4\ 



NATURE 



[December 24, 1914 



to Aristotle. It was the aim of his Hfe to sweep 

 all this intellectual treasure house into the service 

 of the church. 



" He was aiming at an enlarg^ed and renovated 

 Catholicism," says Dr. Bridg-es, "which should 

 bind together and incorporate all that was best 

 and noblest in Hebrew, Greek, and Arabic tradi- 

 tion in the fabric of the Christian Church, for the 

 spiritual government of the world. The keystone 

 of the fabric was supplied by the mistress-science, 

 theology, resting on Mosaic and Christian revela- 

 tion, consolidated by Aristotelian philosophy, and 

 penetrated by the vital and progressive spirit of 

 natural science." 



Profs. Crew and de Salvio have done a great 

 service in their admirable translation (3) of 

 Galileo's less-known dialogues, "Concerning Two 

 New Sciences," i.e. strength 'of materials and 

 dynamics. For though it is Galileo's astronomical 

 work, with its dramatic consequences to himself, 

 which sticks in the popular imagination, he stands 

 among the greatest of the pioneers rather by 

 reason of his advances in mechanics. He was the 

 founder of modern physics, the first to put in 

 practice the method urged by Roger Bacon, where 

 mathematics and experiment go hand in hand. 



This book should be in the hands of all teachers 

 and, better still, of all students of mechanics. In 

 the cut and dried text-book, the science leaps to 

 birth full-armed in its panoply of dry propositions ; 

 but here we see it emerging step by step at the 

 touch of genius from the very problems of prac- 

 tical life from which it took its rise, and the gain 

 in reality is beyond belief. These are real dia- 

 logues, between Salviati, who represents Galileo's 

 views, Sagredo, a wit and scholar, and Simplicio, 

 an Aristotelian philosopher. The conversations 

 are natural, discursive, yet closely reasoned. The 

 Aristotelians are given more than fair play, for 

 Galileo puts into Simplicio's mouth better argu- 

 ments than they had advanced themselves. The 

 inimitable style, with its lucid simplicity, its 

 flashes of humour and sarcasm, gives the same 

 instant impression of modernity that one gets on 

 dipping after a long interval into one of Plato's 

 dialogues. It loses nothing in the translation, 

 where occasional racy Americanisms — "on time," 

 "cuts no figure," "cut loose from" — seem quite 

 in place. 



The lapse of three hundred years is vividly 

 realised in passing from Roger Bacon's scholastic 

 Latin to these conversations that might have 

 appeared in a modern review; from the dim, 

 though explicit, formulation of the true method 

 to its full and easy employment. Here is complete 

 mathematical equipment (of the time) and every 

 deductive conclusion is instantly put to the test 

 NO. 2356, VOL. 94] 



of experiment. And surely the experiments are 

 among the simplest and most truly elegant of all 

 time. The guess that the speed acquired by 

 bodies falling down inclined planes between two 

 fixed horizontal levels is the same for all slopes 

 and just sufficient to carry them to the original 

 level tip any slope (for otherwise a body might be 

 made to lift itself unaided above its level) is 

 tested by the most beautiful experiment of all — 

 where the pendulum is set swinging and when the 

 string is intercepted by a nail fixed at any height, 

 the bob is found always to rise to the same level 

 whatever circle it is compelled to pursue. Here, 

 too, is the immediate inference of the First Law 

 of Motion. For if the slope up which the body 

 travels tow-ards its original level is gradually 

 reduced to the horizontal, it will never get there, 

 and will therefore go on for ever, being now under 

 the action of no forces ! 



There follows the famous discussion of falling 

 bodies. The change of the point of view is at 

 once apparent when the fruitless question why 

 they fall is set aside until it is found how they fall. 

 Simplicio suggests the natural view that the speed 

 acquired is proportional to the distance fallen. 

 But this is shown to be an impossible form of 

 motion, since it implies that it takes as long to 

 fall an inch as a mile. Is it then proportional to 

 the time? In that case it is shown that the dis- 

 tance is proportional to the square of the time ; 

 and this is verified by the experiment of the in- 

 clined plane and water-clock. One wonders 

 whether most to admire the theoretical insight or 

 the experimental skill. Gravity, therefore, adds 

 equal speeds in every second, however fast the 

 body is moving. This is at once extended to the 

 case of a body projected across gravity, hori- 

 zontally, and the whole theory of the parabolic 

 path of a projectile is deduced. The dialogues are 

 full of interesting digressions, e.g. on various 

 orders of infinity (worthy of modern transcenden- 

 talists), terminal velocities, brachistochrones, 

 vibrations of stretched strings, the theory of 

 harmony and discord. What a genius ! 



There are parallels as well as contrasts between 

 these two great men. Both were so convinced of 

 the value of experience that they sought to learn 

 from common people. Thus Bacon, speaking of 

 Peter of Maricourt : — 



" One man I know, and one only, who can be 

 praised for his achievements in this science. . . . 

 He is ashamed that any things should be known 

 to laymen, old women, soldiers, ploughmen, of 

 which he is ignorant. Therefore he hrfs looked 

 closely into the doings of those who work in 

 metals and minerals of all kinds." And again, 

 " They are willing to lower themselves to the level 



