MEGHAN I C S. 
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is neceflary to be able to caft ofF or dop any fpindle at 
pleafure, without difturbing the red; and, in a large mill 
containing many machines, it is effential that anyone may 
be releafed without interruption to the fird mover. Such 
contrivances are called coupling-boxes, or clutch-boxes. 
They are effected in various ways ; but vve wifh here to de- 
i'cribe a recent improvement, very generally adopted in 
cotton and woollen mills; tin? object of which is to avoid 
a jerk being given to any machine when it is put in action, 
from its being fuddenly urged from a date of red to a (fate 
of motion ; for, if the movement is to be rapid, nothing can 
be more dedruftive to the machine than the violence of 
the Ihock it receives from the common clutch-box. To 
avoid this, the arm which gives motion to the machine 
when the clutch of the running fpindle is engaged with 
it, is not fixed fad upon the fpindle, but is made in two 
halves fcrewed together upon a circular part of the fpin¬ 
dle, and pinched upon it lo fad by the fcrews, that it will 
have fufficient fridtion to turn the machine round in the 
ordinary courfecf its work, but Hips round upon the fpin¬ 
dle if the refidance is greater than this fridlion, which 
thus becomes the meafure of the power dealt out to the 
machine. Suppofe a machine of this kind at red, the 
clutch is turned by the fird mover with a confiderable ve¬ 
locity, and is fuddenly connected with the arm above de- 
fcribed ; now it requires fome time (independent of any 
refidance or work of the machine) to put its parts in mo¬ 
tion. In this time the arm flips round upon the fpindle; 
but the friftion afts conflantly and with an equable force 
upon the machine, to turn it round. It commences its 
motion, which gradually accelerates until it arrives at 
the fame velocity as the driving-fpindle ; and then the 
flipping of the box ceafes, and the machine proceeds in 
an uniform manner. Still the box is a very ufeful provi- 
fion in cafe of any accident happening to the machine to 
Hop it, by any thing getting into its movements ; the box 
then flips round without breaking the works. 
All machinery, which is expofed to the chance of 
great violence, (hould be provided with fome equivalent 
contrivance, which permits the movement to flip when 
the machine is overloaded, and would otherwife be broken. 
This effiedf may be produced by conical wheels fitting 
into each other, in the manner of a valve and its feat. 
One of them being fixed to each fpindle, will, when they 
are jambed into each other, communicate the motion, but 
permits it to flip if overloaded. Many other contrivances 
are in ufe for detaching or uniting motions at pleafure. 
In cog-wheels, the fupports for the gudgeons are forrie- 
times fitted up fo as to be moveable, that the wheels can 
be feparated to fuch a diftance as to relieve each other’s 
teeth. At other times one of the wheels is fitted on a 
round part of its axis* and united with it at pleafure by a 
clutch-box. Thus the wheels are always in motion, but 
one of them can be detached at pleafure from its axis, on 
which it flips freely. Bevelled cog-wheels are eafiiy dif- 
engaged, by fuffering the axis of one to move a little end¬ 
ways, and then'their teeth are feparated. 
