Regulating Power





27. Uniformity and steadiness in the rate at which machinery

works, are essential both for its effect and its duration. The

first illustration which presents itself is that beautiful

contrivance, the governor of the steam-engine, which must

immediately occur to all who are familiar with that admirable

engine. Wherever the increased speed of the engine would lead to

injurious or dangerous consequences, this is applied; and it is

equally the regulator of the water-wheel which drives a

spinning-jenny, or of the windmills which drain our fens. In the

dockyard at Chatham, the descending motion of a large platform,

on which timber is raised, is regulated by a governor; but as the

weight is very considerable, the velocity of this governor is

still further checked by causing its motion to take place in

water.



28. Another very beautiful contrivance for regulating the

number of strokes made by a steam-engine, is used in Cornwall: it

is called the cataract, and depends on the time required to fill

a vessel plunged in water, the opening of the valve through which

the fluid is admitted being adjustable at the will of the

engine-man.



29. The regularity of the supply of fuel to the fire under

the boilers of steam-engines is another mode of contributing to

the uniformity of their rate, and also economizes the consumption

of coal. Several patents have been taken out for methods of

regulating this supply: the general principle being to make the

engine supply the fire with small quantities of fuel at regular

intervals by means of a hopper, and to make it diminish this

supply when the engine works too quickly. One of the incidental

advantages of this plan is, that by throwing on a very small

quantity of coal at a time, the smoke is almost entirely

consumed. The dampers of ashpits and chimneys are also, in some

cases, connected with machines in order to regulate their speed.



30. Another contrivance for regulating the effect of

machinery consists in a vane or fly, of little weight, but

presenting a large surface. This revolves rapidly, and soon

acquires a uniform rate, which it cannot greatly exceed, because

any addition to its velocity produces a much greater addition to

the resistance it meets with from the air. The interval between

the strokes on the bell of a clock is regulated in this way, and

the fly is so contrived, that the interval may be altered by

presenting the arms of it more or less obliquely to the direction

in which they move. This kind of fly, or vane, is generally used

in the smaller kinds of mechanism, and, unlike the heavy fly, it

is a destroyer instead of a preserver of force. It is the

regulator used in musical boxes, and in almost all mechanical

toys.



31. The action of a fly, or vane, suggests the principle of

an instrument for measuring the altitude of mountains, which

perhaps deserves a trial, since, if it succeed only tolerably, it

will form a much more portable instrument than the barometer. It

is well known that the barometer indicates the weight of a column

of the atmosphere above it, whose base is equal to the bore of

the tube. It is also known that the density of the air adjacent

to the instrument will depend both on the weight of air above it,

and on the heat of the air at that place. If, therefore, we can

measure the density of the air, and its temperature, the height

of a column of mercury which it would support in the barometer

can be found by calculation. Now the thermometer gives

information respecting the temperature of the air immediately;

and its density might be ascertained by means of a watch and a

small instrument, in which the number of turns made by a vane

moved by a constant force, should be registered. The less dense

the air in which the vane revolves, the greater will be the

number of its revolutions in a given time: and tables could be

formed from experiments in partially exhausted vessels, aided by

calculation, from which, if the temperature of the air, and the

number of revolutions of the vane are given, the corresponding

height of the barometer might be found.(1*)



NOTES:



1. To persons who may be inclined to experiment upon this or any

other instrument, I would beg to suggest the perusal of the

section 'On the art of Observing', Observations on the Decline of

Science in England, p. 170, Fellowes, 1828.





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