734 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1912. 



the water is not a guide as to the proximity of ice, not only because 

 this may be rising and falling, due to other causes, but because in 

 different seasons of the year the arctic current is at different tempera- 

 tures. The variation of temperature as ice is approached is, however, 

 unmistakable, and this the micro thermometer has invariably indi- 

 cated. Should the ice be found in a locality where variations due to 

 other causes are found, the iceberg effect is so characteristic and 

 sharj3 that it will be superimposed on the other curve in such a way 

 as to be unmistakable. 



Nearing Cape Race the temperature fell rapidly several degrees 

 below the surrounding sea temperature. Fresh-water rivers flowing 

 into the vSt. Lawrence, where the waters were salt, produced the 

 iceberg effect, thus indicating the probable cause of that phenomenon 

 as being due to the water from the icebergs diluting the salt water. 

 (vSee Appendix.) 



THE PRACTICAL LOCATION OF ICE. 



The important question arises as to how an iceberg can be defi- 

 nitely located by means of the microthermometer. The exact 

 position of a berg ahead of a ship in a fog is oi the greatest importance 

 to determme. In general, it may be said that an iceberg will make 

 itself felt in the first place by a rapid rise of temperature as it is 

 approached. In the immediate vicinity of the berg the temperature 

 falls quickly. The first wammg will be when the temperature begins 

 to mount up the scale above the surrounding sea temperature. In 

 regions where icebergs are in close proximity safe navigation will be 

 found possible, smce no isothermal line can lead to an iceberg. 



In conclusion, I wish to impress upon the reader the importance 

 of the fact that the actual temperature of the water in the ice track 

 is no guide to the proximity of even the largest iceberg. The expe- 

 riences of north Atlantic sea captains alone testifies to the uselessness 

 of individual observations. It is to the small variations of tempera- 

 ture we must look for the infallible guide, and by means of the 

 character of these variations we can determine the presence of ice, 

 land, or currents. 



