296 THE POPULAR SCIENCE MONTHLY. 



"A storm must be treated as an individual which is subject to development. 

 This is difficult, on account of the nature of the subject, but it is possible and 

 essential. We must take the storm at its earliest appearance, and not lose sight 

 of it for one moment until we know it throughout its whole extent, in all its 

 parts, from beginning to end." 



This view of Prof. Blasius coincides with that of Sir William Her- 

 echel, who says : 



" In endeavoring to interpret the weather, we are in the position of a man 

 who hears at intervals a few fragments of a long history related in a prosy, un- 

 methodical manner. A host of circumstances omitted or forgotten, and the 

 want of connection between the parts, prevent the hearer from obtaining pos- 

 session of the entire story." 



Definition of a Storm. But leaving methods and passing to 

 results, our author defines a storm in general to be " the movement of 

 the air caused by its tendency to reestablish an equilibrium which has 

 been disturbed / and we may call all such movements storms, whether 

 they are gentle breezes or furious hurricanes, whether accompanied by 

 more or less condensation of moisture or clouds, or even by none at 

 all," as in deserts. 



Classification of Storms. As the result of his investigations in 

 aerial movements in the northern hemisphere, Prof. Blasius presents 

 the following classification of all storms : 



1. Local or Vertical Storms. Stationary. Centripetal. Produced by a 

 tendency of the atmosphere to reestablish in a vertical direction an equilibrium 

 that has been disturbed. Characteristic cloud cumulus. 



2. Progressive or Lateral Storms. Traveling. Produced by a tendency 

 of the atmosphere to reestablish in a lateral direction an equilibrium that has 

 been disturbed. They are of two kinds : 



(a.) Equatorial or Northeast Storms. Winter storms. Produced by a 

 warm current displacing a cool one to supply a deficiency toward the poles. 

 Temperature changing from cool to warm. Direction to the northeastern quad- 

 rant. Characteristic cloud stratus. 



(b.) Polar or Southeast and Southwest Storms. Summer storms. Pro- 

 duced by a cool current displacing a warm one to supply a deficiency toward 

 the equator. Temperature changing from warm to cool. Direction to the 

 southern semicircle. Characteristic cloud eumulo-stratus. 



3. Loco-Progressive or Diagonal Storms. . Traveling locally. Rotary 

 tornadoes, hailstorms, sandstorms, water-spouts, etc. Produced by a tendency 

 of the atmosphere to reestablish the equilibrium of a polar storm which has 

 been disturbed in the plane of meeting by a peculiar configuration of the 

 ground. Direction, the diagonal of the forces of the two opposing currents 

 transversely through the polar storm. Characteristic cloud conus. 



In order that the significance of the above classification may be 

 clearly understood, it will be well to notice in brief outline the general 

 movements of the atmosphere surrounding the globe, more especially 

 those in the northern hemisphere. 



