to the determination of the Magnetic Inclination. 159 



axis of the needle coinciding with the major axis of the ellipse. 

 Should the deviation of the needle be thus too great to be con- 

 veniently measured by the scale, only half the amount of wire 

 (about 10 kilogrammes) need be employed for the inductor. 

 This diminution of the mass of the inductor would have another 

 advantage, the rotation of the inductor coil could be made with 

 greater ease. 



In former memoirs* Weber has shown the application of the 

 induction stroke to delicate measurements, and has developed 

 the rules according to which the deviations of the magnetic 

 needle, produced by the induced electric currents, are multiplied 

 in the galvanometer, as well as subjected the observations 

 to mathematical calculation. It is not necessary to repeat 

 these rules here ; it will be sufficient to give the observations 

 made in accordance with them, from which it may be de- 

 cided whether, in this instrument for the measurement of the 

 inclination, the necessary delicacy is combined with the intended 

 simplification of labour, as it should be in order to be an essen- 

 tial improvement upon the best known inclination instruments. 



The magnetometer and galvanometer being prepared, the 

 position of the inductor was so regulated that, — 1, its own axis 

 {i. e, the axis of the cylindiical surface around which the wire 

 was coiled) was horizontal, and parallel to the magnetic meridian ; 

 2, that the axis around which it could be made to revolve 180° 

 backwards and forwards, was perfectly vertical; this could be 

 tested within a few seconds by means of the level. The mag- 

 netometer needle in the galvanometer was at the commencement 

 in a state of perfect rest in the magnetic meridian. This covdd 

 always be secured by the damping force of the galvanometer, 

 which was increased by connecting the two wires from the gal- 

 vanometer to the inductor by means of a copper clamp, the gal- 

 vanometer thus forming a circuit for itself. When the damping 

 foi'ce was thus increased, two succeeding arcs of oscillation of the 

 needle were in the ratio of 100 : 71 ; hence after thirty oscillations, 

 or, as the time of an oscillation was eighteen seconds, in nine mi- 

 nutes, the amplitude was diminished 29,000 times by this damping 

 force ; that is to say, the needle was in a state of rest, no matter 

 how great the original arcs of oscillation might have been. Before 

 commencing observations, the clamp used to increase the damp- 

 ing power was removed, and then the first (positive) induction 

 stroke given with the inductor. The needle being thus set in 

 motion, left the magnetic meridian, and in nine seconds (half its 



• Resultute aus den Beob. desviagn. Ver. im J«7/re 1838 (Leipzig, 1839), 

 anil Ahhmidlunyen iihcr elektrodijnamische Maasbestimminujen (Leipzig, 

 M'eiiimanu'schc liuchkandlung, lSb2), 2''-' Abhaadlung, Beilage C. S.341j^. 



