C. EF. Dutton—Effect of a warmer Climate upon Glaciers. 7 
resulting mean velocity of the winds would be y1:07=1-035, 
or about three and one-half per cent greater than at present. 
But suppose the wind potentials increased in a geometrical 
ratio with the temperature of air. The result would of course 
depend altogether on the form of this ratio. But taking it in 
its simplest form (logarithm of the potential simply proportional 
to the absolute temperature) the increment in the wind-velocity, 
resulting from 20° increase of mean temperature, would be less 
than six per cent. Larger geometrical ratios can of course be 
arbitrarily postulated, but they would require a very stalwart 
defense to entitle them to a hearing. 
(13.) Let us now go back and review our first two factors 
which determine the rate of precipitation; (1) air supply, (2) 
rate of cooling, We have seen that both are dependent—the 
first wholly and the second in great part—on the velocity of 
the winds. The first factor, air-supply, is evidently directly 
proportional to the velocity with which the winds move t 
e found reason to believe that this velocity would not be 
very much increased, though it would to some extent, by an 
increment in the mean temperature of the atmosphere which 
most thinkers would probably consider very,large. The same 
conclusion attaches to the second factor, rate of cooling, in so 
far as it is dependent upon the velocity of the wind. But we 
have noted that this second factor depends for its value upon 
four subordinate or component factors, commingling, expansion, 
contact, and excess of radiation over absorption of heat. The 
first three depend for their value upon the velocity of air move- 
ments solely. The fourth component (excess of radiation over 
absorption) presents other considerations. 
(14.) In the long run, radiation and absorption of heat by 
the atmosphere are equal. For if one or the other predomina- 
ted continuously the air would grow continuously warmer or 
colder. Practically during any short period of time, and in 
every locality one or the other does predominate ; but the ratio 
of the two perpetually oscillates to and fro about an equality. 
ow if air were motionless for a long period of time this oscil- 
lation of temperature would soon cease to precipitate moisture 
upon the land though the vibration might still continue. t 
in reality fresh air laden with new supplics of moisture is con- 
stantly replacing the bodies of air which have been depleted. 
Again we find that the movement of air is a vital considera- 
tion. But the nature of the dependence of that portion of the 
Wind is different from that of commingling expansion, ete. In 
the latter operations their efficiency is proportional in a simple 
ratio to the velocity. Not so the efficiency of radiation. The 
law in this case is a more complex one and the ratio has less 
