_rubbing_: and that where rubbing cannot be found, friction does not
exist; especially that _kind_ of friction which opposes the motion of
machinery--in which respect, the subject is chiefly thought interesting
to mechanicians. It would be abandoning my intended plan in this work,
to treat largely of friction, or any other accident in practical
mechanics; but having already declared myself “no believer in several
sorts of friction,” I am in a measure bound to introduce my description
of the two following articles, by a short reference to the general
subject. I offer then the following remarks, more as hints for the
consideration of learned experimenters, than as conclusions sufficiently
proved to become rules in practice. What I cannot help urging strongly
is, that _rolling_ is not _rubbing_. If it were, I would ask in what
direction it takes place? Is it in that of the plane rolled over? or in
that of the radii of the rolling body? If in the former, it would indeed
_glide_ over that plane, and occasion or suffer _real_ friction; but
this, I think, is not pretended. If this motion is in the latter
direction, (that of the radii of the rolling body) it is indefinitely
_short_, compared with the progressive motion of the rolling body, so
that the _power_ of the latter, to overcome any resistance in that
direction, is _infinite_. Whenever therefore, in experiments of this
kind, a finite resistance is perceived, it must, I should think, be
ascribed to other causes, and not to _friction_. In my wheels for
example, (see a former article) where there is a real and deep
_penetration_ of the surfaces, I have proved that the friction between
the teeth is _less_ than the distance between two of the last particles
of matter: and surely, when penetratration is purposely made as small as
possible (by the use of _smooth_ rollers) the friction thence arising
must be still more imperceptible. But I hear it answered, that _this_
friction is both known and measured! and certain celebrated experiments
are adduced to prove it. But what I most wonder at is, that a person so
truly learned as the author of those experiments, should have adopted so
remarkable a misnomer; in which to all appearance, indentation has
usurped the name of friction. Nor let this surprise, surprise any body:
nor especially, offend this learned author himself; for I am persuaded
that the sole act of placing these wooden rollers, on these surfaces of
wood, must indent them both sufficiently to account for all the facts
observed; and still more so when loaded with weights of 100, 500, or
1000lbs. No friction, therefore, is requisite in accounting for the
resistance of these rollers to horizontal motion. Nay, I submit, whether
a resistance, arising from indentation alone, would not prove to be
“directly as the pressures and inversely as the diameters of the
rollers?” To me the subject presents itself under three aspects: either
the whole indentation takes place on the rollers, when they are very
soft and the _rulers_ very hard; or the latter, when _they_ are very
soft and the rollers very hard: or, which is most likely, this
indentation takes place on both bodies at once; so as to produce a
_surface of contact_, intermediate between the _straight surface_ of the
_rulers_, and the _cylindrical_ surface of the rollers. But in either
case, the _place_ of resistance to horizontal motion, must be _out of
the line of direction_ of the roller’s centre of gravity: and thus would
the roller present more or less resistance, independently of every thing
that can be called friction: and which degree of resistance will
continue to exist as long as the place of contact is made to change on
the rulers--for thus to change this place of contact is to renew this
indentation; which process will elicit a resistance equal to what would
be observed were the roller (without indentation) forced _up_ a plane,
inclined to the horizon in the same angle as a line, drawn from the
centre of the roller to the extreme edge of the _surface of contact_,
makes with the perpendicular.
I cannot possibly enter at length into this subject, as it makes no part
of my engagement to the public: but I would observe that _this_
resistance is, _a fortiori_, something besides friction, since _greasing
the surfaces_ “did not cause any sensible diminution of it;” whereas it
made a difference of _one half!_ in some others of the experiments
alluded to.[4] Were I asked the reason, I should answer, because
friction had little or nothing to do with it; and I would say further,
that greasing or oiling these surfaces would most likely _increase_,
instead of diminishing, their resistance to horizontal motion: namely by
_softening them_, and making them more susceptible of change of figure:
which opinion gathers strength from _another_ fact adduced, viz: that
“rollers of elm produced a friction (or resistance) of about 2/5
_greater_ than those of lignum vitæ:” but why? because elm is relatively
_soft_ and lignum vitæ hard--the only cause that appears sufficient to
account for the facts observed.
