216 
such condensation may, and no doubt does aid in producing 
atmospheric movements. See Meteor ., Arts. 165, 171. 
But as respects the statement that I abandon the Hadleian 
theory of the winds, I can only say that nothing is farther 
from my thoughts, and that I must protest against any such 
mode of expressing my views. It is true that in describing 
the modus operandi in which the sun’s heat, acting on the 
equatorial regions of the earth, ocean, and air, produces that 
ascentional movement and overflow of the atmosphere which 
is what Hadley assumes as the primum mobile of his theory, 
1 have ( Meteorol ., Arts. 54, 55, 58) brought expressly and 
prominently into view the very considerable share which the 
generation and ascent of vapour has in producing that result, 
but without ignoring or in any way unduly depreciating the 
effect of the rarefaction of the air itself. On the contrary, it 
is expressly said (Art. 55), “ The general effect” (of the two 
causes) “ is similar, and as the sun cannot generate vapour 
without at the same time heating the air, it is impossible to 
separate their dynamical effects. Whether the air go forth 
from its place projmo motu or be jostled out of it by the 
introduction of a lighter medium, the local relief of pressure 
is equally produced.” When Hadley wrote, the distinction 
between air and vapour was not recognised. He took the 
atmosphere en masse and attributed to it an ascentional move- 
ment due to the heat of the sun, by the process of “ rarefac- 
tion ;” and this, so worded, remains true, although such 
rarefaction be a more complex process than he understood it 
to be. 
The displacement of air by vapour, the disturbance of 
statical equilibrium* and the dynamical effects consequent 
thereon, are no new principles in meteorology. They have 
been strongly insisted on, and, if I may venture to say so, 
rather over insisted on, and with a premature air of reduction 
to computative precision, by Daniell in his Meteorological 
Essays, and perhaps hardly enough insisted on in my w'ork 
