THE DEVELOPMENT OF METEOROLOGY. 
55 
spread over a layer of warm air, resting quietly upon it with 
the help of an intervening diaphragm, and the latter be re- 
moved, we all know that the cold air must descend and the 
warm air rise — a process of overturning such as is occurring 
every day in the atmosphere. The mechanical conditions 
or mechanical theory of this upsetting were recently worked 
out by Margules, and his views, with some important modi- 
fications, are developed by Professor Bigelow in such a way 
that a certain conclusion is inevitably reached. This over- 
turning takes place not merely in a small way, as in thunder- 
storms, but on the grandest scale in tropical hurricanes. 
Now the question has been discussed pro and con for a hun- 
dred years as to whence comes the energy involved in the 
production of the rapid rotary winds of hurricanes. Espy 
maintained that in thunderstorms this energy was derived 
from gradients due to the condensation of aqueous vapor and 
the evolution of heat in the clouds. I thought it due also 
largely to the sun’s heat acting on the top of the cloud. Pro- 
fessor Bigelow shows that while these are true causes, yet for 
hurricanes they are entirely insufficient, and that the energy 
of these great storms is mainly derived from the gradients 
produced by the overturning of layers of cold air flowing from 
northern latitudes over the warm air that is flowing from 
southern latitudes; by the descent of this cold air to the 
ground the force of gravity gives it great velocity and mo- 
mentum. In other words, we must not look upon a great 
storm as a symmetric cyclone with a center of warm rising air 
and an inflowing peri cyclone of cold air, as was taught by for- 
mer meteorologists, but we must face the problem of a simple 
overturning in the lower strata of the atmosphere below the 
level of the general west wind that is flowing a few miles 
above us. The ideal cyclone and anticyclone probably do 
not exist in the atmosphere. This conclusion gives precision 
to an idea that Ferrel fully acquiesced in, namely, that the 
atmosphere has no simple circulation, cyclonic or anti- 
cyclonic, but is a complex mass of interlacmgs of currents; 
so that the progress made by himself in studying ideal types 
must sooner or later be replaced by researches that adhere 
more closely to the actual phenomena of nature. 
