[KLOTz] MICROSEISMS 205 



From examination it is found that the strongest and most numerous 

 microseisms were recorded during the months of January and February 

 last, while during the period September, 1907, to April, 1908, October 

 had the strongest, and the fewest and weakest were during the summer 

 months of July and August, when the atmospheric barometric gradients 

 were very long. 



We are led to conclude that strong winds liave little effect in causing 

 microseisms by setting up pulsations over large areas of the earth's 

 surface or crust, i.e., the dynamical effect by friction or impact is not the 

 governing factor in the production of microseisms. We are dealing here 

 with the greater effect of strong winds upon large areas and not the local 

 effect upon buildings, which, as is well known, are set in oscillation, and 

 these in turn are communicated to the ground. When the building with- 

 in which the seismograph is housed is large, the oscillations of the former 

 will be recorded. 



When we compare the occurrence of microseisms with the predicted 

 strong winds of the daily forecasts, we find little or no connection be- 

 tween the two phenomena. Considering the two phenomena as inde- 

 pendent events, we see that tlie probability of the simultaneous occur- 

 rence of the two events is as great as the actual happening, i.e., as far as 

 the observations go there is very little to sliow any causal relationship 

 between the two. 



On the -other hand we do find that the winds recorded here by the 

 microbarograph invariably show themselves on the seismograms, not by 

 microseisms, but by irregular movements including deviations of the 

 zero line. Microseisms and these latter movements can never be mis- 

 taken for earthquake records. 



Very recently through the kindness of Dr. W. Bell Dawson, Supt. 

 of Tidal Surveys, I had an opportunity of examining the mareograms 

 of St. Paul Island for the year 1904, and those for :May-December, 1908, 

 the latest received. St. Paul is a small rocky island in Cabot Strait, 

 the main entrance to the Gulf of St. Lawrence, between North Cape in 

 Cape Breton ancl Cape Pay in Newfoundland, but nearer to the former. 



It is almost surrounded by the 100-fathom line (183 metres) and 

 lies just outside, westward, of the St. Lawrence Deep running from the 

 Atlantic ocean (1,000-fathom line) to the mouth of the St. Lawrence, 

 opposite Matane, a distance of about 630 miles. 



Cabot Strait, 65 miles wide, 250 fathoms deep is the main entrance 

 to the Gulf; the other, the Strait of Belle Isle is only 11 miles wide at 

 its narrowest part, and has less than 50 fathoms of water. The Gulf 

 itself is about 450 miles long in a N-W-S-E direction, and 350 in a 



