1888.] On the Sources of the Nitrogen of Vegetation. 205 



force of about 100 c.g.s. units was applied, removed, reversed, again 

 removed, and re-applied, for the purpose of determining the form of 

 the magnetisation curve, the magnetic susceptibility, the ratio of 

 residual to induced magnetism, and the energy dissipated in conse- 

 quence of hysteresis in the relation of magnetic induction to magnet- 

 ising force. Curves are given, to show the character of such cycles for 

 nickel wire in three conditions: the original hard-drawn state, annealed, 

 and hardened by stretching after being annealed. The effects of 

 these have also been examined (1) by loading and unloading magnet- 

 ised nickel wire with weights which produced cyclic variations of 

 longitudinal pull, and (2) by magnetising while the wire was sub- 

 jected to a steady pull of greater or less amount. The results 

 confirm and extend Sir William Thomson's observation that longi- 

 tudinal pull diminishes magnetism in nickel. This diminution is 

 surprisingly great : it occurs with respect to the induced magnetism 

 under both large and small magnetic forces, and also with respect to 

 residual magnetism. The effects of stress are much less complex 

 than in iron, and cyclic variations of stress are attended by much less 

 hysteresis. Curves are given to show the induced and residual mag- 

 netism produced by various magnetic forces when the metal was 

 maintained in one or other of certain assigned states of stress ; also 

 the variations of induced and residual magnetism which were caused 

 by loading and unloading without alteration of the magnetic field. 

 Values of the initial magnetic susceptibility, for very feeble magnet- 

 ising forces, are stated, and are compared with the values determined 

 by Lord Rayleigh for iron, and the relation of the initial susceptibility 

 to the stress present is investigated. The paper consists mainly of 

 diagrams in which the .results are graphically exhibited by means of 

 curves. 



III. " On ;tbe present Position of the Question of the Sources of 

 the Nitrogen of Vegetation, with some new Results, and 

 preliminary Notice of new Lines of Investigation." By 

 Sir J. JB. Lawes, F.R.S., and J. H. Gilbert, M.A., LL.D., 

 F.R.S., Sibthorpian Professor of Rural Economy in the 

 University of Oxford. Received, Part I, July 20, 1887. 

 Parts II and III, May 3, 1888. 



[For Preliminary Notice of this Paper, see vol. 43, p. 108.] 



