290 SEC. 9. MAGNETISM. 



1177. Dip Circle, for determining the magnetic inclination ? 

 adapted to needles of various lengths. (Barrow, London.) 



H. Lloyd, Trinity College, Dublin* 



1178. Theodolite Magnetometer, 9-inch circle, and colli- 

 mator magnets. (Jones, London.) 



//. Lloyd, Trinity Collet, Dublin. 



1179. Dip Circle or inclination compass. James How fy Co. 



1180. Magnetometer, Kew pattern, constructed to^determine 

 the magnetic axis and the magnetic moment of a magnet, and the 

 direction and intensity of the magnetic force of a given place. 



Elliott Brothers. 



The instrument consists of two distinct parts. For the observations of the 

 deflection magnet, the copper box screwed to the centre of the azimuth circle 

 is used ; underneath this passes, through the centre, a divided metal bar with 

 a vernier carrying a magnet ; at right angles to this bar is the observing 

 telescope. The hollow vibration magnet, with a scale on glass at one end 

 and a collirnating lens at the other, is observed through another telescope. 

 The latter magnet is suspended in the mahogany box above the copper box. 



1184. Declinometer for sea and laud observations. 



Carl Bamberg, Berlin. 



The instrument is furnished with gimbals for use at sea, but may be fixed 

 for observations on land. The magnetic system, which is provided with a 

 mirror, oscillates upon a point, and is constructed for reversal ; the ad- 

 justment is effected by means of a collimator telescope, and orientation from 

 terrestrial and astronomical objects. 



1185. Deviation Magnetometer, for determining the mag- 

 netic relations on iron vessels. . Carl Bambcrg, Berlin. 



The deviation magnetometer enables determinations of deviation (horizontal 

 and vertical) to be read off on points, and also determinations of horizontal 

 and vertical intensity by oscillations and deviations. A small telescope serves 

 for determining orientation from terrestrial and astronomical objects. The 

 instrument may be mounted on the same stand as the compasses. 



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 THREAD of the DIADEJUA 

 SPIDER, also THREAD of the DIADEMA SPIDER COCOON. 



