1825.] on the Process of Comhustion': 349 



To consume one inch. 

 At the verge of violet ray it took. . . 4f 36^' 



In the centre of violetfay. . , 4 26 



green ray. 4 20 



red ray 4 16 



This short inquiry then, although, perhaps, not conducted 

 with all that delicacy and precision so necessary for strict philo- 

 sophical research, would appear to warrant two conclusions of 

 some interest. First, that the solar rays in proportion to their 

 intensity are possessed of the power of retarding to a considera- 

 ble extent the process of combustion ; and that consequently the 

 popular ideas on this subject are founded in truth. Secondly, 

 that this phsenomenon is occasioned by the action of the chemi- 

 cal rays on the portion of atmospheric air that immediately enve- 

 lopes a particle of matter about to enter into a state of combus- 

 tion, aided no doubt by the high temperature^ of the portion of 

 materials that have already commenced this process. 



Before concluding, I would suggest it as a subject for further 

 investigation, whether it may not be owing to the action of the 

 deoxidizing rays of the solar beam, on the various combinations 

 of matter diffused over the surface of our globe, that the vast 

 quantities of oxygen consumed on the various deteriorating pro- 

 cesses of nature and of art are again restored to the atmosphere 

 so as to preserve at all periods, and in every situation, a state of 

 constant uniformity of composition. 



Plants, it is satisfactorily ascertained, give out a large quan- 

 tity of oxygen gas when exposed to sunslune, an effect that may 

 very fairly be attributed to the action of the chemical rays on the 

 carbonic acid generated in the minute vascular system of the 

 leaf t Even the ordinary light of day has, in some instances, 

 been found capable of accomphshing the same purpose. Thus 

 marsh plants, as the 'polygonum persicaria and the lythrum salt- 

 catiaj yielded oxygen gas by a weak diffused light when confined 

 in an atmosphere of nitrogen ; and difierent species of epilobium 

 vegetated a long time, and grew as well in pure nitrogen gas as 



portion of the spectrum would appear to suggest the propriety of imparting this colour 

 to objects that we wish to render visible at great distances, such, for instance, as lights 

 situated along the sea coast. I am not aware of the experiment having been tried in 

 light-houses, and I should anticipate but one objection to its success ; namely, that the 

 blue colour of the atmosphere combining with the green would impart a yellowish tinge. 

 In the colouring of our apartments, however, and a variety of other occasions, this prin- 

 ciple might be advantageously attended to. The circumstance of our fields, as well as 

 the greater portion of the vegetable world, having been clothed with this delicate and 

 refreshing colour, may enable those animals that feed by night more readily to discover 

 their wonted repast. This, at all events, may be one end accomplished by it. The same 

 simple agent in the hands of an all-wise Providence is frequently employed to accomplish 

 the greatest variety of purposes. 



* The temperature of a conmion fire, according to Irvine, 18 790°. 



•f- Saussure found that by the deconj position of carbonic acid not only was oxygen 

 discharged fconijkh^ plant, but Uiat tlie proi>ortion of its €«vrboivwa§ mater i^yw^iascd. 