[4] See Dr. Gregory’s Introduction to his Mechanics. Vol. II.
I must now leave these remarks to persons having more means and leisure
than myself, to pursue the subject; wishing only, that _useful truth_
may result from them: and that this unbelief of mine “in several special
kinds of friction,” may at least be found to have _some_ reasonable
ground to rest upon.
But I may be opposed in some of my statements by the fact, that friction
rollers, with centres, have been used with little advantage; and _often_
laid aside. This I acknowledge; and go a step further. Friction is by no
means of so much consequence as it was once thought to be: and is _not_
the source of the greatest defalcations that occur in the use of power.
Yet, to get rid of it, in some cases, would be of considerable
importance; and the subject deserves at least the attention of every
intelligent mechanician.
Those who have used friction rollers, know that it is a thing of great
difficulty, to place their axes exactly parallel to _that_ which they
are intended to support: and even, if rightly placed at first, that a
small degree of abrasion, greater on one pivot than another, will soon
destroy that parallelism; and thus introduce a _growing_ friction,
capable, at length, of rendering the whole completely useless: for
although the original friction is _lessened_ by being transferred to a
slower-moving axis, yet the latter still resists in some degree, say 1/4
of the whole; (its pivots being 1/4 of its whole diameter) so that the
cohesion, or something else, between the main shaft and the friction
roller, (thus resisted) must be sufficient to _drag round_ the latter,
against about 1/4 of the original friction; which in a word it cannot do
without some _relative_ motion between those surfaces, the friction
roller lagging behind the main shaft, until its own friction is overcome
by _another_. And thus it is, that a friction roller of this kind, does
not make so many revolutions on its pivots, as its diameter compared
with that of the main shaft, would imply; for example, if the shaft were
4 inches in diameter and the friction roller 8 inches, the latter would
_not_ complete one revolution against _two_ of the former. There would
thus remain a difference spent in _real_ friction, in addition to that
on the axis of the friction roller. Besides this, we have the want of
parallelism above mentioned; which occasions a rubbing, in the direction
of the shafts, small indeed in quantity, but for that reason very
_powerful_ in bringing on a change of form, and thereby hastening the
common destruction. Both these accidents, therefore, make friction
rollers, in general, an unsatisfactory and perishable expedient: and it
is to make them _less so_, if not entirely to cure these evils, that the
two following articles are designed.
In fig. 6 of Plate 17, _A B_ is an axis which it is desirable to divest
of its _friction_. To do this, as nearly as may be, I connect with it
two rings of hard metal _C D_, formed as truncated cones; and under the
shaft, in the same vertical plane, I place two smaller shafts _E F_,
carrying on their tops, other two cones, similar to the former. The
summits of each pair of cones meet of course in the points _a b_ of the
main shaft; and, on the principle of bevel geer, every contiguous part
of the touching cones moves with the same velocity: so that there is no
sensible _rubbing_ between them--for, 1st. the pivots _c d_, are hard
and pointed, and run on the hardest _steps_ that can be obtained; and,
2ndly. the tendency of the cones _u_ toward each other, is repelled
without friction by the cylinders _e f_, attached to them, and which
_lean_ right and left against each other, turning with the same
velocity, without causing any friction, or any _creeping_, between the
two pairs of cones _e C_, and _f D_. All the weight therefore, of the
shaft _A B_, (which of course is kept in place in the other direction by
proper side cheeks, &c.) rests on the points of the vertical shafts _E
F_, accompanied by no sensible tendency of these points to quit the
places assigned to them.
OF
A SECOND MACHINE,
_To avoid or diminish Friction_.
