193 



SCIENTIFIC SIDE-LIGHTS 



rthquake 



rounding the solid nucleus. One strange 

 fact of terrestrial magnetism may be men- 

 tioned in partial confirmation of the theory 

 that the interior of the earth is of this na- 

 ture a great solid mass, separated from the 

 solid crust by a viscous plastic ocean: the 

 magnetic poles of the earth are changing in 

 position in a manner which seems only ex- 

 plicable on the supposition that there is an 

 interior solid globe rotating under the outer 

 shell, but at a slightly different rate, gain- 

 ing or losing one complete rotation in the 

 course of about 650 years. PROCTOR Our 

 Place among Infinities, p. 17. (L. G. & Co., 

 1897.) 



948. EARTH-CRUST, CHANGES IN, 

 CEASELESS However constant may be the 

 relative proportion of sea and land, we know 

 that there is annually some small variation 

 in their respective geographical positions, 

 and that in every century the land is in some 

 parts raised, and in others depressed in 

 level, and so likewise is the bed of the sea. 

 By these and other ceaseless changes, the 

 configuration of the earth's surface has been 

 remodeled again and again, since it was the 

 habitation of organic beings, and the bed of 

 the ocean has been lifted up to the height of 

 some of the loftiest mountains. LYELL 

 Principles of Geology, bk. i, ch. 7, p. 102. 

 (A., 1851-.) 



949. 



Not Alarming Rela- 



tive Insignificance of Mountain Height. 

 The imagination is apt to take alarm when 

 called upon to admit the formation of such 

 irregularities in the crust of the earth, after 

 it had once become the habitation of living 

 creatures; but, if time be allowed, the op- 

 eration need not subvert the ordinary repose 

 of Nature; and the result is in a general 

 view insignificant, if we consider how 

 slightly the highest mountain chains cause 

 our globe to differ from a perfect sphere. 

 Chimborazo, tho it rises to more than 21,000 

 feet above the sea, would be represented, on 

 a globe of about six feet in diameter, by a 

 grain of sand less than one-twentieth of an 

 inch in thickness. 



The superficial inequalities of the earth, 

 then, may be deemed minute in quantity, 

 and their distribution at any particular 

 epoch must be regarded in geology as tem- 

 porary peculiarities, like the height and out- 

 line of the cone of Vesuvius in the interval 

 between two eruptions. But altho, in refer- 

 ence to the magnitude of the globe, the un- 

 evenness of the surface is so unimportant, 

 it is on the position and direction of these 

 small inequalities that the state of the at- 

 mosphere, and both the local and general cli- 

 mate, are mainly dependent. LYELL Prin- 

 ciples of Geology, bk. i, ch. 7, p. 102. (A., 

 1854.) 



95O. EARTH-CRUST UNDERMINED 



Caverns Subterranean Rivers. In coun- 

 tries where calcareous rocks largely pre- 

 dominate, acidulated water filtering down 

 from the surface through fissures and other 



division-planes has often licked out a com- 

 plicated series of tortuous tunnels and gal- 

 leries. So far has this process been carried 

 on in some regions that the whole rainfall 

 finds its way into subterranean courses, and 

 the entire drainage of the land is conducted 

 underground. The dimensions attained by 

 many well-known limestone caverns, and the 

 great width and depth of the channels 

 through which subterranean rivers reach the 

 sea, help us to appreciate the amount of 

 rock-material which underground water is 

 capable of removing. From the surface of 

 certain regions hundreds of feet of various 

 calcareous rocks have thus been gradually 

 removed; while in other cases the contour 

 of the ground has been notably affected by 

 the collapse of underground channels and 

 chambers. GEIKIE Earth Sculpture, ch. 2, 

 p. 31. (G. P. P., 1898.) 



95 1 . EARTH-LIGHT ON THE MOON 



The "Ashy Light" Earth Sees Herself 

 in the Mirror of the Moon. When the moon 

 is a crescent, during the first days of the 

 lunation, we notice that the rest of the lunar 

 globe is visible, illuminated by a pale light. 

 This is the lumiere cendree [the ashy light] . 

 It is caused by the earth itself. 



In fact, the earth is illuminated by the 

 sun, and reflects the light into space. When 

 the moon is in conjunction with the sun the 

 earth is in " opposition," as seen from the 

 moon; it is the epoch of full earth for an 

 observer on our satellite. The light which 

 our globe then sends to the moon exceeds 

 about fourteen times that which the full 

 moon sends to us. This ashy light, reflection 

 of a reflection, resembles a mirror in which 

 we may see the luminous state of the earth. 

 In winter, when a great part of the terres- 

 trial hemisphere is covered with snow, it is 

 perceptibly brighter. Before the geographic- 

 al discovery of Australia, astronomers sus- 

 pected the existence of that continent from 

 the ashy light, which was very much 

 brighter than could be produced by the dark 

 reflection from the ocean. This lunar light 

 generally presents a greenish-blue tint, indi- 

 cating that our planet, seen from a distance, 

 would show this shade. FLAMMARION Popu- 

 lar Astronomy, bk. ii, ch. 2, p. 99. (A.) 



952. EARTHQUAKE CHANGING 

 LEVEL OF GROUND Houses and Persons 

 Engulfed in Fissures. The soil of the Cala- 

 brian plains was found to be in some parts 

 abnormally raised, in others as strangely de- 

 pressed. " In the town of Terranova," says 

 Sir Charles Lyell, " some houses were seen 

 uplifted above the common level, and others 

 adjoining sunk down into the earth. In sev- 

 eral streets the soil appeared thrust up, and 

 abutted against the walls of houses ; a large 

 circular tower of solid masonry, part of 

 which withstood the general destruction, 

 was divided by a circular rent, and one side 

 was upraised, and the foundations heaved 

 out of the ground." As might be expected, 

 the soil did not continue unbroken by the 



