Several other magazine rifles have the box central magazine, but placed in different positions as regards the shoe and the axis of the bore.  In the original pattern of the Jarman (Sweden and Norway), the magazine is affixed to the upper part of the shoe, inclined at a considerable angle to the right hand (see vertical cross section, Fig. 11).  Here the operation of gravity obviates the necessity of a magazine spring, but the magazine was found to be very much in the way and liable to be injured.  It has therefore been replaced by a magazine underneath the barrel, as in the Kropatschek and other rifles.—­Engineering.

(To be continued.)

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PRESERVATIVE LIQUID.

For a few weeks’ preservation of organic objects in their original form, dimensions, and color, Prof.  Grawitz recommends a mixture composed of 21/2 ounces of chloride of sodium, 23/4 drachms of saltpeter, and 1 pint of water, to which is to be added 3 per cent. of boric acid.—­Annales des Travaux Publics.

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KENT’S TORSION BALANCE.

The United States Torsion Balance Company, of New York, has recently brought before the public a new form of balance which presents so many ingenious and excellent features that we illustrate it below, on the present page.  The instrument in its simplest form is shown in Fig. 1.  It consists of a beam, A, which is firmly attached to a wire or band, B, at right angles to it, and which wire is tightly stretched by any convenient means.  Then, since the wire and beam are both horizontal in their normal position, and since the center of gravity of the beam is immediately above or below the middle line of the wire, the torsional resistance of the latter tends to keep the beam horizontal and to limit its sensitiveness.  When the beam is deflected out of its horizontal position and the wire thereby twisted, the resistance to twisting increases with the arc of rotation.  To counteract this resistance and to render the beam sensitive to a very slight excess of load at either end, a poise, D, is attached to the beam by a standard, C, which poise carries the center of gravity of the structure above the axis of rotation.  This high center of gravity tends to make the beam “top heavy,” or in unstable equilibrium.  By properly proportioning the poise and its distance above the wire to the resistance of the wire, the top-heaviness may be made to exactly neutralize the torsional resistance, and when this is done the beam is infinitely sensitive.

[Illustration:  KENT’S TORSION BALANCE.  Fig 1.]

The moment of the weight or its tendency to fall increases directly as the sine of the arc of rotation, while the torsional resistance increases as the arc, and for small angles the sine and the arc are practically equal.