1912] nn Icebergs and iheir Locaiion in Navuiatinn. 5-Jl) 



and the presence of flocks of birds fur from land is an indication of 

 ice. The temperature of the air usually falls as ice is approached, 

 and mariners describe a peculiar damp cold as distinguished from 

 the cold caused by a change of wind. I shall discuss the fall in 

 temperature of the sea as ice is approached in what follows. 



Failure of previous Efforts to make use of Temperature 

 Changes in the Sea. 



Navigators place no reliance on temperature measurements. As 

 a matter of shipboard routine, the temperature of the water is taken ; 

 but very little, if any, attention is taken of it. The method is to dip 

 a canvas bucket over the side and bring up a sample of sea water. 

 The quartermaster then inserts a good household thermometer in the 

 water, waits for a few minutes, and then reports the reading to the 

 bridge. The thermometer is usually graduated in two-degree intervals, 

 representing a length of stem about one-eighth of an inch long. The 

 interval of time between the dipping of the water and the report of 

 the reading may be anything from five to ten minutes. In the mean- 

 time the ship has sailed some miles beyond the point of observation. 

 It is not surprising, in the light of my results, that no value whatever 

 can be attached to measurements of this kind. As an example I can 

 quote from a standard work on navigation. Captain Lecky's " Wrinkles 

 in Practical Xavigation," fifteenth edition : — 



" Allied to fog is the question of danger from ice. It is a 

 popular delusion among passengers on board ship, that, by taking the 

 temperature of the sea surface at short intervals, the approach to ice is 

 unfailingly indicated. Unfortunately such is by no means the fact, and 

 reliance thereon invites disaster. More than ordinarily cold water 

 merely shows that the ship is in a part of the ocean where ice may 

 possibly be encountered, and not that it is actually present. 



" By kind permission, and on the unexceptional authority of 

 Captains Ballantine, Button and Smith, of the Allan Mail Steam- 

 ship line, all men of high standing in the profession, and well 

 acquainted with ice navigation, it is here stated that no appreciable 

 difference in the temperature of the sea surface is caused Ijy the 

 proximity of even the largest icebergs, and when one considers what 

 a poor conductor of heat water is, their statement can be well 

 believed. ... 



" In a letter to the author. Lord Kelvin says : 'The conducting 

 power of water is so small that there would be absolutely no cooling 

 effect by conduction to a distance from an iceberg"; but there 

 might be a considerable effect by the cold and light fresh water 

 running down from the iceberg, and spreading far and wide over 

 the surface of the sea.' 



" This seems a reasonable supposition, but it is more than likely 

 that the film of cold fresh water would be broken up by the agitation 

 of the wind and waves, and in any case disturbed and turned over 



