454 THE POPULAR SCIENCE MONTHLY 



to four or five miles high. The strongest inward component was in 

 the strata cumulus levels about two miles above the ground. Above 

 this level and below it there was a radial inward velocity of a certain 

 value corresponding to each level. There was no clear indication that 

 the inward component in the lower levels reversed to an outward com- 

 ponent in the upper levels, and it looked as if the intruding vortex of 

 the lower levels did not succeed in reaching the middle plane where 

 theoretically the outward component begins to develop. It looked as 

 if this vortical system was so stripped of its natural features, by the 

 action of its intrusion into the eastward drift, that only the lower half 

 of the vortex really survived, and that there was an insistent struggle 

 of the rotating cyclone with this eastward drift for the mastery. In a 

 word, the upper sections of the vortex were stripped bare, and they 

 gradually died out at the height of three or four miles within the east- 

 ward drift. What remains then is a set of stream lines in the lower 

 levels which have certain features in harmony with the pure vortex 

 system, though only roughly conforming to them, and which in the 

 upper levels is broken down into a very imperfect kind of vortex. 

 It should be said in passing that it is very difficult, on account of the 

 prevailing clouds which occur in the cyclones of the United States, to 

 get satisfactory measures of the cloud motions in the upper levels. 

 Cumulus clouds develop strongly below the one-mile level, and above 

 them it is possible to get the cloud motions in the higher levels only 

 through the more or less occasional rifts in the lower cloud sheets. It 

 is therefore very desirable that an extensive campaign of theodolite 

 measurements of cloud motions in the upper levels of cyclones be insti- 

 tuted, in order to carry out much more fully the details of the discus- 

 sion which have been suggested in this fundamental research. 



Temperature Distribution 



Having now described the general and local circulations in the 

 temperate and tropical zones, it is important to make some further 

 remarks regarding the distribution of temperature in those regions, 

 also including the distribution of temperature in the sun itself. The 

 circulations which take place are accompanied by certain changes of 

 temperature in a vertical direction, called temperature gradients, which 

 are characteristic of them. If a cubic centimeter of air at the sea level 

 is lifted up to higher levels, so that it cools simply by the expansion of 

 its own mass, and there is no mixture of warmer or colder air with it 

 from the outside, then the temperature will fall 9.87° Centigrade for 

 every 1,000 meters. Now it is found by balloon observations that the 

 temperature gradients in different regions do not conform to this fun- 

 damental rule, which is called the law of adiabatic expansion. In the 

 tropics in the lower levels this rate is very nearly approached, but there 



