39 



INTRODUCTORY NOTES TO SEISMIC OBSERVATIONS. 



THE Milne seismograph supplied to the Expedition was erected at Winter Harbour in the Magnetic 

 Variation House during March, 1902. This instrument (No. 37) was made by K. W. MfNRO, London, of 

 non-magnetic materials. The drain-pipe upon which the bed-plate was tightly fixed was 1 foot 6 inches 

 in diameter, and was sunk through a thin layer of ice until it rested upon a solid bed of frozen earth and 

 stones. The height of the pipe above the ground was 19J inches (see figure). 



Seismograph No. 37 March to November; 1902. 



A. Red lamp-shade. 



B. Recording apparatus. 



C. Boom case. 



D. Drain pipe. 



When the column had been made rigid, with bed-plate attached, the instrument was set up in the 

 geographical meridian, the aluminium boom being N. S., and the balance weight and attachment of tie 

 at the regulation distance from the pivot, viz. 7 millims. and 125 millims. respectively. By means of the 

 pivot and front levelling screw the boom was given a period of exactly 15 seconds. When deflected 8 or 

 9 millims. from its normal position, it took about 8 minutes liefore returning to rest. The instrument 

 was kept going in this position from March 14 to November 9, 1902, when it was dismounted, removed 

 to the large store hut, and erected on a masonry pillar (brick) of following dimensions: 



(See figure.) 



Depth sunk in ground ... 12 inches. 

 Height above ground .... 3 feet. 

 Breadth 2 feet by 2 feet. 