Wheels turned by (traps are readily connedled, or call 
off, by removing the ltrap ; but this is not eafiiy done 
while the wheels are in motion ; though fome dextrous 
workmen are able to put on the (traps when the wheels 
are going; but it is attended with much difficulty, and 
great danger, if the motion is quick, of catching the fin¬ 
gers in the (trap. We have known an inftance of a man’s 
arm being torn away at the fhoulder, by careleffnefs in 
performing this operation. For difengaging the motion 
of a ltrap, the contrivance called the live and dead pulley 
is very ingenious; it conlilts of two pulleys placed dole 
together upon any axis which is to receive a circular mo¬ 
tion. The endleis (trap or band, by encompafling one of 
thele pulleys, gives it a conftant rotatory motion. Now 
one of them being fixed fait upon the fpindle, and the 
other flipping freely round upon it, gives the means of 
turning or difcontinuing the motion of the fpindle at 
pleafure, by fh if ting the ltrap either upon the live or dead 
pulley, which, as they are exn&ly of the fame flzc, and 
clofe to each other upon the fpindle, is eafiiy done. The 
live pulley is that which is fixed to its axis, fo called from 
its caufing life or motion to the fpindle, and the machi¬ 
nery appended to it. The dead or idle pulley is that 
which flips upon its fpindle; therefore, when the (trap is 
caufed to run upon it, it turns round without giving any 
motion to the fpindle. This contrivance is extremely 
well adapted to give motion to fmall machinery, from the 
fimplicily of its conftru&ion, and the facility with which 
it is put in motion or at reft. It poflefles alfo another 
great advantage, viz. it occafions no fudden fliock to the 
machinery at fird ftarting, as it does not ir.dantly com¬ 
municate to it the full velocity. To illudrate this, fup- 
pofe the ftrap running upon the dead pulley, and the 
machine therefore at red, the leading-fide of the (trap is in 
general conduced through a notch in a piece of board 
which is fitted in a groove, fo as to have liberty of Aiding 
in fuch a manner that it may conduct the ftrap to work 
upon either of the pulleys; but this is not neceflary, nor 
always attended to, for the perfon who attends the ma¬ 
chine may, by the flighted preffure on the leading-fide of 
the (trap by his hand, caufe it to fhift upon the other pul¬ 
ley ; but, as this is not done indantly, it communicates 
the motion to the live ptslley by degrees ; for, at fird drift¬ 
ing, it begins upon a very narrow furface of the pulley, 
which is, therefore, urged into motion, but without vio¬ 
lence to the machine, as the (trap at fil'd flips partially 
upon the furface of the live pulley, and this, as we have * 
before dated, caufes the ftrap to endeavour to efcape from 
the pulley ; but the attendant continues to prefs the ftrap 
on the leading fide, and force it to a6t upon the live pul¬ 
ley, which, having attained its full velocity, and the ltrap 
no longer flipping upon it, has no tendency to get off, . 
unlefs the machine is overloaded, and then it will get off 
to the dead pulley. The live and dead pulley is very ex- 
tenfively ufed in cotton machinery, and is a very excel¬ 
lent contrivance ; the only objection to it being that the 
bufli in thecentre of the idle pulley is liable to wear very 
loofe in a fhort time. It is fcarcely neceflary to add, that 
the driving-wheel for the ftrap of the live and dead pulley 
mud be as broad in its edge as both the live and dead pul- . 
ley together; indeed it is generally a long cylindrical 
drum, which receives many ftraps for turning different 
machines. 
A motion is frequently required in machinery, by which 
a wheel or axis is made to revolve in one direction for 
any required time, and then at pleafure changed, fo as to 
revolve in the other diredtion. Various means may be 
ufed for effecting this purpofe. The mod common is by 
means of two equal and fimilar bevelled or contrate wheels, 
fituated on the fame axis, and their teeth towards each 
other. A third bevelled wheel is applied with its axis 
perpendicular to the former, and its teeth engaging at 
pleafure with either of the two wheels, which, as they 
turn the fame way round, can be made to adt at one 
or other of the fides of the third wheel, fo as to turn it in 
either diredtion, as it is engaged witii either of the two 
wheels. This movement was applied by Mr. Smeaton to 
a machine he invented for drawing coals from coal-pits. 
In this the third wheel was a trundle, and could be, by a 
lever, made to work in the teeth of either of the cog¬ 
wheels which were mounted upon the axis of a water¬ 
wheel, and thus turned the trundle either way at pleafure, 
to draw up or let down the baikets, or corves, which were 
fufpended from a drum upon the axis of the trundle. 
Some mechanics have conitrudted the contrivance in a 
different manner, by fitting the two wheels upon a circular 
part of the fpindle, and fuffering them to turn round freely 
upon it. Their teeth are always engaged with the teeth, 
of the third wheel; and therefore they are always revolv¬ 
ing in oppofite diredlions, and either can at pleafure be 
connected with the axis by a Aiding clutch-box, but which 
is not long enough to engage both at once. The axis 
can, by this means, be made to reyolve in the .dirc&iou 
ef 
