UPON MAGNETISATION, AND CONVERSELY, IN IRON, STEEL, AND NICKEL. 493 



annealed than in quenched nickel, negligible so far as observed in other cases. A 

 weight of 1 1 ozs. suspended ' from the horizontal arm of the lever kept the wire from 

 sagging, and made its contact with the gong such that the vibrations were transmitted 

 to the thin wire supporting the weight with little apparent loss of intensity. 



The dimensions and other particulars of the six wires used are given in the 

 following table : — 



Metal. 



Condition. 



Diameter. 



Length. 



Steel J 

 (mild). ; 



Annealed. 



•092 cms. 

 '092 cms. 



100 cms. 



Quenched. 



>> 



Iron (not J 

 "soft"), j 



Annealed. 



•0907 cms. 



!! 



Quenched. 



•091 cms. 



)) 



Nickel j 

 (com- j 

 mercial). 



Annealed. 



•092 cms. 



)) 



Quenched. 



•0909 cms. 



1) 



The three wires were annealed in a horizontal position normal to the earth's field, at a 

 red heat, by passing a Bunsen flame slowly along their entire length. The other three 

 wires, cut from the same hanks, were heated to redness by an electric current, and 

 quenched by plunging in water a moment after the current was broken. 



An exploring coil was wound on the central portion of a glass tube 41 cms. long and 

 0"8 cm. bore. Another glass tube of the same length but of greater diameter sur- 

 rounded that of smaller bore and supported a magnetising coil of two layers of copper 

 wire. This arrangement was adjusted in position so that the wire, supported at one 

 end by the gong and at the other end by the lever as above described, coincided with 

 the axis of the concentric tubes at right angles to the earth's magnetic field. 



The exploring and magnetising coils were each in series with one of two solenoids 

 concentrically wound, so connected and adjusted that, before the magnetic wire was 

 introduced, the maximum current produced no motion of the more delicate of the two 

 ballistic galvanometers used. 



The accessory apparatus was such that all the operations could readily be performed, 

 and readings of the galvanometer accurately taken, without the assistance of a second 

 observer. 



The Effect of the Load. 



The weight (11 ozs.) used throughout the experiments subjected each wire under 

 test to a pulling stress not greater than 0"5 kilo, per sq. mm. of sectional area. 

 The four tables submitted show the effects of this load upon magnetisation. 



