Art. XI. The Sunbeam and the Spectrascope, by Howard 

 Townsend, M. D. 



[Read before the Albany Institute, Feb. 17th, 1863.] 



Lavoisier has very beautifully said — 



" The fable of Prometheus is but the overshadowing of a 

 philosophic truth : Where there is light there is organization 

 and life ; but where light cannot penetrate there death 

 forever holds his silent court." 



If a sunbeam be allowed to enter a darkened room, it falls 

 on the floor and forms a disc of bright light. This is radi- 

 ated to the eye which conveys the impression to the brain, 

 and the phenomenon of vision is established. 



Should the hand be placed in the track of the sunbeam, 

 the sensation of warmth is communicated, and we feel there 

 is heat in the ray. 



If a piece of paper covered over with chloride of silver, 

 which is purely white, be placed so that the sunbeam falls 

 upon it, a darkened track will be immediately produced 

 over the space the sun's ray has passed, it has liberated the 

 chlorine, leaving the metallic silver. 



Such remarkable phenomena teach us that we have to 

 deal with agencies in the solar rays, which are in their visi- 

 ble effects very dissimilar. 



Actinism, which means ray power, is nbw the term adopted 

 to express the chemical principle of the sunbeam. 



That these three functions of the sunbeam — light, heat 

 and actinism — all differ from one another, may be thus 

 proven. 



* A piece of black mica will allow no light to pass through 

 it, but offers no obstruction to solar heat. 



A plate of glass, stained apple green with oxydeof copper ? 

 is perfectly transparent to light, but opaque or impermeable 

 to heat. 



