CHAPTER: WV: 
INSTALLATION OF SEISMOGRAPHS AND CONSIDERATION OF 
DEVELOPMENT OF INSTRUMENTS. 
THE site of a seismological station is probably determined in 
most cases by considerations of policy and finance which do 
not concern us here. But we may consider some conditions 
that appear desirable from a scientific point of view. 
Seismographs are sensitive instruments and thus liable to 
be disturbed by artificial causes such as street traffic, so that the 
instruments ought to be installed at some distance froma town 
or railway line. But such local effects do not penetrate to a 
great distance, so that it is only a question of being a kilometre 
or so distant from such a source of disturbance. We remember 
that most of the European stations from which such important 
results have been obtained are at no great distance from busy 
centres of industry. The dominant features of a seismogram 
of a large tectonic earthquake are not determined by local con- 
ditions of the ground, but the smaller details of the seismograms 
may be modified greatly by the geological formation of the 
rocks in the vicinity of the station. Thus a site where the 
formation is known to be of fairly uniform character for a con- 
siderable area would be preferable to one where the rocks vary 
rapidly. A level plain also recommends itself, while a sharp 
ridge or sudden depression are to be avoided. If we remember, 
however, that the most frequent wave lengths experienced are 
from 30 to 70 km. long, the presence of an isolated obstacle in 
the form of a hill is probably not a very serious matter. 
There are few recording instruments of any kind that are 
not prejudicially affected by change of temperature, and thus 
uniformity of temperature in the room containing the seis- 
mographs is a highly desirable condition even from a general 
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