442 Supposed Connection of Meteoric Phenomena, 



Mr. Espy considers that an upper current of cold air over- 

 lapping one near the surface, containing, under the same pres- 

 sure, 30° or 40° less than the one below, would produce a 

 vortex. He refers the enquirers, as to the mode of formation 

 of this upper cold current, to a future number of the Journal, 

 which is to contain an essay on hail, in which this question is 

 resolved. The uppermost strata of the atmosphere are known 

 to be in constant motion from the south-west, throughout the 

 whole northern temperate zone. [Mr. Redfield has shown in 

 Silliman's Journal, xxviii. 155., that the proportions of westerly 

 surface winds in the state of New York are 647 in 1000, 

 and, of the upper wind, 912 in 1000; and it has been demon- 

 strated elsewhere that a s.w. wind blows constantly over the 

 United States.] Now, " the caloric evolved by the condens- 

 ation of vapour into rain causes about five times as much 

 expansion in the air containing the vapour, as condensation 

 by change of vapour to water." {Espy, p. 237.) In all rain, 

 then, there is an expansion, and, of course, an upward motion ; 

 hence, an outward motion in the upper, and an inward motion 

 in the lower, part of the cloud. Thus, a great rain in the 

 north causes a surface current from the south, and an upper 

 (not the uppermost) from the north. The overlapping part 

 after the rain must be very cold ; and an upward vortex may 

 be caused by a sudden rarefaction of the air in some cases of 

 rapid condensation. Mr. Espy considers this upward motion 

 as the cause of atmospherical depositions. 



I have been careful in giving a correct analysis of Mr. 

 Espy's reasonings, because they illustrate many of the positions 

 I have endeavoured to maintain in these essays, respecting 

 winds, aurorse, and other connected phenomena. I must con- 

 fess, however, that, if his notion of the formation of meteors be 

 correct, with what more powerful reason have I a right to 

 insist upon volcanic action, as instrumental in producing an 

 upward vortex ! If, then, my appeal to volcanoes be, as he 

 seems inclined to consider, " a wild speculation, or visionary 

 theory," in the general, thus far he must allow that I have 

 reason on my side in assuming heat suddenly developed from 

 the earth's surface as instrumental in the formation of those 

 phenomena, which, however immediately produced, are, un- 

 less we deny the evidence I have already brought forward, 

 intimately and inseparately connected. 



Mr. Olmsted's cometic theory, against which I have written, 

 must, whatever be the fate of the volcanic agency, be thrown 

 away. That gentleman is not the first who has laid meteoric 

 phenomena to the charge of a comet ; nay, Riccioli, Gregory, 

 Maupertuis, and others, have gone so far as to conclude that, 



