Principles of Mechanism

The third part, on Adjustments, contains several problems relating to the calculation and arrangement of mechanism in which it is necessary to have the power of altering the velocity ratios, changing the directional relations, or breaking off the communication of motion at pleasure.

I have, in the course of the work, endeavoured in every case to acknowledge the sources from whence I have derived any portion of its contents, by references at the foot of the page. But so little of its peculiar subject had been treated mathematically when I wrote my first edition, that I must hold myself answerable for the greatest portion of it. The teeth of wheels was then the only branch of mechanism in which the original papers had been already wrought into a system, and published in a collected form. This was first done by Camus, and was subsequently effected by Buchanan in his Essays, and by Hachette, Ferguson, and Sir D. Brewster, and others (vide note to p. 87 below).

I have incorporated into Chapter V. extracts from the valuable paper of Professor Airy, as well as the entire contents of my own paper from the Transactions of the Society of Civil Engineers,' and have added several original investigations relating to the proportions of the teeth, and their least numbers.

In the present edition, Art. 124, I have restored to Camus the discovery of the method of describing teeth of wheels by employing the same describing circle or curve to trace their forms within and without the respective pitch-lines.*

It will be found that I have calculated all the results that are required in practice, and have arranged them in tables for reference.

On the whole, it will be seen that the present volume is

I may also be pardoned for referring to the description and theory of my Odontograph, for facilitating the setting out of the teeth of wheels; which has been extensively employed since its invention in 1838. Vide below, p. 130.

limited to that portion of the important subject of machinery which deals with the communication of motion. The object of it was, as has been already stated, to systematise this portion of the subject, and to free it from the considerations of force, with which it had been usually mixed up.

In the preface of the first edition I stated that to complete the plan of a treatise on mechanism, it would be necessary to apply these considerations of force to the combinations thus obtained, as well as to describe and investigate those parts of machinery in the action of which forces are essential, adding a hint that I should probably undertake this task at some future time.

But in the year of its publication (1841) Professor Whewell also published his 'Mechanics of Engineering;' into which he introduced many of the results of the French writers, Navier, Poncelet, Morin, &c., who had with so much success applied themselves to this purpose; and he also flattered me by the adoption of my own views upon the classification of the modes in which motion is communicated from one piece to another of a machine, adding to them the investigation of the effects of force and resistance; which might be considered as carrying out a portion of the plan above alluded to, as necessary to complete this arrangement of the science of Machinery.

In concluding the preface of the first edition, I expressed my hopes that, in addition to its principal object of giving a scientific and systematic form to its subject, the results of the volume which I then ventured to present to the world might be found a useful addition to mathematical studies in general, by affording simple illustrations of the application and interpretation of formulæ, and by suggesting new subjects for problems, and for farther investigation.

After the appearance of the first edition at the end of 1841, it took its place as a text-book to my Lectures and

others, but it was not quoted or mentioned in any new mechanical work until Monsieur Tom Richard published in 1848 in Paris, his Aide-mémoire des Ingénieurs,' into which he introduced the whole of my articles on linkwork (Bielles), duly acknowledging the author.

This was the first of a series of works on mechanism, of which I present a list below, which comprises every subsequent work on that subject, in which my classifications, nomenclature and figures have been more or less adopted; and, with two or three exceptions, the source from whence borrowed properly mentioned.

1. M. Tom Richard, Aide-Mémoire des Ingénieurs
2. M. Laboulaye, Traité de Cinematique
3. Tate, Elements of Mechanism, 12mo

4. Baker, Elements of Mechanism, 12mo

5. Rankine, Applied Mechanics.

6. M. Girault, Transformation du Mouvement
7. Goodeve, Elements of Mechanism, 12mo

. 1848

1849

1851