Figs. 7, 8, and 9 represent the pin to which the thread is fastened, seen from one side, from above, and from below. The first view exhibits the two points with which this pin fits into the holes of the staples of the torsion circle, as also the spring which retains it when the stirrup is raised, and the thread loosened. The second view shows the narrow, round aperture through which the thread passes and is held together. The third view exhibits an oval aperture, which is bisected by a round transverse pin. The thread is wound round this latter, and drawn tight, after having been longitudinally drawn through a loop formed by its inferior extremity.
Fig. 10. gives a representation of the scale which is fixed below the theodolite, and the reflected image of which is observed with the theodolite telescope. By employing an astronomical telescope (which, with a similar object-glass, is preferable, for clearness and definition, to the terrestrial telescope) the scale is inverted, so that the figures stand above the divisions, while, in our figure, they are situated beneath them.
Expense of building and furnishing a Magnetic Observatory.
The expenses consist in the cost of the building and the instruments. That of the building is not everywhere the same; at Göttingen, it amounted to 798[1] dollars, Prussian currency. A part of the costs were occasioned by the exclusion of iron in the nails, locks, hinges, and fastenings of all kinds, all of which are of copper.
The costs of the instruments, as supplied by Meyerstein of Göttingen, who has hitherto made the greatest number of such instruments, are as follows:
| Dollars. | |||
| 1. | An 8-inch theodolite | 150 | |
| 2. | A seconds clock | ||
| 3. | A stand for the theodolite | 7 | |
| 4. | A scale, with frame | 1 | |
| 5. | The illuminating apparatus | 11 | |
| 6. | The suspender, with slider and screw | 8 | |
| 7. | The stirrup, with torsion circle | 15 | |
| 8. | A 4-lb. principal bar, with its case; a 4-lb. auxiliary bar, and a 1-lb. quieting bar | 7 | |
| 9. | A brass torsion bar, with magnets inlaid | 9 | |
- ↑ The Prussian current dollar is equal to three shillings.
