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SCIENCE 



[Vol. XVII. No. 421 



minutes. This action may precede the fall in temperature by 

 several hours, or the two may be very near each other, but it is 

 very rarely that the diminution of moisture does not tafee place 

 with sufficient rapidity to prevent the formation of fog from the 

 lowering of temperature to the dew-point. The cause of this 

 marked drying it is not easy to find; but it is not due to a drying 

 wind along the earth's surface, though it may be due, in part, to 

 a settling of dry air from above. 



What causes the cold wave ? The simplest explanation would 

 be that the air radiates its beat to the abnormally clear sky ; but 

 such radiation from the air, it is generally recognized, would 

 produce a very slight cooling. That this cooling is slight can 

 often be determined when no cold wave is in progress. It is a 

 significant fact that the cold wave strikes the high mountain 

 summits before it does the base ; for example, it has been shown 

 that the temperature change at Mount Washington (6,379 feet) 

 occurs from five to ten hours earlier than at the base. The 

 same effect has been noted at Pike's Peak (14,134 feet), and there 

 is no reason to doubt that it may be due to changes in the upper 

 atmosphere many miles above our highest mountains. Does the 

 cold air sink by gravity ? The most serious objection to this view 

 is that such action would seem to call for a displacement of the 

 warm air beneath, or an admixture of the cold and warm air, at 

 a much more rapid rate than can be accepted. The objection 

 that such action would warm up the air from compression does 

 not seem to be well taken. Certainly the appearance of the tem- 

 perature fluctuation, which is precisely the same below as above, 

 at Mount Washington, for example, shows no marked heating at 

 the base. If we increase the density of air by pressure from out- 

 side, it would undoubtedly be warmed, but it is plain that air 

 could not descend by gravity into other air (whether by displace- 

 ment or admixture) unless it were denser than that below, and in 

 such case the natural expansion would tend to slightly cool the 

 air. Some have advanced such an idea in accounting for increased 

 cold in the outskirts of an expanding cold wave, but it is very 

 evident that such an effect would be well-nigh inappreciable. 

 There is one fact that seems to show a tendency to a settlement 

 of the upper air, in that the removal of the moisture occurs before 

 the fall in temperature. This would seem to corroborate the 

 view that the cool, dry air from above is slightly heated at first 

 by contact with the lower air, and possibly by compression, and 

 hence the drying process may anticipate the great cooling, though, 

 according to my belief, such action is not at all needed to dry the 

 air. 



Both of these causes are concerned in some degree in our cold 

 waves, but they do not seem to account for all the facts. What- 

 ever the ultimate cause may prove to be, it is unquestionably re- 

 lated in a marked degree to the removal of moisture from the air; 

 and until we can satisfactorily explain that, we cannot hope to 

 explain the other. The intensity and extent of the cold wave are 

 dependent upon the rapidity of the advance of this drying con- 

 dition; and it is safe to say that this advance, whether in the 

 front of a high-pressure area or in the rear of an area of low press- 

 ure, is entirely independent of the motion of a mass of air. The 

 best proof of this is to be found in the fact that the high area, 

 storm, and drying condition all advance at thirty, forty, or more 

 miles per hour, while the air moves at less than half that velocity. 



This brings us to the most important deduction to be made from 

 this discussion. If there is no horizontal transfer of air in our 

 cold waves, we may conclude that there is none in our warm 

 waves. I am well aware that this proposition, already fully set 

 forth in the Scientific American for Nov, 15 of last year, will call 

 forth most serious opposition, as it strikes at the very heart of 

 present theories of storm-generation. If the sun heats a limited 

 portion of the earth's surface, and thus starts up an ascending 

 column of warm, moist air, then our storms may be due to the 

 forward motion of this column of ascending air which rotates at 

 the same time that it advances; but, if there is no motion of air- 

 particles in our storms, this theory falls to the ground. There 

 have been set forth from time to time most serious objections to 

 the ordinary theories, but it seems to me none have had the 

 weight of this one here presented. This rise in temperature 

 occurs in the upper air before it does at the earth, and is due, in 



part, to a condition of the atmosphere which seems to intercept 

 the heat of the sun. This condition is exactly contrary to that in 

 a cold wave, and is brought about by a marked aggregation of 

 moisture in our storms. This aggregation seems to take place far 

 above our highest mountains. 

