136 GREAT MEN OF SCIENCE 



properly used to do what the muscles of man himself and 

 of his domestic animals could never have done? We may 

 equally well ask where are the enterprising people who set 

 up steam engines in order to make people happier, and not 

 in order to gain the financial profits upon which they have 

 calculated. Watt made other use of the gifts of his mind, 

 than these minds have made of his gifts. 



WILHELM SCHEELE {1742-1786) 

 JOSEPH PRIESTLEY {1733-1804) 

 HENRY CAVENDISH {1731-1810) 



These three great discoverers, all enthusiastic and exact 

 experimenters, founded, together with Black, the science 

 now called chemistry. This happened by the discovery of 

 a large number of facts hitherto unguessed at, which dealt 

 with the commonest substances, such as water and air, and 

 by the discovery of new substances, which although they 

 had always been present around us everywhere, and had 

 always played a very important part, had not yet been 

 separated and examined in a pure state. 



Using their present-day names, these were hydrogen, 

 oxygen, chlorine, which, with their peculiar new properties, 

 suddenly appeared like a new world full of marvels; at the 

 same time much light was thrown on many matters, such as 

 combustion and breathing, which had hitherto remained 

 completely incomprehensible. Furthermore, not a few of 

 the newly discovered bodies were gaseous, and bodies of 

 this kind had hitherto been known simply as 'air,' whereas 

 these investigators showed that there are just as many 

 fundanlentally different kinds of air (for which the word 

 'gas' now came into use), as there are liquid and solid 



