lee-clouds 

 Identification 



SCIENTIFIC SIDE-LIGHTS 



316 



form is undoubtedly a resultant of the 

 struggle between the air currents and the 

 tendency of crystallized water to arrange 

 itself in certain definite lines or forms. 

 ELISHA GRAY Nature's Miracles, vol. i, ch. 

 9, p. 73. (F. H. & H., 1900.) 



1540. ICE-CRYSTALS SHOWN IN 

 SOLID BLOCK Revealing Power of Light- 

 Hidden Structure Made Manifest. There is 

 a way of showing the regularity in the 

 structure of ice, a very simple and in- 

 genious method devised by Professor Tyn- 

 dall. His plan is this: he takes a slab of 

 ice and causes a ray of light to pass through 

 it at right angles to the surface of freezing, 

 and then fall on a white screen behind. 

 Now this ray of light is accompanied by 

 heat, and the heat serves partially to melt 

 the ice through which it passes; but it does 

 not melt a hole right through the ice; it melts 

 a particle here and a particle there, and 

 in doing so reveals the structure that was 

 previously undiscernable. By melting a par- 

 ticle here and there the transparency of the 

 ice is interrupted, and the screen now re- 

 veals a number of figures known as ice- 

 flowers, each of which has a bright spot in 

 the center, and, like a snow-crystal, has six 

 rays, inclined to one another at precisely 

 the same angle, and variously adorned with 

 symmetrical outgrowths. CHISHOLM Na- 

 ture-Studies, p. 27. (Hum., 1888.) 



1541. ICE-HOUSE, A NATURAL Fro- 

 zen Drifts Buried for Ages Siberian Mam- 

 moths. If it be true that the carcass of 

 the mammoth was embedded in pure ice, 

 there are two ways in which it may have 

 been frozen in. We may suppose the ani- 

 mal to have been overwhelmed by drift- 

 snow. I have been informed by Dr. Rich- 

 ardson that in the northern parts of Amer- 

 ica, comprising regions now inhabited by 

 many herbivorous quadrupeds, the drift- 

 snow is often converted into permanent 

 glaciers. It is commonly blown over the 

 edges of steep cliffs, so as to form an in- 

 clined talus hundreds of feet high; and 

 when a thaw commences, torrents rush from 

 the land and throw down from the top of 

 the cliff alluvial soil and gravel. This new 

 soil soon becomes covered with vegetation, 

 and protects the foundation of snow from 

 the rays of the sun. Water occasionally 

 penetrates into the crevices and pores of 

 the snow; but, as it soon freezes again, it 

 serves the more rapidly to consolidate the 

 mass into a compact iceberg. It may some- 

 times happen that cattle grazing in a val- 

 ley at the base of such cliffs, on the borders 

 of a sea or river, may be overwhelmed and 

 at length enclosed in solid ice, and then 

 transported towards the polar regions. 

 LYELL Principles of Geology, bk. i, ch. 6, p. 

 85. (A., 1854.) 



1542. ICE-SHEET OVER NORTHERN 

 ITALY The Glacial Epoch. The glaciers on 

 the southern sides of the Alps were hardly 

 less extensive than on the northern. They 



descended the valleys, they passed over the 

 sites of the Italian lakes and on to the 

 plains of Piedmont and Lombardy. Round 

 one group of moraines the tide of battle 

 ebbed and flowed in the struggle of Sol- 

 ferino. BONNEY Ice-work, Present and Past, 

 pt. i, ch. 1, p. 35. (A., 1896.) 



1543. ICE-STORMS IN FORESTS 



Melting Snow Congealed on Trees Blocks 

 of Ice Hurled Down. Snow may act de- 

 structively ... by giving rise to what 

 are known as ice-storms in forests. When 

 snow falls in forests, and especially in for- 

 ests of coniferous trees, such as are most 

 abundant in those regions where snow falls 

 most plentifully, the branches of these ever- 

 greens become laden with a 'heavy weight of 

 snow, which they may bear until the snow 

 has been converted by partial melting and 

 subsequent refreezing into solid lumps of 

 ice. These present a still greater surface 

 for the reception of fresh snow, which may 

 be converted into ice in its turn. Some- 

 times these accumulations attain such a 

 weight that the branches can no longer sup- 

 port them. The topmost, weakest branches 

 give way and fall down with the lumps of 

 ice that they carry. These, acquiring im- 

 petus as they fall, strike against the lower 

 branches and break them off. Thus the 

 process of destruction is accelerated. The 

 agitation is communicated to the contigu- 

 ous trees, and from these to others, and thus 

 in a brief space of time large areas in a 

 forest may be in great part destroyed. 

 CHISHOLM 'Nature- Studies, p. 32. (Hum., 

 1888.) 



1544. IDEA BEHIND PHENOMENA 



The First Law of Motion Not One In- 

 stance of Its Operation Ever Known Re- 

 vealed to Scientific Faith Only. The law is 

 that all motion is in itself (that is to say, 

 except as affected by extraneous forces) uni- 

 form in velocity and rectilinear in direc- 

 tion. Thus according to this law a body 

 moving, and not subject to any extraneous 

 force, would go on moving forever at the 

 same rate of velocity, and in an exactly 

 straight line. 



Now, there is no such motion as this ex- 

 isting on the earth or in the heavens. It is 

 an abstract idea of motion which no man 

 has ever or can ever see exemplified. Yet 

 a clear apprehension of this abstract idea 

 was necessary to a right understanding and 

 to the true explanation of all the motions 

 which are actually seen. It was long before 

 this idea was arrived at. There was a real 

 difficulty in conceiving it, because not only 

 is there no such motion in Nature, but there 

 is no possibility by artificial means of pro- 

 ducing it. It is impossible to release any 

 moving body from the impulses of extra- 

 neous force. The first law of motion is 

 therefore a purely abstract idea. It repre- 

 sents a rule which never operates as we con- 

 ceive it in itself, but is always complicated 

 with other rules which produce a corre- 



