82 



SCIENCE 



[N. S. VOL.XXXU. No. 811 



gration and the supposed sinking of the ice. 



In Lake Mendota the mean temperature of 

 the water immediately after the disappearance 

 of the ice is about 2.7°, as the result of the 

 average of seven years. It has never been 

 above 3.5° at that time. It rarely happens 

 that the bottom water and mud at 22 m. (the 

 deepest water) reaches 4° before the ice dis- 

 appears. 



The water derived from melting snow and 

 ice remains just below the ice, floating on the 

 water of the lake. It becomes warmed by the 

 sun's rays and often rises considerably above 

 4°. It is lighter than the lake water, having 

 less dissolved matter, and the increase of 

 density as the temperature rises from 0° to 

 4° is not sufficient to carry it down into the 

 lake water. Immediately below the ice there 

 is a very steep temperature gradient to the 

 maximum and a somewhat slower decline 

 below. The maximum usually comes about 

 0.5 m. below the under side of the ice. I give 

 a series taken April S, 1901, when the ice was 

 about 30 cm. thick. The distances are meas- 

 ured from the surface of the water. 



The ice went out April 11; on that day 

 the temperature at 2 m. and below had not 

 changed materially. Facts similar to these 

 appear every year. 



If a lake contains little or no dissolved 

 matter the snow water would mingle more 

 freely with it than in a lake like Mendota, 

 and the rise of temperature in the surface 

 stratum might not be so marked; although it 

 would hardly be absent altogether. But if no 

 surface rise occurred, I see no reason why the 



thawing of the ice should wait until the water 

 below the ice has reached the temperature of 

 4°. From 60 per cent, to 80 per cent, of the 

 sun's energy is delivered directly to the ice 

 in any case, and is employed in melting it, 

 and dissecting it into crystals. As soon as 

 this process has gone far enough to loosen the 

 crystals from each other they will fall apart, 

 regardless of the temperature of the underly- 

 ing water. It is always possible that the ice 

 will disappear in this way, "all at once and 

 nothing first " ; but I have never known it to 

 do so; in Lake Mendota a wind has been the 

 agent which has shattered the last hold of the 

 crystals on each other and converted the sheet 

 of ice into a mush of crystals rapidly melting 

 in the warmer water. 



Professor Barnes thinks that much of the 

 later part of the melting of the ice comes from 

 the warm water below it. I have never seen 

 evidence that such is the case. Unless the 

 water below the ice is warmer than 4° there 

 would be a non-conducting layer of colder 

 water constantly between the ice and the 

 warmer water. If the temperature rose above 

 4°, convection currents might be set up which 

 would subtract heat from the ice. But at a 

 temperature near 4° the convection efficiency 

 is very small and the currents would be weak, 

 especially under the peculiar stratification 

 which obtains below the ice. From another 

 point of view the same conclusion can be 

 drawn. Not more than 100-125 gr. cal. per 

 sq. cm. per day can possibly get through the 

 ice into the water; and only part of this can 

 be used in melting the ice. 



E. A. BlEGE 



Madison, Wis., 

 June 13, 1910 



■ITHE EFFECTS OP DEFORESTATION IN NEW 

 ENGLAND 



To THE Editor of Science : In their enthusi- 

 asm for the conservation of our forests the 

 lecturers and writers on that subject have 

 often been guilty of an over-statement of their 

 case in an endeavor to show that not only are 

 the forests rapidly disappearing but as a re- 

 sult of their removal the land itself is being 



