NavList:

While we're talking about sextants and height over the sea.  I recently had to read a friends paper that included the statement that the on the first two-way crossing of the Atlantic by the the Airship R34 in 1919, the crew checked the accuracy of the altimeter by the use of sextant readings on it's shadow knowing she was 640ft long.  I decided I could do with some Power Point slides so added slide 1.  I then decided that unless the sun was directly above, this wasn't so simple (slide 2).  I asked the audience to think about it and I'd check again at the end of the lecture.   My suggestion was take the shadow angle whilst flying directly into sun.  Mark 640ft to scale on graph paper.  Mark the sun's altitude.  Use fishing line through the hole in a Douglas protractor, slide the protractor up the sun line until the fishing line subtends the angle measured by the sextant.  Read the airship's height to scale from the graph paper.  Comments please.  Hope the PPt slides come out OK. Dave