An escape-pipe, provided with a valve, is inserted into
the top of the chamber. When any upward pressure acts on the top
roller, it is communicated by the plunger to the water, which escapes
through the valve, and the roller rises.
'When the valve is partially closed, the water escapes more slowly;
and the rise of the roller, and consequently the taper of the iron,
are more gradual.
'Any rate of taper may thus be had by regulating the rise of the
opening of the escape-valve. If the water is all driven out before the
bar is entirely through the rollers, the top roller ceases to rise,
and the iron becomes parallel from that point. Then, if the ends of
the bar be reversed, and it be again passed between the rollers, the
parallel portion will become tapered; thus we can get a bar.'
At the same time, a 'Thermometrical Ventilator' was exhibited, which
is described as circular in form, with a well-balanced movable plate.
'Upon the side of the valve is an inverted syphon, with a bulb at one
end, the other being open; the lower part of the tube contains
mercury; the bulb, atmospheric air. An increase of temperature expands
the air in the bulb, drives the mercury down one side and up the
other, thereby destroying the balance, and causing the valve to open
by turning on its axis.
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