Transit fever

[JimmyH155]

With all the excitement over the transit of Mercury last week, a fascinating book I am currently reading reminds me of a really famous transit - namely that observed by good old Lieutenant James Cook. What a bit of luck, he was ordered to go to that island paradise, Tahiti, and set up for the transit of Venus on June 3rd, 1769
Does anybody know what they used to view Venus. There was no Baader solar film, no Thousand oak filters. so what did they use on their objective lens? soot from a candle? mud banana leaves And what was that "quadrant" that they had stolen for a while. It was an important bit of their kit apparently. Cook did have a chronometer of sorts, so I guess he could have timed the transit. Interested for any information

[ving (David)]

they may very well have projected the image of the sun.... thats my guess

[stephenmcnelley]

Hey, that was the best chronometer of its time !
By 1768 John Harrison's new chronometer was finished and Harrison collected his prize of 1000 pounds? from the royal society and admiralty who were encouraging gentlemen scientists to produce a reliable timepiece that kept to within seconds for a year. This was in time for Cooks later voyage, Cook took it because he was one of the few brilliant people that understood exactly how to use it in determining longitude from comparing local noon time to GMT, like our astronomical Right Ascension- that was the crucial bit astronomically in some ways, they already could determine the suns and mercuries behaviour in terms of latitude by the usual latitude reckoning by noon sights or meridian altitude, the longitude problem up until then for navigation and astronomy was only solvable by terrestrial observation and dead reckoning- distance run in knots over time in a easterly or westerly direction. The establishing of a better longitude calculation in association with Lat. enabled the transit data to have much greater value scientifically and for planetary sizes/orbits to be better calculated or something. It also helped establish the better plotting of Mercator and Gnonomic marine charts- the most important admiralty incentive.
That chronometer is today on display at the Greenwich maritime museum i think, at least i thought i saw it there.
I guess i got into astronomy again due to nautical work, they are so well linked.

Jimmy i cant find any info just quickly at hand that goes into how they observing the transit, you are right they would have had to observe it.
My guess is a lensed projection or the old favourite pinhole projector maybe.

[JimmyH155]

Yes, Steven, my son went to Greenwich last year and brought me back a really interesting book on those clocks. Apparently what sparked off the Government's big prize was a terrible tragedy where a British admiral in charge of a fleet of men -o -war ran the whole fleet onto rocks near the Scilly Isles off the Cornish coast all because they thought they were nowhere near the Scilly Isles. Hundreds of sailors lost their lives

[stephenmcnelley]

That is a better explanation of their incentive than just for tactical warfare and territorial protection purposes, and if they lost ships that security was in jepeordy i doubt if it were the men they were concerned about..
From memory apparently the Tahitians borrowed everything they could get their hands on during that visit, even a musket which resulted in a death?
It was probly a good thing the precious instruments were secreted away in the masters cabin!
Cook was truly an amazing man, and from very humble stock too. He is an example of how misdirected the upper social classes and their breeding habits of the time were, and as we know now inbreeding is not a good thing for biological fitness.
Cook, a relative mongrel with few prospects and connections had more brains and raw ability then most of the commissioned officers put together.
Sad thing is after all his astonishing work the admiralty never promoted him beyond the humble rank of captain; he was not of proper stock

After his death his sons died early from sickness and his wife struggled alone to her death. In many ways it is truly a sad tale, he got so little out of achieving so much. The bloke was a true hero and also a new type of humanitarian officer of the times.