These and other objections, such as the omission of explosives, firearms, paper, will readily occur to the reader. Nevertheless, these lists, placed side by side with the record of theoretic discoveries, encourage the belief that, more and more, sound theory is productive of useful inventions, and that henceforth it must fall to scientific endeavor rather than to lucky accident to strengthen man's control over Nature. Even as late as the middle of the nineteenth century accident and not science was regarded as the fountain-head of invention, and the view that a knowledge of the causes and secret motions of things would lead to "the enlarging of the bounds of human empire to the effecting of all things possible" was scouted as the idle dream of a doctrinaire. In the year 1896 three important advances were made in man's mastery of his environment. These are associated with the names of Marconi, Becquerel, and Langley. It was in this year that the last-named, long known to the scientific world for his discoveries in solar physics, demonstrated in the judgment of competent witnesses the practicability of mechanical flight. This was the result of nine years' experimentation. It was followed by several more years of fruitful investigation, leading to that ultimate triumph which it was given to Samuel Pierpont Langley to see only with the eye of faith. The English language has need of a new word ("plane") to signify the floating of a bird upon the wing with slight, or no, apparent motion of the wings (_planer_, _schweben_). _To hover_ has other connotations, while _to soar_ is properly to fly upward, and not to hang poised upon the air. The miracle of a bird's flight, that steady and almost effortless motion, had interested Langley intensely--as had also the sun's radiation--from the years of his childhood. The phenomenon (the way of an eagle in the air) has always, indeed, fascinated the human imagination and at the same time baffled the comprehension. The skater on smooth ice, the ship riding at sea, or even the fish floating in water, offers only an incomplete analogy; for the fish has approximately the same weight as the water it displaces, while a turkey buzzard of two or three pounds' weight will circle by the half-hour on motionless wing upheld only by the thin medium of the air.