310 A SHORT HISTORY OF SCIENCE 



had himself discovered inflammable air or hydrogen, and now 

 he found that by exploding a mixture of this gas with oxygen, 

 water was produced. 



By experiments with the globe it appeared, says Cavendish, 

 that when inflammable and common air are exploded in a proper 

 proportion, almost all the inflammable air, and near one-fifth the com- 

 mon air, lose their elasticity and are condensed into dew. And by 

 this experiment it appears that this dew is plain water, and conse- 

 quently that almost all the inflammable air is turned into pure water. 



In order to examine the nature of the matter condensed on firing 

 a mixture of dephlogisticated and inflammable air, I took a glass globe, 

 holding 8800 grain measures, furnished with a brass cock and an ap- 

 paratus for firing by electricity. This globe was well exhausted by an 

 air-pump, and then filled with a mixture of inflammable and dephlo- 

 gisticated air by shutting the cock, fastening the bent glass tube 

 into its mouth, and letting up the end of it into a glass jar inverted 

 into water and containing a mixture of 19,500 grain measures of 

 dephlogisticated air, and 37,000 of inflammable air; so that, upon 

 opening the cock, some of this mixed air rushed through the bent tube 

 and filled the globe. The cock was then shut and the included air 

 fired by electricity, by means of which almost all of it lost its elasticity 

 (was condensed into water vapors). The cock was then again opened 

 so as to let in more of the same air to supply the place of that de- 

 stroyed by the explosion, which was again fired, and the operation 

 continued till almost the whole of the mixture was let into the globe 

 and exploded. By this means, though the globe held not more than a 

 sixth part of the mixture, almost the whole of it was exploded therein 

 without any fresh exhaustion of the globe. 



BEGINNINGS OF MODERN IDEAS OF SOUND. We have seen 

 above that the Greeks were deeply interested in sound, as well 

 as in music. The invention of the monochord with the dis- 

 covery by Pythagoras of the relation between the length of a 

 vibrating string and the 'sound which it produces was the first 

 step in the right direction, although any mystical relation between 

 sound and number such as the Pythagoreans inferred has no basis. 



From Pythagoras to Galileo little or no progress was made. 

 Galileo recognized that sound is due to vibrations in the air falling 



