i 





ifluence of 



SI7 



Aet. XXni. — Preliminary Researches on the alleged Influence of 

 Solar Light on the Process of Comhustion ; by John Le Conte, 

 M.D., Professor of Natural Pliilosophy in the South Carolina 

 College. 



[Read before the "American Association for the Advancement of Scieoce," at the 



Montreal meeting, August, 1867.] 



A POPULAR opinion has long prevailed in England, and per- 

 haps in other countries, that the admission of the light of the 

 sun to an ordinary fire tends to retard the process of combustion. 

 In some instances, the practice of placing screens before the fire- 

 place, or of closing the shutters of the apartment, may be traced 

 to the prevalent belief, that the access oi sunlight to the burning 

 materials is unfavorable to the continuance of the phenomenon 

 of combustion. Most physical philosophers very naturally re- 

 gard this opinion as a mere popidar prejudice ; probably origina- 

 ting in the well-known apparent dulling or obscuration of flames 

 and of solid bodies in a state of ignition, — which takes place 

 when they are exposed to strong light. The flame of a jet of 

 burning hydrogen is scarcely visible in the diffused light of a 

 clear day ; that of an ordinary alcohol lamp is barely apprecia- 

 ble to tlie eye when exposed to the direct sunshine; while a 

 ortion of ignited charcoal which glows in the dark, appears to 



e extinguished when placed in the sunlight. These familiar 

 phenomena, attributable to well-established physico-physiological 

 laws, seem to afford a much more rational explanation of the 

 origin of the popular opinion, than to suppose it to be based 

 upon observations relating to the actual rapidity of burning. 



About thirty-two years ago, Dr. Thomas M'lCeever pubhshed 

 a series of experiments in the "Annals of Philosophy,* which 

 seemed to show, that there is a real foundation for the popular 

 impression, and that solar light does actually retard the. process 

 of combustion. So far as I am aware, these remarkable ex- 

 periments have never been repeated. Leopold Gmelin, in his 

 ''Hand-book of Chemistry, "f announces^Dr. M'Keever's results 



without comment The 

 to have on the influence of 



"v^ell as on the modern dynamical theory of the mutual convert- 

 ibility of the so-called imponderables, induced me during the 

 3iionths of May and June last, to undertake a series of experi- 

 ments with the view of testing the validity of Dr. M'Keevers 



* Annals of Pliilosophy, New Scries, vol. 10, p. 344, Nov, 1825. 



t Leopold Gmciia's Hnnd-book of Chemistry, (Cavendish Society's Translation,) 

 ^^^' 2, p. 35. London, 1849.— A contemporary journal, in noticing these re-^ults, re- 

 li^arks, " It has always been considered a vulgar error, that the sun's light extia- 

 guishes a fire, but the following experiments by Dr. WKeevet put the matter be- 

 yond a doubt.** (Brewster's Edin. Journal of Science, vol. 5, p. 180. 1826.) 



important bearing ^vhich they appear 

 »f solar light on chemieal processes, as 



