Microscope 

 Mimicry 



SCIENTIFIC SIDE-LIGHTS 



444 



nently. Disease-germs and countless other 

 lower forms of life have been traced out in 

 their development and tracked to their 

 origin. Living things, whose dimensions are 

 to be estimated by the thousandth parts of 

 inches, are as well known to us to-day as is 

 the ostrich or the elephant. So far from the 

 " little things " of the universe escaping our 

 attention, I should be inclined to maintain 

 that they largely monopolize science, to the 

 exclusion of the big things. We are begin- 

 ning to find out, in fact, that only by know- 

 ing something of the actions which proceed 

 in the lower byways of life can existence in 

 the main be understood at all. ANDREW 

 WILSON Glimpses of Nature, ch. 25, p. 80. 

 (Hum., 1892.) 



2173. MIGRATION, IRRATIONAL 



Blind Instinct of Progression of Lemmings. 

 - The lemming of Norway is a sort of vole, 

 very celebrated on account of its sudden 

 and marvelous migrations. WTien a con- 

 juncture of favorable circumstances en- 

 ables them to multiply to an enormous ex- 

 tent a migratory instinct becomes developed 

 in them, whereby they are led to descend 

 to lower-lying lands than those they nor- 

 mally frequent. They migrate slowly and 

 intermittently, journeying only by night, 

 and increasing frequently as they go. Their 

 journey may last for three years before 

 they reach the seacoast, according to the 

 route they may happen to have followed. 

 When they reach the coast they go on into 

 the sea and so perish. As they journey along 

 they are preyed upon by bears, wolves, foxes, 

 dogs, wildcats, weasels, eagles, hawks, and 

 owls. They are also destroyed by man, and 

 even domestic animals, such as goats and 

 reindeer, will spring upon and kill them. 

 Numbers also die of disease, but they never 

 turn back they proceed ever onwards to 

 their ultimate destination. MIVART Types 

 of Animal Life, ch. 12, p. 356. (L. B. & 

 Co., 1893.) 



2174. MIGRATION OF BIRDS, EX- 

 TENT OF Subsistence an Important Factor 

 Change of Diet of Non-migratory Birds. 

 The extent of a bird's migration is, in most 

 cases, dependent upon the nature of its 

 food. Birds that are resident in one place 

 throughout the year generally change their 

 fare with the season, and apparently feed 

 with equal relish on seeds or insects. Those 

 that are dependent upon fruit must migrate 

 far enough to find a supply of berries, while 

 the insect-eaters are obliged to travel even 

 farther south. Most of the migratory birds 

 of our Western States pass the winter in 

 Mexico. Our Eastern sparrows and our 

 berry-eaters, like the robin and bluebird, 

 winter from the Middle States to the Gulf 

 coast, while the majority of our purely in- 

 sectivorous species cross to Cuba and win- 

 ter in the West Indies, or continue to Cen-' 

 tral America and even northern South 

 America. Snipe and plover make the most 

 extended migrations, some species breeding 



within the arctic circle and wintering along 

 the coasts of Patagonia. CHAPMAN Bird- 

 Life, ch. 4, p. 49. (A., 1900.) 



2175. MIGRATION OF PLANTS 



The Struggle for Life Lessened Cross-fer- 

 tilization Secured. The various devices by 

 which plants are shifted from place to place 

 are not merely to extend and multiply the 

 species and reach a fertile soil, but to enable 

 them to flee from the great number of their 

 own kind and from their enemies among 

 animals and parasitic plants. The adven- 

 turers among plants often meet with the 

 best success, not because the seeds are larger, 

 or stronger, or better, but because they find, 

 for a time, more congenial surroundings. 

 We must not overlook the fact, so well es- 

 tablished, that one of the greatest points 

 to be gained by plant migration is to enable 

 different stocks of a species to be cross-fer- 

 tilized, and thereby improved in vigor and 

 productiveness. BEAL Seed Dispersal, ch. 9, 

 p. 85. (G. & Co., 1898.) 



2176. MILDNESS OF THE EURO- 

 PEAN CLIMATE Heated Air from Tropits 

 Descending. Gradually, however, as the up- 

 per stream, which rises from the equator 

 and flows towards the poles, becomes chilled 

 and dense, it sinks towards the earth; at 

 the Peak of Teneriffe it has already sunk 

 below the summit of the mountain. With 

 the contrary wind blowing at the base, the 

 traveler often finds the wind from the equa- 

 tor blowing strongly over the top. Farther 

 north the equatorial wind sinks lower 

 still, and finally reaches the surface of the 

 earth. Europe, for the most part, is over- 

 flowed by this equatorial current. Here, in 

 London, for eight or nine months in the 

 year, southwesterly winds prevail. But 

 mark what an influence this must have 

 upon our climate. The moisture of the 

 equatorial ocean comes to us endowed with 

 potential energy; it comes, if you prefer 

 the language, charged with latent heat. In 

 our atmosphere condensation takes place, 

 and the heat liberated is a main source of 

 warmth to our climate. Were it not for 

 the rotation of the earth we should have 

 over us the hot, dry blasts of Africa; but, 

 owing to this rotation, the w r ind which starts 

 northward from the Gulf of Mexico is de- 

 flected to Europe. Europe is, therefore, the 

 recipient of those stores of latent heat which 

 were amassed in the western Atlantic. The 

 British Isles come in for the greatest share 

 of this moisture and heat, and this circum- 

 stance adds itself to that already dwelt 

 upon the high specific heat of water to 

 preserve our climate from extremes. TYN- 

 DALL Heat a Mode of Motion, lect. 8, p. 212. 

 (A., 1900.) 



2177. MILK NORMALLY STERILE 

 Can Be So Drawn Yet Commonly In- 

 fested with Bacteria Cleanliness the First 

 Great Need. There are few liquids in gen- 

 eral use which contain such enormous num- 

 bers of germs as milk. To begin with, milk 



