FAMILY FUN

New Zealand Tablet, Volume XXXVI, Issue 8, 27 February 1908, Page 38

FAMILY FUN

Sand in. the Hour-glass.— lt is a remarkable fact, that the "flow of sand in the the hour-glass is perfectly equable, whatever may - be the quantity in the glass, that is, the sand runs vno , iister when the upper ha'f of the glass is q.uite full than when it is nearly empty. It would, however, be natural enough to conclude that, when full of sand, it would be more swiftly urged through the aperture, than when the glass,, was only a quarter full, and near the close of the hour. The fact of the even flow of sand may be proved by a very simple experiment. Provide some silver sand, dry it over or before the fire, and pass it through a tolerably large sie\e. Then take a tube, of any length or diameter, closed at one end, in which make a small hole, say the eighth of an inch ; stop this with a peg, and fill up the tube with th© sifted sand. Hold the tube steadily, or fix it to a wa 1, or frame, at any height from a table ; remove the peg, and permit the sand to flow in any measure for any given time, and note the qwantity. Th n, let the tube be emptied, and only 1-alf or quarter filled with the same ; measure again, for a line time, and the same quantity of sand will flow ; even if you press the sand in the tube with a- ruler or stick, the flow of the sand through the hole will not ba increased. The above is explained by the fact that when the sand is poured into the tube, it fills it with a succession cf conical hsaps, and that all the weight which the bottom of the tube sustains is omly that 'of the heap which first falls upon it ,;i as the succeeding heaps do not press downwards, but only against the sides or Walls of the tube. .Resistance of Sand.— From the above experiment it may be concluded t>hit it is extremely difficult to thrust sand 1 out of a tube by means of a fitting pi UR or pisIon;, and this 1 , upon 1 a trial, is -found to be the case. Fit the piston to a tablefexactly like alloy's pop gun),, pour some sand in, and try; with the utmost strength to push out I'he sand. It wii 1 ! be found impossible to do this : rather' than the sand should be shot out,' the tube will burst at the sides.