SHEFFIELD SCIENTIFIC SCHOOL 151 



''How Crops Feed. A Treatise on the Atmosphere 

 and the Soil as related to the Nutrition of Agricultural 

 Plants" was published in 1870. Professor Johnson's 

 object as stated by himself at the time was to ''digest 

 the cumbrous mass of evidence in which the truths of 

 vegetable nutrition lie buried out of the reach of the 

 ordinary inquirer, and to set them forth in proper 

 order and in plain dress for their legitimate and sober 

 uses." He did not seek "to excite the imagination 

 with high-wrought pictures of overflomng fertility as 

 the immediate result of scientific discussion or experi- 

 ment," nor did he attempt "to make a show of revo- 

 lutionizing his subject by bold or striking specula- 

 tions." This was characteristic of the man. It was 

 his cool, judicial weighing of the evidence and pre- 

 sentation of results in a clear, dispassionate way that 

 gave these two books their value and commended them 

 to students of agriculture. They were the beginning 

 of a new and better agricultural literature, and yet 

 their author felt impelled to say: 



It is a source of deep and continual regret to the writer 

 that his efforts in the field of agriculture have been mostly 

 confined to editing and communicating the results of the labor 

 of others. He will not call it a misfortune that other duties 

 of life and of his professional position have fully employed 

 his energies, but the fact is his apology for being a middle- 

 man and not a producer of the priceless commodities of 

 science. He hopes yet that circumstances may put it in his 

 power to give his undivided attention to the experimental 

 solution of numerous problems which now perplex both the 

 philosopher and the farmer; and he would earnestly invite 

 young men reared in familiarity with the occupations of the 

 farm, who are conscious of the power of investigation, to enter 



