874 transactions of the american institute. 



Icebergs. 



Dr. ILiyes. the Arctic explorer, in his work published by Hurd 

 & [loughton, gives a graphic description of the progress of north- 

 ern glaciers toward the sea, which, when fairly launched, are 

 designated as icebei'as. A block of fresh water ice floatino- on 

 sea-water rises above the surface to the extent of one-eighth of its 

 bulk and weight, while seven-eighths of it are below the surface. 

 The cause of this is too well known to need more than a passing 

 explanation. Every school-boy is aware that Avater, in the act of 

 freezing, expands, and that in the crystal condition fresh water 

 occupies about one-tenth more space than when in a fluid state ; 

 and hence, when ice lloats in tlie fresh water from Avhich it was 

 formed, one-tenth of it is exposed above, while the remaining 

 ■ nine-tenths are beneath the urface. When this same fresh water 

 ice (which it will be remembered is the composition of the gla- 

 cier) is thrown into the sea, the proportion of that above to that 

 below being changed from one and nine to one and seven, is due 

 to the greater density of the sea water, caused b}^ the salt wdiich 

 it holds in solution. Now, it will be obvious that, as the glacier 

 continues to press further and further into the sea, the natural 

 equilibrium of the Ice must ultimately become disturbed — that is, 

 the end of the glacier is forced further down into the w^ater than 

 it would be were it free from restraint, and at liberty to float 

 according to the properties acquired by congelation. The moment 

 that more than seven-eighths of its front are below the water line 

 the o-lacier will, like an apple pressed down l:)y the hand in a pail 

 of Avater, have a tendency to rise until it assumes its natural equi- 

 librium. Now it will be remembered that the glacier is a long 

 stream of ice, many miles in extent, and although the end may 

 have this tendency to rise, yet it is, for a time, held down firmly 

 by the continuity of the whole mass. At length, however, as the 

 end of the glacier buries itself more and more in the Avater, the 

 tendency to rise becomes stronger and stronger, and finally the 

 force thus generated is sufficient to break off a fragment, wdiich, 

 once free, is buoyed up to the level that is natural to i(. This 

 fragment may be a solid cube half a mile through, or even of 

 much greater dimensions. The disruption is attended Avith a 

 o-reat disturbance of the Avaters, and Avith violent sounds, Avhich 

 may be heard for many miles; but, floating now free m the Avater, 

 the oscillations Avhich the sudden change imparted to it gradually 



