298 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 8 



Finally, in spite of the greater total precipitation and large annual 

 snowfall, the melting is so great, especially in the summer, that no 

 accumulation at all takes place. 



Although it may seem strange that an increase of temperature can 

 produce increased glaciation, it may be demonstrated by a simple 

 experiment. In four identical glass jars (pi. 1) each containing a 

 layer of water in the bottom and a metal vessel at the top which can 

 be cooled by solid carbon dioxide, the water at the bottom represents 

 the Equator and the metal vessel at the top the polar regions. One 

 jar (second from the left) contains water at the temperature of the 

 room and there is an appreciable deposit of ice at the top. By adding 

 ice to the water in the vessel to the left, equivalent to lowering the 

 equatorial temperature, the deposit of ice at the top is much reduced. 

 The water in the third vessel has been warmed by a small gas jet, 

 and the effect of the heating has been greatly to increase the deposit 

 of ice. In the fourth bottle the temperature has been raised still 

 higher, with the consequence that the ice has almost entirely disap- 

 peared by melting. 



These four bottles can be regarded as representing increasing radi- 

 ation as shown in figure 3. The first bottle has a low temperature 

 (little radiation) and the ice deposit is thin, corresponding to A on 

 the diagram. The second bottle has a higher temperature (more 

 radiation) and therefore corresponds to a point to the right of A on 

 figure 3 and shows a greater accumulation of ice. The third bottle 

 represents the conditions where the ice deposit reaches its maximum, 

 and the fourth bottle represents some point beyond B where the 

 melting and evaporation exceed the deposit. 



The conditions represented by figure 3 and the experiment apply 

 to the polar regions and high mountains. At first an increase of solar 

 radiation causes an increased accumulation of snow and ice in spite 

 of increased temperature. During this stage, ice sheets form and 

 glaciers advance, giving rise to a glacial epoch. As the radiation 

 increases still further, the ice melts away and we have overcast skies 

 and much precipitation but no ice accumulation. When the solar 

 radiation decreases, conditions are reversed and the whole sequence 

 is gone through in the reverse order. 



Figure 4 has been prepared to show the sequence of changes of ice 

 and meteorological factors when the solar radiation makes two com- 

 plete oscillations. The abscissae represent time increasing toward 

 the right. Curve I represents two complete cycles of solar radiation 

 and curve II represents the mean temperature of the world as a whole. 

 Curve III is the curve of precipitation and therefore follows directly 

 the curve of solar radiation. Curve IV is the curve of snow accumu- 

 lation. As drawn, it shows some accumulation at the minima of the 

 solar radiation, but a complete disappearance of the accumulation 



