8 THF. ROYAL SOCIETY OF CAXADA 



horizontal force is small and where the diurnal range of declination 

 amounts to 1^ degrees and where in a few minutes the magnet might 

 pass completely off the scale of the telescope. Greater dependence 

 is placed on results from the total Force instrument in such localities, 

 and yet at Marble Island the two results agreed to within 0. 00027 dynes 

 which is less than the probal^le error of an observation in that region. 

 At all stations in Hudson Bay and Strait both methods for determining 

 horizontal force were used and the results given below are the arithmetic 

 mean of the values from the two methods. 



At Ashe Inlet and Port Burwell the same observing station was 

 used as in the expedition of 1908-9 and at Stupart Bay the same station 

 was used as that on which absolute determinations were made by Mr. 

 R. F. Stupart in 1884-5 when magnetic observations were carried on 

 for about a year. At these three stations then the most accurate data 

 for secular change was secured. At the other stations the exact location 

 of former observing stations could not be found and consequently 

 secular change data may be effected by local disturbances. However, 

 it would seem that some deductions may be made as to the general 

 changes that are taking place over the Hudson Bay and Strait region. 



At the Eastern end of the Strait West declinations are dim inishing 

 at present at the rate of about 9 minutes a year, whilst the mean 

 rate from 1884 to 1909 was slightly in excess of this. This rate of 

 change diminishes, as you proceed westward, until near the western side 

 of Hudson Bay it reaches zero. 



The inclination is diminishing very rapidly at Burwell at present, 

 being about 10' a year, and at Ashe Inlet about half this rate. From 

 1884 to 1909 the diminution for the whole eastern part of Hudson 

 Strait was at the rate of only about 1 minute per year. Over Hudson 

 Bay the Inclination is probably diminishing about a minute per year, 

 the apparent increase at Churchill being probably due to a different 

 location and the presence of local disturbance. 



All stations shew an increased value of Horizontal Force, the 

 mean of all being 24 y per year and this would seem to confirm the 

 fact that Inclinations are throughout this entire region diminishing. 



The data for secular change results is given below in Table I. 

 The values of the elements for 1884 and 1885, except York Factoiy, 

 are taken form the Report of Lieut. Gordon on his expeditions during 

 those years. That for York Factory is from the report of the Chief 

 Astronomer, Department of the Interior, Ottawa, 1909. 



The results for Battle Harbour for 1905 are from data furnished 

 by the Department of Terrestrial Magnetism of the Carnegie Institution 

 and the value for Churchill for 1910 is from observations made by Mr. 

 Savary of the Hydrographie Survey, Department of the Naval Service. 



