Stoney — Apjjreciation of Ultra-Visible Quantities. 535 



calculation will stow that the motion within the molecules of 

 sodium to which the principal double line in its spectrum is due — 

 a motion which is repeated 508,911,000,000,000 {i. e. more than 

 five hundred millions of millions) of times every second within each 

 molecule — would need to have a velocity several times greater than 

 that of the earth in its orbit (which is a velocity of 30 kilometres, 

 19 miles, per second) if the range of these motions is the whole dia- 

 meter we have attributed to the molecule.^ This consideration, 

 though not decisive, is nevertheless quite sufficient foundation on 

 which to base the exjjecfation that, if ever we are able to ascertain 

 the actual range of this motion and others of a like kind, they will 

 turn out to be much smaller than the ordinate of our gauge at a 

 -distance of a millimetre from its apes ; so that if ever we discover 

 any way of quantitatively estimating such events, we shall require 

 another and more acute-angled gauge to aid us in appreciating 

 them. 



YII, — Of the Borderland of the Visible. 



Meanwhile the gauge now proposed will, it is hoped, help the 

 scientific student to obtain a more connected view of nature, by 

 placing before him in somewhat clear evidence the relation in which 

 •some of the larger molecular events stand to the dimensions of the 

 smallest objects he can see with his microscope. 



He should never forget that even the most minute of these 

 microscopic objects is an immense army of molecules,^ or semi- 

 inolecules, crowded together, more numerous indeed than all 

 the inhabitants of Europe. The individuals that constitute the 

 battalions are not seen, nor is there the least glimpse of the active 

 motions that are without intermission going on among or within 

 the individuals : nay more, waves of light are too coarse to supply 

 our microscopes with information about the evolutions of the 

 companies, regiments, and brigades of this great army. It is only 

 when the entire army sliifts its position that anything can be seen; 



1 See Stoney "On Double Lines," Scientific Proceedings, E. D. S., vol. iv., p. 603. 



2 That is, of molecules sucli as are present in the gaseous state of the ultimate 

 chemical constituents of the speck of matter under examination. These in a highly- 

 organized substance like protoplasm are associated into much larger organic groups, that 

 may be called mega-molecules, and may be likened to the companies or regiments of the 

 brigades and corps that make up an army. 



