PROFESSOR TYND ALL'S ADDRESS. 661 



these bodies, when near the horizon. He is aware that the atmosphere 

 decreases in density with increase of height, and actually fixes its 

 height at 58| miles. In the "Book of the Balance Wisdom," he sets 

 forth the conoection between the weight of tlie atmosphere and its 

 increasing density. He shows that a body will weigh diiFerently in a 

 rare and a dense atmosphere. He considers the force with which 

 plunged bodies rise through heavier media. He understands the doc- 

 trine of the centre of gravity, and applies it to the investigation of 

 balances and steelyards. He recognizes gravity as a force, though 

 he falls into the error of making it diminish at the distance, and of 

 making it purely terrestrial. He knows the relation between the ve- 

 locities, spaces, and times of falling bodies, and has distinct ideas of 

 capillary attraction. He improves the hydrometer. The determination 

 of the densities of the bodies, as given by Alhazen, approaches very 

 closely to our own. " I join," saysb Draper, " in the pious prayer of 

 Alhazen, 'that in the day of judgment the All-Merciful will take pity 

 on the soul of Abur-Raihan, because he was the first of the race of 

 men to construct a table of specific gravities.' " If all this be historic 

 truth (and I have entire confidence in Dr. Draper), well may he " de- 

 plore the systematic manner in which the literature of Europe has 

 contrived to put out of sight our scientific obligations to the Moham- 

 medans." ' 



Toward the close of the stationary period, a word-weariness, if I 

 may so express it, took more and more possession of men's minds. 

 Christendom had become sick of the school philosophy and its verbal 

 wastes, which led to no issue, but left the intellect in everlasting haze. 

 Here and there was heard the voice of one impatiently crying in the 

 wilderness, " Not unto Aristotle, not unto subtile hypotheses, not unto 

 Church, Bible, or blind tradition, must we turn for a know^ledge of the 

 universe, but to the direct investigation of !N"ature by observation and 

 experiment." In 1543 the epoch-making work of Copernicus on the 

 paths of the heavenly bodies appeared. The total crash of Aristotle's 

 closed universe w^ith the earth at its centre followed as a consequence ; 

 and " the earth moves " became a kind of watchword among intellect- 

 ual freemen. Copernicus was the Canon of the Church of Frauen- 

 burg, in the diocese of Ermeland. For three-and-thirty years he had 

 withdrawn himself from the world, and devoted himself to the con- 

 solidation of his great scheme of the solar system. He made its blocks 

 eternal ; and even to those who feared it, and desired its overthrow, 

 it was so obviously strong that they refrained from meddling with it. 

 In the last year of the life of Copernicus his book appeared. It is said 

 that the old man received a copy of it a few days before his death, and 

 then departed in peace. 



The Italian philosopher Giordano Bruno was one of the earliest 

 converts to the new astronomy. Taking Lucretius as his exemplar, 

 ^ " Intellectual Development of Europe," p. 359. 



