ATMOSPHERICAL PHENOMENA. 547 



[Aurora of 17th November, 1835.] 



At Schenectady, New York, it rained or snowed every day, from the 

 10th till the 16th, and on the 17th, there was a brilliant aurora at Ger- 

 tnantown, reaching from the north star to the zenith, when, at the same 

 time, precisely, at Philadelphia, five miles south of Germantown, the au- 

 rora was very faint, and did not reach above Lyra, Polaris, and Capella. 

 At New York, it reached from the northern horizon, 12 south of the 

 zenith, and along the horizon to south by east, and south by west; while 

 at Providence, Rhode Island, as described by Professor Caswell, it never 

 extended beyond the zenith, and only reached along the horizon as far 

 as N. W. and N. E. All these have been evidently different auroras, 

 they must have been low in the atmosphere. 



The preceding phenomena, and many others, which 1 have not room 

 to insert, render it certain that the aurora is sometimes low in the atmos- 

 phere. 



[From the Edinburgh New Philosophical Journal, for October to January, 

 Itf40, page 413.] 



Mr. E spy's Theory of Atmospherical Phenomena claimed by Mr. Meikle, 

 of Edinburgh. Respecting Mr. Espy's theory of atmospherical phe- 

 nomena, the leading feature of which', is the fall of temperature which 

 occurs in an ascending current of air, we are requested, by Mr. Meikle, 

 to state, that, in the London Quarterly Journal of Sciences, lor April, 1839, 

 and in the article Hygrometry of the Encyclopedia Britanica, vol. XII. 

 p. J32, he has distinctly laid down the same theory in detail, and accom- 

 panied it with various calculations and illustrations, which show how it 

 will satisfactorily accpunt, not only for the production of clouds, moun- 

 tain caps, rain, snow, &c., but also for thunder, lightning, and water- 

 spouts, if not some of the phenomena of volcanoes, and the northern 

 lights. 



To do justice to Mr. Meikle's claim, I have copied from the Ency. 

 p. 135, the following paragraphs. 



"The sound (in thunder,) may be partly a tremor, which the air sus- 

 tains, at the moment the pressure is relaxed by the vapor suddenly losing 

 the elastic form, and may be partly a tremor due to an effort of the elec- 

 tricity to make its escape from the cloud. 



Page 134. "It is evident that moisture which has ascended in the 

 form of transparent vapor, and descended again as rain, snow, &c., must 

 have left its latent heat above. But much heat, no doubt, moves upward 

 from its natural propensity to render the atmosphere of one temperature 

 throughout its whole height, and from the tendency of warmer air to 

 rise above the colder. There is, therefore, good reason for concluding 

 that air which has just been elevated and dilated should be thereby re- 

 duced to a much lower temperature, than what obtains in air, which has 

 remained at that elevation for some considerable time, receiving heat from 

 below, from the sun, or other sources." 



The principle of the dew point has many applications highly useful. 

 One is given here as a specimen of its connexion with medicine. 

 Others might be adduced of its connexion with the refraction of light in 

 the atmosphere, and of its power in predicting a change of temperature 



