﻿Prof. J. Milne — On the Flotation of Icebergs. 65 



VI. — Considerations on the Flotation of Icebergs. 

 By Professor John Milne, F.G.S., 

 Of the Imperial College of Engineering, Jeddo, Japan. 

 N all our text-books of Geolog}^ the action of floating Ice is 

 referred to as an agent of great power in producing physical 

 changes. Its two chief forms are those of Coast Ice and Icebergs. 

 Much has been written about the latter of these, but about the 

 former very little. In the Geological Magazine, July, 1876, in an 

 article on Ice and Ice- work in Newfoundland, I endeavoured to show 

 that the greater agent of the two was Coast Ice, a view which has 

 been subsequently strengthened by observations on the Coast of 

 Finland. In this paper I had occasion to refer to the laxity with 

 which the conditions under which Icebergs float have been spoken 

 about. Thus, in Jukes and Geikie's Text-Book of Geology, p. 416, 

 we are told that because " about eight times more ice of an iceberg 

 is below water than above," therefore " a mass which rises 300 feet 

 above the waves has its bottom 2400 below them." 



As no regard is paid to what the relative shape of ice above water 

 is to that below, might it not be well to add, in order to render the 

 harmlessness of the doctrine more evident, that the mere fact of 

 planting a Union Jack upon the summit of the berg would cause an 

 addition to its depth equal to eight times the height of the pole ? 



If this were only done. Icebergs might be talked about as grounding 

 in very deep water, where they could " tear up the softer deposits of 

 the sea-bed," and " rub down and groove the harder rocks " to an 

 unlimited extent. This grounding in deep water I endeavoured to 

 show to be, in the generality of cases, untenable, excepting, perhaps, 

 in the case of bergs immediately in the vicinity of their origin, where 

 they more or less approximate to parallelepipeds in their form. In 

 doing this, I also showed that in consequence of the degrading action 

 which takes place, more especially between wind and water, it would 

 seem that bergs as they travel towards low latitudes must be looked 

 upon as a form more like a peak which stands upon a sunken 

 pedestal or foot, rather than as descending perpendicularly into the 

 water. In such a case it is evident that no great depth could be 

 obtained. 



However, to take as favourable a view as possible of ice reaching 

 down to abyssal depths, I will again assume a case which I took 

 before (Geological Magazine, July, 1876, p. 307), where we must 

 imagine the portion of the berg beneath the water to be a general 

 continuation of that above. 



Such a figure I showed might be regarded as approximately equal 

 to a cone or many-sided pyramid. In such a case I have shown 

 mathematically that the depth of ice beloio water is approximately 

 equal to the height lohich is exposed above, the slight difference which 

 may exist depending on the ratio we take as existing between the 

 specific gravity of ice and sea-water, — a conclusion from which I 

 do not see the slightest reason to alter. 



This being the case, it consequently follows that if it is accepted 



DECADE II. — VOL. IV. — NO. II. 5 



