January 2, 1891.] 



SCIENCE. 



ing of the other theory some years before; and, in spite of Profes- 

 sor Ferrel's letter, it still seems to me that I was right in saying 

 that the convectional theory needs revision in the light of Dr. 

 Hand's results, but by revision I do not mean abandonment. 



The incompleteness of the new theory is not a reason for being 

 silent about it. It should be welcomed, if only for the reason that 

 it will cause a healthful revision of previous views. The value of 

 multiple working hypotheses has been so well set before our 

 scientific readers, that nothing more need be said on that point. 

 I will not venture to speak for Professor Ferrel, but I am sure 

 that practically every meteorologist in the country will profit from 

 a serious re-examination of his knowledge of the theory of cy- 

 clones in the light of Dr. Hann's researches. 



As to the process by which the general circulation of the at- 

 mosphere shall produce cyclones and anticyclones, it is not to my 

 mind necessary that this should be worked out completely before 

 the suggestion of it may be profitably made. But it does not 

 seem impossible that the general winds might here and there 

 crowd together, owing to irregularity of flow; that, where 

 crowded together, anticyclones would appear; and that, between 

 the anticyclones, cyclonic whirls might be formed. It would be 

 indeed a satisfaction if I could here answer all the pertinent ques- 

 tions, and give all necessary explanations, about such a problem ; 

 but. if we may judge by the treatment that dynamical meteorol- 

 ogy has received thus far in this country, there is only one Amer- 

 ican who can do that. I wish that he might consider the possi- 

 bilities of some such process arising from the general circulation 

 of the atmosphere as is outlined above, and, after working them 

 out rigorously, state them as clearly as he has explained the gen- 

 eral circulation of the atmosphere itself. Whatever truth there 

 is in the convectional theory of cyclones would not be harmed by 

 such an investigation, while whatever truth there may be in the 

 hypothesis of driven cyclones would pretty surely be discovered 

 by it. 



There is a corollary to the suggestion made by Dr. Hann, that 

 may be of interest to those who seek for an explanation of our past 

 glacial climates. It is generally recognized, that, if there were an 

 increase in the activity of our winter cyclones, there would be an 

 increase of snowfall as well ; and, if this were carried far enough, 

 the accumulation of snow might last over the summer. The in- 

 . crease of cyclonic activity would presumably accompany an in- 

 crease in the general circulation of the atmosphere, if cyclones in 

 our latitudes are driven by the general winds; and this would ap- 

 pear in that hemisphere whose equatorial and polar contrasts of 

 temperature were strengthened. Such strengthened contrasts 

 might be expected in the hemisphere having its winter in aphelion, 

 and particularly at times of maximum orbital eccentricity. I do 

 not mean to imply that a glacial period might depend on this con- 

 dition alone: yet it may be one of many whose varying combina- 

 tions at times produce a glacial climate, as CroUand J. Geikieand 

 many others have shown; but this particular element of the com- 

 bination does not appear to have been recognized. 



W. M. Davis. 



Harvard College, Cambridge, Mass., Deo. 27. 



Moisture in Storms. 



Next to the action of heat in storms, the part that moistiu-e 

 takes in them has been greatly emphasized. The so-called "con- 

 densation theory" of storms has had wider acceptance than any 

 other. We may imagine a limited portion of the earth's surface 

 heated up by the sun, and this more or less of a circular shape. 

 There will be induced a tendency to an uprising current of heated 

 air, which will continue so long as the central portion is warmer 

 than the air surrounding it at the same level. This tendency, 

 however, would be quickly brought to rest were it not for the 

 fact that the uprising column has its moisture condensed, which 

 liberates latent heat and causes the column to rise still faster. 

