72 POPULAR SCIENCE MONTHLY. 



Galileo's dialogues on the system of the world (1632) have, at the 

 head, a Greek epigraph : 



In Every Judgment beware of Your Prejudices! 



They are dedicated to the Grand Duke of Tuscany. The person- 

 ages of the Dialogues are Salviati (Galileo himself) who maintains the 

 Copernican doctrines; Sangredo, a man-of-the-world, intelligent, but 

 not a savant; and Simplicius, a convinced Aristotelian, a dull fellow, 

 always worsted in the argument. Galileo's enemies convinced the 

 Pope that Simplicius stood for the Pontiff himself. The subjects dis- 

 cussed are the fall of bodies, the flight of projectiles, the principles of 

 mechanics, the rotation and revolution of the earth and of the planets, 

 the system of Ptolemy — and here Sangredo remarks that he knows 

 many disciples of Ptolemy who have become Copernicans, but not one 

 Copernican converted to the ancient system. The new star of 1572 

 is shown to have been far more distant than the moon, by long calcula- 

 tions (and it is noteworthy that logarithms are not employed to shorten 

 the work) . The preface recites that, some years previously a ' salutary 

 edict ' had been promulgated at Rome which, to prevent scandals, 

 forbade the teaching of the Pythagorean opinion of the earth's motion,* 

 that some hardy spirits had, nevertheless, dared to declare that this 

 edict had been issued without comprehension of the matter and that 

 it was the result of passion, and not of judicial examination. It had 

 been said that advisers entirely ignorant of astronomy ought not to 

 have thus clipped the wings of philosophers. 



My zeal, says Galileo, can not support these rash complaints. Well 

 understanding this prudent decree, I wish to do justice to the truth. 

 I was then at Rome; the most distinguished prelates heard and ap- 

 plauded me ; the decree would not have been issued without giving me 

 some knowledge of it. I, therefore, wish to show to foreign nations 

 that in Italy, and even at Rome, all that could be advanced in favor 

 of Copernicus was known, before that censure was published. I de- 

 clared myself the advocate of Copernicus. Proceeding according to a 

 mathematical hypothesis, I endeavored to prove it to be preferable to 

 that which declares the earth at rest, not in an absolute manner pre- 

 ferable, but in the sense in which it is attacked by pretended Aristo- 

 telians, who in their philosophizing neglect observations. He will 

 show, he says, certain advantages of the heliocentric system. If 

 Italians have not assented to the mathematical opinion of the motion 

 of the earth, it is not because all of them have been ignorant of the 

 reasons others allege in its support, but because they have other reasons 



* This general edict, of course, included Galileo, whether there was any 

 special command laid upon him or no. 



