410 Scientific Intelligence. 



sufficiently affected by the photogenic rays proceeding from the zenith 

 to attract the white vapors of mercury. This proved that the red rays 

 had no photogenic power. He then operated in a different manner; 

 not content with the slow motion of the sun, he moved the camera ob- 

 scura from right to left and vice versa. In this manner the sun had 

 passed rapidly over five or six zones of the plate. Its passage was 

 marked by long black bands, whilst the intervening spaces were white; 

 showing again that it was sufficient in order to destroy the action of the 

 photogenic rays to let red rays pass rapidly over the spaces previously 

 affected by them. He operated afterwards with colored glasses; after 

 having obtained upon a Daguerreotype plate the impression of a black 

 lace by white light, he covered one half of the plate and exposed the 

 other half to the radiation of a red glass. The mercury developed an 

 image of the lace on the part which had been acted on only by the 

 white light, and the other part which had afterwards received the ac- 

 tion of the red rays remained black. The red glass had destroyed the 

 photogenic effect, as had taken place with the red light of the sun. 

 He made the same experiments with orange and yellow glasses, and 

 obtained the same results but in different periods of time. The photo- 

 genic action of the red rays is 5,000 times longer than the white light, 

 that of the orange is 500 times longer and that of the yellow 100 

 times. The destructive action of the red rays is 100 times longer than 

 that of white light ; the orange 50 times, and yellow only 10 times. 

 When a plate has been exposed to the destructive action of any par- 

 ticular ray, it cannot be affected photogenically by the radiation which 

 has destroyed the first effect ; it is only sensitive to the other radiations. 



Mr. R. Hunt remarked that his own observations had led him to the 

 conclusion, that instead of having to deal with three differently colored 

 rays, we had to deal with three distinct principles,— these three colors 

 being a property of only one of them. Light, heat, and actinism he 

 regarded as antagonistic forces; and it was only because they were 

 found in different proportions in the three classes of colored rays that 

 the results of M. Claudet could be in any way associated with the col- 

 ors of light.— Mr. Maskelyne objected to some of these conclusions. 



5. Report on the Influence of Light on the Growth of Plants ; by 

 R. Hunt, (Proc. Brit. Assoc, 1847, Athen., No. 1027.)— The author 

 confirms the conclusions that seeds will not germinate under the influ- 

 ence of light separated from the chemical principle with which it is 

 associated in the sunbeam ; that germination being effected and t e 

 first leaves formed, light — the luminous rays — become essential to t e 

 plant to enable it to secrete the carbon obtained from the carbonic aci 

 of the atmosphere ; and that the increased action of the heat T p ?s] 

 essential to insure the production of the reproductive elements ol veg- 

 etable life. It is found that the chemical principle of the solar f*J 

 is more active, relatively to heat and light, during the spring xhan ^ 

 any other period of the year; that as summer advances this P° we ^ ol)l 

 minishes and luminous force increases, whilst with the autumn 

 light and actinism are subdued, but the calorific radiations ! ncreaS gui [ 

 Thus we find the conditions of the light of the seasons varying to ^ 

 the necessities of vegetable life. The production of chlorop^ hy , 

 the coloring matter of the leaves, was shown to be due to the J 



