COMPOUNDS AND ELEMENTS. 9 



be, others, such as calcium, caesium or fluorine, are always 

 combined and you never see them as such. They may be 1 

 common as dirt or a thousand times rarer than gold. The 

 important point is that, united together by a force called 

 chemical affinity, in various ways and in different quan- 

 tities, these same seventy things constitute all that is. 

 But these things are found all over. If the world is made 

 of "mud," so are the sun and stars. They consist of the 

 same thing. Iron and hydrogen are found in the sun, 

 together with many an other element ; calcium and man- 

 ganese in the great star Sirius; carbon, the so-called " ele- 

 ment of life" in all the stars alike. The chemistry of all 

 parts of space is the same. 



A Compound is thus a substance that may be decomposed 

 or separated into other substances. 



An Element is a substance that has, so far, resisted all 

 attempts to decompose it. 



MOLECULES AND ATOMS. 



A substance is either infinitely divisible, or it is not. 

 There is no mediate possibility. According to the old 

 scholastic conception, you could, at first practically, and 

 then mentally, go on dividing any specific object into parts 

 smaller and smaller forever and forever and forever. In 

 other words, you could never have a thing so small but that 

 it had two halves. Now we need trouble ourselves with 

 this conception no further than to say that it is absolutely 

 incapable of explaining the observed phenomena of the 

 world. The fruitful conception, the one that not only ex- 

 plains the phenomena of matter to an astonishing degree, 

 but even permits the successful prediction of many forms 

 of matter hitherto unknown, assumes that these forms of 

 matter as we know them are not by any means infinitely 



