CEVA AE Rag iit: 
THE CHIEF TYPES OF SEISMOGRAPHS IN ACTUAL USE. 
THE Milne Seismograph is made by Mr. R. W. Munro, London, 
and to him and to Dr. Milne I am indebted for permission to 
use the photograph shown on Plate 1. The supporting frame 
of the pendulum consists of a vertical iron pillar cast in one 
piece with a triangular bed-plate supported on three levelling 
screws, which rest by hole, slot, and plane on three glass studs 
imbedded in the pier. The pendulum boom is a light rod of 
aluminium nearly I metre long, and at the inner end it is fitted 
with an agate cup which presses against a steel pivot point screwed 
into the pillar. The boom is supported at a point a little 
beyond the stationary mass by means of a fine steel wire ending 
in unspun silk which passes to a pin at the top of the pillar. 
The mass (about 1 kg.) itself is not rigidly attached to the 
boom, but is balanced on a steel pivot. The object of this 
appears to be to reduce the effective moment of inertia of the 
pendulum. The adjustments provide for bringing the boom 
into the horizontal position along a prescribed line, and so as 
to have the desired period of say eighteen seconds. One of 
the levelling screws, having a pitch O°5 mm., carries an arm 
moving over a graduated arc, and provides the means of giving 
a known tilt to the instrument, so that its static sensitiveness 
may be determined. The boom is prevented from sagging at 
its outer end by a silk cord as shown. 
The registration is carried out as follows: The boom 
carries at its end a small transverse plate of aluminium with a 
narrow slit parallel to the boom. This moves over a fixed 
slit at right angles to it in the top of the registration casing. 
This arrangement is illuminated from above so that a small 
dot of light corresponding to the intersection of the slits is cast 
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