Fig. 2 shows the shape of the manometer tubes. They are made
of quarter inch glass tubing bent to shape in a flame and left open at
both ends. They are mounted on a scale board which has several
equidistant horizontal lines running across it. The two bent wires
which support the scale board fit loosely in holes in it and in the
base. This method of mounting is very handy, since it permits the
scale board to be swung to right or left as may be convenient, or
turned round so as to show the fittings on its back, without moving
the bottle. The three manometers are filled to the same level with
mercury, the quantity being adjusted by means of a pipette. A
perforated rubber stopper, fitted with a glass tube on which is
slipped a rubber syringe bulb, completes the apparatus.
When the bulb is pinched between the fingers, the mercury is forced up
to the same height in each of the manometers, thus proving that the
pressure is exerted equally in the three directions, up, down, and
sideways. With the bottle filled with water the same effect follows,
the law being the same for liquids and gases. When using water in the
apparatus it is essential that the rubber tubes, as well as the
bottle, be filled, and when used in the class room it is better to
show the experiment with water first, it being easier and quicker to
empty the bottle and tubes than to fill them.
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