166 THE GROWTH OF SCIENCE IN THE NINETEENTH CENTURY. 



In the philotsophy of the ancients earth, tire, air, and water were called 

 "the element.s.'' It wa.s thought, and rightly thought, that a knowl- 

 edge of them and of their attributes was a necessary basis of a 

 knowledge of the ways of nature. Translated into modern language, 

 a knowledge of these "elements'' of old means a knowledge of the 

 composition of the atmosphere, of water, and of all the other things 

 which we call matter, as well as a knowledge of the genei'al properties 

 of gases, li(juids, and solids, and of the nature and eti'ects of combus- 

 tion. Of all these things our knowledge to-day is large and exact, 

 and, though ever enlarging, in sojiie respects complete. When did 

 that knowledge begin to become exacts 



To-day the children in our schools know that the air Avhich wraps 

 round the globe is not a single thing, ])ut is made up of two things, 

 oxygen and nitrogen,' mingled together. They know, again, that 

 water is not a single thing, but the product of two things, oxygen and 

 hydrogen, joined together. They know that when the air makes the 

 tire burn and gives the animal life, it is the oxygen in it which does 

 the work. They know that all round them things are undergoing that 

 union with oxygen which we call oxidation, and that oxidation is the 

 ordinary source of heat and light. Let me ask you to picture to your- 

 selves what confusion there would bo to-morrow, not only in the dis- 

 cussions at the sections;] meetings of our association, but in the world 

 at large, if it should happen that in the coming night some destroying 

 touch should wither up certain tender structui'es in all our In'ains and 

 wipe out from our memories all traces of the ideas which cluster in 

 our minds around the verbal tokens, oxj'^gen and oxidation. How 

 could any of us, not the so-called man of science alone, but even the 

 man of business and the man of pleasure, go about his ways lacking 

 those ideas? Yet those ideas were in 1799 lacking to all but a few. 



Although in the third (piarter of the seventeenth centur}^ the light 

 of truth about oxidation and combustion had flashed out in the writings 

 of John Ma^^ow, it came as a flash only, and died away as soon as it 

 had come. For the rest of that century', and for the greater part of the 

 next, philosophers stumbled about in darkness, misled for the most of 

 the time by the phantom conception which they called phlogiston. It 

 was not until the end of the third (j[uarter of the eighteenth century that 

 the new light, which has burned steadily ever since, lit up the minds 

 of the men of science. The light came at nearly the same time from 

 England and from France, Rounding oil' the sharp corners of contro- 

 versy', and joining, as we may fith' do to-day, the two countries as twin 

 bearers of a common crown, we maj' any that we owe the truth to 

 Priestlej', to Lavoisier, and to Cavendish. If it was Priestley who was 

 the first to demonstrate the existence of what we now call oxygen, it 

 is to Lavoisier we owe the true conception of the nature of oxidation 



' Some may already know that there is at least a third thing, argon. 



