NEW CONCEPTIONS IN SCIENCE 



of the molecules rests upon wide and solid founda- 

 tions. We may regard it as so well established that 

 if we could take apart the objects of <every-day 

 use books, plates, furniture, not less than foods, 

 water, air we should find them all made up of par- 

 ticles from one to ten million ths of a hair's-breadth 

 in diameter, reckoning two hundred and fifty hairs 

 to the inch ; that is, from i /i/z to o. i /K/K. Our micro- 

 scopes will show microbes from 150 up to 250 /u/u in 

 thickness; so that to be able to see the inorganic 

 bacteria, the molecules, we should have to have 

 microscopes from one to two thousand times as 

 powerful as we have now ; in other words, an instru- 

 ment which would do the same for the present 

 microscope as that has done for the naked eye. 

 The microscope has been improved to very near its 

 theoretical limits, so that if ever we actually behold 

 a molecule we shall need a new light to see with, 

 less gross than common light, or else find new op- 

 tical methods not now dreamed of. 1 



1 Even as this is written, Herrn Siedentopf and Zsigmondy 

 have shown a method by which some of the larger molecules, 

 such as those of the colloids, actually may be seen. The meth- 

 od resembles very much that of darkening a room so that only 

 a single ray of sunshine streams in. In this way, the dancing 

 particles of dust become visible. By the new method, par- 

 ticles from 4 to 7 pp in diameter should be seeable, under some 

 conditions. This is probably below the size of the ultimate 

 units of living matter, so that we have here yet another step 

 into the invisible and the unknown. 



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