Clothing 

 Color 



SCIENTIFIC SIDE-LIGHTS 



106 



variety of tapa, till they found that the first 

 shower of rain spoiled it. Leaves, also, are 

 made into aprons or skirts which clothe va- 

 rious rude tribes. Not only are there " leaf- 

 wearers " in India, but at a yearly festival 

 in Madras the whole low-caste population 

 cast off their ordinary clothing and put on 

 aprons of leafy twigs. TYLOR Anthropology, 

 ch. 10, p. 244. (A., 1899.) 



525. CLOUD-CAPITALS OF VIEWLESS 

 COLUMNS Cumulous Clouds. Similar re- 

 marks apply to the formation of cumuli in 

 our own latitudes; they are the heads of 

 vaporous columns which rise from the 

 earth's surface, and are precipitated as soon 

 as they reach a certain elevation. Thus, the 

 visible cloud forms the capital of an invis- 

 ible pillar of saturated air. The top of 

 such a column, raised above the lower vapor- 

 screen which clasps the earth, and offering 

 itself to space, is chilled by radiation and 

 precipitated as cloud. Mountains act as 

 condensers, partly by the coldness of their 

 own masses, which they owe to their eleva- 

 tion. Above them spreads no vapor-screen 

 of sufficient density to intercept their heat, 

 which consequently passes unrequited into 

 space. When the sun is withdrawn, this 

 loss is shown by the quick descent of the 

 thermometer. TYNDALL Heat a Mode of 

 Motion, lect. 13, p. 384. (A., 1900.) 



526. CLOUD, INCIPIENT Rivals Azure 

 of Italian Sky. It is possible, by duly regu- 

 lating the quantity of vapor, to make our 

 precipitated particles grow from an infini- 

 tesimal, and altogether ultra-microscopic 

 size, to specks of sensible magnitude; and 

 by means of these particles, in a certain 

 stage of their growth, we can produce a blue 

 which shall rival, if it does not transcend, 

 that of the deepest and purest Italian sky. 

 Let this point be in the first place estab- 

 lished. Associated with our experimental 

 tube is a barometer, the mercurial column 

 of which now indicates that the tube is ex- 

 hausted. Into the tube I introduce a quan- 

 tity of the mixed air and nitrite of butyl 

 vapor, sufficient to depress the mercurial 

 column one-twentieth of an inch; that is to 

 say, the air and vapor together exert a pres- 

 sure of one-six-hundredth of an atmosphere. 

 I now add a quantity of air and hydro- 

 chloric acid, sufficient to depress the mer- 

 cury half an inch further, and into this com- 

 pound and highly attenuated atmosphere I 

 discharge the beam of the electric light. The 

 effect is slow; but gradually within the 

 tube arises a splendid azure, which strength- 

 ens for a time, reaches a maximum of depth 

 and purity, and then, as the particles grow 

 larger, passes into whitish blue. This ex- 

 periment is representative, and it illustrates 

 a general principle. Other colorless sub- 

 stances of the most diverse properties, optic- 

 al and chemical, might be employed for this 

 experiment. The incipient cloud, in every 

 case, would exhibit this superb blue; thus 

 proving to demonstration that particles of 



infinitesimal size, without any color of their 

 own, and irrespective of the optical proper- 

 ties exhibited by the substances in a massive 

 state, are competent to produce the color of 

 the sky. TYNDALL Heat a Mode of Motion, 

 lect. 16, p. 484. (A., 1900.) 



527. CLOUDS WITH LINING OF BLUE 



AND GOLD Beauty of Sunrise and Sunset on 

 Worlds Lit by Colored Suns. The skies, 

 however, must be often exceedingly beauti- 

 ful. Our clouds have their silver lining, be- 

 cause it is the white light of the sun which 

 illumines them. Our summer sky presents 

 glowing white clouds to our view, and at 

 other times we see the various shades be- 

 tween perfect whiteness and an almost black 

 hue, corresponding to the various degrees in 

 which the illuminated side of a cloud is 

 turned towards us. But imagine how beau- 

 tiful the scene must be, when those parts of 

 a cloud which would otherwise appear sim- 

 ply darker, shine with a fuller blue light or 

 (as the case may be) with a fuller orange 

 light. How gorgeous again must be the col- 

 oring of the clouds which fleck the sky when 

 one or other sun is setting! At such times 

 on our earth we see the most beautiful tints, 

 owing to the various degrees in which the 

 atmosphere affects the light of our single 

 sun; but how wonderful must be the varie- 

 ties of color when, in addition to this cause 

 of varying tints, there is a sun of comple- 

 mentary color illuminating those parts of 

 each cloud which would be simply dark were 

 there no other sun but the orb which is actu- 

 ally setting! PROCTOR Expanse of Heaven, 

 pp. 235-236. (L. G. & Co., 1897.) 



528. COAL-DEPOSITS PROVE MILDER 

 CLIMATE Tree-ferns Now Only Tropical 

 But it is from the more ancient coal-deposits 

 that the most extraordinary evidence has 

 been supplied in proof of the former exist- 

 ence of a very different climate a climate 

 which seems to have been moist, warm, and 

 extremely uniform in those very latitudes 

 which are now the colder, and, in regard to 

 temperature, the most variable, regions of 

 the globe. We learn from the researches of 

 Adolphe Brongniart, Goeppert, and other 

 botanists, that in the flora of the Carbonifer- 

 ous era there was a great predominance of 

 ferns, some of which were arborescent. 

 . . . This prevalence of ferns indicates a 

 moist, equable, and temperate climate, and 

 the absence of any severe cold, for such are 

 the conditions which, at the present day, are 

 found to be most favorable to that tribe of 

 plants. It is only in the islands of the 

 tropical oceans, and of the southern tem- 

 perate zone, such as Norfolk Island, Ota- 

 heite, the Sandwich Islands, Tristan 

 d'Acunha, and New Zealand, that we find 

 any near approach to that remarkable pre- 

 ponderance of ferns which is characteristic 

 of the Carboniferous flora. It has been ob- 

 served that tree-ferns and other forms of 

 vegetation which flourished most luxuri- 

 antly within the tropics extend to a much 