In Plate 17, figs. 7 and 8, offer a mechanism different from the
preceding, though intended to produce a similar effect. Referring to
_that_ cause of friction which consists in the want of parallelism
between a principal shaft and its friction rollers, I here introduce a
form for the latter, which admits of this consideration being in a
measure neglected. These friction rollers are only portions of
cylinders; and they have _no_ shafts. They turn simply on a sharp edge,
placed in a prismatic box _A B_, in a well formed angle of which, they
move to and fro, without _rubbing_. When at rest, these axes _D C D_,
(fig. 7 and 8) are drawn against the right hand side of the box, by
small weights _E_; and the shaft is carried by one or the other of them,
according as they are, or are not, within reach of its radius. Thus, in
the present position of the shaft, (see fig. 7) the second arc _C_
supports it, the third having fallen behind the first, so as not to be
seen: and the first arc _D_ being on the point of taking up the load. In
short there are _six_ spaces, either _left_ or _cut_ on the shaft,
opposite the three arcs _D C D_. 1st. _one_ space, of 1/3 of the
circumference, left concentric with the real centre of the shaft,
opposite the first arc _D_, followed by 2/3 of a circumference _cut an
eighth of an inch lower_. 2ndly. another third of a circumference
opposite the second arc _C_, beginning where the first ends, and
followed by 2/3 of a circumference cut an eighth of an inch lower: and
3rdly, another space of 1/3 in circumference, opposite the arc _D_,
followed by a similar space of 2/3 cut an eighth of an inch lower. By
these means the shaft is never without _a concentric bearing_: and the
better to secure this property these arcs _left_, may be each of them
_more than one third of a circumference_ in length, so as to avoid the
least _drop_ at each change of roller; and even to give the shaft a
support from two rollers at once, during a good part of its revolution.
In using this mechanism, the vessel _A B_, would be filled, to a certain
level, with oil or water, to prevent any blow from the returning
arcs--which latter might be made to fall on a lining of leather, to
avoid still further all commotion: and thus, even were these rollers not
placed _quite_ parallel to the shaft, this imperfection would be
corrected by the frequent _renewal_ of these movements, and the
consequent absence of _lateral_ friction between the arcs and the shaft.
It may be observed that either of the above methods of destroying
friction is not confined to the vertical direction: but may be so used
as to receive the pressure caused, in any direction, by the action of a
wheel or other agent. And with respect to the best use of each method
respectively, I would propose the former for light and swift motions,
and the latter for slow-going shafts, heavily laden: it being well
understood that the shafts must be kept in their places, in the less
essential directions, by proper steps, at the discretion of the person
who employs these Machines.
Finally, I consider it as a matter of course, that _all_ the surfaces
coming into contact in these operations, should be _as hard and
impenetrable as possible_. For if, by neglecting this precaution, any
_change of form_ occurred, what is said above could not be practically
true: But these properties can be realized, with only those degrees of
hardness that are _often_ employed in the mechanical world. Thus _a die_
of hardened steel, bears almost unimpaired, the strokes and pressure it
suffers in the coining-press. A chisel, _stands_ thousands of blows and
cuts hard metal, without sensibly giving way. The _knife-edges_ which
carry a heavy pendulum, suffer it to vibrate many years without wearing
out; and the fulcrums of scale-beams, bear enormous weights, for almost
an indefinite period, without any injurious effect. I request therefore,
that these facts, may be put into the scale, when my foregoing
statements are _tried_: whether as applied to these anti-attrition
machines, or to my late patent wheel work, _or both combined_: for I
foresee the use of these friction rollers, cut into teeth on that
principle, to insure the proportionality of their respective motions.
OF
AN EQUILIBRIUM COCK,
_To prevent abrasion and leakage_.
In the common form of this useful instrument, no method seems to have
been devised for preventing the _plug_ from being _pressed aside_, by
the weight of the liquid: which provision nevertheless would have
diminished the wear and tear of the touching surfaces, and secured much
longer the perfection of the instrument. This property would be
particularly desirable in cocks which convey a fluid from a great
height; and still more so in those used for containing steam or any
other fluid under a _high_ pressure. I can hardly persuade myself that I
have stood so long alone in my ideas upon this subject; but not having
seen any thing _published_ on the subject, under a name implying the
above mentioned property, I venture to give this as my invention--which
indeed it is, even should other persons have pursued and embodied the
same idea.
