134 THE CANADIAN NATURALIST. [Vol. vi. 



the life-blood of science. In contemplating them we feel as if led 

 out from narrow waters of scholastic dogma to a refreshing excur- 

 sion on the broad and deep ocean of truth, where we learn from 

 the wonders we see that there are endlessly more and more glori- 

 ous wonders still unseen. 



Stokes's dynamical theory supplies the key to the philosophy 

 of Frankland and Lockyer's discovery. Any atom of gas, when 

 struck and left to itself, vibrates with perfect purity its funda- 

 mental note or notes. In a highly attenuated gas each atom is 

 very rarely in collision with other atoms, and therefore is nearly 

 at all times in a state of true vibration. Hence the spectrum of 

 a highly attenuated gas consists of one or more perfectly sharp 

 bright lines, with a scarcely perceptible continuous gradation of 

 prismatic colour. In denser gas each atom is frequently in colli- 

 sion, but still is for much more time free, in intervals between 

 collisions, than engaged in collision ; so that not only is the atom 

 itself thrown sensibly out of tune during a sensible proportion of 

 its whole time, but the confused jangle of vibrations in every 

 variety of period during the actual collision becomes more con- 

 siderable in its influence. Hence bright lines in the spectrum 

 broaden out somewhat, and the continuous spectrum becomes less 

 faint. In still denser gas each atom may be almost as much time 

 in collision as free, and the spectrum then consists of broad 

 nebulous bands crossing a continuous spectrum of considerable 

 brio'htness. When the medium is so dense that each atom is 

 always in collision, that is to say, never free from influence of 

 its neighbours, the spectrum will generally be continuous, and 

 may present little or no appearance of bands, or even of maxima 

 of brightness. In this condition the fluid can be no longer 

 regarded as a gas, and we must judge of its relation to the vapor- 

 ous or liquid states according to the critical conditions discovered 

 by Andrews. 



While these great investigations of properties of matter were 

 going on, naturalists were not idle with the newly-recognized 

 power of the spectroscope at their service. Chemists soon followed 

 the example of Bunsen in discovering new metals in terrestrial 

 matter by the old blow-pipe and prism test of Fox Talbot and 

 Herschel. Biologists applied spectrum analysis to animal and 

 vegetable chemistr}^, and to sanitary investigations. But it is 

 in astronomy that spectroscopic research has been carried on with 

 the greatest activity, and been most richly rewarded with results. 



