ox MAGXETOSl'EIGTION. 15 



established, since the longitudiiml pull only produces diminution of 

 magnetization. 



(d) Reversible nickel steels (Fig. 3, PI. I.). 



The beautiful experiment of Hopkinson revealed a singular pro- 

 perty of irreversible nickel steel as regards magnetization. The dis- 

 covery of reversible nickel steel called forth new demands for the 

 metal on account of its practical utility. Among the various phy- 

 sical properties of nickel steel, the small thermal expansion claims 

 a prominent position in the différent applications of the metal, such 

 as for the construction of scales, or the compensation of chrono- 

 meters and others of similar nature, unfortunately no investigation 

 has as yet been made appertaining to the deformation of the met.al 

 by magnetization. 



Through the kindness of Messrs. Guillaume and Dumas, who 

 supplied us the different samples of nickel steels, manufactured by 

 Commentry-Fourchambault and Decazeville, we were enabled to 

 examine the mao-netostriction of the reversible nickel steel in its 

 various aspects. 



The samples to be tested were either turned into ovoids of the 

 same dimensions as for the other metals, or used in the form of 

 wires. These two different sets of metals do not show serious dis- 

 crepancies in the observed results, which are given below for speci- 

 mens containing different percentages of nickel, either in the form 

 of ovoids or wires. It is to be remarked that the annealing of 

 nickel steel wires was conducted in a glass tube, through which 

 hydrogen gas was kept in constant circulation, and heated to 500° C. 

 for more than three hours. 



The observed chano-es of leno-th are o-iven in the followino; 



tables 



