315 



SCIENTIFIC SIDE-LIGHTS 



Ice-clouds 



supported a wooden bridge on the St. Mau- 

 rice, which falls into the St. Lawrence near 

 the town of Trois Rivieres, lat. 46 20', were 

 thrown down and conveyed by the ice into 

 the main river; and instances have occurred 

 at Montreal of wharfs and stone buildings, 

 from 30 to 50 feet square, having been re- 

 moved in a similar manner. We learn from 

 Captain Bay field that anchors laid down 

 within high-water mark, to secure vessels 

 hauled on shore for the winter, must be 

 cut out of the ice on the approach of spring, 

 or they would be carried away. In 1834 the 

 , " Gulnare's " bower-anchor, weighing half 

 a ton, was transported some yards by the 

 ice, and so firmly was it fixed that the force 

 of the moving ice broke a chain cable suited 

 for a 10-gun brig, and which had rode the 

 " Gulnare " during the heaviest gales in the 

 gulf. Had not this anchor been cut out of 

 the ice it would have been carried into deep 

 water and lost. LYELL Principles of Ge- 

 ology, bk. ii, ch. 15, p. 220. (A., 1854.) 



1536. ICE, TROPICAL ANIMALS EM- 

 BALMED IN Glacial Epoch Came as a Sur- 

 prise. The long summer was over. For 

 ages a tropical climate had prevailed over a 

 great part of the earth, and animals whose 

 home is now beneath the equator roamed 

 over the world from the far south to the 

 very borders of the arctics. The gigantic 

 quadrupeds, the mastodons, elephants, ti- 

 gers, lions, hyenas, bears, whose remains 

 are found in Europe from its southern prom- 

 ontories to the northernmost limits of Sibe- 

 ria and Scandinavia, and in America from 

 the Southern States to Greenland and the 

 Melville Islands, may indeed be said to have 

 possessed the earth in those days. But their 

 reign was over. A sudden intense winter, 

 that w r as also to last for ages, fell upon our 

 globe; it spread over the very countries 

 where these tropical animals had their homes, 

 and so suddenly did it come upon them 

 that they were embalmed beneath masses of 

 snow and ice, without time even for the 

 decay which follows death. AGASSIZ Geo- 

 logical Sketches, ser. i, ch. 8, p. 208. (H. 

 M. & Co., 1896.) 



1537. ICEBERGS, COLORS OF Blue, 



Gray, and White Color Changed by Sudden 

 Revolution Buoyancy Causes Overthrow. 

 In sailing up Muir Inlet or any other arm 

 of the sea on the wild Alaskan shore where 

 tide-water glaciers discharge, one notices 

 that the bergs vary in character, but may be 

 grouped in three quite well-defined classes. 

 Some are of dazzling whiteness; others are 

 of the color of turquoise or beryl; others 

 again are dark with dirt and stones. On 

 watching the ice-cliffs where these children 

 of the glaciers are born, we find that when 

 pinnacles already whitened by exposure to 

 the air fall into the sea, they float away as 

 white bergs. If we watch them drifting over 

 the still water and appearing in the distance 

 like a fleet of gleaming sails, we note that 

 occasionally a white berg suddenly turns 



over with great commotion and joins the 

 fleet having blue for their banner. The rea- 

 son for the change in color is that, previous 

 to turning over, the porous exterior of the 

 submerged portion of the berg was dissolved 

 away so as to expose the compact ice of the 

 interior. The sudden reversion of position 

 is due to unequal melting, which changes 

 the center of gravity of the mass. A cone 

 of ice in which the height is about equal to 

 the diameter of the base with float with its 

 apex down. When a berg approaches a 

 conical form the position of greatest stabil- 

 ity is one in which the side having the 

 larger mass is uppermost. Bergs do not 

 become top-heavy and turn over, as is some- 

 times stated, but become bottom-buoyant 

 and tend to adjust themselves to the me- 

 dium in which they float. RUSSELL Gla- 

 ciers of North America, ch. 6, p. 83. (G. & 

 Co., 1897.) 



1538. The Blue Bergs 



from under Sea Commotion Attends Eman- 

 cipation. Blue bergs are also formed by the 

 breaking away of portions of the submerged 

 ice-foot of tide-water glaciers. These are 

 frequently of large size, and rise from below 

 the surface of the water well in advance of 

 the visible end of the glacier. Their emer- 

 gence is sudden. They bound to the surface, 

 and rising well above it carry tons of water 

 with them. After rocking to and fro for 

 several minutes, as if to be sure of their 

 freedom after centuries of imprisonment, they 

 quiet down and float slowly away as shim- 

 mering islands of the most exquisite blue. 

 RUSSELL Glaciers of North America, ch. 6, 

 p. 84. (G. & Co., 1897.) 



1539. ICE-CLOUDS OF UPPER AIR 



There is another form of cloud that is seen 

 at this season of the year [summer] called 

 cirrus ( a curl ) . It takes the form of a curl 

 at its ends. This cloud usually has a thread- 

 ed shape and sometimes takes the form of 

 a feather, and frequently forms are seen 

 that remind you of frost-pictures on a win- 

 dow-pane. These clouds float very high in 

 the atmosphere, away above the tops of the 

 highest mountains, from six to eight miles 

 above the level of the sea. They are formed 

 only at a season of the year when the at- 

 mospheric conditions are most uniform. At 

 certain times of the day and night the 

 moisture will rise to this height before it 

 condenses, and when it does condense it im- 

 mediately freezes, which makes it take on 

 these peculiar forms that would no doubt 

 conform very closely to the frost-pictures 

 on the window-pane if it were not for the 

 disturbing influences of air currents at this 

 altitude. The fact that they are ice- or 

 frost-clouds instead of water-clouds gives 

 them that peculiar whiteness and brightness 

 of appearance. If ordinary clouds are water- 

 dust, these high clouds may be called ice- 

 dust. Sometimes we see them lying in 

 bands or threads running across the sky in 

 the direction that the wind blows. Their 



