593 



SCIENTIFIC SIDE-LIGHTS 



KSf 



rise from the plains of Hindustan, and still 

 more remarkable is the quantity sometimes 

 poured down in one day. The sea, where 

 the Ganges and Brahmaputra discharge 

 their main stream at the flood season, only 

 recovers its transparency at the distance of 

 from 60 to 100 miles from the delta; and 

 we may take for granted that the current 

 continues to transport the finer particles 

 much farther south than where the sur- 

 face-water first becomes clear. LYELL Prin- 

 ciples of Geology, ch. 18, p. 278. (A., 1854.) 



2930. RIVERS USE ROCK-DEBRIS 

 TO CUT DOWN OTHER ROCKS Rivers 

 are much more than mere transporters of 

 sediment. Just as in desert lands wind 

 employs disintegrated rock material as a 

 sand-blast, so rivers use their stones, grit, 

 and sand as tools with which to rasp, file, 

 and undermine the rocks over which they 

 flow. In this way their channels are gradu- 

 ally deepened and widened. GEIKIE Earth 

 Sculpture, ch. 2, p. 34. (G. P. P., 1898.) 



2931. ROBBER-BARON OF THE 



AIR Eagle and Fish-hawk. What an inspir- 

 ing sight it is to see one [an osprey, or fish- 

 hawk] plunge from the air upon its prey! 

 One can sometimes hear the splash half a 

 mile or more, and the bird is quite concealed 

 by the spray. It is a magnificent perform- 

 ance, and when, after shaking the water 

 from his plumage, he rises into the air, I 

 am always tempted to applaud. 



The osprey, or fish-hawk, as he is also 

 called, adheres closely to a finny diet; 

 neither flesh nor fowl appears on his menu, 

 and he is consequently a migratory bird, 

 coming in April when the ice is melted, and 

 remaining until October. In favorable lo- 

 calities he nests in colonies, returning year 

 after year to the same nest. 



One master, it is true, the osprey has, 

 tho he makes a most unwilling servant. 

 The bald-headed eagle is often an appreci- 

 ative observer of the osprey's piscatorial 

 powers, which so far exceed his own that 

 he wisely, if unjustly, profits by them. 

 Pursuing the osprey, he forces him to 

 mount higher and higher until the poor bird 

 in despair drops his prize, which the eagle 

 captures as it falls. CHAPMAN Bird-Life, 

 ch. 7, p. 122. (A., 1900.) 



2932. Swiftness and Dex- 

 terity of the White-headed Eagle. The 

 white-headed eagle has also developed the 

 plundering instinct in great perfection, as 

 is shown by the following graphic account 

 of Audubon : " During spring and summer 

 the white-headed eagle, to procure suste- 

 nance, follows a different course, and one 

 much less suited to a bird apparently so 

 well able to supply itself without inter- 

 fering with other plunderers. No sooner 

 does the first hawk make its appearance 

 along the Atlantic shore or around the 

 numerous and large rivers, than the eagle 

 follows it, and, like a selfish oppressor, robs 



it of the hard-earned fruits of its labor. 

 Perched on some tall summit, in view of 

 the ocean or of some watercourse, he 

 watches every motion of the osprey while 

 on the wing. When the latter rises from 

 the water, with a fish in its grasp, forth 

 rushes the eagle in pursuit. He mounts 

 above the fish-hawk, and threatens it by 

 actions well understood; when the latter, 

 fearing perhaps that its life is in danger, 

 drops its prey. In an instant the eagle, 

 accurately estimating the rapid descent of 

 the fish, closes its wings, follows it with 

 the swiftness of thought, and the next mo- 

 ment grasps it. The prize is carried off in 

 silence to the woods, and assists in feeding 

 the ever-hungry brood of the eagle." RO- 

 MANES Animal Intelligence, ch. 10, p. 284. 

 (A., 1899.) 



2933. ROCK A SURE FOUNDATION 



Earthquake Resisted by. It would seem 

 the harder rocks form better foundations 

 than the softer ones. One explanation of 

 this appears to lie in the fact that soft 

 strata may be in a state of unstable equi- 

 librium, and, by shaking, it is caused to 

 settle. Another explanation is that in 

 hard ground or rock, altho the motion is 

 more rapid than on soft ground, this is 

 more than compensated for by the small- 

 ness of the range of motion in the former 

 foundation. MILNE Earthquake, ch. 7, p. 

 131. (A., 1899.) 



2934. ROCKS ROUNDED BY WAVES 

 OF ANCIENT SEA We raised another 

 block in a different part of the quarry, and 

 found that the area of a circular depression 

 in the stratum below was broken and flawed 

 in every direction, as if it had been the bot- 

 tom of a pool recently dried up, which had 

 shrunk and split in the hardening. Several 

 large stones came rolling down from the 

 diluvium in the course of the afternoon. 

 They were of different qualities from the 

 sandstone below and from one another; 

 and, what was more wonderful still, they 

 were all rounded and water-worn, as if they 

 had been tossed about in the sea, or the bed 

 of a river, for hundreds of years. There 

 could not, surely, be a more conclusive 

 proof that the" bank which had enclosed 

 them so long could not have been created 

 on the rock on which it rested. No work- 

 man ever manufactures a half-worn article, 

 and the stones were all half- worn! And if 

 not the bank, why then the sandstone un- 

 derneath? MILLER The Old Red Sandstone, 

 ch. 1, p. 7. (G. & L., 1851.) 



2935. ROCKS, THICKNESS OF, ON 

 OCEAN FLOOR Check of Radiant Heat 

 Causes Outburst of Volcano Repression 

 Prepares for Outbreak. If the reader has 

 any difficulty in conceiving the effects of 

 overlaid beds in bringing about a high tem- 

 perature in strata, he may help himself by 

 a homely comparison. Let him imagine a 

 vessel containing hot water exposed to the 



