"As in the middle ages invention busied itself with instruments of torture, and as in our days it is taken up almost as much with the destructive engines of war as with the productive arts of peace, so in those early ages it applied itself to the fabrication of idols, to the mechanism and theatrical contrivances for mysteries and religious ceremonies. There was then no desire to communicate discoveries, science was a sort of freemasonry, and silence was effectually secured by priestly anathemas; men of science were as jealous of one another as they were of all other classes of society. If we wish to form a clear picture of this earliest stage of civilization, an age which represents at once the naivete of childhood and the suspicious reticence of senility, we must turn our eyes to the priest, on the one hand, claiming as his own all art and science, and commanding respect by his contemptuous silence; and, on the other hand, to the mechanic plying the loom, extracting the Tyrian dye, practising chemistry, though ignorant of its very name, despised and oppressed, and only tolerated when he furnished Religion with her trappings or War with arms. Thus the growth of chemistry was slow, and by reason of its backwardness it was longer than any other art in ridding itself of the leading-strings of magic and astrology. Practical discoveries must have been made many times without science acquiring thereby any new fact. For to prevent a new discovery from being lost there must be such a combination of favorable circumstances as was rare in that age and for many succeeding ages. There must be publicity, and publicity is of quite recent growth; the application of the discovery must be not only possible but obvious, as satisfying some want. But wants are only felt as civilization progresses. Nor is that all; for a practical discovery to become a scientific fact it must serve to demonstrate the error of one hypothesis, and to suggest a new one, better fitted for the synthesis of existing facts. But (some) old beliefs are proverbially obstinate and virulent in their opposition to newer and truer theories which are destined to eject and replace them. To sum up, even in our own day, chemistry rests on a less sound basis than either physics, which had the advantage of originating as late as the 17th century, or astronomy, which dates from the time when the Chaldean shepherd had sufficiently provided for his daily wants to find leisure for gazing into the starry Heavens." The observations of a still earlier commentator are of the same general nature. He says: