LAWES AND GILBERT'S EXPERIMENTS. 235 



tensions is, however, of great interest, and it is these feeble 

 tensions that seem to be the most efficacious, the slightness of 

 the effects being compensated by their duration and by the vast 

 extent of the surfaces influenced. We have to do with quite 

 a new kind of action, until now completely unknown, which is 

 working incessantly under the most unclouded sky, to deter- 

 mine a direct fixing of nitrogen upon vegetable tissues. In 

 studying the natural causes capable of acting upon the fertility 

 of the soil, and upon vegetation, causes which it has been sought 

 to define by meteorological observations, we must for the future 

 take into consideration not merely luminous or calorific 

 influences, but also the electrical condition of the atmosphere. 



12. We will now specify more particularly the character of 

 these reactions in nature. When studied at a given spot, and 

 over a small surface, they can certainly be only very limited, 

 otherwise the humic substances in the soil would rapidly 

 become rich in nitrogen ; whereas the regeneration of naturally 

 nitrogenous substances, when exhausted by cultivation, is, on 

 the contrary, as we know, excessively slow. 



But this regeneration is indisputable, for in no other way 

 can we account for the unlimited fertility of soils that receive 

 no manure, such as the meadows on high mountains, as studied 

 by Truchot, in Auvergne. 1 



It will be remembered that Messrs. Lawes and Gilbert, in 

 their celebrated agricultural experiments at Eothampstead, came 

 to the conclusion that the nitrogen in certain crops of leguminous 

 plants exceeds the sum of the nitrogen contained in the seed, 

 the soil, and in the manure, even adding the nitrogen supplied 

 by the atmosphere under the known form of nitrates and 

 ammoniacal salts ; a result which is all the more remarkable, 

 seeing that a portion of the nitrogen combined is eliminated in 

 a free state during the natural transformations of vegetable 

 products. We observe, therefore, only the difference between 

 these two effects, i.e. that the actual fixing of nitrogen is much 

 greater than the apparent. In most cases it is concealed by the 

 causes of loss. The above-mentioned writers concluded from 

 their observations that there must exist in vegetation some 

 source of nitrogen sufficient to account for the great mass of 

 combined nitrogen in existence on the surface of the globe. 

 But the source of this was until now quite unknown. Now, it 

 is precisely this hitherto unknown source of nitrogen that would 

 seem to be established in the author's experiments on the 

 chemical reactions provoked by electricity at low tensions, and 

 especially atmospheric electricity. 



13. To complete this explanation, we will compare the 

 quantitative data of the experiments with the richness in 

 nitrogen of the vegetable tissues and organs that are renewed 



1 " Annales agronomiques," torn. i. pp. 549 and 550. 1875. 