Fig. 9, 10 and 11 of Plate 17, represents one of the forms of this
equilibrium Cock. It consists of a square plug case or chamber _a b_,
with a hole _c d_ bored transversely through it, exactly across its
centre: and to this chamber is fixed by the flanches _e f_, the
bifurcated water-passage _g h_, forming one body at _i_. The plug of
this instrument admits of various forms and proportions; of which I
have shewn two in the figures 9 and 11. The first _m n_, receives the
fluid through the two openings _c d_, which correspond, in one position
of the plug, with the double water-passage before mentioned. And
further, the plug itself is bored lengthwise in its under end _n_, so as
to form the spout of the cock: or otherwise (see fig. 9) this spout is
taken in a double form from the _outer_ surface of the plug at _b a_, so
as to present two streams, thus producing, I think, an instrument of
somewhat greater solidity. All that seems important is, that whatever be
the pressure of the fluid from without, it be made _equal_ on both sides
of the plug, so as to occasion no friction between it and the chamber.
The principle is indeed so effectual, that one might distribute steam
pressure of the greatest strength or even gunpowder pressure, without
_much_ resistance to the operator, and without injuring the mechanism by
oft repeated action.
OF
A MACHINE
_To communicate and suspend Motion_.
In Plate 19, figs. 3 and 4, shew this mechanism in two directions. It is
composed of two wheels _C D_, cut (or cast) into teeth of a peculiar
kind, that both _geer_ with one another, and at the same time, include
the chord or round strap _A B_, by which they are driven. These teeth
can be better represented by a figure than in words; and will I suppose
be understood from figures 3 and 4: They are divided, on the rim of each
wheel by a _space_ too small to admit a tooth of the other wheel: but
then, _every-other_ tooth is cut away in a sloping direction on each
side of the wheel, from the bottom of the tooth to its top on the
opposite side: so that while these teeth are working in each other they
offer two grooves, in the form of a V, which coming together surround
the chord and press it in four points, either to drive the wheels by the
cord, or to pull the chord by the wheels, according to the use it may be
wished to make of this mechanism. In fig. 4 the cord is seen at _A B_,
passing among the teeth of the wheels; and in fig. 3 it is shewn at _C_,
as a mere circle, in the centre of a lozenge formed by the teeth whose
points _now_ geer together. Fig. 5 is a sketch belonging to this
subject, which shews something of the manner of using this _round
strap_ as a _mover_: for by carrying it (either in a horizontal or
vertical plane) _by a line slightly curved_, from one machine to
another, it will drive them all and give the means of stopping any _one_
at pleasure. Suppose then, _A B C D_ fig. 5, to be four machines placed
as above mentioned. If I wish to stop the machine _B_, I merely draw
back the pressure wheel _E_, and the cord ceases to lay hold on the
machine as shewn by the dotted line: but when I want to _set it on_
again, I do it by bringing back the wheel _E_ to its present position.
And thus at a small expence, I could _geer_ a considerable factory, in a
way which I think as durable as it appears economical. The principal
objection, perhaps, is that this cord is liable to wear out soon, by
such incessant action; but then the pressure on it needs not be great;
and of friction properly speaking there is _very_ little: Besides which,
the cords would be made of a peculiar texture, perhaps of leather, sewed
edge to edge and covered like a whip, _by one of the machines I shall
bring forward hereafter_.
It so happens that many of my Inventions are of a generic nature, and
thus apply to cases which, appearing different, have nevertheless some
common properties. The _rule of contraries_ especially applies to many
of them,--of which this is an example. It offers a good method of
driving a boat through a tunnel, or other confined space, either by the
force of steam or any convenient power. To this end a rope laid along
the side of such canal, and fixed at each end, or at several
intermediate points, might be led between a pair of wheels like those
above described; which duly turned, would drive the boat the distance
required with the least possible expence of _power_, and _without_ the
defect of agitating the water.--But I must not anticipate too much on my
intended subjects.
