306 In and Aroiind the Morteratsch Glacier : 



nothing could be more fascinating. The best season for this 

 work is early in July, because in this investigation the physical 

 agency used is the energy of the sun's radiation. This reaches 

 a maximum at noon on the date of the summer solstice, 

 2 1st June, but for quite a month on each side of this date 

 there is hardly any diminution, either of the sun's meridian 

 altitude or of the length of the day, and these are the factors 

 which determine its power of doing work. Consequently the 

 early part of July is quite as good as any date in June ; 

 moreover, before the beginning of July there is no hotel 

 accommodation on the mountain, and the observer must make 

 his visits to the lake from Fiesch or other station in the 

 Rhone valley. 



While studying the bergs and other fragments of the 

 glacier-ice stranded on the margin of the lake, I noticed that 

 the bergs which were afloat were seldom at rest, and this was 

 particularly remarked on days when the sun was most powerful. 

 On observing more closely the bergs which exhibited this 

 unrest I saw that it was accompanied by subdivision of their 

 mass and alteration of their equilibrium. This act is called 

 " calving " by the whale-fishers and causes one of the principal 

 risks to their ships if they approach the icebergs too closely. 

 In the waters frequented by whalers the calving of the bergs 

 is not an everyday occurrence. On the Mergelin See where 

 the mass of even the largest berg is comparatively small, this 

 act can be observed frequently on a hot day. If it be atten- 

 tively observed it will be found, if the "calf," the portion of 

 ice which has been shed by the berg, comes, as it usually 

 does, from the part of the berg under water, that it is quite 

 transparent and has a perfectly smooth surface. If the parent 

 berg be now observed, it will be found that it has altered its 

 " trim." This alteration of trim may amount to only a slight 

 " list " or it may assume the dimensions of a complete capsize. 

 As a rule the alteration of trim is considerable, and the 

 alteration which it produces in the appearance of the berg is 

 due to the submergence of a part of the ice having the rough 

 ^dead-white granular appearance acquired by continued ex- 

 posure in air to the direct rays of the sun, and to the emergence 



