NavList:

   

Reply

I have just completed Stephen Inwood's very informative, if a bit long
winded, "The Man who Knew to Much" the life of the extraordinary English
scientist Robert Hooke (1635-1703). Very informative on a host of matters. I
bet few know that the universal joint which sits under your car and connects
the drive shaft to the transmission (in a rear wheel drive car) was invented
by Hooke in about 1660 and was first fitted to an Astronomical Quadrant.

Also I had thought previously  that the reflecting quadrant was invented by
Isaac Newtown and perfected by Hadley and from there it morphed into the
sextant. Not true. Hooke invented the first reflecting quadrant in 1666 (as
opposed to the Backstaff Quadrant) and even fitted it with a tangent screw
as well as coming up with plans for an endless tangent screw. (Peter
Ifland's excellent "Taking the Stars" gives Hooke his due on page 13, with a
diagram of his instrument.)

One thing which caught my eye and which I invite comment is the passage in
the Hooke book which says "Accuracy to one second of arc in a hand held
instrument was not achieved until the early 1920's, when the Swiss
instrument designer Heinrich Wild produced the  Wild Universal Theodolite"
(Page 88). Is this true? Was there never a sextant made before this date
that could measure to the second? Has there been one made since?  I checked
a couple of modern sextants which measure respectively:

Plath Classic           1/10 minute              6ss
Plath Professional      1/10 minute              6ss
Freiberger Yachtsman    1/60 degree              1 minute
F M Barker Box Sextant 1/60 degree               1 minute
(Vernier)


Why can't a sextant be graduated to the second? It would simply be a matter
of scribing the micrometer drum more closely and possibly adding a
magnifying viewer. Magnifiers were standard on vernier sextants for years.
Is it because it was considered impractical to go down to a second on a
hand-held instrument?

Your advice would be appreciated.

Also on a recent post I asked if anyone was aware of sextants being cast in
bronze other than the Plath Classic and Royal. Why would you cast in bronze?
What is the advantage over brass?

Regards


Kieran Kelly
Sydney
Australia

   

Reply