MECHANICS. 
6C3 
centre of motion is L, and whole other extremity is con¬ 
nected with the cock which admits the (learn into the cy¬ 
linder. The frames C D and Q R prevent the balls from 
receding too far from the axis, or from approaching too 
near it. Now, when this conical pendulum is put in mo¬ 
tion, the centrifugal force of the balls M, N, makes them 
recede from the axis A B. In confequence of this recefs, 
the points C, H, K, are deprefi'ed, and the other extre¬ 
mity of the lever is raifed ; and the cock admits a certain 
quantity of (team into the cylinder. When the velocity 
of the fay is by any means increafed, the halls recede fiill 
farther from the axis, the extremity of the lever is raifed 
higher, and the cock clofes a little, and diminifhes the 
fupply of (learn. From this diminution in the impelling 
power, the velocity of the iiy and the conical pendulum 
decreafes, and the balls refume their former pofiticn. In 
this way, when there is any increafe or diminution in the 
velocity of the fly, the correfponding increafe or diminu¬ 
tion in the centrifugal force of the balls raifes or dtprefles 
the arm of the lever, admits a greater or a lets quantity of 
fteam into the cylinder, and reflores to the engine its former 
velocity. 
Beftdts the utility of fly-wheels as regulators of machi¬ 
nery, they have been employed for accumulating or col¬ 
luding power. If motion is communicated to a fly-wheel 
by means of a fmall force, and if this force is continued 
till the wheel has acquired a great velocity, fuch a quan¬ 
tity of motion will be accumulated in its circumference, 
as to overcome refinances and produce effefls which could 
never have been accotnplifhed by the original force. So 
great is this accumulation of power, that a force equi¬ 
valent to 2.0 pounds applied for the (pace of 37 feconds to 
the circumference of a cylinder 20 feet diameter, which 
weighs 4.713 pounds, would, at the difiance of one foot 
from the centre, give an impulfe to a mufket-ball equal to 
what it receives from a full charge of gunpowder. In the 
fpr.ee of 6 minutes and 10 (econds, the fame effect would 
be produced if the cylinder were driven by a man who 
conllantly exerted a force of 20 pounds at a winch one 
foot long. This has beer, demonfirated by Mr. Atwood. 
See his Treatife on Rectilineal and Rotatory Motion. 
This accumulation of power is finely exemplified in the 
common fling. When the thong which contains the 
(tone is fwung round the head of the {linger, the force of 
the hand is continually accumulating in the revolving 
flone, till it is difeharged with a degree of rapidity which 
it could never have received from the force of the hand 
alone. When a (tone is projected from the hand itfelf, 
there is even then a certain degree of force accumulated, 
though the fione only moves through the arc of a circle. 
If we fix the Hone in an opening at the extremity of a piece 
of wood two feet long, and difeharge it in the ulual wa) - , 
there will be morefoice accumulated than with the hand 
alone ; for the (tone deferibes a iarger arch in the fame time, 
and muft therefore be projected with greater force. 
When coins or medals are liruck, a very confiderable 
accumulation of power is necefl’ary ; and this is effected by 
means of a fly. The force is fir(t accumulated in weights 
fixed in the end of the iiy. This force is communicated 
to two levers, by which it is farther condenfed ; and from 
thefe levers it is trail knitted to a ferew, by which itfuffers 
a fecond condenfation. The damp is then implefl'ed on 
the coin or medal by means of this force, which was firtt 
accumulated by the fly, and afterwards augmented by the 
intervention of two mechanical powers. It is thus alfo, 
that the bluckfmith forges a bar of iron. Swinging the 
great (ledge-hammer round his head, and urging it with 
force the whole way, this accumulated motion is at once 
extinguished by impact on the iron. It is thus alio we 
drive a nail, &c. 
