weights were found, as expected, to be identical, and not multiples; hence Prof.  Meyer is perfectly justified in introducing the necessary modification in the “position in space” theory.  Now that this generalization of Raoult is placed upon a secure basis, it takes its well merited rank along with that of Dulong and Petit as a most valuable means of checking molecular weights, especially in determining which of two or more possible values expresses the truth.—­Nature.

* * * * *

[Continued from SUPPLEMENT, No. 642, page 10258.]

THE DIRECT OPTICAL PROJECTION OF ELECTRO-DYNAMIC LINES OF FORCE AND OTHER ELECTRO-DYNAMIC PHENOMENA.[1]

   [Footnote 1:  An expansion of two papers read before the A.A.A.S.
   at the Ann Arbor meeting.]

By Prof.  J.W.  MOORE.

II.  LOOPS.

If the wire, with its lines of force, be bent into the form of a vertical circle 1-1/8 in. in diameter, and fixed in a glass plate, some of the lines of force will be seen parallel to the axis of the circle.  If the loop is horizontal, the lines become points.

[Illustration:  Fig. 14.]

[Illustration:  Fig. 14a.]

FIELDS OF LOOPS AND MAGNETS.

Place now a vertical loop opposite to the pole of a short bar magnet cemented to the glass plate with the N pole facing it.  If the current passes in one direction the field will be as represented by Fig. 14b; if it is reversed by the commutator, Fig. 14c is an image of the spectrum.  Applying Faraday’s second principle, it appears that attraction results in the first case, and repulsion in the second.  The usual method of stating the fact is, that if you face the loop and the current circulates from left over to right, the N end of the needle will be drawn into the loop.

[Illustration:  Fig. 14b.]

[Illustration:  Fig. 14c.]

It thus becomes evident that the loop is equivalent to a flat steel plate, one surface of which is N and the other S. Facing the loop if the current is right handed, the S side is toward you.

TO SHOW THE ACTUAL ATTRACTION AND REPULSION OF A MAGNET BY A “MAGNETIC SHELL.”

Produce the field as before (Fig. 14), carry a suspended magnetic needle over the field.  It will tend to place itself parallel to the lines of force, with the N pole in such a position that, if the current passes clockwise as you look upon the plane of the loop, it will be drawn into the loop.  Reversing the position of the needle or of current will show repulsion.

Clerk Maxwell’s method of stating the fact is that “every portion of the circuit is acted on by a force urging it across the lines of magnetic induction, so as to include a greater number of these lines within the embrace of the circuit."[2]