1915-16.] The Dynamics of Cyclones and Anticyclones. 175 
that the cyclone np to 10 kilometres is on an average 7°*4 C. colder 
than the anticyclone; while from 10 to 14 kilometres it is 7°*3 warmer; 
and Mr Dines considers that, taken as a whole, the cyclone is colder than 
the anticyclone by 5°. Let us now turn to the effect of pressure. In the 
table referred to cyclones have an average pressure at the earth’s surface of 
29*2 inches, while the anticyclones have a pressure of 30*3. This gives a 
difference of pressure of 1’1 inch, which is 1/28*5 of the anticyclonic pressure. 
The air in its passage to the cyclone will be expanded by fall of pressure 
by 1/28*5 of its volume. Now, air is only expanded by heat by 1/273 of its 
volume at 0° per degree C. With these figures we see that the reduction 
of pressure reduces the density of the air as much as heating it 9° *5 would 
do. So that the reduction in density by loss of pressure more than com- 
pensates for the lower temperature in the cyclone at the earth’s surface, 
and it seems probable that the same relative difference, or even a greater 
difference, will continue up to great heights owing to the velocity of the 
winds increasing with the elevation. 
It may be objected that we should not take the extremes of pressure 
and allow for so great a reduction of pressure, because the cyclone does 
not rise in the anticyclone, but in the air at a lower pressure at a distance 
from the anticyclone. That is quite the case ; but if we allow for a fall of 
only half the amount of pressure, we must also allow for the less difference 
in temperature, as the air surrounding a cyclone has a temperature much 
lower than that of the anticyclone. The above figures work out very 
much the same if we use half the difference in pressure and the mean 
temperatures as given in the table referred to. 
We will turn now to the second objection to the convection theory, 
namely, the lower level of the stratosphere over cyclones, and the higher 
level over anticyclones. But before proceeding to consider these objections 
I should like to call attention to a phenomenon which all of us have 
witnessed. It is so common that we have either not seen the wonder of it, 
or it has ceased to interest us. The wonderful thing to which I refer is a 
jet of steam issuing from a boiler under high pressure. And yet that jet is 
a most perfect illustration of the conversion of potential energy into energy 
of motion. Let us look more closely at the facts. Suppose that there is a 
short open pipe connected directly to the boiler, and that steam is issuing 
from the open end. If you ask, “ What is the pressure of the steam in the 
pipe ? ” many people would say, “ It is the same as in the boiler.” But 
those who have studied the matter know there is no pressure in the steam 
in the pipe ; that is, its pressure is the same as that of the air into which it 
is escaping. A moment’s consideration will convince us that this is correct. 
