144 ANNUAL OF SCIENTIFIC DISCOVERY. 



ON SOME NEW PHENOMENA OF LIGHT AND ACTINISM. 



THE following is an abstract of a paper recently presented to the 

 Royal Society by Robert Hunt, Esq. The chemical change pro- 

 duced in chloride of silver when exposed to the action of the sun's 

 rays, by which powerful chemical affinity is broken up, chlorine lib- 

 erated, and silver in a state of fine division left, was selected as an ex- 

 emplification of the actinic force, which was the subject of considera- 

 tion. This chemical change takes place in white light, and hence all 

 those photographic phenomena which have created so much interest 

 have been referred to luminous power. If, however, we examine the 

 conditions of light as analyzed by the prism, presenting, not seven 

 colored bands, as stated by Sir Isaac Newton, but nine as proved by 

 recent experiments, it is found that these colored bands possess op- 

 posite properties. For instance, the chloride of silver will not darken 

 in the mean luminous ray of the spectrum, nor will it darken either 

 at the end which gives the greatest calorific effect, or at the end which 

 is embraced by the lavender ray, usually regarded as representing the 

 most chemically active part ; consequently we find three points in the 

 spectrum which will not produce any change in chloride of silver. 

 Where we have the most light, and at two extremities where the 

 light ceases to affect the human eye, and also laterally, bands are ex- 

 hibited which show the same physical conditions, and thus it would 

 appear that the circle of light is not the agent producing this peculiar 

 alteration. Regarding, as appears natural, the ordinary prismatic 

 spectrum as the representation actually of two spectra consisting of 

 but three colors, red, blue, and yellow, which is shown by the re- 

 appearance of red light in the blue and of yellow light in the lavender 

 ray, which blue light appears again at the least refrangible end in the 

 extreme red or crimson ray, we have an explanation of the result 

 above mentioned, and the want of chemical action is shown to arise 

 from the operation, indeed, of the most luminous bands. By absorbent 

 media, as colored glasses and fluids, these results were more fully ex- 

 plained. The most remarkable results have, however, been lately ob- 

 tained by the use of colored media ; and it has .been shown that every 

 luminous ray, independent of color, may be made to protect chloride 

 of silver from that chemical change which is induced by the direct ac- 

 tion of diffused daylight, the portion upon which those rays foil be- 

 ing actually preserved as a white space, every other part .being black- 

 ened. It was contended that no hypothesis of interference would 

 explain this result, which more decidedly proved than had hitherto 

 been done, the wide difference between the phenomena of light and 

 actinism. The fact that luminous effect phosphorescence was 

 produced by the blue rays of the spectrum, appears to oppose this 

 view ; but when we find that, in like manner, electricity was interrupt- 

 ed, it appears more rational to refer phosphorescent phenomena to 

 some peculiar electric excitation. The action of the solar rays on the 

 developement of vegetable life was then explained, and the following 

 conclusions suggested as the explanation of experimental results fre- 

 quently repeated; 1. Germination, which will take place in the 



