382 SEC. 10. ELECTRICITY. 



A welded riug ;of soft iron six inches in diameter, of an inch thick, one 

 part covered by a helix A containing about 70 feet of insulated copper wire 

 occupying about nine inches in length upon the ring. The other part covered 

 by a second helix B containing about 60 feet of insulated copper wire. The 

 helices are separated from each other at their extremities by half an inch of 

 the uncovered iron. 



The iron ring was converted into a magnet by passing a voltaic current 

 through the helix A. This induced an electric current in the helix B, and a 

 small spark was for a moment seen at the carbon terminals. Phil. Trans. 1831. 



1733a. Siberian loadstone and Spark Apparatus, 



This was the loadstone employed by Faraday in his experiments 

 on magneto-electric induction, from which he first obtained the 

 induction spark. (See Exp. Researches, vol. II.). 



The Council of King's College^ London. 



1734. Faraday's original Apparatus for Magneto-Electric 

 Induction by a permanent magnet. 



The Royal Institution of Great Britain. 



A paste-board tube is surrounded by a helix C of insulated copper wire. The 

 diameter of the tube allows a cylindrical bar magnet to pass freely into it. 

 The terminal wires of the helix are connected with a galvanometer. On the 

 introduction of a permanent bar magnet into the helix, and on its withdrawal 

 from it, currents of electricity were induced in the helix which caused a 

 deflection of the galvanometer needle. Phil. Trans. 1831. 



1735. Faraday's Rotating Hectangle for illustrating the 

 inductive action of the earth. 



The Royal Institution of Great Britain. 



The wire rectangle provided with a commutator for collecting the currents 

 was attached to a galvanometer, and rotated across the line of the magnetic 

 meridian, the electric current induced in the rectangle deflecting the gal- 

 vanometer needle. Phil. Trans. 1852. 



1736. Various Helices, Spirals, &c. used by Faraday 

 in his researches on Magneto-Electric Induction, &c. 



The Royal Institution of Great Britain. 

 Phil. Trans., 1831. 



1737. Magnet made by Static Electricity, with note by 

 Faraday. The Royal Institution of Great Britain. 



" A magnet made at the London Institution by an electric discharge from 

 70 square feet of charged surface. Present, Sir H. Davy, Pepys Jordan, 

 Bostock, and Faraday." Note by Faraday. 



2434. Metallo- Chrome. A specimen prepared by Nobili, 

 and presented by him to the Koyal Institution. Mrs. Faraday. 



1739. Diagrams of magnetic Curves, prepared by Faraday. 



Mrs. Faraday. 



1740. Coils and Helices, used by Faraday in his magneto- 

 electric researches. Mrs. Faraday. 



