10S 



Sir J. B. Lawes and Prof. J. H. Gilbert. 



2. The velocity of sound in a wire is independent of the load on 

 the wire. 



3. The velocity of sound in a wire is not sensibly altered by perma- 

 nent extensions of the wire, provided sufficient rest be allowed after 

 the permanent extension has taken place. 



4. The value of the modulus of torsional elasticity as determined 

 by the statical method, accords with the value obtained by the method 

 of torsional vibrations for most metals in the hard-drawn condition, 

 provided the deformations produced are sufficiently small. 



"On the 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. B. Lawes, Bart., LL.D., F.R.S., and J. H. Gilbert, 

 LL.D., F.R.S. Preliminary Notice.* Received and read 

 June 16, 1887. 



For many years past the question of the sources of the nitrogen of 

 our crops has been the subject of much experimental enquiry both at 

 Rothamsted and elsewhere. Until quite recently, the controversy 

 has chiefly been as to whether plants directly assimilate the free 

 nitrogen of the atmosphere ; but, during the last few years, the 

 discussion has assumed a somewhat different aspect. The question 

 still is whether the free nitrogen of the air is an important source 

 of the nitrogen of vegetation ; but whilst few now adhere to the view 

 that chlorophyllous plants directly assimilate free nitrogen, it is 

 nevertheless assumed to be brought under contribution in various 

 ways, coming into combination within the soil, under the influence of 

 electricity, or of micro-organisms, or of other low forms which thus 

 indirectly serve as an important source of the nitrogen of plants 

 of a higher order. Several of the more important of the investigations 

 in the lines here indicated seem to have been instigated by the 

 assumption that natural compensation must be found for the losses of 

 combined nitrogen which the soil sustains by the removal of crops, 

 and for those which result from the liberation of nitrogen from its 

 combinations under various circumstances. 



We propose to summarise some of our own more recently published 

 results bearing on various aspects of the subject, to put on record 

 additional results, to give a preliminary notice of new lines of enquiry, 

 and to discuss the evidence so adduced with reference to the results 



* This Preliminary Notice was originally intended to have served as the Abstract 

 of a fuller paper, ana is so referred to in the account of the meeting of "June 16 

 (vol. 42, p. 483). 



