OXYGEN AND NITROGEN. :2l 



rising or the setting sun is shedding over the. t-ysi^t'ii 

 or the western horizon the glory of its coloured ea\ 8 



Thus science points out to us the important uses of 

 the air. "Wo learn that life and combustion are entirely 

 dependent 'on it, and that it is made the means for 

 securing greater constancy in the climates of the earth 

 than could otherwise be obtained. The facts already 

 dwelt upon are sufficient to convince every thinking 

 mind that the beautiful system of order which is dis- 

 played in the composition of the atmosphere, in which 

 the all-exciting element, oxygen, is subdued to a tranquil 

 state by another element, nitrogen, (which, wo sliMl 

 have presently to show, is itself, under certain con- 

 ditions, one of the most energetic agents with which we 

 are acquainted,) indicates a supreme power, omniscient ' 

 in the adaptation of things to an especial end. Oxygen 

 and nitrogen are here mixed for the benefit of tmvn ; 



ro- 



* On the Colour of Steam under certain circumstances : lv 

 fessor Forbes ; Philosophical Magazine, vol. xiv. p. 121, vol. .17. 

 p. 25. In the first paper the following remarks occur : " I cannot 

 doubt that the colour of watery vapour under certain circum- 

 stances is the principal or only cause of the red colour observed io- 

 clouds. The very fact that that colour chiefly appears in the pre- 

 sence of clouds is a sufficient refutation of the only explanation 

 of the phenomena of sunset and sunrise, having the least plausi- 

 bility, given by optical writers. If the red light of the horizontal 

 sky were simply complementary to the blue of a pure atmosphere. 

 the sun ought to set red in the clearest weather, and then most of 

 all ; but experience shows that a lurid sunrise or sunset is always 

 accompanied by clouds or diffused vapours, and in a great 

 majority of cases occurs when the changing state of previously 

 transparent and colourless vapour may be inferred from the suc- 

 ceeding rain. In like manner, terrestrial lights seen at a distance 

 grow red and dim when the atmosphere is filled with vapour soon 

 to be precipitated. Analog}- applied to the preceding observations 

 would certainly conduct to a solution of such appearances; for I 

 have remarked that the existence of vapour of high tension is by 

 no means essential to the production of colour, though of course a 

 proportionally greater thickness of the medium must be employed 

 to produce a similar effect when the elasticity is small." 



