It would require a volume to do the entire subject the merest justice; for, in addition to the examination proposed, it is absolutely necessary, if only for the sake of chronological clearness, to present at least a sketch of Galileo's career, the main events of his personal and scientific life, and a statement of the difficulties that brought on his trial. This we will endeavor to do.
Biography.
Born at Pisa, February 28th, 1564, Galileo-Galilei was, at the age of twenty-six, noticed by the Cardinal Del Monte, and on his recommendation installed lecturer on mathematics in his native city. At this period the doctrines of Aristotle reigned in the schools, although Leonardo da Vinci, Nizzoli, Benedetti, and others, had, by many valuable experiments, already shaken the authority of the Stagyrite on matters of science. The young Pisan followed diligently in their path, and, with the favoring locality of the Leaning Tower, demonstrated the incorrectness of the accepted axiom that the velocity of falling bodies is proportionate to their weight. He was also the first to whom the mechanical principle, since denominated that of the virtual velocities, had occurred in its full extent; and in pure geometry there is no doubt that, at a later period, he anticipated Cavalcanti in the discovery of the calculus of the indivisibles.
Unfortunately, his indiscreet zeal had only words of harshness and rebuke for those who hesitated to accept his demonstrations, and his sarcasms rapidly begot alienation and ill-will. For a prejudice respectable by age he could make no allowance, and with the blindness that in a blaze of light is unable to command vision he had no patience. Galileo was, however, still young, and not yet, if ever in his life, wise enough to reflect, with another great astronomer, that men are not necessarily obstinate because they cleave to rooted and venerable errors, nor are they absolutely dull when they are long in understanding and slow in embracing newly discovered truths.
The young lecturer made so many enemies at Pisa that he was glad to leave it and accept the chair of mathematics at Padua.
The Telescope.
Here he invented, or rather improved, the telescope. Galileo expressly states in his Nuncius Siderius (March, 1610) that he had heard that a certain Hollander constructed (elaboratum) a glass, (perspicillum,) by means of which distant objects were made to appear near. Whether this unknown optician was Zachary Jansen, Moetius of Alkmar, or Henry Lippersheim of Middleburg, it seems impossible to determine.
Indeed, it seems strange that the idea of the telescope had not long before been put to practical use. Passing over the "perspective glasses" of the English astronomer Dee, or modifications of the suggestion in the Pantometria of Digges in 1571, we find that the idea of bringing nearer the image of distant objects by means of a combination of lenses is to be traced almost clearly to a very remote period. Baptist Porta, in his Magica Naturalis, published in 1589, speaks of crystal lenses by which he could read a letter at twenty paces, and was confident of being able, by multiplying such lenses, to decipher the smallest letters at a hundred paces. Going further back, we read in the Homocentrica of Fracastorius, who died in the year 1553, of glasses through whose aid we can decipher writing at a great distance; and yet further, Roger Bacon, who died A.D. 1300, speaks of glasses by which very small letters could be read at an incredible distance.
Galileo's first telescope had only a power of three, his second magnified eight times, his third thirty-three, [Footnote 126] and was soon succeeded by a better one made on a suggestion of Kepler, who wrote to Galileo: "There is as much difference between the dissertations of Ptolemy on the Antipodes and the discovery of a new world by Columbus as between the bilenticular tubes which are everywhere hawked about and thine instrument, Galileo, wherewith thou hast penetrated the depths of the skies."