VI. TERRESTRIAL MAGNETISM. 287 



1141. The Diamagnetic Box of Michael Faraday, con- 

 taining spheres, cubes, and bars of diamagnetic metals ; tubes of 

 various liquids, bars of borate of lead, glass, various crystals, 

 cradles, supports, &c., used by Faraday in his researches on 

 diamagnetism. Prof. Tyndall, F.R.S. 



1142. Instrument used in researches on the Polarity of 

 the Diamagnetic Force. Prof. Tyndall, F.R.S. 



Phil. Trans., 1856. 



1143. Specimen of " Faraday's Heavy-glass." 



George Gore, F.R.S. 



1144. Electro-Magnet for Induction and Diamagnetic 

 Experiments, made in 1850, of a broad plate of annealed iron, 

 so as to obtain a large induQed power from a small voltaic source. 



J. P. Joule, D.C.L., F.R.S. 



The coil is composed of a bundle of copper wires, and has a resistance 

 about equal to that of a Darnell's cell, exposing a surface of one foot square. 



1144a. Large Diamagnetic Apparatus, with glass case, 

 rods, &c. Warmbrunn, Quilitz, fy Co., Berlin. 



1143a. Magnetic Bench, for showing the Rotation of the 

 Polarized Bay. Dr. W. H. Stone. 



1144a. Electro-Magnet, for showing the rotation of a 

 polarised ray. Dr. Stone. 



1144b. Vacuum Tubes (2), to show the rotation of the 

 spark round the magnetic poles. Dr. Stone. 



VI. APPARATUS FOR THE OBSERVATION AND RE- 

 GISTRATION OF THE TERRESTRIAL MAGNETIC 

 ELEMENTS. 



DIP AND INTENSITY INSTRUMENTS USED IN MAGNETIC 

 SURVEYS ON SHORE AND AT SEA. 



EXHIBITED BY THE ADMIRALTY HYDROGRAPHIC DEPARTMENT. 



1145. Dip Circle for observations at sea, fitted with special 

 arrangements for finding the magnetic meridian. By Nairn and 

 Blunt ; date, 1772-1834. 



This instrument may be considered as intermediate in construction between 

 that made by Nairn for Captain Phipps, in his voyage towards the North Pole 

 in 1773, and the Fox circle introduced by Mr. R. W. Fox in 1834, hereafter 

 described. 



