The superiority of these tables over any others available was such that they were used on several of the great voyages of discovery of this period, probably by Columbus himself on his first voyage to America.
In 1475 Regiomontanus was invited to Rome by the Pope to assist in a reform of the calendar, but died there the next year at the early age of forty.
Walther carried on his friend’s work and took a number of good observations; he was the first to make any successful attempt to allow for the atmospheric refraction of which Ptolemy had probably had some knowledge (chapter II., [§ 46]); to him is due also the practice of obtaining the position of the sun by comparison with Venus instead of with the moon (chapter II., [§ 39]), the much slower motion of the planet rendering greater accuracy possible.
After Walther’s death other observers of less merit carried on the work, and a Nürnberg astronomical school of some kind lasted into the 17th century.
69. A few minor discoveries in astronomy belong to this or to a slightly later period and may conveniently be dealt with here.
Leonardo da Vinci (1452-1519), who was not only a great painter and sculptor, but also an anatomist, engineer, mechanician, physicist, and mathematician, was the first to explain correctly the dim illumination seen over the rest of the surface of the moon when the bright part is only a thin crescent. He pointed out that when the moon was nearly new the half of the earth which was then illuminated by the sun was turned nearly directly towards the moon, and that the moon was in consequence illuminated slightly by this earthshine, just as we are by moonshine. The explanation is interesting in itself, and was also of some value as shewing an analogy between the earth and moon which tended to break down the supposed barrier between terrestrial and celestial bodies (chapter VI., [§ 119]).
Jerome Fracastor (1483-1543) and Peter Apian (1495-1552), two voluminous writers on astronomy, made observations of comets of some interest, both noticing that a comet’s tail continually points away from the sun, as the comet changes its position, a fact which has been used in modern times to throw some light on the structure of comets (chapter XIII., [§ 304]).
Peter Nonius (1492-1577) deserves mention on account of the knowledge of twilight which he possessed; several problems as to the duration of twilight, its variation in different latitudes, etc., were correctly solved by him; but otherwise his numerous books are of no great interest.[44]
A new determination of the size of the earth, the first since the time of the Caliph Al Mamun ([§ 57]), was made about 1528 by the French doctor John Fernel (1497-1558), who arrived at a result the error in which (less than 1 per cent.) was far less than could reasonably have been expected from the rough methods employed.
The life of Regiomontanus overlapped that of Coppernicus by three years; the four writers last named were nearly his contemporaries; and we may therefore be said to have come to the end of the comparatively stationary period dealt with in this chapter.