 Here is a most remarkable fact, notwithstanding that the release 

 of this moisture diminishes the total amount in the air, and the 

 latent heat warms up the aii-, both of which causes would stop 

 precipitation at once; yet we are taught that the force of the 

 storm is increased by this process. There is another serious ob- 



jection among many. If rain occurred at the centre of the 

 storm, this theory might be plausible; but since the bulk of the 

 rain in this country occurs three hundred miles to the eastward 

 of the centre, and over only about one-fiftieth part of the area 

 covered by the storm, it requires an enormous stretch of the 

 imagination to grasp the causation of our wide-extended storms 

 through this condensation effect. We may add still another con- 

 sideration. It is fairly well ascertained that the upper limit of 

 our storms, as shown by pressure and temperature observations 

 at Pike's Peak (14,134 feet), is far above four or five miles, and 

 may extend to the limits of the atmosphere. Now, the bulk of 

 our precipitation is formed within 6,000 feet of the earth's sur- 

 face : hence it is plain that the condensation of moisture plays a 

 very subordinate part in our wide-extended storms, and has 

 nothing to do with their generation or maintenance. 



I do not propose to discuss at this time all the objections to this 

 "condensation theory," which have been repeatedly advanced 

 both in this and other journals, and which have not been answered, 

 but I wish to present a recent most extraordinary abandonment 

 of this theory by Dr. Hann, who stands at the head of the old 

 school on the continent. I quote from a translation, by Professor 

 Blanford of London, of a recent statement by Dr. Hann. Speak- 

 ing against the condensation theory, he says {Nature, Nov. 6,, 

 1890), "These views are such as I have always enunciated (for a 

 long time, indeed, without any apparent result) in opposition to the 

 then prevalent theories of the local origin of barometric minima 

 through the agency of condensing water-vapor (as contended by 

 Mohn, Reye, Loomis, and Blanford). They now begin to make 

 way and prevail. Most clearly is this seen in the case of Loomis, 

 who, in the course of his own persistent study of the behavior of 

 barometric minima and maxima, has been compelled by degrees 

 to give up the ' condensation theory ' to which he formerly adhered 

 so strongly, and to ascribe the origin as well as the progressive 

 movement of cyclones to the general circulation of the atmos- 

 phere." 



The importance of this utterance from such an authority can- 

 not be exaggerated. While I have shown that Dr. Hann has been 

 misled by his study of mountain observations, yet it seems to me 

 this avowal on his part reaches out far beyond that. As I have 

 just shown, the very life and existence of the old theory depend 

 upon condensation of moisture. Now, if Dr. Hann, who must 

 iindei-stand this fact most thoroughly, has deliberately set it aside, 

 must we not conclude that it has an inherent weakness in itself to 

 his mind. Those who are familiar with Loomis's work will be 

 surprised to learn that he ever abandoned the condensation theory 

 of storms. ' 



It would seem that this controversy over the condensation 

 theory is rapidly culminating, and the indications point to a speedy 

 downfall of that theory. It is a remarkable fact that all the ob- 

 jections urged against this theory, now these many years, have 

 been studiously ignored; but a few words from a recognized 

 authority, even though based upon a wrong interpretation of 

 facts, seem to make headway very rapidly. Surely Hann, Davis, 

 and Blanford form a most formidable front against this theory, 

 and it is high time its defenders should come to its assistance ere 

 it be too late. H. A. Hazen. 



Washington, Dec. 13. 



[•'Letters to the Editor" continued on p. 8.] 



NOTES AND NEWS. 



At a meeting of the Royal Botanic Society on Dec. 13, as we 

 learn from Nature of Dec. 18, the secretary answered vari- 

 ous questions as to the destructive action of fogs on plants. He 

 said it was most felt by those tropical plants in the society's houses 

 of which the natural habitat was cue exposed to sunshine. Plants 

 growing in forests or under tree shade did not so directly feel the 

 want of light; but then, again, a London or town fog not only 

 shaded the plants, but contained smoke, sulphur, and other dele- 

 terious agents, which were perhaps as deadly to vegetable vitality 

 as absence of light. Soft, tender-leaved plants, and aquatics, such 

 as the Victoria regia, suffered more from fogs than any class of 

 plants he knew. 



