'Contraction 

 Contrivance 



SCIENTIFIC SIDE-LIGHTS 



128 



have acquired a store of heat not only of 

 considerable, but even of colossal, magni- 

 tude. HELMHOLTZ Popular Lectures, lect. 

 4, p. 181. (L. G. &Co., 1898.) 



633. 



This Involves Final 



Extinction. In the very act of parting with 

 heat, the sun develops a fresh stock. His 

 radiations, in short, are the direct result of 

 ^shrinkage through cooling. A diminution of 

 the solar diameter by 380 feet yearly would 

 just suffice to cover the present rate of emis- 

 sion, and would for ages remain impercep- 

 tible with our means of observation, since, 

 after the lapse of 6,000 years, the lessening 

 of angular size would scarcely amount to 

 one second. But the process, tho not ter- 

 minated, is strictly a terminable one. In 

 less than five million years the sun will have 

 contracted to half its present bulk. In seven 

 million more, it will be as dense as the earth. 

 It is difficult to believe that it will then be a 

 luminous body. Nor can an unlimited past 

 duration be admitted. Helmholtz considered 

 that radiation might have gone on with its 

 actual intensity for twenty-two, Langley al- 

 lows only eighteen, million years. The period 

 can scarcely be stretched, by the most gen- 

 erous allowances, to double the latter figure. 

 But this is far from meeting the demands of 

 geologists and biologists. CLERKE History 

 of Astronomy, pt. ii, ch. 9, p. 379. (Bl., 

 1893.) 



634. CONTRADICTION, SEEMING, IN 

 REFLECTION OF LIGHT White Light May 

 Come from a Black Object. The light which 

 falls upon a body is divided into two por- 

 tions, one of which is reflected from the sur- 

 face of the body; and this is of the same 

 color as the incident light. If the incident 

 light be white the superficially reflected 

 light will also be white. Solar light, for ex- 

 ample, reflected from the surface of even a 

 black body, is white. The blackest cam- 

 phine smoke in a dark room through which 

 a sunbeam passes from an aperture in the 

 window-shutter renders the track of the 

 beam white, by the light scattered from the 

 surfaces of the soot-particles. The moon ap- 

 pears to us as if 



" Clothed in white samite, mystic, wonder- 

 ful"; 



but were she covered with the blackest vel- 

 vet she would still hang in the heavens as 

 a white orb, shining upon our world sub- 

 tantially as she does now. TYNDALL Lec- 

 tures on Light, lect. 1, p. 33. (A., 1898.) 



635. CONTRAST, IMPRESSIVE For- 

 est and Steppe. From the rich luxuriance 

 of organic life the astonished traveler [to 

 the steppes of South America] suddenly 

 finds himself on the dreary margin of a tree- 

 less waste. Nor hill nor cliff rears its head, 

 like an island in the ocean, above the bound- 

 less plain : only here and there broken strata 

 of floetz, extending over a surface of more 

 than three thousand English square miles, 



appear sensibly higher than the surrounding 

 district. The natives term them banks, as 

 if the spirit of language would convey some 

 record of that ancient condition of the 

 world when these elevations formed the 

 shoals, and the steppes themselves the bot- 

 tom, of some vast inland sea. HUMBOLDT 

 Views of Nature, p. 1. (Bell, 1896.) 



636. CONTRAST OF GIVING AND 

 WITHHOLDING Mountain Lake with Flow- 

 ing Stream Bitter Waters with No Outlet. 

 The waters of Lake Tahoe overflow 

 through the Truckee caiion and form a 

 bright, swift-flowing stream, which finds its 

 way to Pyramid and Winnemucca lakes, 

 situated 2,400 feet lower, in the desert val- 

 leys to the north. The waters when starting 

 on their troubled journey are as pure and 

 limpid as the melting snows of mountain 

 valleys can furnish, . . . but the lakes 

 into which they flow, and of which they form 

 almost the sole supply, are alkaline and 

 saline owing to long concentration. An ex- 

 ample of an isolated drainage system is here 

 furnished, embracing the cool summits of 

 lofty mountains where the moisture of the 

 atmosphere is condensed; a mountain reser- 

 voir where the waters are stored; a swift, 

 clear stream formed by the overflow of the 

 reservoir; and the bitter lakes where the 

 stream empties and from which there is no 

 escape except by evaporation. RUSSELL 

 Lakes of North America, ch. 4, p. 64. ( G. & 

 Co., 1895.) 



637. CONTRAST OF HEAT AND COLD 

 IN SOUTH AFRICA Solar Radiation 

 Wide Difference between Sunrise and Mid- 

 day. Dr. Livingstone, in his " Travels in 

 South Africa," has given some striking ex- 

 amples of the difference in nocturnal chill- 

 ing when the air is dry and when it is laden 

 with moisture. Thus he finds in South Cen- 

 tral Africa during the month of June, " the 

 thermometer early in the mornings at from 

 42 to 52; at noon, 94 to 96," or a mean 

 difference of 48 between sunrise and mid- 

 day. The range would probably have been 

 found still greater had not the thermometer 

 been placed in the shade of his tent, which 

 was pitched under the thickest tree he could 

 find. He adds, moreover, " the sensation of 

 cold after the heat of the day was very keen. 

 The Balonda at this season never leave their 

 fires till nine or ten in the morning. As 

 the cold was so great here, it was probably 

 frosty at Linyanti ; I therefore feared to ex- 

 pose my young trees there." TYNDALL Heat 

 a Mode of Motion, lect. 13, p. 387. (A., 

 1900.) 



638. CONTRAST OF REFLECTED 

 AND TRANSMITTED LIGHT Sunrise on 

 Mt. Blanc. The sunrise from the summit 

 [of Mt. Blanc] was singularly magnificent. 

 The snow on the shaded flanks of the moun- 

 tain was of a pure blue, being illuminated 

 solely by the reflected light of the sky; the 

 summit of the mountain, on the contrary, 



