Page:Miscellaneous Papers on Mechanical Subjects.djvu/18

 10 engine tools affords an important application of the subject. Here every consideration combines to afford accuracy. It is implied in the very name of the planing engine. The express purpose of that machine is to produce true surfaces, and it is itself constructed of slides, according to the truth of which will be that of the work performed. When it is considered that the lathe and the planing engine are used in the making of all other machines, and are continually re-producing surfaces similar to their own, it will manifestly appear of the first importance, that they should themselves be perfect models. There is, perhaps, no description of machinery which would not afford an illustration of the importance belonging to truth of surface, and at the same time, of the present necessity for material improvement; nor is there any subject connected with machines, the bearings of which, on public interests, whether manufacturing or scientific, are more varied or more extensive.

The improvement so much to be desired, will speedily follow upon the discontinuance of grinding. Recourse must then be had to the natural process. The surface plate and the