20 MODERN SEISMOLOGY 
Plate 4 shows the Galitzin vertical component seismograph 
for electromagnetic registration. The general dimensions of 
the casing are rather over I m. in length and less than I m. 
in breadth and height. The pendulum rod is now replaced 
by a framing to avoid bending. The axis of rotation is very 
neatly arranged to avoid friction by using crossed Cardan 
springs screwed to the fixed framing and to the pendulum fram- 
ing. 
The strong supporting spiral spring is fitted with a screw 
to get rough adjustment, while final adjustment is made by a 
small gravity weight shown to the left of the stationary mass. 
Another adjustable mass shown above the axis of rotation is 
provided to get the centre of gravity of the pendulum in the 
same horizontal line with the axis of support. 
The arrangement of horse-shoe magnets is similar to that 
in the horizontal seismographs, but they have to be twice as 
large, as the attainable period is about half that of the hori- 
zontal instrument. Mirrors and electric hammer are provided 
for standardization and the registration is made exactly as in 
the case of the horizontal components. 
Although these seismographs are far more sensitive than 
either the Milne or Wiechert Seismograph, they are by no 
means difficult to handle. The chief danger to avoid is making 
any adjustment of the pendulum while the galvanometer is in 
circuit with it. 
Further details will be found in Prince Galitzin’s ‘‘ Lectures 
on Seismometry,” published (in Russian) by the Imperial 
Academy of Sciences, St. Petersburg. These lectures embody 
the chief results of separate investigations published (in Ger- 
man) in the Comptes Rendus, Imperial Academy of Sciences, 
St. Petersburg, and the Permanent Seismological Commission, 
St. Petersburg. 
