280 MODERN SCIENCE READER 



science to believe that the atom may itself have a constitu- 

 tion. The atoms of different elements differ from one 

 another. Yet the modern scientist feels with the ancient 

 philosopher that there may, after all, be only one kind of 

 matter, which, being grouped in different ways, gives rise 

 to different elements and bodies. There are certainly dif- 

 ficulties in the suggestion that atoms or molecules should 

 be able to split off corpuscles, and remain substantially what 

 they were, while, on the other hand, radium probably an 

 elementary metal is able to emit radiations which turn 

 into helium undoubtedly a gas. But those researches are 

 not completed yet, and meanwhile chemists continue to 

 adhere to the atomic theory which has proved so fruitful, 

 and to determine atomic weights with the greatest possible 

 care. 



The demonstrations of the possible visibility of molecules 

 are based on observations partly made in less controversial 

 fields. Colloids have furnished the first suggestion of 

 visible molecules or groups of molecules. When mud is 

 stirred up, the particles settle quickly again, and the turbid 

 liquid can, by filtering, be cleared of suspended particles. 

 The particles of an oil emulsion take a long time to settle, 

 and run turbid through the filter. When still finer par- 

 ticles are prepared, for instance, by volatilizing metal elec- 

 trodes immersed in liquids, the cloudy particles will not 

 settle for many days or months, and finally it may be im- 

 possible to decide whether an emulsion or a real solution 

 has resulted. It is quite conceivable that the transition 

 from a suspension to a solution is too gradual to permit of 

 a distinct line of demarkation being drawn, just as the 

 three states of aggregation cannot rigorously be distin- 

 guished. Very small suspended particles now are in con- 

 stant oscillatory movement. These movements were first 

 observed by the botanist Brown in 1827, and are known as 

 Brownian movements. The coarser the particles, the 

 slower and more irregular the movements. For a long 

 time they were ascribed to inequalities of temperature in 



