THE FORMATION OF CLOUDS. 



501 



HIGH 



LOW 



Newton. To lay out the paths of motion in the atmosphere is just as 

 important a work as that of finding the orbits of planets. There is 

 more difficulty in doing it accurately because the motions of the air 

 are much less steady and symmetrical than those of single masses 

 like planets, comets and meteors, but it can be accomplished by 

 patience and well-directed work. Unfortunately for lack of this sort of 

 data much of our common meteorology is incorrect, and must be laid 

 aside as of only an historical value. The subject is itself very complex, 

 and it is unsuitable for a popular exposition, but an idea can be given 

 of its scope and tendency by reference to the accompanying charts. 



The Chart 4, marked 'Storm in the Lake Region' 'Winter Cyclone 

 or Low Area,' is a composite map of the motions of the air around a 

 winter storm central near Lake Superior. The upper or cirrus cloud 

 movements are shown by the dotted arrows, the lower or cumulus, by 

 those drawn with a broken line, and 

 the surface wind by those with one 

 unbroken line. The region affected 

 by this storm extends from the 

 Gulf of Mexico to the Lakes, and 

 from the Atlantic Ocean to the 

 Rocky Mountains. It is noted that 

 the arrows drawn with an unbroken 

 line and those drawn with a broken 

 line generally blow nearly side by 

 side, but that they differ from the 

 dotted arrows in many cases, espe- 

 . cially near the center of the storm 

 and eastward to the ocean. This 

 shows that the real storm circula- 

 tion is confined to the lower strata 

 as if it were quite independent of 

 them. There is seen to be a slight 

 deflection of the dotted arrows south- 

 ward around the low ; a correspond- 

 ing chart of a high area would show a similar deflection to the north- 

 ward of the centej. This feature is brought out in Chart 5. Direction 

 and velocity of the motions of the air in the cirrus, cumulus and on the 

 surface. The arrows are not very smoothly laid down with reference 

 to one another, but this is due to the fact that there were not enough 

 observations taken in order to smooth out the local irregularities. Still, 

 it is easy to trace a sort of wave motion, a crest over the high and a 

 hollow under the low. As we come down from the cirrus, six miles 

 high, towards the ground the sinuous motion becomes more pro- 

 nounced, till in the strato-cumulus level the rotary component is dis- 



ye/aci/y, 

 ■iA/r/es 

 perhoifr 



Chart 5. Direction and velocity of the 

 motions of the air in the cirrus (6 miles high), 

 the cumulus (1 mile high) and on the surface 

 (wind). 



