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ON SEISMOLOGICAL INVESTIGATIONS. 
After-shocks of the Jamaica Earthquake—continued. 
| Date nelond Shide Kew Bidston Paisley | Edinburgh 
1907 
April 25 . 1.15 _ _ 0.35 — 
59 : 9.50 — | — 2 
April 28 . 2.53 — — _ — _ 
“5 : 23.0 — _— 2 — _- 
April 29. 1.30 _ _— q | = = 
May 1 .| 21.35 21.25 — — | 21.31 21.30 
May 2 .| 2.20 2.20 — 2.22 2.21 — 
May 3 allie ly 6 17.2 16.54 _ 17.3 — 
May 4 : 2.42 2.43 _ _ — — 
May ll. 1.30 _— — 1.25 — _— 
Junel3_. | 7.8 71 7.8 — = — 
Junel4 . 7.20 7.24 — _— — — 
Junel6 . 16.15 16.56 16.57 16.55 — — 
Junel8 . 13.20 13.30 — _— — 
June 29. 20.4 —_ — _— — — 
July 1 : 11.0 11.1 — — — — 
July 5 < 20.0 20.3 — 20.0? — — 
Total. , 148 92 22 58 39 18 
‘The movements recorded at Kew are referred to as being very small and ill- 
defined, and in the ordinary way would have been passed over as being due either 
to air tremors or some other non-seismic cause. 
The records from Bidston are spoken of as ‘doubtful,’ ‘ possible,’ ‘ very evident,’ 
‘very pronounced,’ and ‘ clearly marked.’ 
Paisley records were much interfered with by air tremors; it is therefore possible 
that some of the entries are non-seismic in character. 
The Edinburgh records are spoken of as ‘slight thickenings,’ ‘small notches,’ 
‘ roughness of line,’ ‘ slight tremors.’ 
In the Report for this year the Shide list has been increased by 41 entries. 
These have been added because they have been confirmed by records from other 
stations. 
V. Quick Vibrators as applied to Seismometry. 
In a paper on ‘A Neglected Principle that may be employed in 
Earthquake Measurements,’ by Professors J. Perry and W. H. Ayrton 
(see ‘ Trans. Asiatic Soc. of Japan,’ May 23, 1877), it is suggested that 
the essential feature in a seismograph should be a heavy mass so sus- 
pended by stiff springs that its own free period would be about five times 
as fast as that of an earthquake. This was to take the place of the 
steady point in modern seismographs. Inasmuch as this instrument 
was never constructed, we can only surmise about the character of the 
record it would furnish. 
In a paper on ‘ Experiments in Observational Seismology ’ (see 
‘Trans, Seis. Soc.,’ vol. iii. 1881) I make reference to pendulums the 
periods of which were a small fraction of a second. They were only 
used as tremor-indicators. 
Notes on these and on other quick vibrators are referred to in the 
chapter on ‘ Seismometry ’ in a small volume on ‘ Earthquakes ’ pub- 
lished in the ‘ International Science Series,’ 1883. All these instruments 
were intended to record earthquakes which could be felt, the periods of 
which varied between one and three or four seconds. As they merely 
