The difference in imagination among men is shown clearly by the difference--and often the differences--between inventors and engineers, and the scarcity of men who are both inventors and engineers. Ericsson repudiated the suggestion that he was an inventor, and stoutly and always declared he was an engineer. This was at a time, not very long ago, when it was hardly respectable to be an inventor; when, even though men admitted that some inventors had done valuable work, the work was supposed to be largely a chance shot of a more or less crazy man. Yet Ericsson was an inventor--though he was an engineer. So were Sir William Thompson (afterward Lord Kelvin), Helmholtz, Westinghouse, and a very few others; so are Edison and Sperry. Many inventors, however, live in their imaginations mainly--some almost wholly. Like Pegasus, they do not like to be fastened to a plough or anything else material. Facts, figures, and blue-prints fill their souls with loathing, and bright generalities delight them. The engineer, on the other hand, is a man of brass and iron and logarithms; in imagination he is blind, in flexibility he resembles reinforced concrete. He is the antipodes of the inventor; he despises the inventor, and the inventor hates him. Fortunately, however, there is a little bit of the inventor in most engineers, and a trace of the engineer in most inventors; while in some inventors there is a good deal of the engineer. And once in a while we meet a man who carries both natures in his brain. That man does marvels. Despite the great gulf normally fixed, however, between the engineer and the inventor, most of the definite progress of the world for the past one hundred years has been done by the co-ordination of the two; a co-ordination accomplished by "the man of business." Now the inventor and engineer type do not exist only in the world of engineering and mechanics, though it is in that world that they are the most clearly recognized; for they exist in all walks of life. In literature, inventors write novels; in business life, they project railroads; in strategy, they map out new lines of effort. In literature, the engineer writes cyclopædias; in business, he makes the projected railroads a success; in strategy, he works out logistics and does the quantitative work. In that part of strategy of which we are now thinking--the designing of the naval machine--the inventor and the engineer clearly have two separate lines of work: one line the conceiving, and the other line the constructing, of strategic and tactical methods, and of material instruments to carry out those methods. Clearly, these two lines of work while independent are mutually dependent; and, if properly carried out are mutually assistant. The coworking of the inventor and the engineer is a little like that coworking of theory and practice, which has been the principal factor in bringing about the present amazing condition of human society commonly called "Modern Civilization."