OBSERVATION AND EXPERIMENT 79 



world. I trust that I have got hold of my pitcher by the right 

 handle — the true method of treating this study ; for the pseudo- 

 chemists seek gold, but the true philosophers, science, which is 

 more precious than any gold." 



It is a peculiarly noteworthy fact that while much attention 

 was given to chemistry during ancient and medieval times, com- 

 paratively little attention was given to the other branches of physi- 

 cal science. Our knowledge of heat, light, electricity, and mag- 

 netism is almost wholly a development of modern times. The 

 Greeks were acquainted with a few of the more elementary 

 phenomena of electricity and light ; and Ptolemy and Alhazen 

 came near discovering the law of optical refraction ; but there 

 was no contribution made to either of those physical sciences 

 comparable with the discoveries of Hipparchus in astronomy 

 until the epoch of Galileo. What a marvelous increase in the 

 rate of scientific progress began with this epoch is shown on 

 nearly every page of the subsequent history of science. Galileo 

 and his contemporaries may be said to have established the 

 methods of observation and experiment. Their systematic ap- 

 plication has borne fruit in every science. Almost every step 

 forward has led to additional advances, until now each of the 

 physical sciences has its wide array of determinate facts correlated 

 under a great theory. In the domain of light, for example, the 

 only solid contribution of the ancients is the obvious fact of 

 radiation in straight lines. After nearly sixteen hundred years 

 of our era had elapsed, there came Galileo's invention of the 

 telescope, and about the same time Snell's discovery of the law 

 of refraction. To the telescope were soon added the microscope 

 and the camera obscura. Then followed Newton with explana- 

 tions of the rainbow, dispersion, and kindred phenomena ; 

 Hooke with his discovery of the colors of thin plates ; Dolland 

 with the combination of two lenses to produce achromatism ; 

 and Huygens with his discoveries and explanations of double 

 refraction and polarization ; while in the meantime Roemer had 

 measured the velocity of light. All these accessions crowded 

 one another so closely that the emission theory of Newton and 

 the undulatory theory of Huygens followed almost as a matter 



