It is obvious from these spectra that the two loops attract or repel each other according to the direction of the current, which fact may be shown by bringing a loop near to another loop suspended from the ring stand, Fig. 9, or by using the ordinary apparatus for that purpose--De la Rive's battery and Ampere's stand. [Illustration: Fig. 14f.] [Illustration: Fig. 14g.] If two loops are placed in the same vertical plane, as in Figs. 14h and 14i, there will be attraction or repulsion, according to the direction of the adjacent currents. The fields become the same as Figs. 8 and 8a, as may be seen by comparing them with those figures. [Illustration: Fig. 14h.] [Illustration: Fig. 14i.] Having thus demonstrated the practical identity of a loop and a magnet, we proceed to examine the effects produced by loops on straight wires. If the loop is placed with a straight wire in its plane along one edge, there will be attraction or repulsion, according to the direction of the two currents, Figs. 20 and 20a, which are obviously the same as Figs. 8 and 8a. [Illustration: Fig. 20.] [Illustration: Fig. 20a.] [Illustration: Fig. 20b.] [Illustration: Fig. 20c.] If the wire is placed parallel to the plane of the loop and to one side, Figs. 20b and 20c, there will be rotation (same as Figs. 4b and 4c). If the loop is horizontal and the wire vertical and on one side, the Figs. 20d, 20e are the same as 4d and 4e. If the loop is horizontal and the wire vertical and axial, 20f and 20g, there will be rotation, and the figures are mere duplicates of 4g and 4h. [Illustration: Fig. 20d.] [Illustration: Fig. 20e.] [Illustration: Fig. 20f.] [Illustration: Fig. 20g.] [Illustration: Fig. 20h.] Fig. 20h shows a view of 20f when the wire is horizontal and the plane of the loop vertical. It is like 4i. To verify these facts, suspend a loop from Ampere's stand, Fig. 9, and bring a straight wire near. A small rectangle or circle may be hung in a similar manner. When the circuit is closed, it tends to place itself with its axis in a N and S direction through the earth's influence. The supposition of an E and W horizontal earth current will explain this action. To exemplify rotation of a vertical wire by a horizontal loop, Fig. 21 may be shown. A circular copper vessel with a glass bottom (Fig. 21) has wound around its rim several turns of insulated wire. In the center of the vessel is a metallic upright upon the top of which is balanced in a mercury cup a light copper [inverted U] shaped strip. The ends of the inverted U dip into the dilute sulphuric acid contained in the circular vessel. The current passes from, the battery, up the pillar, down the legs of the U to the liquid, thence through the insulated wire back to the battery. [Illustration: Fig. 21.] This is the usual form of apparatus, modified in size for the vertical or horizontal lantern. (_To be continued._) * * * * * POISONS.