112 T. C. Mendenhall — Seismoscopes and 



dynamically similar models of such structures to differently 

 compounded vibrations and studying the results, some light 

 may be thrown upon the confusing and often contradictory 

 phenomena of actual earthquakes. 



Assuming that a satisfactory form of seismoscope has been 

 selected by subjecting all proposed or submitted to the test of 

 the seismic table, it is important to consider next their distri- 

 bution and use. As it is very desirable that they should be 

 as numerous as possible, and as the cost of the equipment of a 

 station is of great practical moment, it may be stated that the 

 whole outfit for a single station, including clock, seismoscope, 

 battery and all, need not cost more than twenty-five dollars, 

 and it is hoped that a sum considerably less than that amount 

 may be found sufficient. In selecting stations it is of the 

 utmost importance that the question of accurate time should 

 be first considered. Standard time signals from one observatory 

 or another are now distributed so generally over the whole 

 country, that in any considerable town no difficulty will be 

 found in determining the clock error and rate, provided that 

 the apparatus is in the hands of a suitable person. It is likely 

 that in many instances jewelers or watch makers, who receive 

 time signals daily will be willing to undertake the care of a 

 seismic station. The seismoscope may be mounted upon a 

 bracket secured to the stone or brick foundation of a building, 

 in the cellar or basement, while the clock should be placed 

 where it will be often seen, or where it may be of real service 

 as a time-keeper to the observer. The use of an electric alarm, 

 while not a necessity, is very desirable, as through its action 

 attention is immediately called to the disturbance, and even a 

 second or two of warning might enable many interesting 

 observations of phenomena which would otherwise escape the 

 observer. 



I have found it very useful to provide for regular tests of the 

 apparatus on the first of each month. An artificial disturbance 

 near the seismoscope takes the place of a real earthquake and 

 the operation of the bell-ringing, clock-stopping apparatus is 

 observed, the clock error and rate applied, and in fact every- 

 thing is done as if a real earthquake had occurred. This will 

 enable the observer to detect any fault in his arrangements and 

 will serve in a great degree to maintain his interest and sustain 

 his patience through months or years of waiting for an actual 

 record. Blanks should be furnished on which the results of 

 these tests may be recorded and forwarded to the person in 

 charge of the whole system of observations. Many other de- 

 tails might be referred to, but they belong rather to a code of 

 instructions for observers. There is one matter connected with 

 the establishment of stations, however, which experience has 

 shown to be important. 