OF
A MACHINE
_To set on, and suspend, rapid Motions_.
This Invention is under the protection of a Patent. It is applied to the
spindles of my spinning machinery called Eagles, from their analogy to
the machines named _Throstles_. It is in my opinion an excellent
machine; as it secures a mathematical equality of twist to _any_ number
of spindles from permitting the use of geering to turn them, which could
not have been done without some means of stopping a single spindle. This
mechanism (see Plate 19 fig. 1 and 2) consists of a toothed pinion _A_
soldered to the box _B C_, (partly cut down in the figure to shew its
contents) and with it running loose on the lower part of the spindle _E
D_. In this box are placed two weights _M N_, like that _M_ fig. 2,
which both together, fill the box loosely, and, rising above it, are
pinned at _O P_ through the spindle. They are moreover kept from
quitting the latter by the ring shewn in section at _q q_, which holds
them _loosely_, yet prevents their flying away or hurting any one. When
now the spindle _E D_, turns swiftly, the centrifugal force of the two
weights _M N_, projects them from the centre as far as possible; and
they lay hold, by friction, of the cylindrical surface of the box _B C_,
and thus _keep_ the revolutions of the spindle to the same number of
turns per minute, as the pinion _A_ receives from the driving wheel.
But when the spindle is stopped and held by the fly as usual, then the
centrifugal force ceases to act, and the box _B C_ does _not_ wear out
much, by its further revolutions. And when as before, the spindle is
again let loose, _that_ friction which takes place on the bottom of the
box sets the spindle running again, when the centrifugal force comes to
its aid, so as to unite again the box and the spindle, thus renewing
that valuable property of all spinning machinery, the mathematical
correctness of its movements.
OF
A MACHINE
_For forging Screws, Beads, &c._
The effect which this Machine is intended to produce, is analogous to
several culinary or officinal processes that might be named. It is
called _rolling_: but not in the same sense in which that word is used
in manufactories, where _rollers_ form or modify the body acted on. Here
this body itself _rolls_ between two surfaces moving different ways and
receives from them the desired impressions, and this idea I have
extended to _screws_; proposing to _finish_ them on some metals and in
some dimensions; and to _rough them out_ in others. The Machine is
represented in figs. 6 and 7 of Plate 19, where fig. 7 shews the _faces_
of the arcs _A B_ of fig. 6. By the form and connection of the arms _A
C_ and _B D_, these arcs move opposite ways: and since they are grooved
obliquely as shewn in fig. 7, if a prepared cylinder of soft metal _a_,
be put between them, and the handle _C_ be sharply pressed into the
position _A E_, the cylinder _a_ will be made to _roll_, and the grooves
of fig. 7 be impressed on it so as to meet and form the screw in
question. The only conditions are, that the arc _B A_ be at least equal
in length to the circumference of the screw, when finished; and that the
grooves (fig. 7) be rightly sloped, and have the _form_ intended to be
given to the threads of that screw. It will occur of course, that the
opening between the arcs at the point where the blank cylinder is
introduced, must be larger than the distance between the arcs by the
whole depth of the threads to be impressed: which therefore will begin
to be formed at two opposite points the moment the screw _a_ begins to
roll. This however, might and would be otherwise, if it were thought
best to form the arcs _A B_ spirally; and let the deepening process be
gradual: in which latter case another consideration would occur, namely;
that the grooves themselves (see fig. 7) must diverge a little instead
of being parallel, so as to permit the screw to lengthen as the pressure
should displace a part of the metal. In all cases the upper surface of
the grooves should be _milled_ so as to lay hold of the soft metal, and
insure the rolling motion: and should this material be hot-iron, the
stroke should be taken in an instant, and the machine be kept cool by
every proper method, in the intervals of working.
I need not add that this rolling process would be still easier
performed, if the impressions to be made were circular and _not_
oblique: such as beads, balls, &c. but these considerations I leave to
my readers.
