416 Description Ampere\s Electro-Magnetic Apparatus. 
jiomena are observed, in virtue of the same action. If we next 
stop the electric current in both conductors, and adapt one of 
the needles to each conductor, they will act upon one another in 
the same manner as the conductors did upon them. 
The apparatus represented in Fig. 11. communicates with 
the pile, and has its moveable conductor suspended nearly in 
the same way as in Fig. 1. It differs from it, however, in 
this, that the two conductors A, B, are here of a spiral form, 
and the moveable conductor B suspended to a vertical tube of 
glass. This tube is terminated below, at the centre of the spi- 
ral which forms this conductor, and receives in its interior the 
prolongation of the brass wire of this spiral. When that pro- 
longation reaches D, at the top of the tube, it is then soldered 
to a copper box F, which carries the copper tube V, into which 
slides the counter-weight H, and a steel point L, which is 
plunged in the globule of mercury of the cup Y ; whilst the 
other extremity of the same brass- wire, after having encircled 
the tube CD in the form of a screw, is soldered to the copper 
box D, to which is attached another steel point K, to be im- 
mersed also in a globule of mercury in the cup X. These two 
cups are made of steel, in order that they may not be injured 
by the mercury, and the parts rest on their concave surface, 
as in Fig. 1, 
Scale of the Figures on Plate VIII. 
Fig. 1, % 3, 5, 9, 10, 11, are drawn in the proportion of one 
inch to a foot. 
Fig. 4. is drawn on a scale of two inches to a foot. 
Fig. 6, 7, are on the scale of one inch to a foot, for the parts 
parallel to the plane of the picture. 
Fig. 8. is drawn on a scale of three inches to a foot, for the 
• parts parallel to the plane of the picture. 
Erratum in Fig. 1. For O (placed above B,) read Q, and in- 
sert C at the angle below X, and D at 
the angle below Y, so that CD may de- 
signate the conductor above, and parallel 
to AB. 
Ditto in Fig 6. Insert r at the left hand of the dotted line, 
so that efmay mark that line. 
