181 



SCIENTIFIC SIDE-LIGHTS 



Distinction 

 Division 



set of plants from its adjacent valley, hill- 

 side, or hedgerow if not always different in 

 the actual species, yet very different in com- 

 parative abundance, some which are rare in 

 the one being common in the other. WAL- 

 LACE Darwinism, ch. 2, p. 12. (Hum., 1889.) 



884. DISTRIBUTION OF SEEDS 



The Milkweed. Every one who has wan- 

 dered along a country road has noticed the 

 peculiar seed-pods of the common milkweed. 

 . . . As the pods open there is revealed 

 a large number of flattened brown seeds. 

 . . . Each seed bears on its smaller end 

 a tuft of silken hairs. When the pod first 

 opens these hairs lie straight and flat, the 

 ends of the hairs being caught in the folds 

 of the membranous partition which runs 

 through the center of the pod. 



On exposure to the air the folds relax 

 their hold upon the hairs, which thus be- 

 come free at their upper ends. Then each 

 hair curls over toward the other end of the 

 seed, until at last nearly all the hairs on the 

 upper seeds are thus curled over, forming a 

 beautiful crown almost as light as air. 

 When a strong wind blows, the seeds are 

 picked up by means of these hairs and car- 

 ried away to be dropped beside some fence 

 or tree or bush. By the beautiful device of 

 this feathery crown the milkweed provides 

 for the scattering of its seeds. It seems a 

 simple process, but as you think it over you 

 see that it is a very admirable one. WEED 

 Seed-travellers, pt. i, p. 1. (G. & Co., 1899.) 



885. DISTRIBUTION OF STARS UN- 

 EQUAL Rich and Poor Celestial Regions 

 Magellanic Clouds Aggregations of Light 

 and Power. In working, then, by the meth- 

 od of charting I began (for I may as well 

 note that I have been practically alone in 

 this work) by charting the stars that we 

 can see, according to a plan by which the 

 laws of distribution should be clearly recog- 

 nized; for the charts I drew were so con- 

 trived that equal spaces on the celestial 

 sphere should be represented by equal spaces 

 in the chart. It quickly became clear that 

 the stars are not scattered at all uniformly 

 over the heavens. There are rich and poor 

 regions; and these are so arranged that 

 while the whole of the galactic region is ex- 

 ceedingly rich in naked-eye stars, two oppo- 

 site rich regions, one in the northern and 

 the other in the southern heavens, are sepa- 

 rated from each other (except where the 

 Milky Way on opposite sides passes from 

 one to the other) by singularly barren re- 

 gions. It appears a noteworthy circum- 

 stance that near the center of the great 

 southern rich region are found those two 

 wonderful objects called the Magellanic 

 clouds, vast globe-shaped conglomerations 

 (scarcely any other word seems so suitable) 

 in which are contained not only myriads of 

 stars of all orders of magnitude after the 

 seventh, but also every kind of star cloudlet. 

 PROCTOR Expanse of Heaven, p. 268. (L. 

 G. & Co., 1897.) 



886. DIVING-BELL, THE FIRST 



Home of the Water-spider Transporting 

 and Storing Air. The water-spider (Argyro- 

 neta aquatica), as is well known, displays 

 the curious instinct of building her nest be- 

 low the surface of water, and constructing 

 it on the principle of a diving-bell. The ani- 

 mal usually selects still waters for this pur- 

 pose, and makes her nest in the form of an 

 oval hollow,, lined with web, and held secure 

 by a number of threads passing in various 

 directions and fastened to the surrounding 

 plants. In this oval bell, which is open be- 

 low, she watches for prey, and, according to 

 Kirby, passes the winter after having closed 

 the opening. The air needful for respiration 

 the spider carries from the surface of the 

 water. To do this she swims upon her back 

 in order to entangle an air-bubble upon the 

 hairy surface of her abdomen. With this 

 bubble she descends, " like a globe of quick- 

 silver," to the opening of her nest, where she 

 liberates it and returns for more. ROMANES 

 Animal Intelligence, ch. 6, p. 211. (A., 

 1899.) 



887. DIVISION BY DEPRESSION 

 AMONG THE FAUNA OF THE DEEP SEA 



It would be quite possible, however, to 

 subdivide the [terrestrial] geographical 

 areas into zones of elevation above the sea- 

 level, not very clearly marked off from one 

 another, it is true, but nevertheless each 

 showing a number of characteristic features. 

 This idea is expressed, for example, when we 

 speak of the Alpine fauna, the Himalayan 

 fauna, or the fauna of the great Andes. 



In the study of the marine fauna and flora 

 we must notice, it is the depth of the water, 

 or in other words the depression of the habi- 

 tats below the sea-level, that forms the most 

 important consideration. Geographical sub- 

 regions may be recognized and defined with 

 a certain amount of accuracy, especially in 

 the case of the fauna of the shallow waters, 

 but by far the most important changes in 

 the general characters of the fauna are 

 found when we pass from one " zone " of de- 

 pression to another. HICKSON Fauna of the 

 Deep Sea, ch. 3, p. 46. (A., 1894.) 



888. DIVISION LESSENS CONDUC- 

 TIVITY Red-hot Iron Ball Held in the Hand 

 Cause of Warmth of Fur. Pure silica, in 

 the state of hard rock-crystal, is a better 

 conductor than bismuth or lead ; but if the 

 crystal be reduced to powder, the propaga- 

 tion of heat is exceedingly slow. Through 

 transparent rock salt heat is copiously con- 

 ducted, through common table salt very 

 feebly. Asbestos is composed of certain sili- 

 cates in a fibrous condition; I place some 

 asbestos on my hand, and on it a red-hot 

 iron ball. The ball can be thus held without 

 inconvenience. That the division of the 

 substance should interfere with the trans- 

 mission might reasonably be inferred; for, 

 heat being motion, anything which disturbs 

 the continuity of the molecular chain, along 

 which the motion is conveyed, must affect 



