Vertical Pendulum Tiltmeter

Alexis Pauline Gumb: "and our streets became forgiving and our buildings became round and we gave up straightness and guess what? nothing was missing.[1]

[1] Hortense Spiller, an element of radical waywardness “Formalism Comes to Harlem,” 81.

The difficulty in earthquake m easurem ents is to find a point which
does not move during the disturbance. This condition is, in certain
cases, fulfilled approxim ately (as regards horizontal motion) by the
bob of a pendulum ,* and, for this reason, pendulum s have been fre
quently used as seismometers. A long pendulum, whose period greatly
exceeds the period of the earthquake waves, suspended from an ex
ceedingly rigid fram e, m akes a fairly good seismograph, the earth’s
motion relatively to the bob being shown by a pair of indicating levers
at right angles to each other, w ith th eir short ends in contact with
the bob near its centre of gravity, their fulcrums fixed to the earth,
and th eir long ends lightly touching a plate of smoked glass which is
kept revolving uniform ly by clockwork. If the bob were to remain
quite stationary during an earthquake, this would give two curves,
showing on a magnified scale two rectangular components of the
horizontal displacement of a point on the earth ’s surface in conjunc
tion with the time, from which the amount and direction of the actual
horizontal movement, and its velocity and rate of acceleration at any
time during the shock, could be deduced. There are, however, two
independent reasons why the bob of a pendulum seismograph does not
remain stationary during an earthquake shock. In the first place, it
is disturbed by the friction and inertia of the recording levers. [It
may be observed here that a considerable multiplication of the
motion is essential, at least in measurem ents of the small earthquakes
which are common in Japan, for the actual motion of the earth’s sur
face is usually only a fraction of a millimetre.] It is not difficult,
however, to reduce this source of disturbance to an almost insensible
quantity by a careful construction and arrangement of the joints,
and by making the mass of the bob excessively great relatively to that
of the levers. The other and by far the more important cause of dis
turbance is the motion of the point of suspension of the pendulum.
The motion communicated to the bob by this means would reach
a maximum, and altogether eclipse the true earthquake motion if the
period of oscillation of the supporting point agreed exactly with the
pendulum’s free period. By making the pendulum long enough, and
the supporting frame rigid, this extreme case can easily be avoided,
but the effect is never entirely absent. The w riter has observed that
a pendulum 20 feet long, suspended as favourably to steadiness as
possible, has been set swinging during even a very slight earthquake,
through arcs about three times as long as the actual motion of the
earth ’s surface. By using a pendulum of as great length as this, how-
ever, and by making it trace a continuous record in the manner de
scribed above, we may distinguish between that part of the record
which is due to the swing of the pendulum and that part which is the
true register of the earth’s motion, the waves produced by the swing
of the pendulum being of much longer periods than those due to the
undulation of the earth. The record thus shows the short earth
quake waves superposed upon a long sinuous curve due to the swing
of the pendulum.


earth ’s surface
the Earth (an)elasticity
instrumental drift

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https://en.wikipedia.org/wiki/Silver_bromide //

Proceedings of the Royal Society of London
On a New Seismograph (pp. 440-446) J. A. Ewing
https://www.jstor.org/stable/114083

The shop of Horace Darwin (son of) probably produced the seismograph in Bidston?
"The Company was responsible for the manufacture of many commercial scientific instruments including, ‘Prof J. A. Ewing’s Seismograph’ in 1891, and in 1910 ‘Darwin’s crack extensometers for St Paul’s Cathedral’."
https://www.christs.cam.ac.uk/horace-darwin-1851-1928

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"The Observatory’s two levels of cellars and other features made it especially suited for calibrating chronometers under controlled conditions of temperature and seismic vibrations."<ref name=stephen"></ref>

"[A] new activity commenced in '''1897''' with the installation in the cellars of a seismograph. This was the first of a series of seismographs of different designs that followed."<ref name="baker">Bidston Observatory: Earth Tides and Ocean Tide Loading, Trevor F. Baker, 2 November 2016 http://www.bidstonobservatory.org.uk/earth-tides/</ref>

Reading and changing the seismographic records was part of the daily routine in Bidston Observatory.<ref>Joyce Scoffield, ''Bidston Observatory, The Place and the People''. p172</ref>

"In '''1900''' Bidston obtained its own Milne-Seismograph. and tables of its observations were published from '''1901'''." <ref>Joyce Scoffield, ''Bidston Observatory, The Place and the People''. p149</ref>

"The Dock Board felt that 'meteorological observations could be taken with equal accuracy elsewhere' and the Dock Board's 'interest in the unfelt tremors of the earth was not immediate'."<ref>Joyce Scoffield, ''Bidston Observatory, The Place and the People''. p150</ref>

[[File:Milne.jpg|thumb|none|Tone Harikaw with her husband, seismologist Prince Boris Galitzin and John Milne (center) in 1910.]]

""In '''1910''', observations were made using instruments designed by Sir George Darwin, Sir Horace Darwin and others to determine the yielding of the land to the load of tidal water, now called the ‘ocean loading effect’."<ref name="baker"></ref>

''Could this be the <ul>Prof J. A. Ewing’s Seismograph</ul> produced by Horace Darwin?''<ref>
https://www.christs.cam.ac.uk/horace-darwin-1851-1928
</ref>

"As a result of the successful tests with the Claustral Pendulum, Bidston acquired a Graf-Askania vertical pendulum of its own, and installed it after modification." <ref>Joyce Scoffield, ''Bidston Observatory, The Place and the People''. p328</ref>

Claustral Pendulum = encased pendulum? A 'Graf-Askania vertical pendulum' or 'gravimeter' or 'Askania vertical pendulum tiltmeter' measures tilt through changes in gravity (which is linked to measuring tidal load but I do not understand yet how).

