SCIENTIFIC RESULTS 111 



-uch cases the specific gravity of the ice in one part of the body will 

 differ from that in another. Such bergs will exhibit a marked sta- 

 bility, at least in their early stages, and the frequent number of flat 

 hergs observed floating with the original Greenland, sand-covered 

 tops, still uppermost, may be a corroboration of tlie above-described 

 cniiditions. 



The density of the ice in an iceberg may change after it has 

 detached from the ice sheet. This development is due to surface 

 wcatliering, a process which does not normally extend to a depth of 

 more than a few feet. Sverdrup has suggested to me that, accord- 

 ing to this view, an iceberg is probably composed of a core which is 

 densest, surrounded by layers in which the density decreases towards 

 tlie surface, depending upon the degree of porosity of the ice there. 



Wright and Priestley (1922) found the density of a sample of 

 ice taken from the Antarctic ghicier to be 0.897. Barnes's (1928 

 p. 345) flgure of approximately 10 per cent covolume of air taken 

 Irom an iceberg stranded off Twillingate, Newfoundland, should give 

 a density flgure of about 0.825. Barnes, however, points out in a 

 letter to me that the density value of berg ice varies by a wide margin, 

 dejiending upon wiiat part of the berg the sample was taken. 



The Coast Guard cutter Tampa in ]\Iarch. 1930. brought to Boston 

 la piece of ice taken from a berg found (>fi' Xewfoundland. Determi- 

 nations of the speciflc gravity were made by means of the displace- 

 ment method in a bath of kerosene at the Jefferson Physical Labora- 

 tory, Harvard University. From two trials with samples taken from 

 v.irious parts of the piece the lowest density was 0.8977, the highest 

 0.9045, and the mean 0.8977. This flgure agrees quite well with that 

 (»f Wright and Priestley for Antarctic glacial ice, but it is greater 

 tlian Ahlmanns's or Barnes's results. It is hoped that several more 

 den-ity determinations will be made from a number of samples to be 

 collected by the ice patrol from various parts of a berg as it disinte- 

 giates. Until more such data is assembled we can not state deflnitel}' 

 what is the figure representative of the mean density of an iceberg. 



X common question met in connection with the subject of icebergs 

 is : What proportions of a berg are above, and what proportions 

 ai'c below, the s\irface of the sea? If we assume that the mean 

 >i)eciflc gravity of iceberg ice is 0.8997, as compared with 0.9107 

 for pure fresh-water ice, we may arrive at the following estimate 

 of mass buoyancy."^ The submerged portion of an iceberg floating 

 in sea water f)f 1.02690 density, a figure representative of the average 

 density of the surface layers along the continental edge, is then about 

 O.,s760 of the entire mass or, in other words, one-eighth of the mass 

 of a berg is above and seven-eighths below the surface of the sea. 

 These figures do not agree with Barnes (1927a, p. 98) who emphasizes 

 the amount of air imprisoned in glacial ice, and states that because 

 of this a berg will float with about one-third of its mass above water. 

 It will require a greater number of density determinations than are 

 now available to ascertain this flgure with accuracy. 



The fact that the icebergs typical of the Xorthern Hemisphere are 

 as a rule irregular in shape causes the question of mass flotation to 

 become a subject mostly of academic interest, and as a result atten- 



'" A cubie foot of iceberg ice weiglis approximately 55 pounds. 



