to the determination of the Magnetic Inclination. 157 



once found they can be fixed there. This position is determined by- 

 seeking the arc through which the induction coil must be moved, 

 so that the induced currents may annihilate one another. The 

 position of the induction coil which corresponds to the middle 

 of this arc is the position of the brass pins at the moment when 

 they should strike the screws. The two ends of the wire of the 

 inductor are led to the clamps ji, p and there fastened. From 

 these clamps the connecting wires pass over the pulley C to the 

 galvanometer. 



Fig. 3 is a section of the multiplication coil together with the 

 magnetic needle. The circumference of the cylindrical surface 

 around which the wii-e is coiled is 1027'4 millims., its diameter 

 is «« = «'«', and its breadth ««' = 225-6 millims. Around this 

 cylindrical surface two copper wires, covered first with spun wool 

 and then with gutta percha, were coiled side by side. Each wire 

 is 992656 millims. long, and the mean sectional area of both 

 wires taken together is 8-1683 square millims. Each of these 

 wires forms 779 coils, arranged in twenty-five strata. The cii-- 

 cumfereuce of the last stratum is i52o-l millims. 



In the middle of the coil the magnetic needle NS is sus- 

 pended on a prismatic bar, which can be moved along a cross- 

 bar bb and screwed fast to it. Above the coil is another 

 cross-bar, parallel to the lower one, and suspended from a fine 

 wire j the two are connected at their extremities by two thin 

 vertical connecting rods which pass outside the multiplication 

 coil. To the upper cross-bar a mirror and torsion cn-cle is affixed. 

 Lastly, the space enclosed by the coil, in which the needle 

 oscillates, is closed on both sides by covers, cccc. 



Fig. 4 is a vertical section of the galvanometer in the direction 

 of the magnetic meridian. Here the direction of the upper 

 cross-bar d, as well as that of the lower cross-bar b, is perpendi- 

 cular to the plane of the figure. Both are connected by thin 

 vertical bars attached to their extremities before and behind the 

 multiplier. The mii-ror e is connected with the cross-bar d 

 by means of a Y-formed hook, and above the mirror, similarly 

 connected, is the torsion circle hung on a thin wire. The case 

 which encloses d, e, and / projects a little both before and behind 

 the multiplier, and on both sides reaches down to the covers 

 cccc, fig. 3 j so that the connected space occupied by d, e,f 

 and the coil is completely enclosed, with the exception of an 

 opening through which the thin sus])ending wire passes. A 

 parallel plate of glass is ])laced in the side of this case immedi- 

 ately before the mirror, so that the image of the scale may be 

 oljserved in the mirror by a telescope. Lastly, the frame of the 

 multipli('r has a hexagonal form, and the undcrmoLt side of this 

 hexagon rests upon a stone pedestal A. 



