9S0 Magnitude of Ultimate Particles of Bodies. 



pressions of their magnitudes. Nay, many bold theoi'etical ex- 

 perimenters of tlie present day seem to have fallen little short, 

 in their own imagination, of in reality seizing the ultimate ele- 

 ments of bodies, and of reconstructing them at pleasure. a. 



Newton long ago taught us to believe that the elements 'of 

 colour were of tolerable magnitude. His words are, " Could 

 the power of the microscope be so increased as to represent ob- 

 jects at a foot distance, magnified 500 or 600 times above what 

 they appear to the naked eye, I imagine that we might discover 

 some of the coarser elements which enter into the formation of 

 colours ; and that, with a microscope which magnified 3000 or 

 4000 times, we might recognise them all, even those which form 

 the black colour." Supposing that Newton has correctly esti- 

 mated the natural power of human vision, his elementary parti- 

 cles, as appears from the following observations, would, for the 

 red colour, not exceed a minuteness oi ^^l^-^'" in diameter, be- 

 tween which and t^j^ooo'^ ^^ coloured particles, not excepting 

 the black, would be included *. But it is probable that Newton's 

 estimate of the acuteness of vision is below the truth, when these 

 elementary particles would become considerably larger. But, as 

 has been already observed by Herschel, in his Optics, it must 

 not be forgotten that Newton made a marked distinction be- 

 tween the elements of colours and atoms, as well as later philo- 

 sophers, although he does not expressly say so. In the above 

 passage, Newton does not speak of atoms but of colouring par- 

 ticles. — {Traite d'Optique, 1704; lib. ii, part iii ; Ed. Franc. 

 1720, p. 357.) 



The small magnitudes which have been required for the ex- 

 plication of the phenomena of light upon the theory of undula- 

 tion, are exactly enough determined by calculation, but they 

 can only be considered as hypothetical, not as really observable 

 quantities, as the whole theory, however great its probability, 

 still requires more complete demonstration. The smallest length 

 of a wave of light on this theory, calculated from the most exact 

 data, does not exceed lOo^g^n'^ or about ^o^oo"- B"t» ^s the 

 particles of ether must be considerably smaller than their undu- 



• The general reader may be informed, that 0" is the mark for inch, 0'" for 

 line or 12th part of an inch. 



