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.