lo Cincinnati Society of Natural History. 



German bacteriologists, with the following results : That the 

 light retards or prevents their development whenever the 

 experiment is tried in the presence of air, and that the retard- 

 ing effect is owing to diffuse light, and above all to the actinic 

 rays of the solar spectrum (Arloing, Les Vivus, p. 93). The 

 action is nearly independent of temperature. Typhoid bacilli 

 are affected by light injuriously, so that there will be a diiTer- 

 ence of two days in growth between those exposed to light 

 and those protected from it. 



In the calorific rays of the sun we have another essential 

 factor of weather, that of temperature. Unlike the quiet 

 action of the luminous and chemical rays, we have in heat the 

 great motive power of weather. Chemical rays have a limited 

 power of originating motion in the plants. Sach's "Text 

 Book of Botany," p. 738, says: "Chemical action, so far as 

 they are in the main dependent on light, are produced chiefly 

 by rays of medium or low refrangibility, (viz : the red, orange, 

 yellow, or green). This is the ca.se. for instance, in the pro- 

 duction of the green color of chlorophyll, the decomposition 

 of carbon dioxide and the formation in chlorophyll of starch 

 or sugar. On the other hand, the rays of high refrangibility 

 (the blue or violet, as well as the invisible ultra-violet rays,) 

 are the principal, or the only ones, which produce mechanical 

 changes, so far as these are dependent on light. It is these 

 rays which influence the rapidity of growth, alter the move- 

 ments of the protoplasm, compel swarm-spores to adopt a 

 definite direction in their motion, and change the tension of 

 the tissues of the motile organs of many leaves, and hence 

 affect their position." 



Compare these limited motions within the plant entirely, 

 with those originating in differences of temperature and 

 humidity, such as the lightest breeze can produce, and the 

 contrast is .striking. Temperature is, therefore, much more 

 potential than mere light, and has greater bearings on the 

 human being, as a unit of weather. The same rays of light 

 that travel from the sun through space, with a temperature 

 — 200°, are differentiated when they reach our atmosphere 

 and the earth, some acting with silent ecjuablc force on the 

 vegetable world and others develoi)ing the prodigious energy 

 of our storms ; some originate molecular and others cyclonic 



