MEMOIR Xlll.] EXPERIMENTS MADE IN VIRGIN 



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MEMOIR XIII. 



AN ACCOUNT OF SOME EXPERIMENTS ON THE L 

 THE SUN, MADE IN THE SOUTH OF VIRGINIA. 



Abstract from the Journal of the Franklin Institute of Philadelphia for June, July, 

 August, and September, 1837 ; Philosophical Magazine, Feb., 1840. 



CONTENTS: Absorption of luminous radiations. The reference spec- 

 trum. Absorption of heat radiations / the apparatus employed. Ab- 

 sorption of chemical radiations. Screen of bromide of silver. Color- 

 ation of chloride and bromide of silver by radiations that have passed 

 through correspondingly colored solutions. Early application of pho- 

 tography to the investigation of physical problems. Crystallization of 

 camphor towards the light. The side of vessels towards the sky is the 

 colder. 



IF a beam of the sun's light be passed through a so- 

 lution of chromate of potassa, it can no longer blacken a 

 piece of sensitive paper paper covered over with chlo- 

 ride or bromide of silver. If the light which has thus 

 passed through a stratum of this liquid be converged by 

 means of a lens, the chloride of silver will remain for a 

 long time without change in the focus. 



I made many such experiments with a view of deter- 

 mining the effect of absorbent media on the luminous, 

 calorific, and chemical rays. Such, at that time, was the 

 accepted subdivision of the solar radiations. A ray of 

 the sun was caused to pass through a trough with paral- 

 lel sides containing the absorbent solutions, and for the 

 sake of exactness a reference spectrum was employed, 

 such as is now used in spectroscopic experiments. In 

 this manner the particular luminous rays absorbed by 

 any given solution could be determined, the absorbed 



