THE reverend and ingenious Dr. Hales, from whom mankind has received
such benefit by his useful application of ventilators, being inclined
to extend its use to those, who work in mines at great depths under
ground, where the lives of many are lost by damps and noxious vapours,
occasioned by the want of a free circulation of air; and finding by
experience, that ventilators worked by wind do not operate above one
third part of the year, and in calm hot weather, when most wanted, do
not operate at all; did me the honour of applying to me for assistance
in contriving a machine to work the ventilator, by the help of the
fire-engine, which is now generally used in all mines for drawing off
the water; and which I have accordingly attempted, and hope it will
answer the purpose.
As the lever of the fire-engine works up and down alternately, and
performs at a common medium about a dozen strokes in a minute, it
was necessary to contrive some way to make the beam, tho’ moving
alternately, to turn a wheel constantly round one way, and also to
increase the number of strokes to fifty or sixty in a minute.
The model of a machine for this purpose is composed of four wheels of
different sizes, two clicks, three pinions, and a fly; which is put
into motion by the part of a wheel fixed to the arch of the lever of
the fire-engine.
The wheel, which is turned by the lever, or rather moved up and down
by it, is loose on its arbor; and likewise one of the rochets, and the
wheel next to it. The outside rochet and outside wheel are fixed on the
arbor.
There are two pinion-wheels fixed on the arbor; one on each side, near
the edge of the wheel moved by the lever, which turns them.
There are also two clicks; one fixed to the great wheel, the other to
the frame. These exclusive of the wheel that moves the fly.
The effect is, When the lever moves the wheel downwards, its click
forces the rochet fixed on the arbor to move along with it, and the
other wheels the same way. When it moves upwards, the click fixed on
the frame stops the larger rochet, and the wheel next to it, which are
pinned together. This wheel being stopped, and the great wheel carried
upwards by the lever, the pinion towards the edge of the great wheel
is forced round it, and moves the pinion on the other side the great
wheel; which pinion moves the wheel fixed on the arbor, the contrary
way to the great wheel, which is carried upwards by the lever. By which
means, the arbor is constantly turned the same way, when the lever of
the fire-engine is moved either upwards, or downwards.
Upon the arbor there is also another great wheel fixed, which turns
a pinion: on the arbor of which pinion is a crank to move the
ventilator, and also a fly fixed to the end, to help the motion of the
crank, which in the model is turned three times for each stroke of the
lever, and may be increased or diminished, according to the number of
teeth in the pinion.
The number of teeth in the great wheel moved by the lever is sixty-six;
but need not have teeth above half way round.
The wheel fixed to the rochet has thirty-three teeth, and its pinion
eleven.
The wheel fixed on the arbor, on the outside, has twenty-four teeth,
and its pinion sixteen.
The wheel, which turns the fly, has ninety teeth, and the pinion turn’d
by this wheel ten.
The greater the number of teeth in the rochets, the better.
This machine may also be applied to other useful purposes at mines; and
it may be easily made to turn a mill to grind corn; or to turn a wheel
to raise coals, or whatever else is wanted to be raised from the mines.
As I have not met with any thing of the kind described, I take the
liberty of desiring you to lay it before the Society; and I hope it may
be made some way useful to the public.