i 9 io] FORMATION OF THE PACK 19 



' With the coming of summer the northern edge of the sheet 

 decays and the heavy ocean swell penetrates it, gradually break- 

 ing it into smaller and smaller fragments. Then the whole body 

 moves to the north and the swell of the Ross Sea attacks the 

 southern edge of the pack. 



' This makes it clear why at the northern and southern limits 

 the pieces or ice-floes are comparatively small, whilst in the 

 middle the floes may be two or three miles across; and why the 

 pack may and does consist of various natures of ice-floes in ex- 

 traordinary confusion. 



1 Further it will be understood why the belt grows narrower 

 and the floes thinner and smaller as the summer advances. 



1 We know that where thick pack may be found early in Janu- 

 ary, open water and a clear sea may be found in February, and 

 broadly that the later the date the easier the chance of getting 

 through. 



* A ship going through the pack must either break through 

 the floes, push them aside, or go round them, observing that she 

 cannot push floes which are more than 200 or 300 yards across. 



1 Whether a ship can get through or not depends on the thick- 

 ness and nature of the ice, the size of the floes and the closeness 

 with which they are packed together, as well as on her own 

 power. 



1 The situation of the main bodies of pack and the closeness 

 with which the floes are packed depend almost entirely on the 

 prevailing winds. One cannot tell what winds have prevailed 

 before one's arrival; therefore one cannot know much about the 

 situation or density. 



' Within limits the density is changing from day to day and 

 even from hour to hour; such changes depend on the wind, but 

 it may not necessarily be a local wind, so that at times they seem 

 almost mysterious. One sees the floes pressing closely against 

 one another at a given time, and an hour or two afterwards a 

 gap of a foot or more may be seen between each. 



1 When the floes are pressed together it is difficult and some- 

 times impossible to force a way through, but when there is re- 

 lease of pressure the sum of many little gaps allows one to take 

 a zigzag path.' 



