o" 



und 



SCIENTIFIC SIDE-LIGHTS 



634 



314O. 



Nitrogen Essential 



to Fertility of Soils Bacteria Seize Nitro- 

 gen of Air and Fix It in the Earth. A more 

 important factor of soil fertility is its nitro- 

 gen content, without which it is completely 

 barren. The origin of these nitrogen ingre- 

 dients has been more or less of a puzzle. 

 Fertile soil everywhere contains nitrates 

 and other nitrogen compounds, and in cer- 

 tain parts of the world there are large 

 accumulations of these compounds, like the 

 nitrate beds of Chile. That they have come 

 ultimately from the free atmospheric nitro- 

 gen seems certain, and various attempts 

 have been made to explain a method of this 

 nitrogen fixation. It has been suggested 

 that electrical discharges in the air may 

 form nitric acid, which would readily then 

 unite with soil ingredients to form nitrates. 

 There is little reason, however, for believing 

 this to be a very important factor. But in 

 the soil-bacteria we find undoubtedly an effi- 

 cient agency in this nitrogen fixation. As 

 already seen, the bacteria are able to seize 

 the free atmospheric nitrogen, converting it 

 into nitrites and nitrates. We have also 

 learned that they can act in connection with 

 legumes and some other plants, enabling 

 them to fix atmospheric nitrogen and store 

 it in their roots. By these two means the 

 nitrogen ingredient in the soil is prevented 

 from becoming exhausted by the processes of 

 dissipation constantly going on. Further, 

 by some such agency must we imagine the 

 original nitrogen soil ingredient to have been 

 derived. Such an organic agency is the only 

 one yet discerned which appears to have been 

 efficient in furnishing virgin soil with its 

 nitrates, and we must therefore look upon 

 bacteria as essential to the original fertility 

 of the soil. CONN Story of Germ Life, ch. 

 4, p. 115. (A., 1900.) 



3141. SOLIDITY DECEPTIVE 



Earth's Surface a Thin Crust Covering a 

 Molten Ocean. [We infer that the earth 

 was once a molten mass] because the earth 

 we tread is but a thin crust floating on a 

 liquid sea of molten materials; because the 

 agencies that were at work then are at work 

 now, and the present is the logical sequence 

 of the past. From Artesian wells, from 

 mines, from geysers, from hot springs, a 

 mass of facts has been collected, proving in- 

 contestably the heated condition of all sub- 

 stances at a certain depth below the earth's 

 surface; and if we need more positive evi- 

 dence, we have it in the fiery eruptions that 

 even now bear fearful testimony to the 

 molten ocean seething within the globe and 

 forcing its way out from time to time. The 

 modern progress of geology has led us by 

 successive and perfectly connected steps 

 back to a time when what is now only an 

 occasional and rare phenomenon was the 

 normal condition of our earth; when those 

 internal fires were enclosed in an envelope 

 so thin that it opposed but little resistance 

 to their frequent outbreak, and they con- 



stantly forced themselves through this crust, 

 pouring out melted materials that subse- 

 quently cooled and consolidated on its sur- 

 face. AGASSIZ Geological Sketches, ser. i, 

 ch. 1, p. 3. (H. M. & Co., 1896.) 



3142. SOLIDITY NOT REVEALED 

 BY SIGHT The Visual Impression of Relief 

 an Unconscious Derivation from Touch 

 Optical Illusion. That this idea of solidity 

 is a matter of judgment was well shown by a 

 photograph of a marble statue which I had 

 an opportunity of seeing at a late exhibi- 

 tion. It was impossible not to believe that 

 a marble statue was being looked at. The 

 photograph was at the end of a room, and 

 lighted on both sides, and not looked at 

 through glass, nor the ordinary vision inter- 

 fered with in any way. It will thus be seen 

 that ideas of form gained by the sense of 

 sight are essentially distinct from those de- 

 rived by touch, and it is as impossible to ex- 

 plain to a congeni tally blind man how form 

 can be represented on a plane surface as it 

 is to give him any ideas of color. ELDRIDGE- 

 GREEN Memory and Its Cultivation, pt. i, 

 ch. 3, p. 11. (A., 1900.) 



3143. SOLIDS CONQUERED BY 



YIELDING FLUIDS Air and Water Carve 

 the Earth's Crust. We may take it that the 

 denudation of the [earth's] surface, ren- 

 dered everywhere so conspicuous by the 

 discontinuity of strata, has been effected 

 mainly by the atmosphere and running wa- 

 ter. GEIKIE Earth Sculpture, ch. 2, p. 40. 

 (G. P. P., 1898.) 



3144. SOLITUDE THE TERROR OF 



INFANCY A Protective Instinct. The great 

 source of terror to infancy is solitude. The 

 teleology of this is obvious, as is also that 

 of the infant's expression of dismay the 

 never-failing cry on waking up and find- 

 ing himself alone. JAMES Psychology, vol. 

 ii, ch. 24, p. 418. (H. H. & Co., 1899.) 



3145. SORROW RECALLS SORROW 



Memory Dominated by Mood Joy Recalls 

 Joy. The same objects do not recall the 

 same associates when we are cheerful as 

 when we are melancholy. Nothing, in fact, 

 is more striking than our utter inability to 

 keep up trains of joyous imagery when we 

 are depressed in spirits. Storm, darkness, 

 war, images of disease, poverty, and perish- 

 ing afflict unremittingly the imaginations 

 of melancholiacs. And those of sanguine 

 temperament, when their spirits are high, 

 find it impossible to give any permanence 

 to evil forebodings or to gloomy thoughts. 

 In an instant the train of association dances 

 off to flowers and sunshine, and images of 

 spring and hope. JAMES Psychology, vol. 

 i, ch. 14, p. 576. (H. H. & Co., 1899.) 



3146. SOUL IN STONE First Expla- 

 nation of Magnetic Power The Magnet at 

 the Foundation of Philosophy. Aristotle 

 reports the sayings of Thales only by hear- 

 say, and then with extreme caution: the 



