46 REPORTS ON THE STATE OF SCIENCE.—1914. 
IV.—Discussion of Results from Different Seismographs. 
The card catalogue system introduced at Shide for records from 
January 1913 onwards facilitates the comparison of results from 
different instruments. The following discussion is only preliminary, and 
the unit of time adopted (0°l m. or 6 sec.) is not small enough to 
do justice to the best instruments. But itis as small as can reasonably 
be adopted for the Milne instruments, and the main object of the 
discussion is to bring out the comparative attainments of the Milne 
seismographs as compared with modern and much more sensitive 
apparatus. 
From the beginning of 1912, the weekly Bulletins issued from 
Pulkovo give epicentres for the large earthquakes, determined by 
Galitzin’s method for a single station. Adopting these as correct 
and using the table printed by G. W, Walker on p. 54 of his mono- 
graph on ‘ Modern Seismology,’ or by Galitzin in his ‘ Vorlesungen 
iiber Seismometrie,’ p. 137, we can deduce from the times recorded at 
Pulkovo for either P or S, the time of the earthquake itself. Re- 
applying the table we can deduce the theoretical times of arrival of 
P and S at other stations, for comparison with their records. For 
this purpose the distances of the stations from the epicentre were read 
to whole degrees from a globe, which again is a method unsuitable to 
refined investigation, but sufficiently accurate for the present pre- 
liminary examination. 
As an example, the times recorded for the earthquake of 1913, 
January 11, were as follows :— 
P S 
haem” 8 be, moses 
13 29 45 13 40 9 
Subtract ‘ : ; ; 12 36 22 54 
Time at epicentre. . . . LSP ee =D 13 17 15 
The distance of Florence from the adopted epicentre (6° N., 1179 B..) 
was read off as 98°, and the calculated and observed times were: 
For P | For S 
C Cppaabie Ooh Hae ergata 
i Mitt || sae eee h m. | m. 
| 18 31-1] 13 30:2) —0-9 | 18 42-7 | 13 35 | —7:7 
These differences O—C were collected and discussed for the following 
five earthquakes :— 
Date Adopted Epicentre aoe mere oa 
° ° ° h. m. 
1913, January 11 Rite ge 6-0 N., 117-0 E. 83 13. 17-2 
1913, March 23... . «(| 26-3N., 143-38. 78 20 47-2 
1913, April30 . . . «| 50-2N., 176-:3.E. 67 13 34-4 
1913, May 18 . . . . | 263N., 143-7E. 79 2 9-7 
19lesdune 22) 2 ae a OO N. al7S8-1 66 13 50:3 
