EXPERIMENT 7: ROD+c. Vessel upright and swung through eastern semicircle, resting two minutes on each point. Tube: one of the 14-inch tubes used in Experiment 6; placed forward of compass, vertically, in vertical plane through keel, upper pole in horizontal plane of needle, and nearest point of tube ten (10) inches from compass-pivotFig. 472. This rod represents the smoke-stack, ventilators, stanchions, or any vertical soft iron whose upper pole is near the horizontal plane of the compass. The curve of Fig. 473 is enlarged twice. The difference between the deviations on corresponding points of the two quadrants (Table 59) is not readily explained by raising the tube 14 inches, that is, until the lower pole came into the plane of the needle, it was found that the curve was nearly symmetrical. The observations in the unfavorable position are given, however, to show the identity of effect of the rod c and magnet P, as stated in Art. 270. EXPERIMENT 8: ROD +e. Vessel upright and swung through western semicircle, resting two minutes on each point. Tube: the same one used in Experiment 1, that is, a 28-inch tube, formed by screwing together the two 14-inch tubes of which it was originally composed; placed horizontally, axis in plane of compass-pivot and also in plane transverse to vertical section through keel; wholly to starboard of compass, as rod +e, and nearest point 7 inches from compass-pivot— Fig. 474. The curve of Fig. 475 is made from Table 60 and is enlarged twice; it corresponds beautifully to theory. The rode may represent a deck beam cut amidships for a hatch. EXPERIMENT 9: ROD —e. Vessel upright and swung through eastern semicircle, resting two minutes on each point. Tube: same one used in Experiment 1, 28 inches long; placed horizontally, at right angles to vertical plane through keel, middle point over compass-pivot; axis of tube 11 inches above plane of needle-Fig. 476. The curve of Fig. 477 is enlarged six times. As in Experiment 8, the deviations are in strict conformity to theory-Table 61. This rod represents iron deck beams. |