On the Question of the Fixation of Free Nitrogen, 85 



the surface of the crystal. Fine cracks, set along the spark tracks, 

 quite distinct from the pitting, and bent in cleavage directions, add 

 to the curious appearance in the field of the microscope. Sometimes 

 a track approximating to those obtained on glass is met with, but the 

 side rays are bent and distorted. I found, also, that the appearance 

 of the tracks varied with the direction which the spark took in re- 

 ference to the cleavage lines. 



A similar experiment on a plate of selenite gave like results, the 

 pits being more elongated in accordance with the more acute cleavage 

 intersection. Mica plates showed a fine net of hexagonally arranged 

 lines covering the surface where the spark had passed. Further 

 experiments in this direction might be of interest, but other work has 

 hindered me from pursuing the subject. 



(25.) Sparks from the Leyden jar will produce tracks on glass 

 similar to those described in the foregoing ; but experimenting with 

 such sparks is difficult, as their very explosive nature leads to a rapid 

 break up of the cover glass. 



January 9, 1890. 



Sir G. GABRIEL STOKES, Bart., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



I. " New Experiments on the Question of the Fixation of Free 

 Nitrogen. (Preliminary Notice.)" By Sir J. B. Lawes, 

 Bart, LL.D., F.R.S., and Professor J. H. Gilbert, LL.D., 

 F.R.S. Received (in part) and read January 9, 1890. 



Received January 9. 



In a paper presented to the Royal Society in 1887 — 18S8, and 

 printed in vol. 180 of the 'Philosophical Transactions,' we discussed 

 the history and the present position of the question of the sources of 

 the nitrogen of vegetation. We referred to the conclusions arrived 

 at about thirty years ago from the results of Boussingault and from 

 those obtained at Rothamsted, up to that time. We gave the results 

 of some experiments which had been recently made at Rothamsted in 

 connexion with the subject, and reviewed the evidence and conclusions 

 of others published within the last few years. 



It was considered that the earlier results obtained by Boussingault, 



H 2 



