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RULER AND TRIANGLE FOR HATCHING.

The instrument shown in the cut is the invention of Mr. Maginnis, and is designed for producing equidistant hatchings.  It consists of a short ruler, A, and a triangle, B, supposed to be one of 45 deg., but which may be of any angle.  The triangle carries two stops, c c, while the ruler is provided with a conical piece, D, which is slotted, and is held by a screw.  The play that occurs between this conical slide and the stops varies according to the position of the former.

[Illustration:  RULER AND TRIANGLE FOR HATCHING.]

The apparatus operates as follows:  In the figure, the stop to the right being in contact with the piece, D, a line is drawn along the right side of the triangle.  Then the ruler is made to slide along the triangle until D touches the other stop, and then the triangle is slid along the ruler until the stop to the right touches D again.  In this position another line is drawn, and so on.  The position of the piece, D, between the stops is regulated according to the fineness of the hatching to be done.—­Chronique Industrielle.

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THE DISTILLATION OF SEA WATER.

The supplying of the troops at Suakim and in the Soudan with water is one of the most important items in the whole conduct of the Egyptian war.  Even in cold or temperate latitudes fresh water is a first necessity for animal life; much more is this the case in the desert; and the wells in the country forming the scene of our military operations form in themselves valuable strategical points.  Their supply, however, has to be supplemented, and to do so artificial means and the aid of the engineer have to be enlisted into this service.

Many of our readers see notices from time to time in the newspapers about this or that ship being employed, or at least her steam fittings, in distilling water for the use of the troops; and although most of, if not all, our readers are engineers, still it is no disparagement to some of them to assume that they are more or less unfamiliar with sea water distillation on the scale on which the process is now being carried on at Suakim; and as the subject is of general interest, we give a short description of the process.

In a general sense, fresh water is obtained from sea water by simply generating steam from the sea water, passing the said steam through a surface condenser, and filtering the resulting water.  The obtaining of fresh water in this way has been in practice on board sea-going ships for many years.  It is supposed by some authorities on this subject that the first time fresh water was thus obtained at sea was by an old captain of a brig which ran short of water, and he cut up some pewter dishes into strips, which he bent and soldered into a pipe.  He, with the carpenter’s