This accumulating power of a fly has occafioned many 
to imagine that a fly really adds power or mechanical force 
to an engine and, not underdanding on what its efficacy 
depends, "they often place the fly in a (ituation where n 
only adds a ufelefs burden to the machine. It Ihould al¬ 
ways be made to move with rapidity. If intended for a 
mere regulator, it (hould be near the firft mover ; and, if it 
be intended to accumulate force in the working point, it 
fiiould not be far feparated from it. In a certain fenfe, a 
fly may be faid to add power to a machine, becaufe, by ac¬ 
cumulating into the exertion of one moment the exertions 
of many, we can fometimes overcome an obftacle that we 
never could have balanced by the fame machine unaided 
by the fly. And it is this accumulation of force which 
gives fuch an appearance of power to fome of our firft 
movers. When a man is unfortunately caught by the 
teeth of a paltry country mill, he is crulhed almoft to 
mummy. The power of the dream is conceived to be 
prodigious ; and yet we are certain, upon examination, 
that it amounts to the prefiure of no more than fifty or 
fixty pounds j but this force has been acting for (ome 
time, and there is a miillione of a ton weight whirling 
twice round in a fecond. This is the force that cruihed 
the unfortunate man j and it required it all to do it, for 
the mill flopped. We have been informed of a mill in 
the neighbourhood of Elbingroda, in Hanover, where 
there was a contrivance which difengaged the millftone 
when any thing got entangled in the teeth of the w heels. 
On being tried with a head of cabbage, it crufhed it, but 
not violently ; and would by no means have broken a man’s 
arm. 
Of the Management of the Moving Power; and of 
Reciprocated Motion. 
Profefibr Robifon has given fome general obfervations 
on the confiruction of machines, and on the regulating 0 f 
their motions, which appear highly worthy of the reader’s 
attention, and are therefore extracted, as below. 
When heavy dampers are to be failed, in order to drop 
on the matters to be pounded, the wipers by which they 
are lifted fiiould be made of fuch a form, that the (tamper 
may be raifed by an uniform prefiure, or with a motion 
alinod perfectly uniform; direftions for which are given 
at p. 665. If this is not attended to, and the wiper is 
only a pin flicking out from the axis, the damper is forced 
into motion at once; which occafions violent jolts to the 
machine, and great drains on its moving parts and their 
points of fupport; whereas, when they are gradually lifted, 
the inequality of defultory motion is never felt at the im¬ 
pelled point of the machine. We have feen pidons moved 
by means of a double rack on the pifion-rod. A half¬ 
wheel takes hold of one rack, and railes it to the required 
height. The moment the half-wheel has quitted that fide 
of the rack, it lays hold of the other fide, and forces the 
pilton down again. This is propofed as a great improve¬ 
ment, as correcting the unequable motion of 4 the piflon 
moved in tiie common way by a crank. But it is far in¬ 
ferior to the crank-motion. It occafions fuch abrupt 
changes of motion, tiiat the machine is lhaken by jolts. 
Indeed, if the movement were accurately executed, the 
machine would be (haken to pieces, it tne parts did not 
give way by bending and yielding. Accordingly, we 
have always obferved that this motion foon failed, and 
was changed for one that was more faiooth; A judicious 
engineer will avoid all fuch Hidden changes of motion, 
elpecially in any ponderous part of a machine. 
When feveral (tampers, piltons, or other reciprocal 
movers, are to be railed and deprefi'ed, common (enie 
teaches us to diltribute their times of aftion in a uniform 
manner, (6 that the machine may always be equally loaded 
w ith work. When this is done, and the obfervations ia 
the preceding paragraph attended to, the machine may be 
made to move aim it as fmoothly as it there were no reci¬ 
procations 111 it. Nothing (hows the ingenuity of the au¬ 
thor more than the artful yet li in pie and effectual contri¬ 
vances for obvi.ning thole ditficulties that unavoidably 
arile from the'very nature o( the work that mult be per- 
fornied by the machine, and of the power employed. 
There 
