January i6, 1891.] 



SCIENCE. 



39 



of cyclones in the higher latitudes, because a few surface obser- 

 vations merely of temperature, which, as has been shown I think, 

 should have no weight, seem to indicate that the complete condi- 

 tions of a cyclone, upon the condensation theory, do not exist. 



Mr. Clayton, in his communication, sets out in a very com 

 mendable way by discarding mere authority in scientiflc ques- 

 tions. He, however, proceeds to give two columns of citations 

 from different authorities. But the most of this is entirely 

 proper; for we have to depend more or less upon authority for 

 observational data, and it is only where the decision of a question 

 depends merely upon the use and application of scientific princi- 

 ples that mere authority should be discarded. All observations, 

 however, should be well considered and weighed, especially where 

 they seem to conflict with well-established scientific principles. I 

 have been familiar vvith all of Loomis's meteorological papers, 

 and I do not call to mind any cases in which his results deduced 

 directly from observation seemed to be in conflict with any theo- 

 ries which I have advocated, but of course there are some things 

 which I cannot satisfactorily explain. I have always made nu- 

 merous quotations from Loomis's papers in confirmation of mf 

 theories It is a little singular, however, that Mr. Clayton should 

 cite some of the same thiogs against me. From some of Loomis's 

 theoretical deductions from the observations I dissent. 



With regaid to the comparisons of observations at Denver and 

 Pike's Peak, both merely surface observations at a long distance 

 apart, in order to show whether the air is in a state of stable or 

 unstable equilibrium over an area hundreds of miles in diameter, 

 it is not necessary for me to add any thing more to what I have 

 already stated on that subject. These cases were mostly in the 

 summer season, when mountain-peaks are cooler than the sur- 

 rounding air at a distance, and when lowland stations are abnor- 

 mally heated, and the vertical temperature gradient, for some 

 distance from the surface, large. If the lower temperatures had 

 been taken a little above the surface, and compared with one 

 vertically above it, no unstable state, probably, would have been 

 indicated when, as is stated, no extraordinary disturbances 

 occurred The' reason why most of these cases of unstable, and 

 approximately unstable, states occurred in May, I have explained 

 in my book. Whether heated dry air has much ascensional force 

 depends upon the state of the air. In the stable state it can only 

 ascend until it becomes cooled down to the temperature of the 

 surrounding air at a distance on the same levels. In the unstable 

 state, the higher it ascends, the warmer it becomes relatively to 

 the surrounding air ; and so, of course, it rushes up with great 

 ■violence until the stable state is again restored. 



The fact which Loomis has established, and which is a matter 

 of common observation, that very heavy rains do not continue 

 very long, is very reasonable ; for the more rapidly the store of 

 energy in the uncondensed vapor is spent, the sooner, of course, 

 must the store of energy become exhausted. 



I have been at great pains to show that the unstable state, 

 which gives rise to cyclones and tornadoes, may be induced in 

 perfectly dry air ; and I have cited Loomis in conformation of 

 this, when he shows that cyclones of moderate barometric de- 

 pression in the centre, and without any violence, do exist. But 

 Mr. Clayton brings in the same thing against the condensation 

 theory, under the impression, I suppose, that, because I call the 

 theory of cyclones the condensation theory in deference to Espy, 

 I consider vapor and its condensation entirely indispensable. The 

 vapor is a very essential part, and without it cyclones would, no 

 doubt, be of much less frequent occurrence, and would have little 

 violence. Loomis has shown that when there are cyclones in dry 

 ■weather, with little or no rain, the depressions are small. These 

 take place mostly in the summer season, when the air over a 

 large area becomes much heated ; and although the ascent of air 

 over this region is not sufficient to give rise to much rain, or even 

 cloudiness perhaps, yet it is suiflcient to cause haziness in the 

 atmosphere, in which state the heat energy is absorbed directly 

 from the sun's rays, instead of getting it indirectly from conden- 

 sation after it has been absorbed in evaporation. Mr. Clayton 

 cites a number of authorities to show that there is a body of warm 

 air, a little above the eai'th's surface, in areas of high pressure, and 

 that the vertical temperature gradient here is small, much less 



often than in cyclones. I have never denied this. It is simply 

 storming a camp in which I am not to be found. More than six 

 years ago, in " Recent Advances in Meteorology," I gave seven 

 cases of this sort, one in which detailed observations were given to 

 show that the vertical temperature Kfadient may become inverted. 

