A Study in the Natural History of fee 297 



were still stranger to me than those that I had witnessed in 

 summer: perhaps because the descriptions of glacier-ice in 

 winter were rare and not very informing. The glacier restau- 

 rant was but little frequented and no one visited the grotto, 

 the entrance of which was snowed up. I had, however, very 

 little difficulty in clearing a way into it, and I was astonished 

 at the difference in its appearance as compared with that 

 which it presented in the previous summer. The roof had 

 sunk considerably and the pillars and longitudinal buttresses 

 which supported it were much sheared in the direction of the 

 entrance. There were also fewer air-bells in the ice than in 

 summer, and the outer surface of the ice as well as the inner 

 surface of the air-bells was dry ; the temperature of the ice at 

 a depth of three or four centimetres was 4 C., which was 

 also the temperature of the air in the grotto at the time. It 

 must be remarked that, not being visited, the grotto had been 

 practically lying in darkness for some months, and the features 

 of the ice in these circumstances would certainly be different 

 from those encountered in summer, or in winter when it is 

 continuously open to t/ie light of day. 



In the summer of 1906 I began to use photography in my 

 work, and it has naturally proved a great assistance. Since 

 the above date I have visited the Morteratsch grotto at least 

 twice, and in the last years four times in the year. The 

 critical dates for the glaciers, as for the seas and lakes, are the 

 equinoxes and the solstices. 



Granular Features of the Ice in Summer. 



At the entrance of the grotto the ice is exposed partly to 

 the direct rays of the sun and partly to its indirect radiation 

 from the sky. Under these combined influences the ice at 

 the entrance contracts the texture and general appearance of 

 that on the upper surface of the glacier. 



The occurrence of continuous white ice depends princi- 

 pally on the receipt of a considerable proportion of the whole 

 radiation of the sky, so that the surface and the ice im- 

 mediately below the surface may be disarticulated, and the 



