Dr. M'Keever on the Influence of Solar Light [Not, 



' ^ ' To' consume one inch it took 69' 0'^ 



In darkened room (temp. (38° F.) . » . ^ , ^ 5& Q 



In ordinary light of day (temp. 68° F.) . . 57 Iflfd 1,.^.. 



^ ixper, 4. — A piece of taper, seven inches in length; kn^'^fit- 

 eighVhs of an inch in circumference, w^s carefully divided into 

 inches, and, as in former experiment, submitted to bright sutf- 

 shiue : thermometer 79°. Mrt 



To consume one inch it took 5' 0" 



Transferred to darkened room (temp. 67°) 4-1- 

 In ordinary light of day (temp. 67°) .... 4 62 



Exper, 5. — In order to vary the experiment, and to guard as 

 much as possible against the agitation of the surrounding atmo- 

 sphere, I procured two lanterns ; one of them I coated with 

 black paint; the other I left naked. In these I placed two, 

 portions of taper, of precisely equal weights, and expose^ ^1^!^ 

 both to a strong glare of sunshine. I^T *^ ' ^ 



In 10 minutes that placed in painted lantern lost . . 16J- grs. 

 that placed in uncoated lantern lost. 15* 



Eocper, 6. — With the view of ascertaining whether similar 

 results were to be obtained by exposure to the light of the moon, 

 I prepared the lanterns as in the last experiment, and took an 

 opportunity lately when this luminary shone forth with pecuUar 

 splendour, of trying its effects ; but although I employed an 

 exceedingly delicate balance for the purpose, I could detect no 

 difference whatever in the loss sustained by the two portions of 

 taper. 



After I had made these experiments, I naturally turned my 

 attention to an explanation of the principles on which results o f 

 so singular a nature could depend ; and it occurred to me that 

 they probably were owing to the well-known decomposing 

 power possessed by the solar ravs, in consequence of which the 

 shell of air that immediately encircles a particle of matter about 

 to enter into combustion, is deprived, to a certain extent, of its 

 oxygenous principle, and is thus rendered less fitted for the 

 maintenance of this important process.^ Thus in order to nar- 

 row and simplify the matter, let us suppose that one atom of 

 carbon is about to enter into combination with two atoms of 

 oxygen, we can readily conceive that the chemical rays may 

 possess the power of withdrawing one of those atoms from the 



• The diminished rate of consumption in this experiment was probably owing to the 

 want of a free current of air through the interior of the lantern. 



f That an affinity or attraction is exerted between light and tlie particles of bodies 

 may be justly inferred from the great refractive jxjwer of inflammable bodies, which, all 

 other things being equal, must be supposed to attract light more powerfully than otliet 

 substances.— (See Ellis on Atmospheric Air, p. 167.) 



