[KLO.z] MICROSEISMS 207 



(3) The period is practically constant throughout the year and 

 years (1904 and 1908), being about 4.6™, deviating from this by only 

 one or two-tenths, and this latter may be partly due to difficulty in 

 sometimes measuring the period accurately. 



(4) Small oscillations in amplitude show less interference pheno- 

 mena than do the larger ones. 



(5) There is a fair correspondence between the occurrence of Low 

 areas with steep gradients in or about the Gulf and large amplitudes 

 for the secondary oscillations ; but this coincidence is not nearly so well 

 marked as in the relation between such Lows and micrôseisms. 



(6) 'The cause of these secondary oscillations is in the main due to 

 changes of baromietric pressure. 



(7) As the period of the oscillations is practically constant and 

 the disturbing cause variable, the period must be a function of the 

 topography, that is, the depth of water and extent of basin. 



An examination of the mareograms for Trepassey, near Cape Eace, 

 Newfoundland, the extreme point jutting into the broad Atlantic showed 

 Tjery marked secondary oscillations, exceeding both in period and in 

 amplitude those of St. Paul island greatly. Wliile the main period of 

 the latter is 4.6"^, that of the former is 67.6™, about 15 times as large; 

 and the amplitude or range reaches over three and a half feet, while 

 for the other it seldom reaches half a foot. — The distance apart of these 

 two stations is about 300 miles, but the tidal movement coming from 

 the southeast reaches them about simultaneously. The general movement 

 of the atmosphere or areas of Lows and Highs is easterly, and the 

 barometric conditions prevailing at the two stations are, allowing for 

 time interval in passing from one to the other, fairly similar, yet we 

 find these great diiïerences in the secondary oscillations. So we must 

 again conclude that their period as well as amplitude must be dependent 

 upon surroundings of the station, i.e., topography, or depth of water and 

 extent of basin. — Land-locked basins, as shown by the mareograms at 

 Halifax and other places, show little, and those irregular of these 

 secondary oscillations, which is an experience different from that cited 

 for the Japanese coast. 



Taking the above two stations which are exposed to the Atlantic, 

 and noting their very different periods, there does not appear to be any 

 very obvious connection between them and the microseisms. 



Professor Wiechert believes that the breaking of the waves on the 

 shore sets up tremors in the earth crust, and which may manifest them- 

 selves to great distances. To this I am not prepared to give assent. 



