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with the country, no man of it would ever be of the slightest use to you in laying out your detailed plans? To that he must have [rejournies?], "I do not say that because I might wish to stick in pins in order to trace our the daily changes of the situations." To that again my surrejoinder should have been, "Well, General, that precisely corresponds to the advantage of a diagram of the course of toguht, Indeed, just there is the advantage of diagrams in general. Namely, one can make exact experiments upon diagrams and look for unintended change ther by brought about in the relations of different parts of the diagram to one another. These operations in reasoning take the place of the experiments upon real things that one performs in chemical and physical research. Chemists have sometimes described