Leonardo also did distinguished work in the biological sciences, so that Duval, Professor of Anatomy at the University of Paris and himself well known both for his researches in biology and his knowledge of the history of science, entitles an article with regard to him in the French Revue Scientifique (Dec. 7, 1889), "A Biologist of the Fifteenth Century." His biological discoveries are discussed in the chapter on the Biological Sciences.
Sometimes it is asserted by those who are so little familiar with the history of science that they venture on such assertions rather easily, that the true scientific spirit had not yet awakened and that while men were making many observations and acquiring new information they had not as yet the proper scientific attitude of mind to make really great discoveries. It is [{356}] rather amusing to be told that of a century when Copernicus and Vesalius and so many other distinguished modern scientists were alive. Some writers suggest that the true rising of the modern spirit of scientific inquiry did not come until Francis Bacon's time. Francis Bacon is one of the idols of the marketplace, but surely no serious student of history accords him the place in science that our English forbears gave him when they were insular enough to know very little about continental work, and above all about Italian workers.
Francis Bacon, of course, had been long anticipated in all that concerns the inductive method in science by his much greater namesake Roger Bacon. In Columbus' Century however, a hundred years before Bacon's time, Bernardino Telesio, the Italian philosopher, stated fully the inductive method and recognized all its possibilities. In Science for December 19, 1913, Professor Carmichael said of him:
"He abandoned completely the purely intellectual sphere of the ancient Greeks and other thinkers prior to his time and proposed an inquiry into the data given by the senses. He held that from these data all true knowledge really comes. The work of Telesio, therefore, marks the fundamental revolution in scientific thought by which we pass over from the ancient to the modern methods. He was successful in showing that from Aristotle the appeal lay to nature, and he made possible the day when men would no longer treat the ipse dixit of the Stagirite philosopher as the final authority in matters of science."
The tendency of this century to make scientific principles of value for practical purposes is well illustrated by the references to the sympathetic telegraph which began to be much talked of at this time. According to the story as told, friends at a distance might be able to communicate with each other by having two dials around which the letters of the alphabet were arranged with a magnetic needle swinging free as the indicator. When the needle on one of the dials was moved to a letter, the other by magnetic attraction was supposed to turn to the same letter. This ingenious conceit has been attributed to Cardinal Bembo, one of the great scholars of the Renaissance, who was private secretary to Pope Leo X. His friend [{357}] Porta, the versatile philosopher, made it widely known by the vivid description which he gave of it in his celebrated work on "Natural Magic," published just after the close of Columbus' Century.
A very important development in science came in the application of chemistry to medicine, both as regards physiology and pathology. Basil Valentine at the beginning of Columbus' Century led the way and Paracelsus did much to indicate what the advantage of the application of chemistry to medicine would be. Paracelsus compared the processes in the human body with chemical phenomena and declared that alterations in the chemical conditions of organs were the causes of disease. He set himself up in opposition to the humoral theory of the ancients and denied that the heart was the seat of heat manufacture in the body, for every portion of the system had, he asserted, its source of heat. It was through Paracelsus that chemistry was added to the medical curriculum and George Korn in his chapter on Medical Chemistry in Puschmann's "Handbook" attributes the foundation of certain professorships for chemistry at the universities of this time to Paracelsus' influence. Andreas Libavius did much to advance chemical science in various directions by his study and preparation of sulphuric acid and his recognition of the identity of the substance made from sulphur and saltpeter with that obtained from vitriol and alum. Studies of this kind brought a broad realization of the possibilities of chemistry.
The spirit of the period as regards science and the development of the faculty of observation at this time is very well illustrated by Columbus' own observations on the declination of the magnetic needle during his first voyage across the ocean. Brother Potamian has told the story in "Makers of Electricity" (Fordham University Press, New York, 1909), page 22:
"It is one of the gems in the crown of Columbus, that he observed, measured and recorded this strange behavior of the magnetic needle in his narrative of the voyage. True, he did not notice it until he was far out on the trackless ocean. A week had elapsed since he left the lordly Teneriffe, and a few days since the mountainous outline of Gomera had disappeared [{358}] from sight. The memorable night was that of September 13th, 1492. There was no mistaking it; the needle of the Santa Maria pointed a little west of north instead of due north. Some days later on September 17th, the pilots, having taken the sun's amplitude, reported that the variation had reached a whole point of the compass, the alarming amount of 11 degrees.
"The surprise and anxiety which Columbus manifested on those occasions may be taken as indications that the phenomenon was new to him. As a matter of fact, however, his needles were not true even at the outset of the voyage from the port of Palos, where, though no one was aware of it, they pointed about 3° east of north. This angle diminished from day to day as the Admiral kept the prow of his caravel directed to the West, until it vanished altogether, after which the needles veered to the West, and kept moving westward for a time as the flagship proceeded on her voyage.
"Columbus thus determined a place on the Atlantic in which the magnetic meridian coincided with the geographical and in which the needle stood true to the pole. Six years later, in 1498, Sebastian Cabot found another place on the same ocean, a little further north, in which the compass lay exactly in the north-and-south line. These two observations, one by Columbus and the other by Cabot, sufficed to determine the position of the agonic line, or line of no variation, for that locality and epoch.
"The Columbian line acquired at once considerable importance in the geographical and the political world, because of the proposal that was made to discard the Island of Ferro and take it for the prime meridian from which longitude would be reckoned east and west, and also because it was selected by Pope Alexander VI to serve as a line of reference in settling the rival claims of the kingdoms of Portugal and Castile with regard to their respective discoveries. It was decided that all recently discovered lands lying to the east of that line should belong to Portugal; and those of the west to Castile."
The first observation of magnetic declination on land appears to have been made about the year 1510 by [{359}] George Hartmann, Vicar of the Church of St. Sebald, Nuremberg, who found it to be 6° East in Rome, where he was living at the time. He observed it also in Nuremberg, where the needle pointed ten degrees East of North. Columbus' explanation of the declination to his sailors is interesting. He kept silence about it at first, but when they grew alarmed, believing that the laws of nature were changing as they advanced farther and farther into the unknown, he told them that the needle did not point to the North Star, which had been called the Cynosure, but to a fixed point in the celestial sphere and that Polaris itself was not stationary, but had a rotational movement of its own, like all other heavenly bodies. They trusted him and their fears were allayed and a mutiny averted. When on his return to Spain he reported the many and definite observations on the variation of the compass which he had made he was told by the scientists of the time that he, and not the needle, was in error, because the latter was everywhere true to the pole. Just why they were sure it was so they could not tell, but they refused to believe even observations which showed that it was not so; though these were reported by a man who had just overturned quite as strong convictions by sailing westward and reaching land. It is such contradictions of what seem to be obviously first principles of science that in all ages have constituted great discoveries and required genius to make them.