446 THE POPULAR SCIENCE MONTHLY 



what we call our storms, but technically are called cyclones and anticy- 

 clones. It would be beyond my province to attempt to analyze the tech- 

 nical side of the theories of cyclones and anticyclones, and yet the 

 subject of circulation would be so incomplete without at least alluding 

 to the prominent attempts which have been made to solve these great 

 questions that I shall venture a few remarks along this line. 



The circulation of the air is classified as general and local, " gen- 

 eral " applying to the whole hemisphere, of which some description 

 has been given, and " local " as applying to the individual storms and 

 their accompaniments. The local storms are known as cyclones and 

 anticyclones, hurricanes, tornadoes and water spouts. They are all 

 features or phases of the circulation and can be referred back to a 

 few simple mathematical laws. Two attempts were made to solve the 

 question of the general circulation, but the year 1896-7, which repre- 

 sents a new era in meteorology, when the international cloud observa- 

 tions were established under the leadership of Dr. Hildebrandsson, 

 marks an epoch in the theory of the subject. I refer to those of Ferrel 

 and Oberbeck regarding the general circulation. They had one picture 

 in mind, namely, that of the simple canal, heated at one end, to which 

 allusion was made in the early paragraphs of this lecture. They con- 

 ceived the air to flow from the tropics northward towards the poles in 

 the upper levels, and from the poles towards the equator in the lower 

 levels, the northward current being separated from the southward cur- 

 rent by a neutral plane along which there was no motion. Ferrel dis- 

 cussed the equations of motion adapted to the general hemisphere, and 

 threw considerable light upon the subject. He conceived the rings of 

 parallel 33° to move towards the poles with increasing velocity, and he 

 made serious efforts to account for the fact that the velocity in higher 

 latitudes is comparatively moderate instead of excessively great, as his 

 equations demanded. If Ferrel derived an excessive velocity near the 

 poles, Oberbeck, as a result of his complex integration, derived an ex- 

 cessive velocity in the upper levels over the tropics. Neither of these 

 authors accounted for the reversal of direction from west to east at a 

 moderate elevation, as 10,000 meters over the tropics, nor did they at- 

 tempt to take into account the great irregularities in the circulation in 

 an east and west direction, which we have described in discussing the 

 centers of action. The result of the work of the Weather Bureau in 

 the international cloud observations in the year 1896-7, was to destroy 

 this theory of a neutral plane separating the upper northward current 

 from the lower southward current. In place of that it was explained 

 that these interchanging currents, instead of passing over each other 

 at different levels, really interpenetrate and pass by each other on the 

 same level ; that is to say, warm air moves from the tropics towards the 

 poles in all levels, and cold air from the poles towards the tropics in 



