May 30, 1890.] 



SCIENCE. 



333 



locomotive made the piston-rod move in the cylinder; in fact, 

 that the engine was a dummy. And yet this curious conclusion 

 appears to be analogous to the one now prepented by Dr. Hann. 

 The cyclonic machine does not drive itself by its own store of en- 

 ergy: it is driven by an external motor, the general circulation of 

 the winds. Some of the warm tropical cyclones may at first de- 

 pend on their own energy; these would be true motors: but, if 

 the definite records quoted by Dr. Hann prove to be of wide ap- 

 plication, cyclones generally may come to be considered dummies. 

 The cyclonic air does not rise because it is warm, but, according 

 to Dr. Hann, it is lifted in spite of becoming cool. The anticy- 

 clonic air does not sink because it is cold, but is pushed down in 

 spite of becoming warm: The ascending air is cooler than the 

 normal because its adiabatic rate of cooling by expansion in ascent 

 is, on the whole, greater than the mean vertical temperature gra- 

 dient of the atmosphere; the descending air is warmer than the 

 normal because its adiabatic rate of being warmed by con)pres- 

 sion in descent is greater than the mean vertical teniperature gra- 

 dient. Cyclones do not work themselves: they are worked by the 

 general winds. 



Red field advocated a theory analogous to this in his early es- 

 says. He suggested that cyclones are not generated at places of 

 rarefaction, but are only eddies in the general winds. Other early 

 observers made similar suggestions; but it was not then possible 

 to deduce tests by which this eddy theory could be confirmed or 

 excluded. Faye's modification of Redfield's theory involves so 

 many contradictions to well-established physical facts and laws, 

 that it receives little acceptance Espy was the first to call at- 

 tention to the general occurrence of convectional movements in 

 the atmosphere, and to the importance of liberated latent heat in 

 promoting these movements. Reye, in later years, gave precis- 

 ion to Espy's ideas, and advanced the convectional theory greatly 

 in the estimation of many meteorologists. I do not see that his 

 deductions are in any way inaccurate. His calculation of the 

 available horse-power supplied by the latent heat in a tropical cy- 

 clone appears to be pertinent, even under Hann's new interpreta- 

 tion of the cause of cyclonic movements. But through all the 

 statements of the convectional theory, it has been tacitly assumed 

 that the warmed air of the cyclone would be cooled by radiation 

 in the anticy clonic area; and this does not seem to be the fact. 

 The anticyclonic air is not much cooled till it approaches the 

 ground; and in this we find confirmation of Searle's theory con- 

 cerning the atmospheric economy of solar radiation. 



The warmth of the body of air in anticyclones has been recog- 

 nized for some time. Dr. Hann was among the first to give 

 pioper emphasis to the fact; but its relation to tlie convectional 

 theory of cyclones has been slowly perceived. In this country, 

 Hazen has drawn attention to the absence of indication of the 

 "neutral plane," called for deductively; and for this and other 

 reasons he has discarded pretty much all parts of the cyclonic 

 theory, following Faye more closely than any other. The reason 

 why Dr. Hann's objection to the convectional theory of cyclones 

 appears to me so cogent and convincing is that it is presented, not 

 as a contradiction, but as a corollary to the principles of modern 

 physical meteorology, with which this eminent meteorologist is so 

 thoroughly familiar, and to which he has himself contributed so 

 much of value. The theory of the foehn. for example, was known 

 in a general deductive way from the suggestions made independ- 

 ently by Espy, Dove Tyndall, Helmholtz, and others; but it vpas 

 demonstrated by Hann. So in the present case: Redtield and 

 many others have thought that the general circulation of the at- 

 mosphere might produce cyclones and anticyclones, somewhat in 

 the way that rivers form eddies when flowing in an meven chan- 

 nel; but there is a long distance between suggestion and proof. 

