August 12, 1886] 
as occur in our existing seas—and this notwithstanding 
the very different levels at which Pliocene beds now occur 
CLEMENT REID 
EARTHQUAKE-RECORDERS FOR USE IN 
OBSERVATORIES 
ae ee years ago the writer described in NATURE (vol. 
xxx. pp. 149 and 174) some of the instruments which 
NATBGRE 
he had designed and used in Japan for the registration and 
ANAC oTONEU I Ute 
TE AL LE ac LCC ALE LL 
JER MCRUIID UU GSAN AE 
Fic. r.—Complete three-component seismograph, for motions in all direction .. 
making them easily capable of use by observers who have 
not made seismometry a special study. They are entirely 
self-recording, and require little attention during the long 
intervals which must, in most situations, be expected to 
elapse between one period of activity and the next. 
-One group of instruments is arranged to give a com- 
plete record of every particular of the movement by 
resolving it into three rectangular components-~-one 
vertical and two horizontal—and registering these by 
three distinct pointers on a sheet of smoked glass which 
is made to revolve uniformly by clockwork. A single 
S43 
analysis of earthquake movements. In response to appli- 
cations from the directors of several observatories, who 
wished to add seismometric apparatus to their other 
equipment, arrangements were some time ago made with 
the Cambridge Scientific Instrument Company for the 
manufacture of instruments by aid of which the observa- 
tion of earthquakes might become part of the ordinary 
work of any meteorological or astronomical station where 
such movements occasionally occur. In the design of 
these seismogravhs the object has been kept in view of 
Fic. 2.—Duplex pendulum seismograph, for horizontal motion. 
earthquake always consists of many successive displace- 
ments of the ground; hence the record traced by each 
pointer on the moving plate is a line comprising many un- 
dulations, generally very irregular in character. The ampli- 
tude, period, and form of each of these are easily measured, 
and by compounding the three we obtain full information 
regarding the direction, extent, velocity, and rate of 
acceleration of the movement at any epoch in the dis- 
turbance. 
This group of instruments is shown in Fig. 1. In the 
centre is the plate of smoked glass, which gets its motion 
