712 



THE POPULAR SCIENCE MONTHLY. 



which the Arctic flatlands are so well known. 

 This marshy condition is produced every 

 summer by the deeply-frozen ground thaw- 

 ing but a foot or two under the nover-setling 

 sun of that season, the deeper strata of ice re- 

 maining to act as an impervious shield to 

 prevent the water from draining through, and 

 on the prairies it remains as ice-water, sur- 

 rounding the hardy mosses that thrive in it, 

 and into which a traveler will sink up to his 

 knees in the worst parts. A few stunted 

 willows grow along the sluggish streams, 

 but otherwise everything is bare of all ex- 

 cept the moss. On this moss graze many 

 herds of reindeer that roam with the wind 

 and migrate backward and forward with 

 the seasons." These reindeer furnish the 

 Eskimos of the north and the Indians of 

 the Yukon Eiver with their meat and warm 

 clothing. 



Iridescent Clonds. — Mr. J. C. McCon- 

 ncl has studied the phenomena of irides- 

 cent clouds at Saint Moritz, Switzerland, 

 where they are very common in winter, oc- 

 curring usually whenever there are scatter- 

 ed clouds near the sun. Within a circle of 

 about 2° radius, he says, the clouds are 

 white, faintly tinged with blue. This space 

 is surrounded by a ring of yellow or 

 orange. The region of most vivid hues is 

 comprised between 3° and 7°, and the most 

 striking tints are purple, orange, green, and 

 red. These colors arc not arranged in rings, 

 but are distributed over the thinner parts of 

 a cloud in irregular patches. Beyond this 

 region the only colors visible are green and 

 red, which become fainter as the distance 

 from the sun is increased. The author has 

 detected them in a few cases at a distance 

 of 21°. At some distance from the sun the 

 greens and reds are frequently arranged in 

 bands parallel to the edge of the cloud. 

 The author supposes these colors to be the 

 result of diffraction of light by fine particles 

 of ice. The particular color assumed by any 

 part of the cloud is determined by the dis- 

 tance from the sim and the average size of 

 the particles. The i)articlcs are supposed 

 to be in the form of thin hexagonal prisms, 

 that being the shape among the known 

 forms of ice-crystals best adapted to pro- 

 duce diffraction. Mr. McConnel calculated 

 the probable diameter of the filaments, and 



found it to be between '017 and •009 mil- 

 limetre for the purple, *021 to '010 milli- 

 metre for the orange, and '014 to '009 

 millimetre for the blue. The absence of 

 the colors from clouds composed of water- 

 particles is accounted for by the want of 

 uniformity of size in the water-drops. 



Accnmnlations of Atmospheric Dost. — 



Ruins of ancient cities and buildings are 

 nearly always found wholly or partly buried. 

 The material with which they are covered 

 has been supposed to originate in the debris 

 of buildings that have been erected and hu- 

 man works that have been going on upon 

 their sites, but this can not always, or sel- 

 dom wholly, be the case ; for the same fact 

 appears in desert and wilderness sites. Much 

 is possibly due to superficial disintegration 

 and the work of vegetation ; but still anoth- 

 er factor, more effective than has heretofore 

 been supposed, may be sought in the deposi- 

 tion of atmospheric dust. In a note on this 

 1 subject, readby him before the Geographical 

 ; Society of Paris, M, Violet d'Aoucst referred 

 j to Eichthofen's account of a vast aerial for- 

 ] raation of loess in Cliina, and described his 

 own observations in Mexico, where he found 

 I on the flanks of the highest mountains argil- 

 laceous strata not deposited by waters nor 

 \ by the decomposition of the rocks ; but in- 

 ' vestigation showed that they were produced 

 by dust raised by tlie wmds from the plains 

 and deposited on the hills. Tlicse deposits 

 varied from one hundred feet to — in some 

 places — more than three hundred feet in 

 thickness. They grow finer and finer as the 

 height increases, and cease at the limit of 

 vegetation. 



Results of NerTe-Shock. — 3Iany persons 

 who experienced the earthquake in the Ri- 

 viera have since suffered seriously from nerv- 

 ous shock, although they did not at the time 

 appear to be greatly disturbed. This indi- 

 cates that more injury may be done to the 

 nerves by an undue excitement than is per- 

 ceived at the time. The ncrvo-ccnters may, 

 as an English medical journal suggests, be 

 likened to batteries, and regarded as apt to 

 be discharged suddenly and sometimes tm- 

 consciously ; and when once their residual 

 stock of energy is consumed, it can be re- 

 stored only after a long time and by the 



