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[Vol. XVII. No. 413 



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NEW YORK, Januabt 2, 1891. 



No. 413. 



CONTENTS: 



a Cure for Tetanus and Diph- 

 theria. E. H, JSankin 



Health Matters. 

 Risks to Health in East Africa. . 



Notes and News 



Letters to the Editor, 

 a New Kansas Meteorite 



F. H. Snow 

 Dr. Haunts Studies on Cyclones 

 and Anticyclones 



W. M. Davis 



Moisture in Storms 



S. A. Hazen 

 The Subtropical Zones of High 

 Barometric Pressure 



Wm. Ferrel 

 Recent Investigation on the 

 Causes of Cyclones and Anti- 

 cyclones. H. Helm Clayton... 

 Book-Reviews. 

 Handbook of Problems in Direct 



Fire 



4 Among the Publishers 



LETTERS TO THE EDITOR. 



[Continued from p. 5.] 



The Subtropical Zones of High Barometric Pressure. 



There is an old theory, if a mere popular notion which has no 

 scientitic basis whatever may be so called, that the two zones of 

 high barometric pressure, extending with a few interruptions 

 around the globe, and having their maxima of pressure about the 

 parallel of 35*^ in the northern hemisphere, and 30° in the southern, 

 are caused by the crowding of the air, in its passage in the upper 

 part of the atmosphere from the equatorial to the polar regions, 

 into iutermeridian spaces, becoming gradually narrower toward 

 the poles. It is supposed that the air, as it is forced into narrower 

 spaces, is turned down toward the earth's surface, and that this 

 descent of the air causes increased pressure on the surface. The 

 barometric pressure in both hemispheres increases from the poles, 

 or at least from some high parallel, toward the equator, until the 

 parallels above mentioned are reached, and then there is a small 

 decrease of pressure to the equator; so that these parallels are 

 simply the limits between the increasing and decreasing pressure 

 gradients in going from the pole to the equator, and the culminat- 

 ing parallels of the convexity of the isobaric surfaces. 



The writer's attention was first directed to this feature of these 

 isobaric surfaces about thirty-five years ago, in reading Lieut. 

 Maury's " Physical Geography of the Sea; " and, having no faith 

 in the popular explanation, he made it a matter of study in order 

 to discover the true cause. This was found in the now well-known 



law of the deflecting force of the earth's rotation, which was first 

 discovered at that time. By this law the air, in moving from 

 west to east in the middle and higher latitudes, is pressed toward 

 the equator; but, in moving the contrary way in the lower lati- 

 tudes, it is pressed a little toward the poles, thus causing a bulging- 

 up of the isobaric surfaces with the culminating lines between 

 the two systems of easterly and westerly currents about the, 

 parallels of 35° or 30°. The results were published in an " Essay 

 on the Winds and the Currents of the Ocean," which was subse- 

 quently republished in " Professional Paper of the Signal Service," 

 No. XTI. 



Subsequently this Whole subject was treated in a more thorough 

 and mathematical manner, and the results were published in a 

 memoir entitled "Motions of Fluids and Solids Relative to the 

 Earth's Surface." This was afterwards republished in "Profes- 

 sional Paper of the Signal Service," No. VIII., with extensive 

 notes by Professor Frank Waldo. In this memoir it was shown 

 that with certain assumed values for the velocities of the easterly 

 and westerly motions of the air, which were quite reasonable and 

 probable from what was known of these somewhat uncertain data, 

 the deflecting force of the earth's rotation would give the observed 

 increase of pressure, on the one hand from the pole, and on the 

 other from the equator; so that there was no room to doubt that; 

 the maximum pressure a little above the tropics in each hemi- 

 sphere was caused by this force. A very full abstract of this 

 memoir was also given in Silliman's Journal, January, 1861. 



Subsequently this same subject was taken up again, and treated 

 in a more thorough manner and with better data, and the results 

 published in "Meteorological Researches," Part I., ''Coast Survey 

 Report for 1875." 



The same subject was again treated by the use of mathematical 

 processes somewhat simplified, and given in "Recent Advances 

 iu Meteorology," forming Part II. of the " Report of the Chief 

 Signal Oflicer for 1885." 



Finally the whole matter was gone over again by the writer in 

 a popular manner, and explained by means of various simple 

 illustrations, and was given in his "Popular Treatise on the 

 Winds," etc. 



Dr. Hann, however, has not accepted the results, nor has he 

 ever attempted to show that they have been deduced from errone- 

 ous principles or processes, but has continued to use and uphold 

 the old theory. Not only this, but he has based upon it a new 

 theory with regard to the cause of the high-pressure areas of the 

 middle and higher latitudes. In the Zeiischrift fur Meteorologie 

 for 1879, p. 39, he first suggests that these regions of high baro- 

 metric pressure may be simply the places where the upper equa- 

 torial and westerly currents settle down towards the earth's sur- 

 face, as in the case of the zones of high pressure at the polar 

 hmits of the trade- winds. His idea is. that as the upper poleward- 

 moving currents in the latter are deflected down by their being 

 crowded between intermeridional spaces, gradually becoming 

 narrower toward the poles, so, even beyond these belts of high 

 pressure, there must be local hinderances, or a damming-up of 

 these currents, by which they pass into descending ones toward 

 the earth, and so cause the high-pi-essure areas. 



In the next volume of the Zeitschrift he again refers to this 

 matter, and suggests that the reason why cyclones and great 

 barometric disturbances are more frequent in winter than in sum- 

 mer is that in winter the temperature and pressure gradients of 

 the upper strata of the atmosphere, in a poleward direction, are 

 greater, and hence there is a greater sti-ength of current at this 

 season of the year. 



Again, in his ''Climatology," published a few years ago, this 

 same old theory is given in explanation of the subtropical zones of 

 high pressure. 



Finally, in his recent memoir published by the Royal Academy 

 of Sciences of Vienna, the old theory of the subtropical high- 

 pressure belts is introduced, and also his new theory, deduced 

 from it, of the causes of high-pressure areas; and he refers to his 

 preceding papers in the Zeitschrift on these subjects. 



Although the teaching of Dr. Hann on these subjects has been 

 entirely at variance with the writer's own views on the same sub- 

 jects, previously published at so many different times, yet he has 



