“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.