246 A SHORT HISTORY OF SCIENCE 



My purpose is to set forth a very new science dealing with a very 

 ancient subject. There is, in nature, perhaps nothing older than 

 motion, concerning which the books written by philosophers are neither 

 few nor small ; nevertheless I have discovered by experiment some 

 properties of it which are worth knowing and which have not hitherto 

 been either observed or demonstrated. Some superficial observations 

 have been made, as, for instance, that the free motion (naturalem 

 motum) of a heavy falling body is continuously accelerated ; but to 

 just what extent this acceleration occurs has not yet been announced ; 

 for so far as I know, no one has yet pointed out that the distances 

 traversed, during equal intervals of time, by a body falling from rest, 

 stand to one another in the same ratio as the odd numbers beginning 

 with unity. 



It has been observed that missiles and projectiles describe a 

 curved path of some sort ; however no one has pointed out the fact 

 that this path is a parabola. But this and other facts, not few in 

 number or less worth knowing, I have succeeded in proving ; and what 

 I consider more important, there have been opened up to this vast and 

 most excellent science, of which my work is merely the beginning, ways 

 and means by which other minds more acute than mine will explore its 

 remote corners. 



This discussion is divided into three parts ; the first part deals 

 with motion which is steady or uniform ; the second treats of motion as 

 we find it accelerated in nature ; the third deals with the so-called 

 violent motions and with projectiles. . . . 



Throughout this work Galileo depends on results of experiment 

 rather than on mere speculation. He recognizes that air has 

 weight and that water can be raised but a certain height by 

 the ordinary pump, 1 but he still accepts the ancient notion that 



1 ' This pump worked perfectly so long as the water in the cistern stood above 

 a certain level ; but below this level the pump failed to work. When I first noticed 

 this phenomenon I thought the machine was out of order ; but the workman whom 

 I called in to repair it told me the defect was not in the pump but in the water 

 which had fallen too low to be raised through such a height ; and he added that it 

 was not possible, either by a pump or by any other machine working on the principle 

 of attraction, to lift water a hair's breadth above eighteen cubits ; whether the 

 pump be large or small this is the extreme limit of the lift. Up to this time I had been 

 so thoughtless that, although I knew a rope, or rod of wood, or of iron, if suffi- 

 ciently long, would break by its own weight when held by the upper end, it never 

 occurred to me that the same thing would happen, only much more easily, to a 



