Regarding wire suspensions in seismometers:

These have been experimented with since the earliest years
of seismometers for making pendulum sensors for horizontal
motion. Clearly the most basic is a plumb-bob on a string.
But to constrain the degrees of freedom of this mass, two or
more suspension wires are neeeded, or else a flat flexure
is used as for the pendulum of a grandfather clock. The thin
flexure strip is adequate to keep the dish-shaped mass from
rotating and banging on the door.

For more complete restraint four wires are used as a pair of
inverted Vs, one at each end of a rod-like horizontal boom or
mass. An example of this is the assembly of in-line chrome balls
that are suspended from a wooden frame as an office toy (that
actually demonstrates conservation of momentum). 

This suspension is also used for the dashpots to damp the
motion of the Wiechert 80kg inverted pendulum seismometer of
the early 1900s. The wires suspend a shaft supporting the 
pistons that translate within the fixed cylinders. The wires
are about 20 cm long (high?) to minimize up and down motion.

A number of early optical mirror and moving coil horizontal 
sensors were made, some with suspensions over a meter high.
(a 1 meter simple pendulum has a period of 2 seconds).
However, it was quickly realized that longer period sensors
were only practical with horizontal boom configurations, as 
the Bosch-Omori 25kg horizontal sensors of the 30s.

The interesting variable is the attachment of the pivot end 
of the boom at the support post. Some (Milne-Shaw) used a
compressional pivot; later a tension member from the back of
the support post was preferred, as in large horizontals today.
An extreme of the second tension wire is the Zollner suspension, 
where the taught wire extends as far below the boom as the
upper suspension is above the boom. This still required	
some points of attachment to fix the axis of rotation,
and in the Wenner seismometer these became crossed flexures.
THis provided a fairly rugged way to suspend a large mass
and boom while using lightweight flexures to fix the axis
of rotation. It also required a cavity in the pier.

The Zollner-Wenner wires had problems with bow-string oscillations
which would vibrate from local noises like steps and shorten slightly.
In the Wood-Anderson, which is an extreme case of the Zollner
opposed wires, the vibration of the wires is damped by oil cups.
(The copper mass itself is magnetically damped).

Regards,
Sean-Thomas

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