466 



SCIENCE 



[N. S. Vol. XXXVII, No. 952 



the time when Galileo was born; but he 

 was the first man to offer experimental 

 evidence against the conclusions of Aris- 

 totle; and in so doing he established what 

 we now call the experimental method. He 

 was not handing on an opinion which some 

 "dusty-minded professor" had inherited 

 from an ancestor of the same type. 



Only two methods of investigation were 

 known to the ancients, the philosophical 

 and the mathematical; to these Galileo 

 added a third, the experimental. The 

 philosophical method consisted in assuming 

 certain general principles and trying to 

 find in them an a priori explanation of the 

 universe. Briefly described, the attempt 

 was to stare nature out of countenance. 

 Failure was inevitable, not for want of 

 intellectual acumen, but because, as every 

 one in this assembly knows, it sometimes 

 requires a lifetime of effort to explain a 

 single detail. Witness almost any chapter 

 in Darwin's "Origin of Species." Details 

 must be mastered before one can pass to 

 general principles. 



The mathematical method consisted only 

 in applying geometry to certain well- 

 known areas, volumes and angles, espe- 

 cially to those angles observed in the sky, 

 but always with the idea of describing the 

 known rather than of discovering the un- 

 known: the mathematicians do not appear 

 to have put any deliberate questions to 

 nature; or as Rowland said: 



A mathematical investigation always obeys the 

 law of the conservation of knowledge: we never 

 get out more from it than we put in. The knowl- 

 edge may be changed in form, it may be clearer 

 and more exactly stated; but the total amount of 

 the knowledge of nature given out by the investi- 

 gation is the same as we started with. 



The experimental method, established 

 mainly by Galileo, not only combines the 

 obsei'vations of the philosophers with the 

 measurements of the mathematicians, but 



adds deliberate experiment with a distinct 

 purpose to interrogate nature concerning 

 some detail of her behavior. Generaliza- 

 tions based upon these details the experi- 

 menter reserves for a later date. The high 

 regard in which Galileo held experimental 

 facts is reflected in the following from a 

 letter* to the Grand Duchess Christina, 

 dated 1615. He says: 



I would entreat these wise and prudent fathers 

 to consider , diligently the difference between 

 opinionative and demonstrative doctrines, to the 

 end that they may assure themselves that it is not 

 in the power of professors of demonstrative sci- 

 ences to change their opinions at pleasure. 



Or witness the following paragraph 

 from the "Saggiatore"^ as illustrating the 

 great weight which Galileo attached to ex- 

 perimental evidence. He says: 



We examine witnesses in things which are 

 doubtful, past, and not permanent, but not in 

 things which are done in our presence. 



If discussing a difficult problem were like carry- 

 ing a weight, then since several horses will carry 

 more sacks of com than one alone, I would agree 

 that many reasoners avail more than one; but 

 discoursing is like coursing, and not like carryings 

 and one barb by himself will run faster than a 

 thousand Friesland horses. 



In all his thinking nothing is exempt 

 from experiment. Astronomy even, in his 

 hands, ceases to be a purely observational 

 science; for when he wishes to discover 

 whether the bright portions of the moon's 

 surface are rough or smooth, he sets up 

 two surfaces, one rough and one smooth; 

 then illuminates them with Italian sun- 

 light. Desiring to learn at what rate fall- 

 ing bodies gain speed, he devises a time- 

 measuring machine, invents a method of 

 "diluting gravity" and actually measures 

 the rate at which speed is gained. His dis- 

 cussions begin and end with experiment — 



'" Nat. Ed.," Vol. 5, p. 326. Translated in 

 Fahie's "Galileo," p. 157. 



'"Nat. Ed.," Vol. 6, p. 340. Translated in 

 Fahie's "Galileo," p. 187. 



