410 



SCIENCE. 



[N. S. Vol. XVI. No. 402. 



is known to date and the direction of cur- 

 rent progress is ascertained. The investi- 

 gator loses no time or energy in following 

 false leads. 



The empirical, the imaginative and even 

 the guess-work systems, or perhaps lack of 

 of system, more accurately speaking, have 

 their place, however, even in scientific re- 

 search. The work of Copernicus, of Kepler, 

 Newton, even, must be thus classed in im- 

 portant parts. 



' ' The dim Titanic figure of the old monk 

 seems to rear itself out of the dull flats 

 around it, pierces with its head the mists 

 that overshadow them and catches the firet 

 glimpse of the rising sun 



' * * * like some iron peak, by tlie Creator 

 Fired with the red glow of the rushing morn.' " 



But Copernicus first made a shrewd guess 

 and then followed scientific and logical 

 mathematical work and confirmation. This 

 illustrated what Tyndall called 'the scien- 

 tific use of the imagination'; it was not a 

 scientific beginning. 



Kepler, also, was 'strong almost beyond 

 competition in speculative subtlety and 

 innate mathematical perception.' His 

 method of procedure was illustrative of 

 that of 'trial and error' without scientifi- 

 cally established premises or Euclidian 

 sequences. For nineteen years, he guessed 

 at the solution of a sufficiently well- 

 defined problem, finding his speculation 

 erroneous every time, until, at last, a 

 final trial of a last hypothesis gave rise to 

 deductions confirmed by observation and 

 the laws of Kepler were established. His 

 first gtiess had been that the orbits of the 

 planets were circular, his next that they 

 were oval, his last that they might be el- 

 liptical. Only in the latter case could the 

 observed data be reconciled with the as- 

 sumption of Kepler. 



In somewhat similar manner, Galileo 

 sought to prove the correctness of his hy- 



pothesis regarding gravitation ; consistency 

 with which would compel falling bodies, 

 unresisted, to fall at the same rate, what- 

 ever their magnitude. He proved this 

 fact by an experiment, taking two iron 

 shot, the one large and the other small, to 

 the top of the Leaning Tower of Pisa and 

 showing that their fall occupied the same 

 time. The ' guinea and feather tube ' in 

 which, within a vacuum, the two drop with 

 similar rapidity, is but a refinement of that 

 first experimental confirmation of Galileo's 

 idea. 



'The simultaneous clang of those two 

 weights sounded the death-knell of the old 

 system of philosophy and heralded the 

 birth of the new,' not as condemning specu- 

 lation and guess-work or the 'scientific use 

 of the imagination, ' but as enforcing the 

 principle that no hypothesis can be accept- 

 ed until given raison d'etre by an experi- 

 mental or observational appeal to nature. 



Even Newton, witnessing the fall of the 

 apple— an apocryphal but not improbable 

 story— and thus set thinking, necessarily 

 began by speculating upon the probable 

 cause of the phenomenon and its laws. 

 Kepler had shown how the planets moved 

 in their orbits; Galileo had discovered the 

 method of action of gravitation and had 

 revealed the Laws of Motion now adopted 

 by Newton. The time was ripe for another 

 step. Newton conceived the idea that the 

 gravitational force must be universal and 

 must affect every substance throughout 

 space, its laws being without limit, the con- 

 stants in the formulas expressing them hav- 

 ing the same value. The law of gravity is 

 that of a central force acting throughout 

 space with an intensity varying inversely 

 as the square of the distance from the cen- 

 ter of attraction. Newton at once applied 

 his hypothesis to the solar system, and 

 proved that the motions of the planets, as 

 revealed by Copernicus, were consistent 

 with this new ascertained fact. The sun 



