[Illustration:  BRITTON’S plate straightening machine.]

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THE SCHOLAR’S COMPASSES.

Among the numerous arrangements that have been devised for drawing circles in diagrams, sketches, etc., one of the simplest is doubtless that which is represented in the accompanying figure, and which is known in England as the “scholar’s compasses.”  It consists of a socket into which slides a pencil by hard friction, and to which is hinged a tapering, pointed leg.  This latter and the pencil are held at the proper distance apart by means of a slotted strip of metal and a binding screw.  When the instrument is closed, as shown in the figure to the left, it takes up but little space, and may be easily carried in the pocket without the point tearing the clothing, as the binding screw holds the leg firmly against the pencil.

The mode of using the apparatus is so well shown in the figure to the right that it is unnecessary to enter into any explanation.—­La Nature.

[Illustration:  The scholar’s compasses.]

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THE INTEGRAPH.

In scientific researches in the domain of physics we often meet with the following problem:  Being given any function whatever, y = f(x), to find a curve whose equation shall be

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     /
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y = | f(x)dx + C.
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   _/

[TEX:  y = \int f(x) dx + C.]

Let us take an example that touches us more closely; let us suppose that we know an induced current, and that we can represent it by a curve y=f(x).  The question is to find the inductive current, that is to say, the curve represented by the equation

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     /
     |
y = | f(x)dx + C.
     |
   _/

[TEX:  y = \int f(x) dx + C.]

The apparatus called an integraph, constructed by Messrs. Napoli and Abdank-Abakanowicz, is designed for solving this problem mechanically, by tracing the curve sought.  Let us take another example from the domain of electricity, in order to better show the utility of the apparatus; let us suppose that we have a curve representing the discharge of a pile or of an accumulator.  The abscisses represent the times, and the ordinates the amperes.  The question is to know at every moment the quantity of coulombs produced by the pile.  The apparatus traces a curve whose ordinates give the number of coulombs sought.  We might find a large number of analogous applications.

[Illustration:  The integraph.]