442 SHORT MEMOIRS ON METEOROLOGICAL SUBJECTS. 



responds to a rotation from right to left in the northern hemisphere, 

 but the contrary in the southern hemisphere. In our hemisphere, v, 

 and therefore AB, will be negative for a motion from left to right; that 

 is to say, a higher pressure prevails in the center. Ferrel now explains 

 by his formula the diminution of atmospheric pressure toward the 

 poles, in that he treats the prevailing easterly movement of the air out- 

 side of the tropics as "polar cyclones." In a similar manner originates 

 the low pressure at the equator and the high pressure in the neighbor- 

 hood of the tropics between the two great cyclonic movements of the 

 atmosphere. 



We refer those of our readers who are further interested in this part 

 of Ferrel's deductions, besides the memoir just reviewed, especially to 

 the memoir in the number for January, 1861, of Sillimau's American 

 Journal, 2d series, vol. xxxi, entitled "The Motions of Fluids and Solids 

 Eelative to the Earth's Surface." We find therein a complete theory 

 of a new, somewhat complicated, system of atmospheric circulation.* 



From this latter, earlier memoir of Ferrel's, we will here quote some 

 additional paragraphs having reference to storms, because they present 

 his views in reference to the origin of storms, which are scarcely to be 

 inferred from the memoir just reviewed. In the third chapter, "The 

 Motions of the Atmosphere arising from Local Disturbances," are found 

 the following remarks : 



Excess of heat or increased amount of aqueous vapor is the first 

 cause of the ascent of air and the influx from all sides. The inflowing 

 air ascends, condenses its aqueous vapor, whereby its ascensional power 

 is further increased, and from this cause the disturbance can continue 

 for some time. For reasons previously given, this process can, in the 

 equatorial regions, give rise at the most to tornadoes only, and in fact 

 Eeid's charts show no cyclone traced back to 10° latitude, no typhoon 

 traced beyond 9°. The greater expansion of the air in consequence of 

 higher temperature and greater quantity of vapor must without doubt 

 exert an influence upon the barometric pressure. Notwithstanding this, 

 that theory is untenable which ascribes all barometric variations to the 

 condensation of cyclonic vapor, for according to it the variations of 

 atmospheric pressure would be greatest at the equator. The atmosphere 

 is exceedingly mobile. Every disturbance of equilibrium will be quickly 

 restored hy an inflow of air, provided no whirl arises. If, therefore, the 

 earth had no rotation about an axis, then would the non-periodical 



* Our author lias apparently not had access to the more important and earlier memoir 

 of Ferrel "On the Motions of Fluids and Solids, &g.," in "Runkle's Mathematical 

 Monthly," volumes i, ii, and iii; Cambridge and New York; 1357 to 1859. These 

 volumes, although rare in Europe, are, however, still easily obtained by American 

 students from Sever & Francis, of Cambridge, Mass., and should be consulted. Copies 

 of a subsequent separate reprint of this fundamental memoir were published by Ferrel 

 in 1860. The memoirs referred to by Hann in Silliman's Journal are to be considered 

 as elementary expositions of the rigorous equations published in the Mathematical 

 Monthly.— Note added by the Translatok. 



