President's Address. 41 



light had a finite velocity. Note these small differences: to 

 any but the scientists a trifle, yet to him whose training has 

 been such as to demand absolute accuracy when his personal 

 equation is accounted for, furnish a line for investigation. 

 The manufacture of nitrogen compounds from the atmosphere 

 by bacteria also illustrates the growth of scientific problems. 

 This one has been attacked by chemists, physicists, and biolo- 

 gists, each with more or less success. Professor Nobbe found 

 that a certain kind of bacteria had the power of causing free 

 nitrogen to combine with other elements, forming nitrates, 

 which compound is a valuable plant-food. Botanists had no- 

 ticed little tumors on the roots of clover and other leguminous 

 plants, which they had named nodules. It was soon discov- 

 ered that plants having these nodules would grow in a soil 

 free from nitrogen, while plants devoid of these nodules would 

 not grow in such a soil. This led to an investigation, which 

 found that the nodules were the results of minute bacteria 

 in the soil. Then the problem arose, if these nodules were 

 caused by the soil bacteria, and should not be present in a 

 soil, would it not be possible to supply them, and in this way 

 replenish a worn-out soil and restore it to its original fer- 

 tility? While this question was pending, Doctor Moore, who 

 had been studying Algae and had learned something of the 

 properties of these organisms, and who had commenced to 

 apply this knowledge to the purification of polluted water- 

 supplies, was asked by our secretary of agriculture to under- 

 take the solution of the problem of the inoculation of nitro- 

 gen in impoverished soil. The problem was finally attacked 

 by the infection of the seed and resulted in some progress, 

 yet the complete solution awaits additional facts, and when 

 all the necessary facts are found the full solution may then 

 be expected. 



From the examples mentioned, it may be seen that the 

 methods of planning and conducting a scientific investiga- 

 tion involves finding an exact statement of the problem to be 

 solved, obtaining an accurate knowledge of the work that has 

 been done in this and related fields, and the formation of some 

 definite plan whereby the experimental part is to be faith- 

 fully, rigorously and intelligently prosecuted, with the eyes 

 opened and the imagination sharpened to see new relations 

 and applications. When all this is done with the proper fore- 

 sight in regard to apparatus and material, and the work is 



