Mr. Editor,--I have a saw-mill which draws thirty-six square inches of
water, under thirty feet head. I wish to build another below with only
twenty feet head of water. How many square inches aperture will be
required to discharge the same quantity in the same time? If some of
your correspondents will give me an answer, they will much oblige me.
R. C. Navarino, Sept. 7, 1846.
We shall have no occasion to depend on correspondents for the
intelligence above required. Thirty-six inches of aperture under
thirty feet head, will admit the discharge of 660 cubic feet of water
per minute; the velocity of the water being forty-four feet per
second. Under twenty feet head the velocity is only thirty-six feet
per second, and consequently forty-four inches aperture is required to
discharge an equal quantity.
_Rule in Hydraulics_: (never before published.) To ascertain the
velocity of water issuing through an aperture under a given head:
Multiply the head in feet by 62, and the square root of the product
will show the velocity in feet per second.
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