Page:Miscellaneous Papers on Mechanical Subjects.djvu/6

vi 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)