Finally, I would remark, that the two last rounds in the rack of the arc o might be rather larger than the intermediate ones, and turn, moreover, on pins, so as to suffer less friction when rolling on the conducting curves q and t. There might also be a plate or cap rivetted or screwed over all the teeth, so as to strengthen each one, by the force of the whole, as is shewn in [fig. 1], [Plate 29]; from which, as before observed, this Mechanism is deduced.
The foregoing completes the Third Section of my work: and gives an article beyond the twenty, first intended:—which I thought important enough to claim this distinction. I now beg leave to add a remark or two on the text and plates of this, and the Second Part, by way of clearing up some obscurities, that might otherwise embarrass my readers.
And, first, in [fig. 1], of [Plate 21], the receiving vessel M, erroneously appears to form part of the wheel D E; but is, in reality, placed before it, as in all similar cases.—And, further, a small deviation of the circular lines, in [Plate 22], has set the plate and it’s description, in [page 192], at variance; the difference between the lines o p and C q being not “imperceptible,” as there stated. I wish, then, that the dotted radius A o p, in the said [fig. 2], may be carried (or supposed) halfway between p and C. Finally, in [page 200], line 8, the 24th Plate is incorrectly called the 25th.
I shall conclude this Part, by an observation or two on the reception my System of Toothed Wheels, as described in this work, has met with—not intending to speak of the local difficulties I experienced at a former period. But, here, the interests of truth force me to break silence. The necessity I stood under of bringing out this work in Parts, has, at least, had one advantage: it has given me an opportunity of watching the workings of prejudice—not to say of envy,—and thus of neutralizing, in some degree, the effects of either: from which, however, I claim nothing but the right of making my labours the more extensively useful, by making them better known. I have, then, to say that, among a few other objections to the System, this error has come from so respectable a quarter, that it would be unjust to Science, and injurious to truth, to let it pass unrefuted. It has been said, that “my wheels are a Chinese Invention;” and this proof has been adduced of it—namely, a sugar-mill, from China, having it’s cylinders fluted in a spiral direction. Now, the fact is, it would have been difficult to give a better proof that the wheels are NOT a “Chinese Invention;” for two inventions are then only alike when they produce the same effect, by similar means. But here the effects intended are totally different. A sugar-mill acts in or near the plane of the centres; and one of it’s cylinders is not intended to drive the other independently of pressure between them. This is so true, that the rollers of many sugar-mills are not fluted at all. Besides this, my wheels exert no pressure in that direction; and if they did, they would not be cog-wheels. In a word, their action is at right angles to the former, and has an object of quite a distinct nature. These, then, are by no means the same machine; and, therefore, mine is not a “Chinese Invention.”
Here, however, I beg not to be misunderstood! I should feel no regret at appearing on the mechanical stage, a few hundred years after so ancient and astonishing a nation as the Chinese! But, in this case, truth did not permit me to sanction, by my silence, this flagrant error.
Finally, an opinion exists, somewhere, that these wheels will never be generally used, from the difficulty of making them; and this opinion has been expressed, apparently, with no very amiable feeling. But, amiable or hateful, the opinion is highly erroneous! It is so far from fact, that, in a competent manufactory, they can be made more cheaply than others now are; and many persons are already calling for them from every quarter; nor is any thing wanted to insure their immediate prevalence but a common degree of commercial energy.