62 REPORTS ON THE STATE OF SCIENCE.—1914. 
too frequent. Occasional traffic along a neighbouring road would not 
cause much confusion on the record. 
A curve is shown attached giving the magnification of movement 
in both the Milne and Galitzin types. It refers solely to the case 
300 
B00 | Galitzmadjusted ! salthat the pendulum 
f and galvanometer have the same period 
| of 24-7secs.and hee! damped so 
| 
| 
| 
700 — Z } 
| . 
as to be just aperiodic 
| 
600 | I al fae 
x | 
A] 
2 
Si | ——— irs — 
S00 = S t - T + figs 
SES | 
Se 
400 
Magnific 
continue 
300 
ae 4 es {ete 
fon long 
| 
Omort, just speriodic, Undamped\ period /5secs 
motion of hip af boom magmbied 6 Hmes optically _ 
| [Sat oa sd ati i Hai 
SS 
9 5 10 15 20 25 
of a long-continued series of uniform waves; but it is noteworthy that 
in the Milne type it cannot be applied to any other kind of motion and 
may be considerably in error even one or two minutes after the 
commencement of the series. 
In the Galitzin type, however, the free motion dies away much 
more rapidly. 
VII.—Present Value of the Milne Instrument. 
We may summarise the present situation as follows :— 
(a) The Milne instrument is undamped, but for one purpose—viz., 
the determination of times of arrival of P and S—this does not matter. 
There has been an idea that S (or P:) is not easy to read on Milne 
records; but S has often been read in mistake for P, and when these 
readings are counted properly S seems to be identifiable as often as P. 
On the other hand, the absence of damping makes the readings of 
maximum of uncertain significance. 
(b) The time scale of the Milne instrument is small and its magni- 
fication is also small. Both might be increased with advantage, and 
it seems probable that then the times of arrival of P and S$ could 
be read as well as on most other instruments. 
(c) The present wide dispersion of Milne stations makes the records 
of great value. Most of the modern instruments are in Europe. For 
a 
