APPENDIX C XCV 



Magnetic disturbances, were of very infrequent occurrence, and on 

 230 days the Magnetic curves were classified as normal, and on 12G days 

 as being lightly disturbed, whilst only on 10 days were the disturl:)ances 

 of any magnitude. The larger disturbances occurred in the months of 

 April, May, August and September, 1912. In Declination the greatest 

 amplitude recorded was 54'. 9 during the disturbance of May the 11th 

 and 12th, 1912, whilst in Horizontal Force the greatest amplitude was 

 lôô-y, and occurred during the disturbance of April the 15th and 16th. 



The mean diurnal range of Declination varied from a maximum of 

 12'. 1 in August, 1912, to a minimun of 5'. 2 in December, 1912, whilst 

 in Horizontal Force it varied from a maximum of 427 ^^^ May, 1912, to 

 a minimum of I87 in November and December, 1912. 



Ninety-two theodolites with magnets attached were compared 

 with the Agincourt Standard Declinometer and index corrections were 

 determined and supplied to the Surveyor General. 



Assistance was given to Mr. French of the Dominion Observatory 

 in comparing his instruments with the Agincourt Standards both before 

 and after his field work. 



An officer of the Meteorological Service, Mr. W. E. ^^'. Jackson, 

 .M.A., was assigned to the Hydrographie Surveys Branch for the summer 

 of 1912, to carry on a magnetic survey of Hudson Bay and Strait. The 

 results obtained are given in Mr. Jackson's paper on ''Magnetic Observ- 

 ations in Hudson Bay and Strait" which appears in this number of 

 the transactions. 



SEISMOLOGICAL OBSERVATIONS 



The Milne Seismographs at Toronto and Victoria have l)een kept 

 in successful operation throughout the year. Although no very large 

 disturbances have been recorded, still the total number of earth tremors 

 has been greater than usual, Toronto showing 157 and Victoria 150. 

 Of this number four may be considered of a moderate character, and" 

 occurred on May 6th, June 8th, 10th, and December 9th. The largest 

 range of motion was 10mm. on June 8th. A prolonged series of 

 small tremors at both stations began on June 3rd, culminating in a 

 marked disturbance on the 8th, at 7.55. The Katmai Volcano, Alaska, 

 was in eruption during this period and earthquakes in the region were 

 of frequent occurrence which resulted in much loss of property in that 

 vicinity. 



We continue to furnish a number of scientific Societies with tabu- 

 lations of all earth tremors recorded, also copies of important seismo- 

 grams. The British Association are gradually increasing the network of 



