154 Prof. Weber on the Application of Magnetic Induction 



determiuatiou of the vertical magnetic force thus obtained can 

 never possess that degree of precision which a determination of 

 the horizontal magnetic force now enjoys, inasmuch as the latter 

 is deduced from effects produced by this force alone, and unin- 

 fluenced by any other forces. Secoiutly. The magnetometric 

 arrangements, on which the possibility of accurate observation 

 depends, cannot be applied to instruments for measuring the 

 inclination, on account of the influence of friction which is inse- 

 parable from such instruments ; and as long as this exists, the 

 application of more accurate methods of observation would simply 

 lead to deceptive results. These defects are so intimately con- 

 nected with the conditions under which the action of the vertical 

 component of the earth's magnetism on the magnetism of other 

 bodies must be observed, that they cannot possibly be avoided ; 

 the most ingenious arrangement and combination of observations 

 may sene to diminish the prejudicial consequences of these de- 

 fects, but never to remove them. 



Soon after Faraday's discover}'^ of magnetic induction. Gauss 

 drew attention to the possibility of investigating the earth's 

 magnetism by observing its action on the electricity of bodies ; 

 and, acting on this suggestion, Weber, in 1837, constructed a 

 new instrument for measuring the magnetic inclination, which he 

 named the " Inductian-Inclinatorium^." This instrument was 

 completely free from the first of the above-mentioned defects, 

 that is to say, no interference of the force of gravity took place, 

 and hence no demagnetization was necessary to separate its 

 effects from those of the vertical magnetic force. The second 

 defect, however, was not removed ; magnetometric arrangements 

 could not yet be combined with this instrument so as to obtain 

 accurate results, hence this new method was of no avail. 



At length Weber has succeeded in removing this second defect 

 also, and has discovered an arrangement whereby the electric 

 action of the vertical as well as the horizontal component of the 

 earth's magnetism may be measured, by the unifilar magneto- 

 meter, with a degree of precision of which hitherto the magneto- 

 metric determination of the horizontal elements alone could 

 boast. For the practical solution of the problem, an accurate 

 and complete investigation of the earth's magnetism, this ex- 

 tended application of the magnetometer to measurements of the 

 inclination is of some impoi-tance. 



A simple and general notion of Weber's new instrument may 

 be obtained by a reference to the well-known construction of the 

 electro-magnetic telegraphs now in use. These, it will be remem- 

 bered, are of two kinds. In one the electric currents made use of 



* Resultate aus den Beob. des magn. Vereins im Jahre 1837, S. 81. 