 General indefinite suggestion of what is afterwards shown to be 

 the correct view is not much superior to the suggestion of what 

 ultimately turns out to be the wrong view. Precise definition 

 and demonstration are of much higher value, and these qualities 

 are truly characteristic of Hann's work. If further observation 

 prove the general applicability of thesenewer views as to cyclones 

 and anticyclones, the credit of the demonstration will go prima- 

 rily to Dr. Hann. W. M. D. 



Harvard College, May, 1890. 



An Hypothesis for the So-called Encroachments of the Sea 

 upon the Land. 



It is assumed that there is no substance which is absolutely 

 rigid. The earth is a plastic mass. Let a mountain-range disap- 

 pear, the plain on which it once stood rises when relieved of its 

 weight. Let a lake disappear, and its bed becomes contorted, and 

 the contour of its shure-liue is changed. The walls of the Grand 

 Canon of the Colorado are moving toward each other, and, should 

 it become an arid chasm, they would some time meet. 



Now, in the southern and eastern portions of the United States 

 the "fall-line" is the boundary of the permanent continent. The 

 "continental outline" is the one-hundred fathom hydrographic 

 contour, as determined by the United States Coast Survey; and 

 from its erf st there is a drop of over three thousand feet, — a 

 front equal to one side of the Grand Canon. From the " fall-line " 

 to this front there is a creeping-forward, which is comparable to 

 the ice sheets of Greenland: therefore cannot we say that the land 

 at present is crowding down into the sea, instead of the sea en- 

 croaching upon the land, which is only an apparent movement, 

 not the real one? The distance from the backbone of the Appa- 

 lachians to the historic-geologic cedar-stumps of the New Jersey 

 coast has increased, and is increasing. 



The deltas of the Mississippi valley and the Gulf coart are not 

 only increasing by deposits of sediment, but are moving forward 

 as well. Therefore may it not be expected in geodetic work on 

 the North American continent that there will be encountered dis- 

 crepancies between successive determinations of positions which 

 can only be thus accounted for and understood ? 



Gilbert Thompson, 



Washington, D.C., May 23. 



The Winnebago County (Iowa) Meteorites. 



As the Iowa meteor of May 3 has received notice in your paper, 

 it may be desirable to make the record still more complete I 

 therefore offer the following notes from the south-western corner 

 of that State. The writer was not in position to see it, nor did 

 the sounds appear to him enough unlike thunder to attract par- 

 ticular attention at the time. It was seen by perhaps a dozen 

 citizens of this place, one of them being at the time less than ten 

 miles from the south-west corner of the State. Most agree in 

 thinking that it passed from the south-west toward the north-east. 

 Some who saw it felt so sure that it struck fields close by to the 

 north north-east, that they searched diligently for it. Many 

 heard it, and thought it thundered. Some compared it to an 

 earthquake shock, the jarring of the ground was so evident. Four 

 distinct explosions were observed by one. A local paper of Mal- 

 vern, nine miles away, stated that three pieces had fallen in that 

 vicinity, but the statement was based on observations similar to 

 thf).«e already given. J. E. Todd. 



Tabor, lo., May 20. 



Tornadoes. 



Some years since, I visited the scene of a small tornado shortly 

 after its occurrence, and found the arrangement of tree trunks 

 and other debris in its track very similar to what is represented 

 in the article by Professor Hazen at p. 318 of Science for May 23. 

 It seemed to me, however, that the peculiar arrangement found 

 might be due to the combined effect of a whii-ling motion of the 

 tornado, together with its motion of translatioA as a whole. In 

 such a case there must be a compounding of forces, and the direc- 

 tion of the fall of a tree or other object can only be determined 

 theoretically by a somewhat elaborate computation. Practically, 

 and as a matter of fact, I have noticed, however, that when a 

 small whirlwind is passing over a corn-field, the stalks incline in- 

 ward toward its centre with a twisting motion, and likewise bend 

 forward in the direction toward which it is advancing. I have 

 never seen stalks actually uprooted and left prostrate in this waj ; 

 but it looks very much as if they would be left with their tops 

 inward and forward if this should happen, thus corresponding 

 precisely to what is found after tornadoes. M. A. Veeder. 



Lyons, N.Y., May 23. 



