Extremes 

 Fact 



SCIENTIFIC SIDE-LIGHTS 



240 



1 1 7 O . EXTREMES MEETING Ice Pre- 

 served under Molten Rock. A thick lava- 

 stream must take an enormous period to 

 cool down probably many hundreds or even 

 thousands of years. It is possible to walk 

 over lava-streams in which at a few inches 

 below the surface the rock is still red-hot, 

 so that a piece of stick is lighted if thrust 

 into a crack. Lava is a very bad conductor 

 of heat, and loose scoriae and dust are still 

 worse conductors. During the eruption of 

 Vesuvius in 1872, masses of snow which 

 were covered with a thick layer of scoriae, 

 and afterwards by a stream of lava, were 

 found three years afterwards consolidated 

 into ice, but not melted. The city of Ca- 

 tania is constantly supplied with ice from 

 masses of snow which have been buried 

 under the ejections of Etna. JUDD Vol- 

 canoes, ch. 4, p. 110. (A., 1899.) 



1171. EXTREMES OF TEMPERA- 

 TURE IN AMERICA In China "Insular 

 Climates" vs. "Excessive Climates." In 

 consequence of the more equal temperature 

 of the waters of the ocean, the climate of is- 

 lands and of coasts differs essentially from 

 that of the interior of continents, the more 

 maritime climate being characterized by 

 mild winters and more temperate summers ; 

 for the sea-breezes moderate the cold of win- 

 ter as well as the heat of summer. When, 

 therefore, we trace round the globe those 

 belts in which the mean annual temperature 

 is the same, we often find great differences 

 in climate; for there are insular climates 

 in which the seasons are nearly equalized, 

 and excessive climates, as they have been 

 termed, where the temperature of winter 

 and summer is strongly contrasted. The 

 whole of Europe, compared with the eastern 

 parts of America and Asia, has an insular 

 climate. The northern part of China, and 

 the Atlantic region of the United States, 

 exhibit " excessive climates." We find at 

 New York, says Humboldt, the summer of 

 Rome and the winter of Copenhagen; at 

 Quebec, the summer of Paris and the winter 

 of Petersburg. At Peking, in China, where 

 the mean temperature of the year is that 

 of the coasts of Brittany, the scorching 

 heats of summer are greater than at Cairo, 

 and the winters as rigorous as at Upsala. 

 LYELL Principles of Geology, bk. i, ch. 7, 

 p. 94. (A., 1854.) 



1172. EXTREMES, OPPOSITE, HAVE 

 SIMILAR EFFECTS Drought Produces Tor- 

 por Like Cold Crocodile Boa-constrict- 

 or. Gradually, too, the pools of water, 

 which had been protected from evaporation 

 by the now seared foliage of the fan-palm, 

 disappear. As in the icy North, animals 

 become torpid from cold, so here the croco- 

 dile and the boa-constrictor lie wrapped in 

 unbroken sleep, deeply buried in the dried 

 soil. Everywhere the drought announces 

 death, yet everywhere the thirsting wan- 

 derer is deluded by the phantom of a mov- 

 ing, undulating, watery surface, created by 



the deceptive play of the reflected rays of 

 light ( the mirage ) . A narrow stratum sep- 

 arates the ground from the distant palm- 

 trees, which seem to hover aloft, owing to 

 the contact of currents of air having differ- 

 ent degrees of heat and therefore of den- 

 sity. Shrouded in dark clouds of dust, and 

 tortured by hunger and burning thirst, oxen 

 and horses scour the plain, the one bellow- 

 ing dismally, the other with outstretched 

 necks snuffing the wind, in the endeavor 

 to detect, by the moisture in the air, the 

 vicinity of some pool of water not yet 

 wholly evaporated. HUMBOLDT Views of 

 Nature, p. 14. (Bell, 1896.) 



1173. Thirst in Arctic 



Snow-fields, as in Sahara. Their [the Es- 

 kimos'] drink consists of blood or water: 

 during the greater part of the year they 

 have considerable difficulty in obtaining 

 sufficient water to satisfy their thirst, and 

 it is much too precious to be used for wash- 

 ing. It may seem surprising that people 

 who are surrounded by snow and ice should 

 suffer from want of water, but the amount 

 of heat required to melt snow is so great 

 that a man without the means of obtaining 

 fire might die of thirst in these arctic re- 

 gions as easily as in the sandy deserts of 

 Africa. Any direct " resort to snow," says 

 Kane, " for the purpose of allaying thirst, 

 was followed by bloody lips and tongue; 

 it burnt like caustic." When the Eski- 

 mos visited Captain Parry, they were al- 

 ways anxious for water, which they drank 

 in such quantities " that it was impossible 

 to furnish them with half as much as they 

 desired." AVEBURY Prehistoric Times, ch. 

 14, p. 476. (A., 1900.) 



1174. EYE, IMPERFECT ACHROMA- 

 TISM OF Eyes Differ in Perception of Color. 

 The low dispersive power of water masks, 

 as Helmholtz has remarked, the imperfect 

 achromatism of the eye. With the naked 

 eye I can see a distant blue disk sharply de- 

 fined, but not a red one. I can also see the 

 lines which mark the upper and lower bound- 

 aries of a horizontally refracted spectrum 

 sharp at the blue end, but ill-defined at the 

 red end. Projecting a luminous disk upon a 

 screen, and covering one semicircle of the 

 aperture with a red and the other with a 

 blue or green glass, the difference between 

 the apparent sizes of the two semicircles is 

 in my case, and in numerous other cases, ex- 

 traordinary. Many persons, however, see 

 the apparent sizes of the two semicircles re- 

 versed. If with a spectacle-glass I correct 

 the dispersion of the red light over the 

 retina, then the blue ceases to give a 

 sharply defined image. Thus examined the 

 departure of the eye from achromatism ap- 

 pears very gross indeed. TYNDALL Lectures 

 on Light, lect. 1, p. 30. (A., 1898.) 



1175. EYES OF DEEP-SEA ANIMALS 



Can Sunlight Reach Them? Within the 

 last few years a few authors have main- 

 tained that it is quite possible that a few 



