riumpliH 

 ruth 



SCIENTIFIC SIDE-LIGHTS 



706 



3490. TRIUMPHS OF MECHANICAL 



SKILL Microscopic Lines Ruled on Glass 

 Plate. Let not, then, these numbers [the 

 dimensions of light-waves] impair your con- 

 fidence in our results; but remember that 

 the microscope reveals a universe with di- 

 mensions of the same order of magnitude. 

 Moreover, the magnitudes with which we 

 are here dealing are not beyond the limits 

 of mechanical skill. It is possible to rule 

 lines on a plate of glass so close together 

 that the bands of fine lines thus obtained 

 cannot be resolved even by the most powerful 

 microscopes; and I am informed that the 

 German optician Nobert has ruled bands 

 containing about 224,000 lines to the inch. 

 He regularly makes plates with bands con- 

 sisting of from about 11,000 to 112,000 lines 

 to the inch. These bands are numbered from 

 the 1st to the 19th, and are used for micro- 

 scopic tests. COOKE New Chemistry, lect. 

 1, p. 17. (A., 1899.) 



3491. TROPICS, PROLIFIC VEGE- 

 TATION OF Numerous Species of Orchids. 

 In the tropics the species [of orchids] 

 are very . . . numerous; thus Fritz 

 MiilJer found in South Brazil more than 

 thirteen kinds belonging to several genera 

 growing on a single cedrela-tree. Mr. Fitz- 

 gerald has collected within the radius of one 

 mile of Sydney in Australia no less than 

 sixty-two species, of which fifty-seven were 

 terrestrial. Nevertheless, the number of in- 

 dividuals of the same species is, I believe, 

 in no country nearly so great as that of very 

 many other plants. Lindley formerly esti- 

 mated that there were in the world about 

 6,000 species of Orchidece, included in 433 

 genera. The number of the individuals which 

 come to maturity does not seem to be at 

 all closely determined by the number of 

 seeds which each species produces; and 

 this holds good when closely related forms 

 are compared. DARWIN Fertilization of Or- 

 chids, ch. 9, p. 279. (A., 1898.) 



3492. TROPICS, PROTECTIVE COL- 

 ORS IN Why Parrots Are Green. Passing 

 on to the tropical regions, it is among their 

 evergreen forests alone that we find whole 

 groups of birds whose ground color is green. 

 Parrots are very generally green, and in the 

 east we have an extensive group of green 

 fruit-eating pigeons; while the barbets, bee- 

 eaters, turacous, leaf -thrushes (Phyllornis), 

 white-eyes (Zosterops), and many other 

 groups have so much green in their plu- 

 mage as to tend greatly to their concealment 

 among the dense foliage. There can be no 

 doubt that these colors have been acquired 

 as a protection, when we see that in all 

 the temperate regions, where the leaves are 

 deciduous, the ground color of the great 

 majority of birds, especially on the upper 

 surface, is a rusty brown of various shades, 

 well corresponding with the bark, withered 

 leaves, ferns, and bare thickets among 

 which they live in autumn and winter, and 



especially in early spring, when so many of 

 them build their nests. WALLACE Darwin- 

 ism, ch. 8, p. 131. (Hum.) 



3493. TROPICS, RAINFALL IN THE 



Condensation of Vapor by Mountains 

 Monsoons. Warm, southerly winds, blowing 

 over the Bay of Bengal, and becoming laden 

 with vapor during their passage, reach the 

 low level delta of the Ganges and Brahma- 

 putra, where the ordinary heat exceeds that 

 of the sea, and where evaporation is con- 

 stantly going on from countless marshes and 

 the arms of the great rivers. A mingling 

 of two masses of damp air of different 

 temperatures probably causes the fall of 

 70 or 80 inches of rain, which takes place 

 on the plains. The monsoon having crossed 

 the delta, impinges on the Khasia Moun- 

 tains, which rise abruptly from the plain 

 to a mean elevation of between 4,000 and 

 5,000 feet. Here the wind not only encoun- 

 ters the cold air of the mountains, but, what 

 is far more effective as a refrigerating cause, 

 the aerial current is made to flow upwards, 

 and to ascend to a height of several thou- 

 sand feet above the sea. Both the air and 

 the vapor contained in it, being thus relieved 

 of much atmospheric pressure, expand sud- 

 denly, and are cooled by rarefaction. The 

 vapor is condensed, and about 500 inches 

 of rain are thrown down annually, nearly 

 twenty times as much as falls in Great 

 Britain in a year, and almost all of it 

 poured down in six months. The channel 

 of every torrent and river is swollen at this 

 season, and much sandstone horizontally 

 stratified, and other rocks are reduced to 

 sand and gravel by the flooded streams. 

 LYELL Principles of Geology, bk. ii, ch. 14, 

 p. 200. (A., 1854.) 



3494. 



Landslides The 



Turbid Ganges. In another part of India 

 [see 3493], immediately to the westward, 

 similar phenomena are repeated. The same 

 warm and huinid winds, copiously charged 

 with aqueous vapor from the Bay of Bengal, 

 hold their course due north for 300 miles 

 across the flat and hot plains of the Ganges, 

 till they encounter the lofty Sikkim Moun- 

 tains. On the southern flank of these they 

 discharge such a deluge of rain that the 

 rivers in the rainy season rise twelve feet 

 in as many hours. Numerous landslips, some 

 of them extending three or four thousand 

 feet along the face of the mountains, com- 

 posed of granite, gneiss, and slate, descend 

 into the beds of streams, and dam them 

 up for a time, causing temporary lakes, 

 which soon burst their barriers. " Day and 

 night," says Dr. Hooker, " we heard the 

 crashing of falling trees and the sound of 

 boulders thrown violently against each other 

 in the beds of torrents. By such wear and 

 tear rocky fragments swept down from the 

 hills are in part converted into sand and 

 fine mud; and the turbid Ganges, during 

 its annual inundation, derives more of its 