 We may conclude as follows : — 



1. High-pressure areas and storms (or low-pressure areas) are 

 conditions brought about by some effect other than the abstraction 

 or addition of heat. Possibly they are produced by some form of 

 electric energy, and are transported or transferred through the air 

 without tbe motion of air-particles. 



2. A portion of the cold in our cold waves is due to radiation, 

 and another portion to the cold of the upper atmosphere, while 

 possibly a larger portion cannot yet be accounted for. 



3. A portion of the heat in our storms is due to a peculiar con- 

 dition of the atmosphere which intercepts the heat of the sun, and 

 this heat gradually works down from the upper atmosphere to the 

 earth. H. A. Hazen. 



Washington, D.C., Feb. 23. 



The Instruction of the Deaf. 



I DO not desire to take part in the discussion now going on in 

 Science concerning the comparative excellence of the various 

 methods of instructing the deaf. The truth with respect to these 

 methods has recently been happily expressed by Miss Yale, the 

 able principal of one of our best oral schools (" Twenty-third An- 

 nual Report of the Clarke Institution for Deaf-Mutes, " 1890, p. 15): 

 " Each system claims for itself distinctive merits and special 

 adaptation. The justice of these claims is now generally con- 

 ceded by the great body of those engaged in teaching the deaf." 



I wish merely to correct an erroneous statement in Dr. Alexan- 

 der Graham Bell's open letter to the Hon. William B. Allison, 

 published in the last number of Science, with respect to the Co- 

 lumbia Institution for the Deaf, with which I have been connected 

 for twenty-five years. Dr. Bell says, "3. In the Columbia Insti- 

 tution a foreign language (the sign-language) is used as the 

 medium of instruction, whereas the rival methods employ the 

 English language alone for this purpose."' 



In the Columbia Institution the sign-language is not used as 

 the medium of instruction. In some classes it is used as a medium 

 of instruction, being employed to communicate with deaf chil- 

 dren at the beginning of their course, when they have no other 

 means of communication whatever, and to promote their mental 

 development, with respect to which Dr. Bell himself has said 

 (" Proceedings of the Fifth Conference of Principals of Schools 

 for the Deaf," 1884, p. 195), "In regard to mental development, 

 undoubtedly nothing could reach the mind of a child like the 

 language of signs ; " it is also used, but very sparingly, in the 

 earlier part of the course of instruction in connection with the 

 English language, to explain and illustrate the meaning of words, 

 where otherwise the explanation could not be given at all ; and it 

 is used throughout the whole course for public lectures and devo- 

 tional exercises, no means of using the English language having 

 yet been discovered which will satisfactorily take its place for 

 this purpose. 



Under all other circumstances — and these comprise the great 

 part of the teaching given in the institution — the English language 

 is the medium of instruction. There are classes in both the Ken- 

 dall School and the National College — the two departments of the 

 Columbia Institution — in which the English language is the only 

 medium of instruction. I do not think that any of the schools 

 following ' ' rival methods " use the English language as a medium 

 of instruction more than the Columbia Institution does. 



Edwaed Allen Fat. 



National Deaf-Mute College, Kendall Green, 

 Washington, D.C., Feb. 23. 



P. Blakiston, Son, & Co. , Philadelphia, will publish in March 

 "A New Systematic Work on Surgery," by C. W. Mansell Moul- 

 lin, surgeon to the London Hospital. They have also nearly ready 

 "Plain Talks on Electricity and Batteries," for medical men, by 

 Dr. Horatio R. Bigelow. 



