4 Mr. J. Ball on the Cause of the Descent of Glaciers. 



not, I think, been remarked that, if it were proved that radiant 

 heat did penetrate into the interior of glaciers, the only result 

 would be to bring the mass to the fixed limit of 32° F. (above 

 which it can never rise) at an earlier period in its life-history 

 than really occurs, and thus to destroy at its source the supposed 

 physical agency which forms the basis of the " crawling theory." 



As the greater glaciers originate in reservoirs wherein the snow 

 is converted into neve, and whose annual mean temperature is 

 below the freezing-point, we have every reason to believe that, 

 during the long period of its descent in the form of an ice-river, 

 the interior of the mass undergoes a slow secular elevation of 

 temperature until it finally attains that limit. "We know that the 

 winter cold does not penetrate the surface more than a moderate 

 number of feet, and that of the night scarcely so many inches, 

 while heat is gained (though with extreme slowness) by con- 

 duction and by infiltration. 



The last assumption involved in Canon Moseley's theory is 

 that the glacier does, as a matter of fact, increase and diminish 

 in length with every alternation of temperature, and, as a neces- 

 sary consequence, that there must be portions of an advancing 

 glacier that stand still, and others that at certain times actually 

 retrograde, or crawl up hill. The first impression of any one 

 who had up to this point admitted Canon Moseley's conclusions 

 would be that he had proved too much. If it be true that, in 

 his own words, " glacier-ice being a solid, it cannot but dilate 

 and contract under the variations of temperature to which it is 

 subjected, and, dilating and contracting, it cannot but descend," 

 we must follow the argument to its legitimate consequences. 

 The mean range of a thermometer in the shade at a height of 

 about 7000 feet in the Alps is usually not less than 25° F. in fine 

 summer weather, but that of an instrument exposed to the sun 

 and to radiation may often reach 80° or even 100°. If Canon 

 Moseley's argument be sound, there is no reason for measuring 

 the expansion by the smaller instead of the greater figure. If 

 the surface of a glacier comports itself as though it were a solid 

 sheet of ice, and ice expands for all temperatures, above as well 

 as below the freezing-point, in the ratio of -00002855 for every 

 degree of Fahrenheit, there is no escaping from the necessary 

 conclusions. Leaving out of account the upper portions of the 

 glacier, which are covered with neve, we should have on the Mer 

 de Glace a space of 20,000 feet — on the Aletsch glacier a length 

 of fully 50,000 feet — exposed, at least occasionally, to alterna- 

 tions of 100° of temperature. In other words, the length of the 

 Mer de Glace would increase by 57 feet in the course of nine or 

 ten hours, and diminish by the same amount between day and 

 night; and on the Aletsch glacier the expansion and contraction 



