SECTIONAL TRANSACTIONS.—A. 371 
1913-1924 just completed, the maximum sun-spot, 1917, August 11, was accom- 
panied by a violent magnetic storm, as was also the great sun-spot group of 
1920, March 22-24. But there is no parity between the size of a sun-spot and 
the character of the concomitant magnetic disturbance. Great activity is more 
effective than great area in sun-spots. An example is the very great magnetic 
storm of 1919, August 11-13, which accompanied a relatively small, but very 
active spot, and the moderate magnetic disturbance which occurred when a 
very much greater sun-spot group was on the sun’s disc, 1919, August 19. 
2. The terrestrial magnetic disturbances are more numerous after the maxi- 
mum phase of sun-spot activity in a cycle. From the numbers of moderate, 
great, and very great disturbances, mean magnetic ‘character’ figures have 
been derived, which are compared with the mean disc-areas of the sun-spots 
in the following table :— 
Disc-area | Magnetic Disc-area Magnetic 
Bene Spots Character aca Spots | Character 
1912 0°20 0°05 | 1918 7°90 0:27 
1913 0°04 0-06 1919 8°40 0°39 
1914 0°82 0:07 1920 4°05 0:26 
1915 4°51 0-12 1921 3°14 0°26 
1916 4°52 0°20 1922 1°73 0°45 
1917 12°10 O14 1923. 0°37 0°19 
The phenomenon is apparent in the last three solar cycles. It is also brought 
out in the well-established twenty-seven day period in terrestrial magnetic 
disturbance, which is much more developed with a tow sun-spot frequency, and 
a low latitude of the spots. In individual storms of greater violence it is shown 
in those of 1920, March 22, and 1921, May 13-14. 
3. Magnetic disturbances of considerable activity may occur at a period of 
solar calm, when there are no sun-spots, or even facule, visible on the sun’s 
disc. Examples in the last cycle are the disturbances of 1923, March 23-25, 
and of 1924, January 29-30. Such storms are connected with the synodic pre- 
sentment to the earth of solar areas, which had been previously disturbed by 
sun-spots. They remain intermittently effective, so far as their relation to 
‘terrestrial magnetism is concerned, even after the spots have disappeared. 
38. Mr. EH. A. Hopason.—Correlation of Records of two Distant 
Milne-Shaw Seismographs. 
The Milne-Shaw seismographs, Nos. 17 and 23, of the Dominion Observatory, 
were used experimentally in 1923. No. 17 was kept in constant position to 
register the E-W component. The constants were the standard set recom- 
mended by the makers with the magnification set at 250-fold. No. 23 was 
first kept on the same pier and a series of records made with the constants 
standard and then with all standard except the damping ratio, which was 
varied, after several earthquakes had been recorded at each setting. No. 23 
was then set up at Shirley Bay, Ont., about eight miles, approximately, west of 
the Observatory. It was set to record the E-W component, and the constants 
were kept standard. Time was checked by wireless communication with the 
Observatory, the same time signals being recorded on the two instruments. 
The Tokio earthquake was recorded in this experiment. The instrument was 
next set up at Kemptville, Ont., about thirty-five miles, approximately, south 
of Ottawa. The same experiment was repeated. A severe micros storm was 
secured on both instruments and about twenty earthquakes. Time was checked 
by wireless signals from Annapolis. The paper will deal with the peculiarities 
of the instruments with respect to one another and the correlation of particular 
phases as recorded on the widely separated instruments. It will be fully 
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