CHAPTER 3.
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.
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.
posted by Shaq Attaq at 2:06 AM
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