397 



SCIENTIFIC SIDE-LIGHTS 



Light 



changes wrought by light in animals are of 

 but secondary moment. . . . 



On plants, however, the solar rays that 

 produce in us the impression of yellow, are 

 the immediate agents of those molecular 

 changes through which are hourly accumu- 

 lated the materials for further growth. Ex- 

 periments have shown that when the sun 

 shines on living leaves, they begin to exhale 

 oxygen and to accumulate carbon and hydro- 

 gen results which are traced to the decom- 

 position, by the solar rays, of the carbonic 

 acid and water absorbed. It is now an ac- 

 cepted conclusion that, by the help of cer- 

 tain classes of the ethereal undulations 

 penetrating their leaves, plants are enabled 

 to separate from the associated oxygen those 

 two elements of which their tissues are 

 chiefly built up. SPENCER Biology, pt. i, ch. 

 2, p. 30. (A., 1900.) 



1937. LIGHT IN OCEAN DEPTHS 



Few Animals Wholly Blind. The condi- 

 tions in the deep sea are not quite the same 

 [as in terrestrial caves]. In some regions 

 there is probably a very considerable illu- 

 mination by phosphorescent light, and it is 

 quite possible that many of the character- 

 istic deep-sea forms may occasionally wan- 

 der into shallower regions where faint rays 

 of sunlight penetrate, or even that the young 

 stages of some species may be passed at or 

 near the surface of the sea. Taking these 

 points into consideration, then, it is not sur- 

 prising to find that, in the deep seas, there 

 are very few animals, belonging to families 

 usually provided with eyes, that are quite 

 blind. HICKSON Fauna of the Deep Sea, ch. 

 4, p. 68. (A., 1894.) 



1938. 



Illumination by 



Phosphorescent Animals Like a City Street 

 at Night. if we may be allowed to compare 

 the light of abysmal animals with that of 

 surface forms, we can readily imagine that 

 some regions of the sea may be as brightly 

 illuminated as a European street is at night 

 an illumination with many very bright 

 centers and many dark shadows, but quite 

 sufficient for a vertebrate eye to distinguish 

 readily and at a considerable distance both 

 form and color. HICKSON Fauna of the 

 Deep Sea, ch. 2, p. 25. (A., 1894.) 



1939. LIGHT, LAW OF ITS ABSORP- 

 TION Each Substance Selects and Stops Its 

 Own Kind of Light Identification by Spec- 

 troscope. A general principle first enun- 

 ciated by Kirchhoff in a communication to 

 the Berlin Academy, December 15, 1859, and 

 afterwards more fully developed by him . . . 

 may be expressed as follows : Substances of 

 every kind are opaque to the precise rays 

 which they emit at the same temperature; 

 that is to say, they stop the kinds of light 

 or heat which they are then actually in a 

 condition to radiate. But it does not follow 

 that cool bodies absorb the rays which they 

 would give out if sufficiently heated. Hy- 

 drogen at ordinary temperatures, for in- 

 stance, is almost perfectly transparent, but 



if raised to the glowing point as by the 

 passage of electricity it then becomes 

 capable of arresting, and at the same time 

 of displaying in its own spectrum, light of 

 four distinct colors. CLEBKE History of As- 

 tronomy, pt. ii, ch. 1, p. 168. (BL, 1893.) 



1940. LIGHT OF PHOSPHORES- 

 CENCE IN THE BANDA SEAS In the 

 Baiida Seas, on calm nights, the whole sur- 

 face of the ocean seems to be a sheet of 

 milky fire. The light is not only to be seen 

 where the crests of waves are breaking, or 

 the surface disturbed by the bows of the 

 boat, but the phosphorescence extends as far 

 as the eye can reach in all directions. It is 

 impossible, of course, to say with any de- 

 gree of certainty whether phosphorescence 

 such as this exists at the bottom of the deep 

 sea, but it is quite probable that it does in 

 some places, and hence the well-developed 

 eyes and brilliant colors of some of the deep- 

 sea animals. HICKSON Fauna of the Deep 

 Sea, ch. 2, p. 26. (A., 1894.) 



1941. LIGHT OF SUN HAS HEALTH- 

 FUL INFLUENCE -.Represses or Destroys 

 Bacteria. Light acts as an inhibitory or 

 even germicidal agent. This fact was first 

 established by Downes and Blunt in a 

 memoir to the Royal Society in 1877. They 

 found by exposing cultures to different de- 

 grees of sunlight that thus the growth of the 

 culture was partially or entirely prevented, 

 being most damaged by the direct rays of 

 the sun, altho diffuse daylight acted preju- 

 dicially. Further, these same investigators 

 proved that of the rays of the spectrum 

 which acted inimically the blue and violet 

 rays acted most bactericidally, next to the 

 blue being the red and orange-red rays. 

 The action of light, they explain, is due to 

 the gradual oxidation which is induced by 

 the sun's rays in the presence of oxygen. 

 NEWMAN Bacteria, ch. 1, p. 24. (G. P. P., 

 1899.) 



1942. LIGHT PASSES UNCHANGED 

 IN QUALITY THROUGH ABYSMAL 

 SPACES Spectrum Analysis in Astronomy. 

 Spectrum analysis may be shortly described 

 as a mode of distinguishing the various 

 species of matter by the kind of light pro- 

 ceeding from each. This definition at once 

 explains how it is that, unlike every other 

 system of chemical analysis, it has proved 

 available in astronomy. Light, so far as 

 quality is concerned, ignores distance. No 

 intrinsic change, that we yet know of, is 

 produced in it by a journey from the far- 

 thest bounds of the visible universe ; so that, 

 provided only that in quantity it remain 

 sufficient for the purpose, its peculiarities 

 can be equally well studied whether the 

 source of its vibrations be one foot or a hun- 

 dred billion miles distant. Now the most 

 obvious distinction between one kind of light 

 and^ another resides in color. But of this 

 distinction the eye takes cognizance ir an 

 esthetic, not in a scientific sense. Tt finds 

 gladness in the " thousand tints " of Nature, 



