MUSEUM OF COMPARATIVE ZOOLOGY. 



29 



mograph. In the accompanying tabulated results of records ac- 

 count is taken, in consequence of this lack of damping, of the 

 maximum displacement of the stylus on the drum rather than an 

 attempt to present an inaccurate estimate of the intensity of the 

 shock at this Station. 



At certain times almost as soon as the plant was installed, long 

 period wanderings of the pendulums were observed, frequently 

 resulting in the too rapid spreading out of the lines or in their 

 crowding on the chronographic drum, in the latter case in such a 

 manner as to utterly confuse the record of an earthquake. The 

 duration and character of these long period wanderings have been 

 carefully gone over by Mr. B. M. Varney under the direction of 

 Professor Ward, on the basis of the record kept during the first 

 half-year, with the view of comparing them with known barometric 

 changes. These movements of the pendulums are quite distinct 

 from the shorter swayings due to the shift of weights about the build- 

 ing, as when persons approach or enter the instrument room. There 

 is also a readily recognized diurnal tilting of the ground on which 

 the Station stands, producing a corresponding crowding and spread- 

 ing of the record lines, a feature which Mr. Varney finds very defi- 

 nitely associated with sunny and cloudy days, pointing to local 

 solar influences. It is to be hoped that further studies will be 

 made of the indications furnished by the instrument regarded as 

 a tiltometer. When the pendulums are adjusted to a period of 50 

 seconds or greater it is very sensitive to these tilts. As a seismo- 

 graph it gives best results when adjusted to a period of 25 seconds. 



Mr. W. G. Reed, Jr. voluntarily acted in charge of the Station in 

 the latter part of August, 1909, and during the year Mr. Flint 

 has performed the ordinary daily routine of the Station. 



In order to facilitate the ready computation of the distance from 

 this Station to the probable point of origin of a shock, Laska's 

 rules for computing the distance with Benndorf 's corrections have 

 been made the basis of a graphic table for all possible earthquakes 

 and distances. At the same time a mercator map has been pre- 

 pared on which great circles passing through Cambridge and the 

 antipodes of the Station have been drawn after the plan of Lambert's 

 meridian mercator projection, and on the same map have been 

 placed circles showing equal distances from Cambridge, for the 

 purpose of readily locating areas of frequent seismicity at appro- 



