S6 Mr. H. H. Howorth on 



why the glaciers in the Arctic regions should advance in 

 winter, and we ought to find proofs of retrogression due to 

 winter contraction as well as of summer progress. On this 

 theory again, why should the advance of a glacier be greater 

 both at the top and the bottom than half way up, why more 

 rapid in its medial portion than near its edges ? Again, to 

 quote an argument of Mr. Blake's, a glacier for purposes of 

 this experiment is like a piece of ordinary ice, and "if one will 

 flatten out under the influence of heat, the other ought to do. 

 But whoever saw a block of ice bulge out under the influence 

 of heat ? If anyone has seen such a thing, or has made any 

 experiments upon it, it would be far more to the point than 

 theory, or if these molecular changes could go on even in a 

 large mass of ice without any vis-d-tergo^ surely some 

 tendency to a definite shape ought to have been observed 

 in icebergs which should, as the mass widens out, grow 

 thinner and thinner." 



Forbes pertinently urges that in order to account for 

 the observed rate of the motion of glaciers by this theory, 

 the entire mass of the Mer de Glace of Chamounix must 

 have an average range of temperature of 4)^ Reaumur or 

 9^ Fahrenheit, which is quite contrary to experience. The 

 expansion and contraction of ice by heat and cold can only 

 take place when it is below its freezing point. If it is 

 percolated by water it cannot rise above 32° or expand, 

 and, as we know it is so percolated during the daytime, we 

 cannot believe that during the night the temperature can 

 be lowered throughout to a depth of from 300 to 600 feet 

 of ice through a range of 9 J^ degrees. As a matter of fact, 

 according to the observations of De Saussure and others, 

 the actual range of temperature attributable to a glacier is 

 between limits absolutely incapable of effecting the expan- 

 sion of the ice in the smallest degree {id.^ 41). 



Mr. Matthews, in a paper published in the Alpine 

 journal for 1 870, says : — " The whole superstructure of the 



