W. Ferrel—Cyclones, Tornadoes and Waterspouts. 39 
vanish and change signs, then giving rise to the anticyclonal 
part of the system, as in an ordinary cyclonic system. 
A local cyclone of this sort, with much violence or long con- 
tinuance, cannot take place. For if there was a central colder 
area which would give rise to the initial motions of such 
a cyclone, the air in its descent in the interior would become 
° C. warmer for each one hundred meters of descent, and 
hence the colder initial temperature of the central part would 
soon be so increased as to equal that of the atmosphere generally 
surrounding, when the condition giving rise to initial motion 
would be destroyed and all motion cease. In such a case 
there would be no advantage in a moist atmosphere, since if it 
were even saturated as soon as descent in the interior would 
commence, it would become unsaturated. Hence we never 
have any violent cyclones of this sort, and nothing more than 
initial disturbances which continue generally only a short time. 
Fixed Cyclones.—Where the primary cause of temperature 
disturbance is fixed to one spot on the earth and kept up con- 
tinuously, it gives rise to a fixed cyclone. Such an example is 
furnished by a warm island surrounded by a colder sea. This, 
unless it were very near the equator, would give rise to consid- 
erable cvclonic disturbance, and, if the island were of consider- 
able extent, to an observable barometric depression. A ver 
remarkable example of such a cyclone exists in the northern 
part of the Atlantic ocean. ere, on account of the Gulf 
In the summer season the temperature gradients nearly 
disappear, and’ there is very little cyclonic disturbance over 
this region or barometric depression in the vicinity of Iceland. 
