# Miscellaneous Papers on Mechanical Subjects/Preface

PREFACE
These miscellaneous papers were written at various periods, some of them many years ago, and a few of the statements must be considered with reference to the objects for which they were respectively written, and to their dates. The paper upon plane metallic surfaces was read at the British Association in Glasgow, in the year 1840, with the view of showing how a true surface, or perfectly straight line, may be produced. At that time it was the custom to prepare what were intended to be used as original surfaces (presumed to be true) by grinding them; and I was anxious to direct the attention of those engaged in mechanical pursuits to the inherent defects of the grinding process, and to prove the necessity of adopting the system of correction, by which alone error is eliminated, and surfaces practically true can be produced. ​At the same time I urged the necessity of supporting all original surfaces or “true surface plates” on three points, that being the only means by which truth of surface can be maintained.
For some years prior to the date of the paper (in order to conciliate then existing prejudices) I used the grinding process to a limited extent, merely to give surfaces, such as those of slide-rests, the regular even appearance that was generally considered to be the proper indication of truth, to which I knew it in no way contributed.
Now, however, the mottled appearance produced by the scraping instrument is recognized as an indication of truth, and is sometimes applied to surfaces which have not undergone the process of correction, and are not true. It is very satisfactory to me to find that the advantages of the system are now universally recognized.
The paper on the screw threads was read at the Institution of Civil Engineers, in London, in the year 1841; since that time the system has been generally adopted in this country, and is becoming extensively used in America, and in other countries.
The report founded on the official visit of the Royal Commission (of which I was a member) ​to the New York Exhibition, in 1853, was made in that year. It has been appended to the other papers, as many parts continue to be of interest, and inquiries are still made for it.
The address to the Institution of Mechanical Engineers was delivered in Glasgow in the year 1856, and the paper on “Standard Decimal Measures of Length” was read at the meeting of the Institution in Manchester in 1857, during which years I had the honour of being President.
The subject of rifled fire-arms, including artillery, has, during the last three years, occupied much of my time. It is so comprehensive in its nature that I have, in the following paper, purposely avoided going into details, and have confined myself to an explanation of the principles on which I have proceeded.
I could not help taking an interest in a subject so intimately connected with those branches of mechanics to which I have long paid special attention; believing as I do that the greater the precision with which fire-arms may be used at long distances, and the more their powers of destruction are increased, the more reluctant will civilized nations become to use them against each other, while, at the same time, a greater superiority will be given to wealth and civilization over mere numerical strength.
​With these explanations I have thought it advisable to allow the earlier papers to remain in the form in which they were originally read, as in many respects the information they respectively contain, and the opinions then expressed, are applicable to the present time.