air: 



SCIENTIFIC SIDE-LIGHTS 



632 



as the consequence of two apparently widely 

 different conditions. Insensibility is equally 

 produced by a deficient and an excessive 

 quantity of blood within the cranium 

 (coma) ; but it was once supposed that the 

 latter offered the truest analogy to the nor- 

 mal condition of the brain in sleep, and in 

 the absence of any proof to the contrary 

 the brain was said to be during sleep con- 

 gested. Direct experimental inquiry has led, 

 however, to the opposite conclusion. 



By exposing, at a circumscribed spot, the 

 surface of the brain of living animals, and 

 protecting the exposed part by a watch- 

 glass, Durham was able to prove that the 

 brain becomes visibly paler (anemic) during 

 sleep; and the anemia of the optic disk dur- 

 ing sleep, observed by Hughlings Jackson, 

 may be taken as a strong confirmation, by 

 analogy, of the same fact. BAKER Hand- 

 look of Physiology, vol. ii, ch. 18, p. 135. 

 (W. W., 1885.) 



313O. SLOWNESS OF ACTION OF 

 TITANIC FORCES Gradual Growth of Con- 

 tinents Earth Behaving Now Substantially 

 as in Former Ages. When geologists began 

 to unravel the earth's history, they were 

 naturally led to suppose that the present 

 was a time of unusual repose, the earlier 

 ages having been periods when the forces 

 which affect the earth were in a state of 

 often recurring and violent activity. As 

 long as the observer was compelled to con- 

 ceive the construction of the world to have 

 been accomplished in a few thousand years, 

 it was inevitable that he should assume 

 a certain violence in the development of the 

 earth's features. Gradually the fancy for 

 startling theories concerning the past his- 

 tory of this sphere which led to these views 

 has, under the influence of better knowledge, 

 been put aside. Geologists now believe that 

 the continents have grown slowly from the 

 seas, and that the mountains, with all their 

 exhibitions of titanic energy, have likewise 

 gradually come to their present state in 

 a word, that the crust of the earth behaves 

 at the present day substantially as it has 

 acted at all stages in its history, since life 

 came upon it. SHALER Nature and Man in 

 America, ch. 4, p. 131. (S., 1899.) 



3131. SMOKE AS A PRESERVATIVE 

 OF FOOD AMONG SAVAGES Smoke as 

 a preservative of food is a very early in- 

 vention. No sight is more common in a 

 savage hut than that of a frame suspended 

 over the fire in the center of the cabin for 

 holding fish or meat to be dried out and 

 smoked for future use. It will be readily 

 seen that this was a potent factor in the 

 increase of longevity, not only securing pro- 

 visions for time of famine, but eliminating 

 a portion of the noxious creatures that prey 

 on subsistence and shorten life. MASON 

 Origins of Invention, ch. 3, p. 105. (S., 

 1899.) 



3132. SNOW HOLDS WATER IN 

 STORE Gradual Distribution in Place of Tor- 

 rents and Floods. In mountainous regions 

 it [snow] accumulates moisture that might 

 otherwise have fallen in repeated torrents, 

 tearing the soil from the mountainsides, 

 inundating the valleys, and spending almost 

 all its energy in destruction, and allows that 

 moisture to be stored up for future use, 

 to feed the streams that water the valleys, 

 and to keep them filled with comparative 

 regularity and constancy. In level coun- 

 tries it performs a similar service in another 

 way, keeping the underlying ground re- 

 freshed with water that trickles from the 

 snow as it is slowly melted from underneath 

 by the warmth of the earth itself. CHIS- 

 HOLM Nature-Studies, p. 31. (Hum., 1888.) 



3133. SNOW-CRYSTALS ON MOUN- 

 TAINTOPS Prisms Like Delicate Needles- 

 Type Preserved through All Change. On the 

 tops of mountains and in high latitudes, 

 where the snow falls through the air at a 

 very low temperature, the particles may 

 take the form of extremely delicate needles, 

 or may seem to resemble a fine vhite dust. 

 But these needles, on a close examination, 

 are found to be minute six-sided prisms, the 

 sides of which are inclined to one another 

 at precisely the same angle as would be 

 formed by two lines joining the ends of 

 three adjoining rays in an ordinary snow- 

 flake; and the particles of snow-dust may 

 generally be found on examination with a 

 lens to show at least the minute beginnings 

 of rays such as are seen in more elaborate 

 forms. Some of the beauty may be want- 

 ing, but the exquisite mathematical regu- 

 larity is always there. It is this regularity 

 which makes the form of a snowflake more 

 wonderful, as we have said, than the form 

 of the rain-drop. Wonderful it will always 

 remain, even tho science should ultimately 

 be able to explain the general laws under 

 which particles of water assume this form 

 in freezing. CHISHOLM Nature-Studies, p. 

 26. (Hum., 1889.J 



3134. ' SOAP-BUBBLE A UTENSIL 

 OF SCIENCE Prismatic Colors Shown in 

 Films. Any film whatever will produce 

 these colors. The film of air letween two 

 plates of glass squeezed together exhibits, 

 as shown by Hooke, rich fringes of color. 

 . . . Nor is even air necessary; the rup- 

 ture of optical continuity suffices. Smite 

 with an ax the black, transparent ice black 

 because it is pure and of great depth under 

 the moraine of a glacier; you readily pro- 

 duce in the interior flaws which mo air can 

 reach, and from these flaws the colors of 

 thin plates sometimes break like fire. But 

 the source of most historic interest is, as 

 already stated, the soap-bubble. With one 

 of those mixtures employed by the eminent 

 blind philosopher Plateau in his researches 

 on the cohesion figures of thin films, we ob- 

 tain in still air a bubble ten or twelve inches 



