NavList:

Coralline Algae wrote some nice words about the book  "The Ship", with
which I had a marginal involvement. Yes, it was produced to a high
quality, as are many books from the BBC. I only wish the same could be
said about the TV series on which it was based.

" I did not mean to imply that the
atmosphere of venus and the blackdrop were the same effect but that
more
than one factor affected the observations."

Although the effects of Venus' atmosphere were thought by many, over a
long period, to contribute to the "black drop", it fact there was no
such observable contribution. The "black drop's causes were entirely
terrestrial.

"It is mentioned in wikipedia, after the 1761 transit of venus was
observed a russian
http://en.wikipedia.org/wiki/Mikhail_Lomonosov
predicted the existence of an atmosphere on venus.

I have looked up that web page on Lomonosov, and can find no mention
there of the transit of Venus, or an atmosphere. Of course, Venus does
indeed have an atmosphere, so in that respect Lomonosov was right, if
he predicted it. But if he did so on the basis of the "black drop"
observations, then it must be a classic case of getting the right
answer for the wrong reasons. If Coralline Algae can provide more
details about the matter, I would be interested.

" The work of James Short
and Thomas Hadley in the analysis from the 1769 observations brought
the
size of the AU to within 1 percent of todays figure."

James Short was an instrument maker, so it would be a bit surprising
if he were to be involved in serious analysis of the transit results;
it would be interesting to learn more. I haven't come across Thomas
Hadley; not the Hadley who invented the octant, that was John. Again,
it would be good to learn more.

"One very interesting aspect about all this is that the Board of
Longitude
awarded monetary prizes to the widow of Tobias Mayer for his lunar
tables
and an unsolicited gift to Leonhard Euler for his mathematical works
used by
Mayer for the tables in 1765, which was well before the transit
observations.  Also Nevil Maskelyne began printing an almanac in 1767
along
with lunar tables in 1767, so the precise value of the AU was not
required
to compile fairly accurate  ephemerides at that time."

Yes, that deduction is right. The transit of Venus observations were
intended to produce precise answers for the size of the solar system,
and thus such matters as the velocity of light and, to an extent, the
gravitational constant. Scientifically interesting information in
itself, but having little impact on the prediction of ephemerides;
only affecting such minor matters as the parallax of the Sun and
planets. Indeed, because the Earth-Sun distance had such small effects
in positional astronomy, that in itself explains why that distance was
so hard to measure.

Mayer's lunar prediction method was communicated to the Admiralty as
early as 1755, and provided the basis for trial voyages made by
Maskelyne for testing the lunar distance method. By the time of
Mayer's death in 1762 he had significantly improved its accuracy, and
that formed the basis of the lunar distance tables for the first
Nautical Almanac, published in 1766 for the year 1767.

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.



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