Section III., 1913. [3] Trans. R.S.C. 



Magnetic Observations in the Hudson Bay and 

 Straits Region. 



By W. E. W. Jackson, M.A. 

 Presented by Mr. R. F. Stupart, F. R.S.C. 



(Read May 28, 1913) 



When the Government of Canada decided to open up a trade 

 route from some port on the western side of Hudson Bay to Europe, 

 it became at once necessary to correct the navigation charts, and of these 

 corrections, not the least important was to bring the Magnetic values 

 up to date. The latest admiralty chart was published for that region, 

 originally in 1884, and republished with alterations and corrections up 

 to 1908. However, in view of the close proximity of this region to 

 the Magnetic pole and the lack of sufficiently accurate data for the 

 determination of secular changes, it can readily be understood that 

 the inaccuracies may be of considerable moment. 



For instance, if an error of 1 degree in the value of the declin- 

 ation existed in the charts, and a ship were proceeding on a course 

 through Hudson Strait determined on the presumption that the charts 

 were correct, at the end of 100 miles run it would be about 2 miles 

 from the calculated position, whilst if the error were 5 degrees, the ship 

 would be almost nine miles from the calculated position, and this of 

 itself might be sufficient to cause disaster. 



The Hydrographie Surveys Branch of the Department of the 

 Naval Service were therefore asked to secure the necessary data for 

 making these corrections, and in the spring of 1912 the Director of 

 the Meteorological and Magnetic Service was asked by the Navy De- 

 partment to furnish an observer to carry out the Magnetic survey 

 work, and I was deputed to take charge of the expedition, and Mr. 

 W. B. Wiegand, B.A., was appointed as my assistant. 



The C.G.S. "Arctic" was requisitioned for the Magnetic survey 

 and placed in my charge by the Director of the Hydrographie Survey 

 on the 26th of June, fully provisioned for a cruise of six months. This 

 vessel was built by the Germans in 1901 for their Antarctic expe- 

 dition, and special care was taken in her construction to make her 

 suitable for Magnetic Survey work-. No iron was placed nearer than 

 27 feet from the observing bridge, and the rigging was wholly of hemp. 

 She has a length between perpendiculars of 151 feet, a beam of 36 



