342 Wisconsin Academy of Sciences , Arts, and Letters. 
’14, p. 574). The underlying principle was there stated as 
follows: 
“The work to be done in warming a stratum of water which lies 
below the direct influence of the sun is done against gravity which 
resists the descent of the warmer and lighter water. The net work 
done in warming a stratum of water to a given degree may be 
measured by the energy which would be needed to transport the 
mass of water, thus warmed, to the place where it is found, against 
the resistance of denser water at a temperature of 4°. We may 
think of such a stratum as pushed down to its place through water 
at 4°, somewhat as a sheet of cork might be forced down through 
the water. The weight to be moved is the difference in weight 
between the warmed water and water at the temperature of maxi¬ 
mum density. The distance through which it is carried is the 
mean distance of the stratum in question from the surface.” 
The general question was left with this brief statement in 
that paper because I desired to discuss the matter of the heat 
budget more fully before taking up that of the distribution 
of heat. The subject of the heat budget was presented last 
year (Birge 15), and it is my purpose to state more fully in 
the present paper the subject of the work of the wind in 
distributing heat and to give illustrations of methods em¬ 
ployed in studying it. I leave most of its applications to a 
general report on temperatures of Wisconsin lakes. 
2. GENERAL EFFECT OF WIND. 
The wind blowing over the surface of a lake performs 
certain mechanical operations on the water. Their results 
may be grouped under the heads of waves and currents. We 
are not at present concerned with the work done in making 
waves, but consider the effect of currents only. 
If a lake had no shores, or if its dimensions were indefin¬ 
itely larger than those of the air movement constituting the 
wind, there might be produced a simple current in the water 
moving with the wind, greatest at the surface and rapidly 
dying out below. But in an inland lake the current induced 
by wind meets the shore very promptly, and this fact is of 
great importance to this discussion. The current is stopped 
and if the wind continues, it must turn back or turn down. 
Such are the currents whose effect is discussed here. 
If the lake is homothermous the current easily turns down¬ 
ward into the deeper water or along the bottom of the lake. 
