334 ANNUAL OP SCIENTIFIC DISCOVERY. 



not entitled to assume that the sudden diminution of the electrical 

 tension of a cloud by a lightning discharge can have any material in- 

 fluence upon the rain-forming processes going on in the cloud. As, 

 however, very heavy showers of rain do almost invariably follow light- 

 ning discharges, it seems necessary to seek some other cause to account 

 for them. But if we admit that a violent concussion of the air has a 

 tendency to facilitate the conversion of rain-forming material into 

 actual drops of rain, then we may well suppose that the violent con- 

 cussions produced by lightning discharges, acting on such enormous 

 and dense masses of rain-forming material as are usually collected in 

 heavy thunder clouds, are amply sufficient to produce these sudden 

 and heavy showers of rain. 



" I am aware that the effect of a discharge of ordnance is usually 

 supposed to be produced by an upward current of air caused by the 

 heat and the gases evolved during the combustion of the gunpowder ; 

 but as an hour's sunshine through an opening in the clouds, especially 

 when the sun is at a considerable altitude, would produce a much 

 greater effect in heating and increasing the bulk of the air, this can- 

 not be received as the true explanation of the mode in which the ef- 

 fect of a discharge of heavy artillery is produced." 



RECURRING MONTHLY PERIODS AND PERIODIC SYSTEM OF THE 



ATMOSPHERIC ACTIONS. 



The above is the title of a recent English publication, by W. H. 

 Webster, a surgeon in the Royal Navy, who has devoted much atten- 

 tion to meteorology and collected an abundance of data from all quar- 

 ters. 



Mr. Webster believes himself to have discovered that the weather is 

 constantly marked by recurrences, separated by a solar month of 30 

 days. Accordingly, to him the same days of the month, or nearly 

 the same days, are critical, either show the highest or lowest barome- 

 ter of the month, or else the highest or lowest thermometer. This he 

 affirms he has verified in an enormous number of instances, of which 

 he gives a few. Of course we neither admit nor deny this discovery : 

 our business is only to describe it. We shall show our readers what 

 he gives us, from observations, for the year Sept. 1819 to Sept. 1820. 

 It appears that, 1819, Sept. 20 was the highest day of the barometer 

 for the month ; Oct. 22, Nov. 20, Dec. 22,"were the lowest. Feb. 15, 

 1820, and March 15, were highest days. Feb. 24 and March 24 were 

 lowest days ; April 23 was a highest day. May 1 and June 1 were 

 lowest days ; July 1 was a highest day. As to the thermometer, Jan. 

 15 and Feb. 17 were lowest days. March 6 and May 5 were lowest 

 days; but April 5 was highest. March 30 was highest, April 30 

 lowest. July 31 was highest, August 29 was lowest. 



Mr. Webster sets aside the supposed influence of the moon altoge- 

 ther, his periods being solar. 





