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SCIENCE 



[N. S. Vol. XL. No. 1035 



planations or illustrations. In presenting 

 such new and revolutionary views as these 

 of Galileo the dialogue form is really the best 

 that could have been used. It enables the 

 author to consider the questions he treats from 

 various points of view and to answer objec- 

 tions or confirm and enlarge upon his proposi- 

 tions, and to do this in an interesting way. 

 The literary skill with which Galileo uses the 

 advantages which the dialogue affords him is 

 remarkable. 



The discussion of the first and second day 

 is devoted to the subject of the resistance 

 which solid bodies offer to fracture. On the 

 first day the talk is not very systematic. 

 Salviati introduces the subject by calling at- 

 tention to a fact known to all practical men, 

 though seemingly forgotten by the philos- 

 ophers, that a large structure built of the 

 relative dimensions of a small model is not of 

 the same relative strength, but is always 

 weaker; and declares his intention of proving 

 the relations which must obtain among the 

 dimensions of such structures in order that 

 they shall be of equal strength; but he soon 

 drifts off into other matters. Not to mention 

 them all, we find in this book a discussion of 

 the horror vacui, in which is described the 

 famous experiment which showed that a suc- 

 tion pump will not lift a column of water 

 more than eighteen cubits, and in which 

 Salviati describes an experiment to determine 

 the limits of the horror vacui; a most inter- 

 esting discussion of infinitesimals and of infi- 

 nites ; an experiment to determine the velocity 

 of light; a study of the resistance which the 

 air offers to a body moving through it, with a 

 clear statement about the terminal velocity, 

 and the general relation of this to the weight 

 and surface of the body; experiments to deter- 

 mine the specific gravity of air; the isochron- 

 ism of the pendulum and the relation between 

 its period and its length; and lastly the rela- 

 tion of the pitch of a musical tone to the fre- 

 quency of the vibration, demonstrated and 

 illustrated by beautiful observations. The 

 range of Galileo's interests and the acute- 

 ness of his thought can not be better appre- 

 ciated than by a study of this book. 



On the second day Salviati, after giving 

 Galileo's famous demonstration of the law of 

 the lever, goes on to a more formal study of 

 the relations of the dimensions of beams to 

 their breaking strength. 



The third and fourth day are devoted to the 

 study of the motion of bodies. The discussion 

 is the one that is familiar to every one from 

 its use in text-books of mechanics. On the 

 third day the subject considered is linear 

 motion with constant acceleration on inclined 

 planes. On the fourth day it is the path of 

 projectiles. Both these books contain, be- 

 sides the fundamental propositions which are 

 well knovm and are still used, a great num- 

 ber of others of less importance, which never- 

 theless serve to show Galileo's fertility of in- 

 vention and geometrical skill. 



This outline of their contents will show 

 why it was worth while to translate Galileo's 

 Dialogues into English. The book is a recog- 

 nized classic in physics. The freshness and 

 beauty of the thought and the importance of 

 the matter are unsurpassed. It is a book 

 which should particularly be examined by 

 students of physical science at a stage in their 

 progress at which the appreciation of the great 

 original work of the present day would be 

 impossible. It will bring such students at 

 once into a range of thought which they can 

 understand and will illuminate the arid 

 wastes of the text-books in mechanics with the 

 light of genius. 



The translators have succeeded remarkably 

 well in preserving the lightness and grace of 

 the style without sacrificing accuracy of ex- 

 pression. The language used by Galileo is so 

 unsystematic that it must have been often 

 difficult to give the proper equivalents to his 

 words and phrases. One suspects that the 

 correct rendering of a word had sometimes to 

 be determined by geometry. "Without being 

 pedantic about it, the translators have tried 

 to use the modern technical equivalents of 

 Galileo's less accurate words, and have suc- 

 ceeded so well that the book can be read easily 

 by any one who has the slightest knowledge of 

 mechanics. The beginner will probably once 

 in a while agree with Simplicio in his rueful 



