_a._ A stick of sealing-wax excited A glass tube similarly excited. by friction with flannel or silk. A glass tube excited by rubbing it with fur. _b._ The zinc disc of an arrangement The copper disc of the same, the of two zinc and copper discs odometer being held over against moistened with salt and water, the the surface of the copper disc; odometer being held opposite to the for again, if it be held to the middle of the zinc disc; for if it edge of the copper disc, the be held beyond the disc, half an opposite result follows, and the inch from and on the exact level rotation is clock-rotation. of the zinc disc, versed-rotation is manifested round the whole circumference. _c._ A mixture of half a drachm of A mixture of half a drachm of bicarbonate of soda and five grains tartaric of bicarbonate acid and five grain of tartaric acid, of soda. when effervescing upon a plate after the addition of water. _d._ The northward pole of a horse-shoe The southward pole of the same. magnet, or of a magnetic needle freely suspended. _e._ One pole of a large crystal, which, The opposite pole. is to be found out by this experiment. _f._ The root of a garden weed freshly The leaves of the same. taken from the ground. _g._ The stalk end of an orange, and The opposite points of the same. of an apple, and of an orange pip. _h._ The small end of an egg. The large end of the same. _i._ The tips of the fingers on either The top of the thumb and great hand, and of the toes of either toe. foot. _k._ Right side of the head of a Left side. sparrow. The last holds likewise with the greater part of the human body; but the results of trying the odometer with the human frame are so complicated, that I shall reserve their consideration for a separate section. V. The mechanical solution of these phenomena is simple enough. The odometer must be under the influence of two constant and unequal rectilinear forces, operating at right angles to each other on the gold ring, the effects of which are modified by the centripetal force of its gravitation. All that is required is, to determine by observation the place, direction, and limits of the two forces. It will render the description which follows easier, to suppose that the pole of the Od-subject which causes clock-rotation be turned directly from the experimenter; for example, that an egg be placed longways to the experimenter with its small end from him, or a bar magnet with its northward pole from him. In the case of a horse-shoe magnet, both poles are then turned from you. So, too, in the case of the hand, the fingers and thumbs are both to be turned away.