[klotzJ MICROSEISMS 203 



are the result of the passage of a " Low " and especially of its presence 

 in the Gulf. Some investigators believe the microseisms may be the 

 forerunoier of coming weather conditions, and hence may assist in making 

 forecasts. The seismograms examined here are not very encouraging on 

 that point, the microseisms indicating rather " that we have had wea- 

 ther, than that we are going to have weather." This statement refers to 

 the microseisms and not to the effect of bending, or displacement of tin 

 pendulum zero, brought about by unequal pressure over a large area. 

 The writer is not as yet prepared to say whether the approach of a 

 "Low," with the consequent lifting or rising of the earth's surface, is 

 a distinctly measurable quantity as registered by our seismograph, for 

 the measurements of the two components of the change of pendulum zero 

 for the year have not yet been tabulated and critically compared with the 

 movements of " Highs " and " Lows " in the eastern part of the continent. 



It is found that, broadly speaking, the microseisms are more numer- 

 ous during the colder season than during the warmer one, and some have 

 rought therein a relationship of cause and effect. In our climate here we 

 have a large range of temperature, during the past year of 127° F. (96° 

 and — 31° F.) During Febiniary, when the thermometer reached its 

 lowest and we had some continuously very cold weather, the seismograph 

 showed no evidence thereof. 'The connection is assumed to be from the 

 fact that the frozen ground on the one hand lends itself for the better 

 transmission of pulsations, and the other that the act of freezing itself 

 sets up stresses and consequent oscillations that manifest themselves as 

 microseisms. From extreme cold it does not necessarily follow that the 

 ground is frozen to any great depth, such as the case during the past 

 winter. The reason that there was very little frost in the ground, was 

 that an early and heavy snowfall together with its subsequent accumula- 

 tion to many feet, covered the earth with a mantle that the cold could 

 not penetrate. 



By far the large majority of microseisms show themselves by a 

 serrated record, *' sawtooth " type as I designate it ; more rarely occur 

 those of the " spindle " type, where the oscillations or rather the ampli- 

 tudes rise and fall, increase and decrease, with certain cadence, as in the 

 vibrations of a string between two fixed points. The interval between the 

 maximum amplitudes is very variable, varying from one to several 

 minutes. The rate of increase and decrease of the amplitudes is less 

 than that produced by the damping of the pendulum, so that we can 

 scarcely attribute it to the latter on the supposition that the pendulum 

 itself is set in motion and the oscillation dies down by damping, to be 

 renewed by a fresh impulse. This, however, would preclude a gentle in- 



