GALILEO 



2364 



GALL 



totle's philosophy in the university of that 

 city. Not content to follow the beaten path 

 of learning, at the age of eighteen he made 

 an important discovery quite outside his reg- 

 ular course of study. The great lamp hanging 

 from the roof of the cathedral at Pisa was one 

 day accidentally set in motion, and as Galileo 

 watched it swinging to and fro he was so im- 

 pressed by the regularity of its movements 

 that he conceived the idea of a simple pendu- 

 lum used for the measurement of time. This 

 discovery he turned to good account years 

 later in the construction of a clock for astro- 

 nomical purposes. 



About the same time he abandoned the 

 study of medicine for that of mathematics, a 

 subject which opened up to him a new field 

 of research that gave him untold delight. 

 Though for lack of funds he was obliged to 

 leave the university in 1585, he continued his 

 mathematical studies in private, the first re- 

 sults of his investigations being his invention 

 of a balance for weighing substances in water. 

 By 1589 his achievements had won him such 

 renown that he was appointed professor of 

 mathematics in the University of Pisa, where 

 he remained for two years. During this period 

 he discovered the law that all falling bodies, 

 regardless of their weight, travel through air 

 with the same rate of speed. Galileo proved 

 the truth of his theory by dropping balls of 

 different weights from the leaning tower of 

 Pisa, but his success only brought him into 

 disfavor with the followers of Aristotle, whose 

 faces were turned toward the past, and he 

 found it advisable to resign his professorship 

 in 1591. 



The following year he accepted an invitation 

 to lecture on mathematics in the University of 

 Padua, and there he remained for eighteen 

 years. His sojourn at Padua was a period of 

 triumph and prosperity, and students from all 

 parts of Europe came in vast numbers to hear 

 his lectures. He was then at the height of his 

 creative powers. In 1597 he invented the sec- 

 tor, a form of compass still used in geometri- 

 cal drawing, and about the same time he con- 

 structed the first thermometer. Though he 

 was not the actual inventor of the telescope, 

 he was the first to make extended and prac- 

 tical use of it, and when in 1609 he began to 

 sweep the starry heavens with an instrument 

 of his own making, he opened up a wonderful 

 era in modern astronomy. 



He discovered that the moon was not a 

 smooth sphere shining by its own light, but 



that its surface was marked by valleys and 

 mountains and that it gave out only the light 

 which it reflected. Brushing aside the fables 

 and superstitious tales concerning the nature 

 of the Milky Way, he declared that it was a 

 great field of myriad individual stars. In 1610 

 he made his crowning discovery of the four 

 satellites of Jupiter, which he named the Med- 

 icean stars. In the same year he observed 

 the peculiar form of Saturn, the rings of which 

 were recognized several years later. He also 

 detected the movable spots on the sun, infer- 

 ring from their regular advance from east to 

 west the rotation on its axis and the inclination 

 of that axis to the plane of the ecliptic. 



In 1610 Galileo was invited by his friend 

 and patron, the Grand Duke of Tuscany, to 

 establish himself at Florence as his official 

 mathematician and philosopher, and soon after 

 he made observations of the phases of Mer- 

 cury, Venus and Mars. The following year 

 he visited Rome, where he was received with 

 high honors, but he was then just entering 

 upon a period of discord and disappointment. 

 His publication of a treatise on the sun's spots, 

 in which he openly stated his belief in the the- 

 ory of Copernicus (see COPERNICUS, NICHOLAS) 

 that the earth moves around the sun, brought 

 him into trouble with the Church authorities, 

 and in 1632 the appearance of his great mas- 

 terpiece, A Dialogue Concerning the Two 

 Great Systems of the World, caused him to be 

 summoned before the Holy Office (see INQUI- 

 SITION). 



After a long trial he was ordered to renounce 

 his scientific theory and was sentenced to an 

 indefinite term of imprisonment. The sentence 

 was not strictly enforced, however, as he was 

 given permission to reside first at Siena, and 

 later at Florence, where he died. His interest 

 in his labors continued to the end, even when, 

 stricken with blindness, he could no longer 

 look upon the wonders of the earth and sky. 

 He was buried in the Cathedral of Santa Croce, 

 at Florence, where a great monument has been 

 erected' in commemoration of his imperishable 

 services to the cause of learning. 



Related Subjects. The name of Galileo is 

 forever associated with the following, and the 

 reader is referred to the descriptive articles : 

 Falling Bodies Pendulum 



Gravity, Specific Telescope 



GALL, gahl, FRANZ JOSEPH (1758-1828), the 

 founder of the system of phrenology, was 

 born at Tiefenbrunn, Baden, Germany. He 

 studied and practiced medicine in Vienna. 



