298 Our Climatic Vicissitudes. [June, 



condensed in a slow drizzling rain ; but even then the weight of the 

 shower comes on, when in the upper regions the western current has 

 already commenced its work of condensation ; and this generally happens 

 before we have any suspicion that the occidental current has set in ; for 

 the base of any wind would be retarded by the friction of the earth, and 

 its top leans forward in the direction of its course, and may be busy 

 shaking down the rain over our heads, while its tardy base is miles be- 

 hind the shower. In such cases we do not perceive the current that 

 caused tlie shower, until the shower itself has passed. It is only in the 

 van of the western current, then, that Jupiter Pluvium rules and rains, 

 for as long as the west wind steadily blows, so long will drought prevail. 

 But the fertility of our valley is insured by the frequent intrusion of 

 the deflected trades with its wealth of refreshing waters. 



But we must notice Espy's theory, which is somewhat different. He 

 supposes that all, or nearly all, storms, are produced by an uprushing 

 current of air, in the place where the center of the storm is raging. 

 Some local circumstances first set this upward flow in motion, such as 

 land heating faster than water under the sun's rays, or a valley becoming 

 warmer than the surrounding country, or some soil heating faster than 

 others, or great fires, or any such cause of sufficient intensity to initiate 

 the ascending current. Then, he says, the development of latent heat 

 by the condensation of the moisture in the upflowiug air, will intensify 

 the upward flow, and thus air will blow from all points toward the center 

 of the storm, and drop its load of moisture as it mounts to the sky. 



Believing this the true theory, he maintains that showers could be 

 produced by building large fires, and proposed this remedy for drought. 

 He tells of many instances of rain brought on by fires ; and, among 

 others, the following interesting account is given by George Mackay, 

 who was, at the time spoken of, engaged in surveying in Florida, and in 

 running their lines, they frequently encountered marshes, covered at the 

 time (it being the dry season,) with large quantities of dried grass and 

 reeds, which greatly impeded their progress, and to remove them, they 

 would sometimes set them on fire. On one occasion, the narrator says, 

 " AVe were now on the confines of a saw-grass pond, and a much more 

 formidable one than any we had yet encountered. Being surrounded by 

 a cypress sv>'amp, we concluded that it had never yet been burned. My 

 assistant, Cnpt. Alexander Mackay, who was standing by my side, men- 

 tioned his having, in a former conflagration, observed the formation of a 

 c'oud at the apex of the smoke. He added, that it had frequently since 

 brought to his mind some account which he had read of Professor Espy's 

 theory. He suggested that there could not be a better opportunity than 