OF
A DIFFERENTIAL STEEL-YARD,
_To weigh vast Weights with short Levers_.
Plate 19, figs. 8 and 9, offers two representations of this Machine--one
intended to shew its manner of acting, and the other _one_ of its
practical forms. By means of the first, (fig. 8) we may compare it with
the common steel-yard; and even shew the latter as a part of the former.
If a weight, or load to be weighed _M_, were suspended to the arm _A B_,
and the counter-weight _W_, placed at the point _C_, of the arm _A C_,
we should have a common steel-yard whose power would be as 5 to 1: for
the arm _A B_ is just 1/5 of the arm _A C_, and this is the principle on
which steel-yards are commonly made. But instead of this, my steel-yard
_G E B D C H_ fig. 8, is now infinitely powerful: so much so indeed, as
to be infinitely useless. If millions of pounds were now to be suspended
at _P_, they would not raise the weight _W_ one tittle, for they hang
_entirely_ on the point of suspension _A_. But although the Machine is
_now_ useless, it can be altered in a moment and made both useful and
commodious; only I thought its principle would be the better understood
from being thus shewn _in excess_. To make it a useful and powerful
Instrument, I only move the hanging bar _D G_, to _a b_; and the bar _E
B_ to _c d_, the lever _b d_ being similar to that _E G_. In this state
of things, the whole load _P_ is found at the point _o_ of the lever _B
H_, (for the lever-arms _c o_ and _d e_, and those _e b_, and _a o_ are
equal) and the power of this steel-yard is as the line _A C_ to the line
_A o_; that is as 20 to 1, instead of being as 5 to 1 which it before
was. But this is not _yet_ a powerful Machine; being chiefly intended to
shew the principle on which it acts--and to prove that however small the
distance _A o_, that distance, dividing the arm _A C_, gives the real
power of the steel-yard. And supposing now the arm _A C_ to be four feet
in length, and the distance _a D_, _B c_, and _A o_, to be 1/10 of an
inch, then the power of the weight _w_ to raise (or weigh) the load _P_
is as 48 inches to 1/10 of an inch, or as 480 to 1: so that if the
weight _w_ were 10lbs. this steel-yard would weigh 4800lbs. or upwards
of two tons; and it is easy to see that this power can be almost
indefinitely extended.
Fig. 9 of this Plate shews a real steel-yard made on this principle; the
power of which, under its present length, is as 40 to 1. In this Machine
all the centres are fixed: and the load is suspended on knife-edges, the
distances of which from each other and from the common centres are
invariable--as they _must_ be in all instruments of this nature.
OF
A RETROGRAPH,
_Or a Machine to write backwards, for Engravers_.
This Machine is exhibited in the two figures 10 and 11 of Plate 19. It
is composed of a straight ruler _A B_, having an exactly dove-tailed
mortice made along it, to receive the rollers, (or slides) by means of
which the parallelogram _C D E_ _F_ slides up and down in this mortice.
This parallelogram is composed of four rulers _C D_, _D E_, _E F_, and
_F C_, connected by cannons or tubes fixed to every-other arm: and on
which the contiguous rulers turn very correctly. Through which moreover,
in two cases, _F D_ the drawing pencils are introduced, and under which
in other two cases, _C_ and _E_, the guide rollers already mentioned are
nicely fixed by the screws on which they turn. This is seen by an
elevation in fig. 10, where _p_ marks one of these rollers, and _o q_
the end of the ruler supposed fixed to the paper by proper blunt points,
&c. At _r_ is seen one of the tubes which form the joints _C_ and _E_:
and _r t_, are, one the writing pen, and one the retrographic style or
pencil. Fig. 11 is a plan of the whole Machine: where if the hand
guiding the pen _D_ goes upward, the tracer _F_ rises too. But if the
pen or hand _D_ moves to the right, the tracer moves to the left at the
same moment. In a word this is to write backward in the sense of
engravers, who thus write that their letters may proceed forward after
_one_ impression.