190 SIZE OF ULTIMATE ATOMS. 



ultimate atoms of matter is at most su.oo'o^.oim ^^ ^^ 

 inch in diameter. Under these circumstances, we 

 cannot, it would seem, hope at present for any great 

 increase of our knowledge of atoms by improvements 

 in the microscope. With our present instruments we 

 can perceive lines ruled on glass which are -g-Q.oiro ^^ ^^^ 

 inch apart. But, owing to the properties of light itself, 

 the fringes due to interference begin to produce con- 

 fusion at distances of 7 4,|)-oo> and in the brightest part 

 of the spectrum, at little more than 9-0,0 o'o* ^^^7 would 

 make the obscurity more or less complete. If, indeed, 

 we could use the blue rays by themselves, their waves 

 being much shorter, the limit of possible visibility 

 might be extended to i2o!ooo » ^^^» ^^ Helmholtz has 

 suggested, this perhaps accounts for Stinde having 

 actually been able to obtain a photographic image of 

 lines only T^-oaiWo^ ^^ ^^ ^^^^ apart. This, however, 

 would appear to be the limit, and it would seem, 

 then, that, owing to the physical characters of light, 

 we can scarcely hope for any great improvement so 

 far as the mere visibility of structure is concerned, 

 though in other respects, no doubt, much may be 

 hoped for. At the same time, Dallinger and Koyston 

 Pigott have shown that, as far as the mere presence 

 of simple objects is concerned, bodies of even smaller 

 dimensions can be perceived. According to the views 

 of Helmholtz, the smallest particle that could be 

 distinctly defined, when associated with others, is 

 about -go^.Voo ^^ ^^ ^^^^ ^^ diameter. Now, it has 

 been estimated that a particle of albumen of this size 

 contains 125,000,000 of molecules. In the case of such 

 a simple compound as water, the number would be 

 no less than 8,000,000,000. Even then, if we could 



