[time-nuts] pneumatically synchronized clocks
bill at iaxs.net
Tue Mar 10 23:52:47 EDT 2009
Peter Galison wrote a fascinating book, "Einstein's Clocks, Poincare's
Maps," in 2003, subtitled "Empires of Time."
>From the bottom of page 92,
"But if France could lock space and mass in the protected basement of
Bretuil [kilogram and meter], time proved more elusive. At the beginning
of the 1880s, one French review lamented that clocks were
extraordinarily recalcitrant, each one's own "personality" repelling any
attempt to regularize it . . ."
"Not that French astronomers and physicists had not tried. All over
Europe, neighborhoods, cities, regions, and countries were struggling to
standardize and unify their clocks. In Paris and Vienna during the late
1870s, industrial steam plants injected subterranean pipes with
compressed air, then modulated that pressure to set clocks pneumatically
around the city."
[There are no details of the modulator or the regulating mechanism in
the clocks, probably for the same reason that equations are not used in
books for wide audiences. There is a drawing of the control room at the
Rue du Telegraphe, circa 1880, but the operation remains obscure.]
"At first the fifteen-second delay caused by the time it took the
pressure pulse to race under the streets of Paris seemed like nothing.
Yet time sensitivity had sufficiently mounted by 1881 that even this
tiny delay (. . .) became visible. Astronomers caught the problem, so
did the engineers of bridges and roads. Soon the public did as well."
"At first the engineers tried to shrug off the discrepancy: "this small
discordance, indisputable in theory, has little practical importance
since we are dealing with clocks that display minutes, and where the
minute hands jump in steps and do not permit further divisions, even
approximately between that division of time.""
"The clock minders hastened to add that they would offset the
Observatory's clock by the fifteen seconds the pulse took to reach the
outermost reaches of the network. To be exact, they then mounted
retarding counter-weights on each pneumatic clock based on its distance
from the center."
"Two striking features of time coordination emerge from this little
vignette. First, time awareness had become acute. Before the nineteenth
century, clocks normally did not even have minute hands. . . . Second,
the transmission time - even of a pressure wave traveling at the speed
of sound - looked to professionals and the public like a problem
[Of course, electrical transmission soon solved the problem, but
certainly not overnight.]
IMHO, a little history helps to put today's problems in perspective.
Google provides some useful hits. An 1881 article in the London Times
(reprinted by the NY Times) reveals that the system runs on pulses at
one minute intervals that index the minute hand. Paris had 16 miles of
clock air piping to over 2000 clocks and 14 public clocks at that time.
There is no mention of time synchronization, just the pulse from a
The US had pneumatic clocks made by Hals and Wenzel. NAWCC has some
articles - need to follow up on that.
Would like to see one of those pneumatic clocks. If I owned one, I'd
build a GPS disciplined pneumatic oscillator for it.
From: Tom Van Baak
Sent: Tuesday, March 10, 2009 12:52 PM
1pps = 1 puff per second?
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