28 



ANNUAL REPORT OF THE 



The Shaler Memorial Expedition to Brazil and Patagonia, 1908- 

 . '09. Amer. journ. sci., October, 1908, ser. 4, vol. 26, p. 404. 

 Reports on geology and related subjects. Reports of Delegates 

 to the Pan-American Scientific Congress, 1908-1909. Wash- 

 ington, 1909, Appendix 1, p. 34-35. 



Appendix. 



REPORT ON THE HARVARD SEISMOGRAPHIC STATION. 



By J. B. Woodworth. 



The Seismographic Station, described in last year's Report 

 (p. 17-19) was during the first half of the year in charge of Dr. 

 G. R. Mansfield, who gave much time and careful attention to a 

 voluntary task. Particular pains were taken to arrest the rusting 

 of the exposed steel rods and parts of the pendulums, the oxidation 

 of which has very largely been checked. It was necessary in this 

 work for a time to dismantle the seismograph. At the beginning, 

 the Station clock was regulated by comparison with a watch set 

 after a chronometer at Harvard Square which time in turn was 

 compared with the Western Union noon signal sent out from 

 Washington. This unsatisfactory and indirect method was later 

 replaced by direct comparison with the Harvard Astronomical 

 Observatory time received at the Station by telephone. In this 

 manner it is usually possible to ascertain the error of the Station 

 clock within a second. Dampers especially devised to be con- 

 nected with the pendulums of the 100 kilogram Bosch-Omori type 

 were received in January. After a period of trial in the spring 

 which lasted several weeks, it seemed best to detach the dampers, as 

 it was not possible to adjust them so as to permit of the excitation 

 of the pendulums by distant earthquakes, satisfactory records of 

 which were during this interval obtained at Albany and Washington 

 on 25 kilogram seismographs of the same general type. The use 

 of the damping device is made necessary for the determination 

 of the motion of an earth particle during an earthquake by the 

 fact brought out by Wiechert that unless the oscillations of the 

 horizontal pendulum be reduced in the ratio of 8:1 the magnifi- 

 cation is not uniform at all phases of the movement of the seis- 



