MODERN SCIENCE. 219 



of his disk, out of the colours of the spectrum. He next 

 demonstrated the cause of colours to exist in light (not in the 

 eye), and to be dependent upon the bodies which reflect or 

 refract it (1666 1671). ACOUSTICS are likewise under the 

 greatest obligation to him. He discovered how sound is 

 transmitted through the air in waves, thus completing the 

 discovery which Pythagoras and Galileo had already made, 

 though not elaborated, that sound is a vibration of the 

 atmosphere " which we feel when it strikes the drum of the 

 ear" (page 102). Newton explained what sort of vibration 

 it is; he calculated also its velocity the speed of sound 

 ranging between 1,090 feet to 1,112 feet per second at a 

 temperature of from 30 to 50 Fahrenheit. In fact, his theory 

 of sound formed a very important epoch in science opening 

 the way, as it did, to all the later applications of mechanical 

 principles to the insensible motions of molecules. (See Crookes 

 and Thomson.) Even chemistry is indebted to Newton : 

 he pointed out that many substances attract one another and 

 combine to make one compound substance ; the instance of 

 the dissolution of copper in nitric acid, and its reappearance 

 after iron had been plunged into the liquid, was the hint 

 which led Bergmann to draw up his table of elective affinities, 

 as we have seen. Newton also enunciated the law of cooling 

 an important fact determined by mathematical, physical, 

 and chemical considerations, fully elaborated by Dulong. 

 We may finally mention that he constructed the first 

 REFLECTING TELESCOPE. In any one of the branches in 

 which we have had occasion to speak of this unique genius, 

 he would have made his name famous for all time, so im- 

 portant were his labours and discoveries. AVE ! 



1647 I 7 I 4 Papin was the first to study the effects of 

 the production of vapour in closed vessels ; he invented the 

 DIGESTER, now used in the preparation of food and especially 

 in extracting gelatine. This was the earliest steam machine 

 ever invented in the modern era. It is a CYLINDER with a 

 PISTON working inside, and with a SAFETY-VALVE three of 

 the essentials of the modern steam-engine which made the 

 latter a possibility (1690). Papin improved Guericke's air- 

 pump, and showed that the syphon gives the same results 



