buildings, a positive conviction may be acquired, that their influence on each other is harmless, or, if this should not be the case, that their effect may be reduced to calculation.
Explanation of Plate X.
In this plate the several parts of the magnetometer are represented, with the exception of the clock, theodolite, measuring scales, the box, the torsion and quieting bar, which partly require no particular representation, and in part have been already shown on a smaller scale, in Plates II. and III. On the other hand, the arrangement of the suspender with the elevating screw, the stirrup with the torsion-circle, the mirror-holder, with its corrections, the weights and the weight-holder, stand in need of a more accurate representation, which is given from various sides in this plate, on a scale of half their actual magnitude. The stirrup, the torsion-circle, and the magnet bar in its place, have been represented in three different positions—from the west, from the south, and from above; the mirror-holder, and the suspender, with the elevating screw, have been figured from two sides—from the west, and from the south. In the south view of the stirrup, with the torsion-circle and the magnet bar in its place, is shown the manner in which the weight-carrier may be placed on the magnet bar in a west and east direction, and the two weights, each of half a kilogramme, suspended to the points with which it is furnished, for the purpose of determining, in absolute measurements of intensity, the moment of inertia of the vibrating portion of the magnetometer. To spare room on the plate, the two views of the bearer, with the elevating screw, have been placed in the upper series, close to one another, but this has prevented the bringing of the two into the correct position relatively to the vibrating portion of the magnetometer suspended from them. It is, however, easily seen how the view of the suspender, with the elevating screw in fig. 1., is connected with that of the stirrup, torsion-circle, magnet bar, and mirror-holder in fig. 3. if we attend to the commencement indicated in fig. 1. and the termination indicated in fig. 3. of the vertical line connecting them. These two figures represent the main parts of the magnetometer in a westerly view. In the same manner fig. 2. and fig, 6. are connected, and represent the instrument as observed from the southern position. In fig. 6. the mirror-holder has been taken off from the southern extremity of the magnet bar, so that
