Chapter V 

 THE GROWTH OF PHYSICAL IDEAS 



The science of physics originated in the study of the move- 

 ments of the heavenly bodies. The apparent movements of 

 the sun and moon in relation to the earth and the movement 

 of the planets through the constellations of the stars, the an- 

 nual rise and fall of the altitude of the sun, were obviously 

 related to the seasons and, therefore, to agriculture, to seed 

 time and harvest, and to such phenomena as the inundation 

 of the Nile, upon which the existence of Egypt depended. 

 After the first fanciful images, the traverse of the heavens by 

 the sun in a boat, for instance, a very definite cosmology was 

 developed to account for the observed facts; and this system 

 became more and more complicated as the accuracy of the 

 observations increased. The practical requirements of en- 

 gineering also demanded a system of mensuration, which 

 involved methods of determining the volumes of spheres, 

 cylinders, pyramids, and the areas of conic sections. The 

 early methods available to the astronomers and engineers 

 were essentially geometrical in form, and geometry continued 

 as the principal mathematical discipline until the eighteenth 

 century, when it was largely replaced by algebra. 



It was in physical science that the Alexandrian school of 

 philosophers approached the discovery of the method of ex- 

 perimental science; * and it was, again, in physical science 

 that Galileo initiated the scientific revolution.f Galileo's 

 experiments showed that the acceleration of falling bodies 

 is not proportional to their weight, as was believed by the 

 followers of Aristotle, but that light and heavy bodies fall 



* Chapter IV, p. 72. 

 t Chapter IV, p. 78. 



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