CLAYTON. — THE ECLIPSE CYCLONE. 315 



cyclone are eliminated except that of a direct and rapid change of tem- 

 perature. The results derived from the observations by eliminating the 

 influence of other known phenomena give quantitatively the effects of 

 a oriven fall of temperature near the earth's surface in a given time. 

 They show that a fall of temperature is capable of developing a cold-air 

 cyclone in an astonishingly short time, with all the peculiar circulation 

 of winds and distribution of pressure which constitute such a cyclone. 

 They show, furthermore, that a fall of temperature of the air does not 

 act primarily to cause an anticyclone but a cyclone, and the anticyclone 

 is a secondary phenomenon, or rather a part of the cyclone. 



The eclipse cyclone shows no apparent lag or dynamic effect due to 

 the inertia of the air. To keep pace with the eclipse shadow moving 

 about two thousand miles an hour the eclipse cyclone must continuously 

 have formed within the shadow and must have dissipated in the rear 

 almost instantly. In this way its motion may be considered to have a 

 certain analogy to wave motion. Any given particle of air moving with 

 the velocity of the eclipse winds could not have moved more than Ave 

 miles as a maximum during the passage of the eclipse. Hence all the 

 changes of pressure must have been derived from the deflective influence 

 of the earth's rotation acting on air moving this distance. 



In brief, the meteorological effects of the eclipse are important — 



(1) Because they confirm so fully P^errel's theory of the cold-air 

 cyclone ; 



(2) Because they show the wonderful rapidity with which cyclonic 

 phenomena can develop and dissipate in the atmosphere ; and 



(3) Because they show that cyclones do not necessarily drift with the 

 atmosphere, but move with their originating cause, which in the eclipse 

 had a progressive velocity of about two thousand miles an hour. 



The DruRNAL Cyclones. 



The discovery that the brief fall of temperature attendiug a solar 

 eclipse produces a well-developed cyclone which accompanies the eclipse 

 shadow at the rate of about two thousand miles an hour, suffsests that 

 the fall of temperature due to the occurrence of ni^ht must also produce 

 or tend to produce a cold-air cyclone. Since the heat of day produces or 

 tends to produce a warm-air cyclone, there must tend to occur each day 

 two minima of pressure, one near the coldest part of the day, and an- 

 other near the warmest part of the day, with areas of high pressun; 

 between them due to the overlapping of the pericyclones suirouiiding the 



