Part 9

“_C D_, in this same figure, presents another form of the head and stern of two contiguous Boats or _parts_; (which, to save room, are both supposed to be _broken off_ at some point between their ends:) where as in the former case, the Boats are connected so as to remain horizontally flexible. These forms are semi-cylindrical, the stern concave, and the _head_ convex, to the same radius; and the motion takes place around a bolt and pulley _p_, reeved with a rope coming from one side of the first Boat near _C_ and led again to a small windlass or capstan placed on the other side near _D_. _E F_, is another modification of the same kind of joint: the centre of which is a bolt or stud _q_, (better seen at _q_ in the 2d. figure) over which a triangular frame falls from the preceding Boat, and thus connects them instantaneously; leaving a certain flexibility in the horizontal direction.”

“Finally, _G H_ shews a simple mean of connecting these Boats, on the supposition that both ends of each are formed alike to an obtuse angle in the middle of their breadth. It is a kind of hook _r s_, mounted in a frame turning on centres in the _preceding_ Boat, and reaching over into the succeeding one; where it finds a hollow _step_ of metal which receives and fits it, so as to hold these neighbouring Boats with sufficient tightness, but still with a certain degree of flexibility. Many other methods might be suggested, by which to form these joints; and almost _any_ might be made to answer the purpose. I shall therefore leave this branch of the subject, observing only, that the second figure of Plate 18, is an _elevation_ of the same things: which, generally, are marked with the same letters as far as they are visible.”

“The third figure presents the same objects in perspective; to which are now added _two_ masts _I K_, placed obliquely on that Boat which forms the Head of the whole vessel. This obliquity is useful when the boat is drawn from one side only; but is injurious where the traction takes place indifferently on both sides: so that I should not, _now_, advise the use of this method--which indeed, I have avoided in fig. 4 of this Plate.”

“In every case, each of the masts carries a pulley near _I_ _K_, over which passes a rope, the ends of which are fastened to the masts by proper brackets, near the deck: and to the middle of this rope is fastened the track rope _L_, by which the horses draw the Boat along. By these means the vessel is _steered_ either to or from the land: for if the knot of the track rope is brought near the mast _I_, the Boat (which as before observed is the head of the whole vessel) veers towards the horses; and the contrary when the knot is drawn towards the mast _K_: both which effects are rendered the more prompt and decisive, by the use of the _lee boards_ _K M_, the nature and use of which are already fully known.”

“But there are cases in which, from its great length, this Serpentine Boat would require a particular direction, for some intermediate point between its extremities; as although, in theory, every separate part ought to pass through the same water, yet in canals or rivers much bent, _this_ may not invariably take place; and _then_ a rudder would be useful, even in the middle of the vessel. I have therefore placed a pair at _P R_, fig. 3. Their motion is a vertical revolution, round a horizontal centre; and as they are formed obliquely to the sides of the Boat, when one of them is plunged into the water, it tends to drive the Boat in a sidewise direction: and if at any time it should be desired to stop the whole vessel, _both rudders_ would be plunged at once into the water, when they would greatly contribute to that effect.”

“The fourth figure in this Plate 18, presents a general view of the vessel, comprising five articulations, (or Boats) besides the head and stern--which latter would fit each other without any intermediate parts, and form a Boat alone. Nor do these five parts by any means limit the useful number: but the Plate would not have contained more, unless on a scale too small to be distinctly understood.”

“Returning now to fig. 1, we observe the ropes _A D F H_ and _B C E G_, which are supposed fixed to the stern Boat, and carried to the capstans represented in the _Head_. These ropes consolidate the whole fabric, and act, occasionally, as a kind of _muscle_, to govern the larger evolutions. These ropes pass in the brackets placed near the joints _A B_ and _C D_, &c. being _under_ the gang ways, of which a portion appears at _S_ fig. 3, hung upon hinges, that they may be turned up when the Boat is used in narrow water.”

To the above specification were added the following remarks, which still apply to this kind of vessel, navigating on canals and inland rivers: “this vessel admits of the use of every kind of _mover_; such as men, horses, wind, or the steam engine; the latter of which I propose to apply to it in a manner equally simple and effectual; especially so as _not_ to injure the banks of any canal, &c. by acting against and disturbing the water.”

I need not repeat that this Invention dates as high as 1795: as the _Brevet_ was issued in that year. It may be added that four _parts_ of such a Boat were executed about the same time; namely, the head, the stern, and two intermediate _pieces_: making together a length of 100 feet; and these, loaded to a certain depth with stones, were drawn _up_ the river Seine by a single horse _on a trot_--which would likewise have taken place had the Boat been ten times as long; since, as before mentioned, _the resistance of this kind of vessel bears no given proportion to the Load it carries_.

OF A MACHINE _For destroying, or lessening Friction_.

I think it may be assumed that _friction_ is fully expressed by the word _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_.