"New tidal tilt observations were made in the Bidston cellar in the '''1930s'''. Doodson and Corkan ('''1934''') used a Milne-Shaw seismometer for one month of observations. In '''1934''', funds were used from a Cambridge mathematics prize that was awarded to Proudman to purchase a new Milne-Shaw seismometer. Beginning in March '''1935''', one year of observations of the north-south tilt were made using this instrument (Corkan, 1939)."<ref name="baker"></ref>

"Geoff Lennon made further observations of the north-south tilt at Bidston using the Milne-Shaw seismometer between '''1952''' and '''1954'''. For the International Geophysical Year 1957-1958 there were increased efforts to make observations of Earth tides around the world."<ref name="baker"></ref>

"In the Bidston cellar, modified Milne-Shaw seismometers were used to measure the tilts in both the north-south and east-west directions from July '''1957''' to December '''1958''' (Lennon, 1959)."<ref name="baker"></ref>

"The Bidston cellar provided a useful test site for comparing various tiltmeters, before installation in the tunnel at Llanrwst."<ref name="baker"></ref>

[[File:Glasses.jpg|thumb|none|Photograph of a scientist with tiltmeter in situ, installed in the cellar of BOAC (2021)]]
[[File:Milne-Shaw.jpg|thumb|none|A Milne–Shaw seismograph in use at 'the Honolulu station' in Hawaii. (b) is the same instrument as shown in (a), but with the cover on. [https://prd-wret.s3.us-west-2.amazonaws.com/assets/palladium/production/s3fs-public/styles/full_width/public/thumbnails/image/Preserving%20Historic%20Earthquake%20Records-%206.gif USGS]]]
[[File:Plinth.jpg|thumb|none|Bedrock connection plinth (current situation, BOAC, 2021)]]
[[File:North.jpg|thumb|none|The plinth on which the tiltmeter was installed, is oriented on the North-South axis (2021)]]

''The Milne-Shaw Tilt Meter (or maybe there was more than one?) was transferred to the University of Aberdeen in '''1997'''''.

"The NSA (National Seismographic Archive) holds the ex-Bidston Milne-Shaws, examples of modern Willmore instruments, and probably the only Jaggar shockrecorder in existence."<ref>''Historical Seismological Observatories in the British Isles'', British Geological Survey, 1999 http://www.earthquakes.bgs.ac.uk/hazard/pdf/wl9913.pdf</ref>

Joyce Scoffield, Bidston Observatory, The Place and the People:

In 1900 Biddston obtained its own Milne-Seismograph. and tables of its observations were published from 1901.
p149

The Dock Board felt that "meteorological observations could be taken with equal accuracy elsewhere" and the Dock Board's "interest in th unfelt tremors of the earth was not immediate".
p150

As a result of the successful tests with the Claustral Pendulum, Bidston acquired a Graf-Askania vertical pendulum of its own, and installed it after modification.
p328

Daily Routine
7.15 Change and develop seismographic records
p172

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seismograph vs scanner
difference between seismograph and tiltmeter
pendulum vs airbubble [waterpas]

straightness

Clock cellar

calibration/compensation/evening out

Actuarial Methods --> against prediction

https://www.usgs.gov/natural-hazards/earthquake-hazards/science/seismographs-keeping-track-earthquakes?qt-science_center_objects=0#qt-science_center_objects

https://science.gc.ca/eic/site/063.nsf/eng/97237.html

https://www.ssplprints.com/image/85947/milne-shaw-seismograph-no-1-1914

However, a new activity commenced in 1897 with the installation in the cellars of aseismograph. This was the first of a series of seismographs of different designs that followed. In 1910, observations were made using instruments designed by Sir George Darwin, Sir Horace Darwin and others to determine the yielding of the land to the load of tidal water, nowcalled the ‘ocean loading effect’.

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Geoff Lennon made further observations of the north-south tilt at Bidston using the Milne-Shaw seismometer between 1952 and 1954. For the International Geophysical Year 1957-1958 there were increased efforts to make observations of Earth tides around the world. In the Bidston cellar, modified Milne-Shaw seismometers were used to
measure the tilts in both the north-south and east-west directions from July 1957 to December 1958 (Lennon, 1959)

New tidal tilt observations were made in the Bidston cellar in the 1930s. Doodson and Corkan (1934) used a Milne-Shaw seismometer for one month of observations. In 1934, funds were used from a Cambridge mathematics prize that was awarded to Proudman to purchase a new Milne-Shaw seismometer. Beginning in March 1935, one year of observations of the north-south tilt were made using this instrument (Corkan, 1939).

The Bidston cellar provided a useful test site for comparing various tiltmeters, before installation in the tunnel at Llanrwst (Figure 2 shows one day of the record from the Askania vertical pendulum tiltmeter installed in the Bidston cellar in 1971).

Bidston Observatory: Earth Tides and Ocean Tide Loading, Trevor F. Baker, 2 November 2016 http://www.bidstonobservatory.org.uk/earth-tides/

-> transferred in 1997

2.6 The NSA (National Seismographic Archive) holds the ex-Bidston Milne-Shaws, examples of modern Willmore instruments, and probably the only Jaggar shockrecorder in existence. Milne-Shaw seismographs are held by the Universities of Aberdeen and Birmingham; the latter also houses the JJ Shaw papers in its Lapworth Museum.
http://www.earthquakes.bgs.ac.uk/hazard/pdf/wl9913.pdf

http://earthquakes.bgs.ac.uk/archive/Archive_reports.htm