2oO SEC. 9. MAGNETISM. 



1190. Drawing of a Dip Circle. J. P. Joule, F.R.S. 



The needle, constructed of a thin ribbon of annealed steel, weighing 

 20 grains, is furnished with an axis made of a wire of standard gold. This 

 axis is supported by threads of the Diadema Spider attached to the arms of a 

 balance suspended by a fine stretched wire. The whole is hung by a wire 

 which can be twisted at the head through 180. At the bottom is attached 

 a paddle immersed in castor oil, which brings the instrument speedily to rest 

 in a fresh position. The deflections are read off by a short -focus telescope, 

 placed on an arm revolving on an axis in the centre of the circle. With this 

 instrument the dip can be determined within the fraction of a minute of a 

 degree in less than a quarter of an hour. 



With this drawing is exhibited a specimen of the THBKAP of the DIADEMA 

 SPIDER, also THREAD of the DIADEMA SPIDER COCOON. 



1191. Portable Unifilar Magnetometer. An instrument 

 for determining the horizontal intensity of terrestrial magnetic 

 force ; and also the declination. 



Kew Committee of the Royal Society r , Kew Observatory. 



It consists of two parts : one for determining the time of vibration of a 

 suspended magnet; the other for determining the amount of deflection it pro- 

 duces when caused to act upon a second needle. 



In addition there is a third magnet, which is subsequently suspended, 

 and its position referred to the astronomical meridian, by means of a 

 mirror, which serves to allow of an observation of the sun's azimuth being 

 made. 



Used by the Eev. S. J. Perry, F.H.S., during the late Transit of Venus 

 Expedition to Kerguelen. 



1192. Two 12-inch Dipping Needles. Royal Society. 



1193. Kew Pattern Dip Circle. 



Kew Committee of the Royal Society, Kew Observatory. 



Dip circle of the pattern adopted by the Kew Observatory, having needles 

 3^ ins. long, which are read by microscopes, carried by a circle in front of the 

 needle frame. It is also provided with accessory needles, for determining 

 total force, after the method of Dr. Lloyd. 



1196. Portable Theodolite for the observation of the Mag- 

 netism of the Earth, constructed by Dr. Meyerstein, Gottingen. 



Prof. Dr. A. Kundt, Strasburg. 



1197. Edelmann's graduated Telescope for reading re- 

 flecting instruments (small). M. Th. Edelmann, Munich. 



1198. Edelmann's graduated Telescope for reading re- 

 flecting instruments (large). M. Th. Edelmann, Munich. 



1 199. Edelmann's graduated Telescope for two observers. 



M. Th. Edelmann, Munich. 



1200. Edelmann's Rider belonging to the graduated tele- 

 scopes for observing two objects at the same time. 



M. Th. Edelmann, Munich. 



