CLASSIFICATION 53 



had a practical object ; whereas to combine elements of 

 known valency is to work out a problem in solid mathe- 

 matics. It can be done on paper before it is done in the 

 laboratory. 



Another object for chemical research presented itself to 

 the natural philosopher, who was also a physican, as the 

 most legitimate outcome of the theories of his day. The 

 human body, which seemed to be a properly constructed 

 machine with an innate tendency towards health, was never- 

 theless constantly deviating towards dyspepsias, rheums, 

 fevers. What cause for these aberrations could there be 

 save something wanting in its chemical constitution ? The 

 alchemists gave place to the iatro-chemists, whose quest 

 was not gold but the elixir vitae. 



Scientific Method. A "control-experiment" is the 

 compass of Science. As the mariner checks the course of 

 his ship by comparing it with the magnetic meridian, so 

 the man of science estimates the bearings of his observa- 

 tions by comparing them with the negative position the 

 zero-line from which they diverge. It may be easy to 

 devise a control experiment, or it may be the crux of the 

 problem. When a farmer is persuaded by the agent for a 

 manure company that "there is nothing like kainit for 

 clover," he scatters it broadcast over his fields and then, 

 as the crop grows, asserts that it is heavier or not heavier 

 than it would have been had no kainit been used. Probably 

 his judgment varies according as he is a "go-a-head man " 

 or " one of the old school, who doesn't hold with artificials." 

 The scientific agriculturist, on the other hand, divides his 

 fields into sections, and sets aside in each a control-plot on 

 to which no manure is cast. The weight of clover obtained 

 from the "control" is compared with the weight obtained 

 from the manured ground. The cost of the manure is 

 deducted from the increment in value of the crop, and the 

 difference is the profit which accrues from the use of the 

 manure. So far no difficulty in checking results has been 



