VI. TERRESTRIAL MAGNETISM. 293 



1216. Dipping Needle with microscopes for the observation 

 of the needle points, constructed by Dr. Meyerstein in 1843. 



Magnetic Department of the Observatory, Gottingen, Prof. 

 Dr. Schering, Director. 



1217. Microscopic Apparatus for the determination of the 

 Collimation of Dipping Needles, constructed by Dr. Meyer- 

 stein in 1843. 



Magnetic Department of the Observatory, Gottingen, Prof. 

 Dr. Schering, Director. 



1218. Reflecting Dip Circle, after Dr. Meyerstein. 

 Physical Institute of the University of Gottingen, Prof. 



Dr. Riecke. 



The instrument is so constructed that the magnetisation can be effected 

 either by touching with a steel magnet, or by means of electric coil. In 

 order to carry out the latter, the case is carefully taken off and the coil pushed 

 over pillar and needle. 



1219. Model for the illustration of the Deviation in Iron 



Ships, after Neumayer, constructed by the Joint-stock Company 

 for the Manufacture of Meteorological Instruments, formerly 

 Greiner and Geissler. 



Hydro graphical Department of the Imperial Admiralty, 



Berlin. 



This model represents an important apparatus of instruction, which 

 illustrates all the phenomena of deviation and compensation of the com- 

 passes. The apparatus is in use in the institutions of the Imperial Navy 

 and schools of navigation. 



1220. Gauss's Magnetometer, constructed by Breithaupt 

 and Son, Cassel, with apparatus for suspension. 



Polytechnic School in Cassel, Dr. Gerland. 



The instrument has been constructed, according to the instructions and 

 under the supervision of Professor W. Weber in Goettingen, by Messrs. 

 Breithaupt and Son. Since the magnetometer with which Gauss and Weber 

 had carried out their magnetic labours, and which is identical with the one 

 here exhibited, has not been sent to London, this instrument may be con- 

 sidered as one of the oldest of its kind in the present exhibition. 



1221. Photographic self-registering Horizontal Force, 

 or Bifilar Magnetometer, constructed in 1847, at the Kew 

 Observatory, by Mr. Francis Ronalds. 



Kew Committee of the Royal Society. 



Described in the British Association Eeport for 1849. 



The magnet, 15 inches long, is suspended in a loop of fine wire, by means 

 of a pulley, forming a bifilar arrangement. It carries, attached to its lower 

 side, a light brass bar, which moves a little shutter in front of an oil lamp, 

 allowing a pencil of rays to pass through a hole in it. The light is then 

 thrown, by means of a lens, upon a daguerreotype plate, which is steadily 

 drawn upwards by means of a clock. 



