250 DETERMINATION OF THE ELEMENTS OF TERRESTRIAL 



wooden ships fifty to one liundred years ago." *^^ For this rea- 

 son, part of the programme of the Department of International 

 Research in Terrestrial Magnetism is a magnetic survey of 

 ocean areas. It is probable that very serious errors exist in 

 these charts near the coast lines of the continents. When the 

 declination has been determined at a large number of stations 

 over a small area, the isogonic lines are found to be very 

 irregular and the easy curves drawn on charts merely indicate, 

 as a rule, the general positions of the lines. On the coast of 

 Nova Scotia, on several occasions, shipwrecks have been attri- 

 buted to an unknown variation of the compass, and it has been 

 stated that the last great disaster at Rockall, when on the 29th 

 of last June the Danish S. S. Norge was wrecked and about 600 

 lives lost, was due to the same cause. In Nature of Sept. 15th, 

 Dr. August Krogh, of the University of Copenhagen, calls 

 attention to this fact and publishes letters from two captains 

 who state that they have observed changes in the magnetic 

 declination to an amount of from 9° to 11" in the neighbourhood 

 of Rockall. 



Declination and Land Survey.^. 

 The importance to the land surveyor of an accurate know- 

 ledge of the magnetic declination and its changes has been 

 already noted. In many cases the value of the declination at 

 the time when a survey has been made has not been recorded, 

 and in some cases, doubtless, the land surveyor has but hazy 

 ideas of the value of the declination and its changes. Much 

 time and money has been already wasted in disputes over old 

 lines, and still the method of describing lines by these magnetic 

 bearings is in use in this province. The author suggests that 

 true north and south lines should be laid down in all the 

 principal towns, so that surveyors might test their compasses 

 and note the changes in declination from time to time in the 

 particular localities in whieh they were working. Such a line 

 was laid down at the University of New Brunswick, Fredericton, 



(1) L. A. Bauer. Terrestrial Magnetism, March, 1934. 



