70 MODERN SEISMOLOGY 
up to 40 km. by means of observations which are only 
given to the nearest second. Only at 500 km. and then only 
for 40 km. depth do the two values differ by 1 second, and as 
a matter of fact we can hardly suppose the value of v, to be 
so accurately known as to give much security. 
Distance Time from focus to station in secs. Differences. 
A. h =1 km. h =10km, h = 40 km. Ty - Th. Tg) — Ty. 
S. S. Ss. 
o Only 1°39 5°58 1°25 5°44 
50 6:98 rata 8°92 o'13 I°94 
Too 13°95 I4°O1 14°99 0°06 I°04 
I50 20°91 20°94 21°57 0°03 0°66 
200 27°88 27°90 28°35 0°02 0°47 
250 34°81 34°81 35°14 0°00 0°33 
300 41°83 41°83 42°08 0°00 0°25 
350 48°81 48-79 48°98 — 0°02 O17 
400 55°76 55°73 55°86 — 0'03 (ode ce) 
450 62°78 62°75 62°84 — 0°03 0°06 
500 69°75 69°72 69°76 — 0°03 O°O1 
We may, however, conclude that on either hypothesis 
the observations between 200 and 400 km. should give us the 
actual time of occurrence of the shock at the focus to less than 
$ second as practically independent of % for 2<40 km. and that 
is an important point gained. Next, to get the depth we 
must use only the observations for 4<200 km. and even then 
it is really only the observations for 4<50 km. that ought to 
count heavily. Here also it is impossible to discriminate 
practically between the two hypotheses, so that the simpler 
one should have the preference. 
Turning now to the actual data in the table on the opposite 
page, we note that the distances were computed from the 
epicentre determined by noting that the times at Ziirich and 
Strassburg were the same, as were also the times at Aachen and 
Gottingen. The co-ordinates so obtained were 
p48) 19 INdand in, Onzsae 
Galitzin, from the time at Karlsruhe, Strassburg, and Ziirich, 
finds the time at the focus to be 21 hours, 25 minutes, 52°5 
seconds, and his conclusion is that the depth was 9°5 km. with 
a probable error + 3°38 km. The data, however, show dis- 
