January 15, 1886.] 



SCIENCE. 



55 



freeze again, and others subject to drainage (and a 

 few other causes), often have ice permeating the 

 mass, sometimes in little fine needles, which make 

 the mass worthless, and now and then in little crystals 

 scattered through it. If these crystals are much 

 larger than a pea, and more numerous than one to 

 about every four square inches exposed by a section, 

 the bank is rejected by the Eskimo snow-builder, 

 unless others cannot be found. 



The packing of the wind and low temperature are 

 needed to produce the true building-snow, and, in 

 the absence of either one of these conditions, the 

 action of the other seems to be worthless. As to 

 temperature, this is shown by the snow not being 

 good, as judged by the Eskimo, until it is ikkee-oo- 

 ad-lo (very cold) despite the fiercest gales having 

 occurred. It is shown as to the wind by not finding 

 good building material in deep gorges, and other 

 places where the wind cannot get at the snow to pack 

 it down, long after it is perfect in other localities. 

 My information on these points did not conie from 

 such observations, however, but directly from Eski- 

 mo explanations, and I add these to corroborate 

 them. I do not believe— although I do not positively 

 know — that both wind and low temperature must 

 come together, but both must have happened before 

 the Eskimo will use the snow for building, though 

 possibly the two may be independent in time. 

 When I say the Eskimo will not use it, I mean as a 

 usual thing and in a general way; for in his cheerless 

 country he is often driven to dire expedients, and 

 does many things under a sort of polar protest. 



After my detailed description of an Eskimo snow- 

 house in Science, and some popular accounts in other 

 periodicals, I learned in several ways (by correspond- 

 ence and from account's given me by the editor of St. 

 Nicholas) of attempts to reproduce these domiciles in 

 our country having ended in failure. Of course, the 

 main reason of such failures was in the lack of knowl- 

 edge to construct the igloo, the manual dexterity 

 needed, it being an art which requires no small 

 amount of the early life of an Eskimo to acquire to 

 that perfection we often see among them ; yet the 

 builders who failed in their undertakings may console 

 themselves with the fact that it is only in rare cases 

 that the snow will be of the right texture in so low 

 a latitude. The alpine districts, as Mount Washing- 

 ton in the winter, and similar places, might do. 

 Ebierbing (Eskimo Joe, as he was known in the United 

 States), my interpreter, told me that he had built a 

 few igloos in the United States for the edification of 

 curious crowds, but he was only too glad not to see 

 them tumble in and ruin his reputation as well as the 

 house ; but, as to living in them, he would never 

 have thought of it. Fred'k Schwatka. 



New York City. 



' Chinook winds.' 



Dr. Dawson's interesting note on the Chinook 

 winds of the north-west does not fully represent the 

 views on the origin of the foehn held by Dr. Hann. 



The foehn winds, and presumably the Chinook 

 also, are often felt on the leeward side of a range 

 before any rain falls on the windward side : there- 

 fore, while the evolution of latent heat by condensing 

 vapor is a true and important cause of the warmth 

 of the foehn in the manner indicated by Dr. Dawson, 

 it is not the first or the only cause, and I think it is 

 not the most efficient cause. Dr. Hann has shown 



that the first cause of the warmth is the descent of 

 air from the level of the passes and peaks in response 

 to the needs of a low-pressure area on the leeward 

 side of the range ; and, as the temperature of the 

 upper air is not greatly lower than that of the sur- 

 face air in winter (the vertical decrease of temper- 

 ature in the atmosphere being slow in this season), 

 the descent of the upper air gives it a warmth and 

 dryness that is very abnormal. The foehn is indeed, 

 like our north east winds, a current that is propa- 

 gated backwards; first, the air is withdrawn from 

 the plains in front of the mountains by the approach 

 of a low-pressure area ; then the air in the valleys 

 flows out over the plains ; next the upper air de- 

 scends from the passes into the valleys, warming as 

 it falls ; finally the air rises on the farther side of the 

 range, clouds form in it, rain falls from it, and it 

 therefore cools slowly in its ascent ; but, as soon as 

 the little cloud that crosses the range is dissolved, 

 the air warms rapidly in its descent ; and thus the 

 foehn is established. Doubtless the last two pro- 

 cesses go on together. 



. I have used the accompanying figure (based on a 

 diagram by Hertz) to illustrate the foehn problem : 

















.// 



ys 



6000' A :' 





rf 









/ '> 



/ •• 

 / " ■■ 



/ ' 





y 3ooo' / , 











/ / 

 / * 



<* / */' ' 







i 7 





' / 



y '7c " 1 ~ ~ 







the full lines represent the variation of mean tem- 

 perature with altitude for the year (YY'), summer 

 {SS') and winter {WW) ; while the broken lines are 

 ordinary adiabatics, showing the change in tempera- 

 ture of ascending or descending masses of air that 

 are warmer than their dew-point ; and the dotted 

 lines are adiabatics for the retarded cooling of 

 masses of air in which vapor is condensing. Now, 

 in winter, when the lower air at a station one thou- 

 sand feet above the sea, with a temperature of 24 D F., 

 (shown at T), moves away, and is replaced by air 

 that descends from an elevation of seven thousand 

 feet, where its temperature is 10° (A), the latter will 

 reach the ground (B) with a temperature about 42°, 

 and a very low relative humidity : it is almost twenty 

 degrees warmer than the air whose place it has taken. 

 The descent must be rapid, or else the air will be 

 much cooled on approaching the cold ground. 



A second example shows the action of rain : start- 

 ing on the farther side of the mountains, with a 

 temperature of 85°, suppose the air ascend five hun- 

 dred feet from C to D before any condensation takes 

 place ; then, clouds forming and rain falling, further 

 cooling is slow, as shown by the steeper dotted line, 

 DF. Where this line crosses the temperature of 

 32°, there will be a brief ascent without any cooling, 

 until all the cloud-particles are frozen : this is shown 

 by a short vertical turn at E, but the effect is small. 



