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302 of Nature, we will not say; certain it is, however, that the former work suggested the latter, though the prior claim does not seem to have been considered by the American Commissioner of Patents.

"On the 18th of October, 1870," we read, "letters-patent of the United States were granted to General B. C. Tilghman, of Philadelphia, for the cutting, grinding, etching, engraving, and drilling stone, metal, wood, or any hard substance, by means of a jet or blast of sand." We are also informed, from the same official source, that the inventor of the sand-blast process obtained his first hints from Nature, and, by means of a mechanism which is a marvel of simplicity, has been able to utilize this same force so as to make it render most efficient service in several departments of the applied arts.

It is the object of the present paper to describe and illustrate the invention known as the Tilghman Sand-Blast, an invention which, in simplicity of construction, and yet extent of application, has hardly an equal in the annals of the American Patent-Office. We are aware that this is a broad claim, when it is remembered that under the protection of the same authority the sewing-machine, reaper, and mower, positive-action loom, and a score or more of great mechanical devices, first saw the light. It is possible that there is that in the idea of the sand-blast which adds to its charm, and secured for it the admiring indorsement of Torrey, Tyndall, and other men of science; and yet a careful study of ils principle, and an observance of its practical operation, seem to justify all and more than is claimed for it by the inventor or his distinguished indorsers.

If the reader will refer to the simple "claim" as given above, he will notice that it is proposed to accomplish the several results there named "by means of a jet or blast of sand." The italics are our own, and are now introduced since it is in this idea of a jet of sand that the first principle of the device rests; and, moreover, it was an attempt made by others to adopt this falling jet of sand that compelled the inventor to institute his first proceeding against infringement. With the legal history of the sand-blast, however, we have nothing to do, save as it concerns the general history of the invention and its progress. In order that the methods by which a simple falling column or stream of sand is made to do service as an engraver of glass and metal plates may be understood, attention is directed to Fig. 2, which may be described as follows:

A is a box, elevated as high above the engraver's table as the height of the ceiling will permit. When designed for several workmen, this box may be divided into compartments, as indicated, each compartment being filled with common quartz or sea-sand, of varying degrees of fineness. From the bottom of each division a metal tube, c, depends, reaching to within a few inches of the table below. A slide, B, serves to regulate or check the flow of the sand. Thus much for the simplest form of sand-blast. A word as to the manner of its operation; and