Intelligence and Miscellaneous Articles. 311 



the velocity to be given to the plate to photograph the most acute 

 sound spreads out the image of the deeper one, and the measure- 

 ment becomes very difficult. — Comptes Rendus, August 2, 1886. 



ON A NEW METHOD FOR DETERMINING THE VERTICAL INTENSITY 

 OF A MAGNETIC FIELD. BY R. KRUGER. 



The methods hitherto used for measuring the vertical intensity 

 of a magnetic field depend on the electromotive action which it 

 exerts on a spiral which rotates about a horizontal axis. If, more- 

 over, the spiral turns about a vertical axis, the ratio of the currents 

 induced in the two rotations gives the inclination of the magnetic 

 lines of force to the horizon. If, again, the current induced by a 

 rotation about a horizontal axis be determined in absolute measure 

 by a galvanometer, the vertical intensity of the field is determined 

 from the contents of the surface enclosed by the windings of the 

 spiral, and from the absolute resistance of the circuit formed by the 

 spiral and the galvanometer. In a field of small extent the rotation 

 must be replaced by a parallel displacement of the spiral in its 

 plane. In any case the determination of a vertical intensity by 

 these means is a difficult and tedious operation. 



In contrast with this, the deflection which a disk suspended 

 horizontally by means of a vertical wire in a solution of copper 

 sulphate experiences when traversed in a radial direction by a cur- 

 rent, forms a very convenient means of determining the vertical 

 magnetic force which produces that deflection. 



In order to test the capability of this method, it was used to de- 

 termine the vertical intensity of the terrestrial magnetism, or rather 

 the magnetic inclination. 



The value of the vertical intensity was thus found to be 



V=2-2903xT, 



in which T is the horizontal intensity. Simultaneous observations 

 with the terrestrial inductor gave 



Y =2-2899 xT; 



while the vertical intensity deduced from the formula for variations 

 given by Prof. Schering* would be 



V=2-2895T. 



Taking as a mean, 



V=2-2899T, 



* Gott. Nach. 1882, p. 388. 