 The same is given in my recent work. 



Mr. Clayton thinks that Dr. Hann's recent investigations of 

 cyclones in the Alps should add a link to the chain of evidence 

 that the temperature of the air-column as a whole is lower in 

 cyclones than in the surrounding air ; but, if this is even admit- 

 ted, where are the other links? So far as I can see, they all seem 

 to be " missing links." He ^Iso gives bis views with regard to 

 various other things, which is well enough if they are not in- 

 tended as arguments, and they do not seem to be. But still it is 

 of much more importance to know what he can prove and 

 establish than to know what he thinks. He thinks that mechani- 

 cal action has much to do with the origin of storms ; but what 

 this meansr I am unable to say. The mere origin of a cyclone, 

 although of importance, is of little importance in comparison 

 with the great question of where the energy comes from to sup- 

 port the cyclone after it has been originated. 



Finally, Mr. Clayton proposes three questions for my answer. 

 To the first and second I answer emphatically, " No." If Mr. 

 Clayton thinks that a cyclone can originate and be maintained in 

 this way, let him show in what way. But let him remember that 

 he is not to commence with his high areas and his troughs, for 

 this is not a normal condition of the atmosphere, but let him first 

 account for these, and then proceed to show how the air in flow- 

 ing into his trough is thrown into a gyration ; and as the air in this 

 area of gyration, according to the new theory, is heavier than the 

 surrounding air, and at the same time rises up, let him especially 

 show where the energy comes from to support the gyration and 

 force up the heavier air in the interior. I do not say that in 

 such a case there would not be a certain very small amount 

 of gyratory movement produced by the flowing of the air 

 into the trough while it was being filled up, as it would be at 

 once if there were no restraining force to keep the air from the 

 high pressures on each side from rushing in. But such high- 

 pressure areas continue often a long time, and do not fill up the 

 troughs ; and the question is, what maintains them 't 1 have fully 

 explained all this at various times upon my principles, and I now 

 leave it to him to explain upon his. I commence with a normal 

 state of air without high-pressure areas and troughs of low press- 

 ure, and show how the unstable state is induced, how from this 

 the cyclone originates, and how the gyrations cause a wave of 

 high pressure all around, and, where there are two cyclones, how 

 the ridge of high pressure between is caused. The low-pressure 

 between two cyclones, together with other irregularities of press- 

 ure, permanent or otherwise, in some rare cases, gives a very 

 oblong low-pressure area, or trough. Mr. Clayton proceeds in 

 the reverse order, and commences with the high pressures without 

 first accounting for them, which he makes a basis of his whole 

 process. The world is supported upon the shoulders of Atlas, and 

 Atlas upon the back of a tortoise ; but the question still arises, 

 upon what does the tortoise stand? Let Mr. Clayton first show 

 upon what his tortoise stands. 



With regard to Mr. Clayton's last question, I know nothing 

 with regard to the circumstances of the cyclone to which he refers. 

 It was in the winter, when surface temperatures are very low, 

 and vertical temperature gradients small, and even reversed some- 

 times near the earth's surface. This, however, does not affect the 

 gradient, estimated from a little distance above the earth ; but I 

 have said so much with regard to the inadequacy of a few surface 

 observations at the bottom of the great ocean of atmosphere to 

 prove that the air, or no part of it above, is not warmer than the 

 surrounding air, all of which is just as pertinent in this case, 

 that certainly nothing more can be required. As I have said be- 

 fore, the mere surface condition may have little or nothing to do 

 with a cyclone. But suppose I cannot esplaia it, as Jlr. Clayton 

 seems to think, " upon the assumption of a higher mean tem- 

 perature of the air-column within the field of the cyclone :" how 

 does he explain it upon the assumption of a lower mean temper- 

 atui'e and heavier air-column ? He proposes his question with an 



