His attitude toward the reform movement, twenty years of which he lived through in Germany, is interesting. He was an intimate friend of Bishop Maurice Ferber of Ermland, who kept his see loyal to Rome at an epoch when the secularization of the Teutonic Order and the falling away of many bishops all around him make his position and that of his diocese noteworthy in the history of that place and time. Copernicus continued loyal to the old Church and in 1541 his great book "De Revolutionibus Orbium Celestium" was dedicated to Pope Paul III, who accepted the dedication and until the Galileo matter brought Copemicanism prominently into question there was never any thought of Copernicus' book as containing matters opposed to faith. It was then placed on the Index, but only until some minor passages should be corrected which set forth the new theory as if it were an astronomical doctrine founded on facts and demonstrations and not a hypothesis still to be discussed by scientists.
The scientific spirit of this century is often scouted because in spite of their scientific knowledge many of the astronomers and mathematicians of this time as well as, of course, other educated men following their example, could not quite rid themselves of the idea that the stars were powerful influences over man's life and health. The history of this idea, however, minimizes the objection. All down the centuries men like Roger Bacon, Albertus Magnus, Nicholas of Cusa, Marsilio Ficino and Pico della Mirandola insisted that there could be nothing in what we now call astrology. Men parted with the older ideas very slowly, however. Almost a hundred years after Columbus' Century even Galileo made horoscopes and seems to have thoroughly believed in them, though some of his prophecies were sadly mistaken. Kepler drew up horoscopes, confessing that he had not much confidence in them but that they were paid for much better than other mathematical work and he sadly needed the money. Lord Bacon could not quite persuade himself that there was nothing in astrology. As late as after the middle of the eighteenth century Mesmer's thesis for graduation in medicine at the University of Vienna, which [{353}] at that time had one of the best medical schools of Europe, was on the influence of the stars on human constitutions. It was accepted by the faculty and he got his degree. Even in our time, though now the educated contemn, the mass of the people still have not entirely rejected astrology. The men of Columbus' Century can scarcely be thought less of for having accepted it, though many of the scientists of the time did not.
The counterpart to the great scientific genius that Copernicus was, the generalizer who discloses a new horizon, was to be found in his contemporary, Leonardo da Vinci, who was an inventor, a practical genius applying discoveries to everyday life. He solved most of the mechanical problems, invented locks for canals, the wheelbarrow and special methods of excavation, a machine for making files by machinery, run by a weight, a machine for sawing marble blocks instead of separating them by natural cleavage, the model of those still employed at Carrara, as well as machines for planing iron, for making vices, saws and planes, for spinning, for shearing the nap of cloth, as well as an artist's sketching stool, a color grinder, a spring to keep doors shut, a roasting jack, a hood for chimneys, movable derricks quite similar to those in use among us to-day, with contrivances for setting up marble columns on their bases, one of which in principle was used to set up Cleopatra's Needle on the Embankment in London in our time. A favorite field of invention was that of all sorts of apparatus relating to war, military engines, devices for pushing scaling ladders away from walls and many others. He was probably the greatest inventive genius in the world's history. He had an eminently practical mind. He devoted himself to the problem of flying, studied the wings of birds and produced a series of mechanical devices, tending toward the solution of that problem.
Taine said of him: "Leonardo da Vinci is the inventor by anticipation of all the modern ideas and of all the modern curiosities, a universal and refined genius, a solitary and inappeasable investigator, pushing his divinations beyond his century so as at some times to reach ours." There was scarcely anything that he touched that he did not illuminate wonderfully by his genius. In studying the muscles of animals he invented a [{354}] dynamometer, he improved spectacles and studied the laws of light, invented the camera obscura and in his steam experiments anticipated Watt. A very curious feature of his work is his series of experiments with the steam gun, with which he was sure that great destruction might be worked.
A very interesting invention of a scientific instrument of some precision by Leonardo was what may be called a weather gauge. This was made of a copper ring with a small rod of wood, which acted as a balance. On it were two little balls, one covered with wax and the other with material that absorbed moisture readily. When the air was saturated with moisture this ball grew heavy and inclined the beam till it touched one of the divisions marked on the copper ring set behind it. The degree of moisture could thus be seen and the weather, or at least changes in it, could be predicted. We have a whole series of such arrangements mainly in the shape of toys in the modern time. The hygroscopic qualities of cord or the tendency of certain colors to change their tints when more moisture is present are used to indicate approaching changes in the weather. Leonardo seems to have been the first to make use of this practically and he deserves the credit of priority in the invention.
His studies in optics might almost naturally be expected from a painter so much occupied with color and whose intense curiosity prompted him to know not merely the use of things but the causes of and the reasons for them. He evolved much of the science of color vision, suggested the principles of optics that came to be known only much later, analyzed and explained the construction of the eye, invented the camera obscura in imitation of it and gave us a theory of color vision which is as good as any other that we have down to the present day. These optical studies alone might well be considered as enough to occupy an ordinary lifetime, but they seem to have been only the results of a series of interludes of the nature of recreation for Leonardo. He made his notes on the subject, filed them away with others, made no attempt to print his conclusions, probably found very few with whom he could discuss the subject, but he had satisfied himself. That was what he wanted.
After knowing such facts as this we are not surprised to learn of his anticipating by some sort of divination the laws of gravitation, the molecular composition of water, the motion of waves, the undulatory theory of light and heat, the earth's rotation and rotundity before Columbus' time and many other surprising things. One finds in his diary that he was planning the construction of a harbor and studying the music of the waves on the beach at the same time.
Poggendorff, in his great Biographical Dictionary of prominent men of science, quotes Libri's "History of Mathematics in Italy" as authority for the declaration that Leonardo discovered capillarity and diffraction, made use of the signs + and -, knew the camera obscura (without a lens), made observations on resistance, on density, on the weight of the air, on dust figures, on vibrating surfaces and on friction and its effects.
All sorts of machines came from Leonardo's hands. He had a positive genius for practical invention that has probably never been equalled, surely not surpassed, even down to our own day. His inventive faculty worked itself out, in machines of such variety as have never come from the brain of a single individual before. Nor were these merely primitive mechanical devices that we would surely despise now. On the contrary, nearly all of them have endured in principle at least and some of them almost as they came from him.