October 24, 1890.] 



SCIENCE. 



237 



said that uj^on this earlier theoretical computation depends a great 

 deal of Ihe present theory of the generation of storms. 



Dr. Hann tries to show by observations at Pic du Midi, Feb. 19- 

 March 14, 1883, that the lowest pressure at that station did not 

 accompany a high (anticyclone) at the base. It seems to me that 

 this case establishes my position; and if Dr. Hann still insists that 

 he is right, in the face of these observations, there is no possibility 

 of our coming to an agreement, but others must settle the point 

 between us. I have repeatedly insisted that we must discuss con- 

 ditions at the centre of low and high only, and that we can never 

 take a diminished or a low pressure either at the base or summit 

 of a mountain to indicate that the centre of a low (cyclone) is 

 passing over. It is also probable that there must be added to this, 

 that the low or high m'ust advance at some velocity from a westerly 

 direction, or they must have simply their normal condition, as in 

 the United States. In Europe I find tracks of both these condi- 

 tions exceedingly erratic, frequently wandering toward the west, 

 then again stopping, especially highs, for a week or more. We 

 are almost totally unacquainted with such conditions in this coun- 

 try. It seems highly probable that the general acceptance of 

 Espy's stationary low (cyclone) theory by the authorities in Europe 

 is largely due to this cause. A velocity of forty miles an hour 

 (eighteen metres per second), such as we encounter in this coun- 

 try, might stagger our Eastern meteorologists. In the case given 

 by Dr. Hann there is a steady fall of pressure at Pic du Midi and 

 Toulouse from about March 5 to March 10. On examining the 

 weather-map, I find a wandering low moving erratically just be- 

 fore and up to March 9. It has very little intensity as we regard 

 them in this country, and cannot be taken as a typical low (cy- 

 clone) in any sense. On the other hand, a high (anticyclone) 

 appears in Spain on March 10, exactly the condition I have insisted 

 on. In any event, it is plain that the low temperature is due to 

 the strong northerly and north westerly winds induced by the 

 high and low combined, and has absolutely no connection with 



the distribution of temperature in a vertical direction in the centre 

 of a low (cyclone). The low does not approach Pic du Midi till 

 March 9, when it is in North Italy. How any one can think that 

 such a position of the low can have any bearing on this discussion 

 seems impossible to understand. The low temperature at the 

 summit undoubtedly was a factor in keeping down the pressure 

 there. 



Dr. Hann attempts to show that on the approach of a low on 

 Mount Washington the temperature rises, owing to south and 

 south-east winds in front. Loomis proved many years ago that 

 the circulation in a low at sea-level does not take place at Mount 

 Washington, so this speculation falls to the ground. It seems to 

 me the discussion published in Science, Sept. 5, settles this question 

 beyond a peradventure, although it would be a matter of gratifi- 

 cation if some one else should be induced to repeat the investiga- 

 tion. I have just received a letter from Dr. Hiring of Germany, 

 who has studied the matter thoroughly, and who agrees with my 

 position that there is no reversal of temperatui-e in a low, but is 

 not quite willing yet to accept the same for a high. It seems to 

 me the evidence is all one way, and that, if we accept the results 

 of this investigation in the case of a low, we must do so also in 

 that of a high. H. A. Hazen. 



Washington, Oct. 10. 



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