting tube depends chiefly upon the depth of its immersion. But ifthe upward movement exclude nearly all the water, the downward oneif made with due velocity prevents it, or much of it, from entering beforethe tube itself gets nearly to the end of its stroke, and consequently theeffective height of the hydrostatic column is then increased to an extentequal to the length of the stroke. On the other hand, if the upwardmovement be made so quick that the air has not time to fill the enlargedspace below before the stroke is finished, then little or no rise will takeplace. The Operation in this case is the converse of the experiment withthe matrass, No. 225.

When the movements of one of these instruments are properly timed,the inertia of the descending air and ascending liquid is peculiarly beneficial. In ordinary machines, where the direction of moving masses isreversed, or when they are alternately brought into a state of rest andmotion, the inertia is overcome by an outlay of the force employed; butthis is not the case with spouting tubes. Thus when a tube is raised, theair descends into the vacuity left by the retiring liquid, and when its mo-mentum is expended, its motion is continued by inertia alone, and conse-quently the water is pushed down still further. Then again, on the ascentof the liquid the elevation of the jet, or the volume discharged, will beincreased if the inertia of the rising wave be sulfered to expend itselfwithout interference by an untimely movement of the instrument.

A reciprocating rectilinear movement might be given to spouting tubesby a spring-pole, as in the canne hydraulique. The movement, however,should be regulated by that of the wave. This might be accomplished inlarge tubes by connecting to the moving apparatus a heavy pendulum,whose length could be increased or diminished according to that of thestroke.

If a tank or reservoir be not sufficiently deep for the employment ofthese tubes, an opening of the proper size and depth might be made at