256 SEC. 9. MAGNETISM. 



passes through the centre of the ball. The point of this rod, which can be 

 moved up and down in the ball, shows, when the instrument is set according 

 to the astronomical meridian, the azimuth and depth (or height) of the con- 

 verging points of the aurora pencils. This point of convergence does not 

 exactly coincide, as the exhibitor has shown at the time of the great display of 

 aurora borealis, Feb. 4th, 1872, with the point towards which the inclination 

 needle directs. From the deviation of the two points, the height of the aurora 

 can be calculated. 



The instrument, which is easily manipulated, is much recommended to 

 arctic explorers. 



Instrument for navigators in the Arctic Kegions for ascertaining the con- 

 nexion of the Northern Lights with terrestrial magnetism, and for determining 

 the altitude of the Northern Lights. By means of an instrument designed by 

 the exhibitor, the point of convergence of the north light rays is to be 

 accurately determined, as well when at the appearance of the corona it is 

 situated above the horizon, as when it is below the same, and in regard to 

 height, depth, and azimuth. By the deviation of the point of convergence 

 from the direction of the dipping needle, the height of the north light rays 

 can be calculated. 



1231a. Apparatus for the Demonstration of Magnetic 

 Friction, made by the late Mechanict Kleemann, at Halle. 



Prof. Dove, Berlin. 



1231b. Compass with Diamond Fin. 



Ernst Winter, Hamburg, Eimstustet. 



