GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 41 



Figs. 7j 8, and 9 represent the pin to which the thread is 

 fastened, seen from one side, from above, and from below. The 

 first view exliibits the two points Avith which this pin fits into 

 the holes of the staples of the torsion circle, as also the spring 

 Avhich retains it when the stirrup is raised, and the thread loosen- 

 ed. The second view shows the narrow, round aperture thi'ough 

 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 haA-ing been longitudinally drawn through a loop formed 

 by its inferior extremity. 



Fig. 10. gives a representation of the scale which is fixed be- 

 low 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 instru- 

 ments. That of the building is not everywhere the same ; at 

 Gottingen, it amounted to 798* 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 supphed by Meyerstein of 

 Gottingen, 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 fi-ame ...... 1 



5. The illuminating apparatus . . . . .11 

 C. 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. 



