Warner, Deborah J. warnerd@......
Sent: Mon, 16 Jul 2012 14:45
Subject: Early American Seismology



Check out my blog: http://blog.americanhistory.si.edu/osaycanyousee/2012/07=
/joseph-henry-and-the-origins-of-american-seismology.html
=20
Deborah Warner
Curator, Physical Sciences Collection
National Museum of American History
=20
 Dear Deborah Warner,=20
=20
    This is an interesting note, but the apparatus is incomplete. Can you c=
heck examples in other museums ?=20
    The pendulum needs to be screened from air drafts, probably with a glas=
s cylinder, or a 'jar', but with no=20
base.=20
    There seems to be no sensing mechanism, but three electrical terminals =
are fitted. The long thin wires on=20
the outside pair are not connected to anything. This suggests that two pair=
s of electrical contacts, mounted=20
very close to the ball mass, may be missing. These could give off/on electr=
ical readouts, maybe driving fast=20
relays ?=20
    There seems to be no damping mechanism, but some of the older type sens=
ors were not damped.=20
    The length of the pendulum is not mentioned. If this was made about 9.8=
" long, it would resonate at 1 Hz,=20
about the frequency of Teleseismic P waves. Some damping would reduce the s=
ensitivity, but could prevent=20
multiple bouncing contacts. A wooden frame may not be stable over weeks / m=
onths.=20

    Regards,=20

    Chris Chapman






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=20
=20
=20





































Warner, Deborah J. warnerd@......




Sent: Mon, 16 Jul 2012 14:45





Subject: Early American Seismology































Check out my blog: http://blog.americanhistor=
y.si.edu/osaycanyousee/2012/07/joseph-henry-and-the-origins-of-american-sei=
smology.html










 










Deborah =
Warner










Curator, Physical Sci=
ences Collect=
ion










National Museum of American=
 History










 










 Dear Deborah Warner, 










 










   =
 This is an interesting note, but the apparatus is incomplete. Can you chec=
k examples in other museums ? 



   =
 The pendulum needs to be screened from air drafts, probably with=
 a glass cylinder, or a 'jar', but with no 

base. 



   =
 There seems to be no sensing mechanism, but three electrical terminals are=
 fitted. The long thin wires on 

the outside pai=
r are not connected to anything. This suggests that two pairs of elect=
rical contacts, mounted 

very close to the ball mass, may be missing. These cou=
ld give off/on electrical readouts, maybe driving fast 

relays ? 



   =
 There seems to be no damping mechanism, but some of the older type sensors=
 were not damped. 



   =
 The length of the pendulum is not mentioned. If this was made ab=
out 9.8" long, it would resonate at 1 Hz, 

about the frequenc=
y of Teleseismic P waves. Some damping would reduce the sensitivity, b=
ut could prevent 

multiple bouncing =
contacts. A wooden frame may not be stable over weeks / months. 


 

   =
 Regards, 

 

   =
 Chris Chapman