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George wrote [NavList 10129]

Geoffrey Kolbe pointed us to a website explanation of an "equiangulator",

Then....

There's
nothing said, in that account, about measuring the time interval between two
equal altitudes for the one star, though there would be no objection to
doing so.

It looks like a simple operation which could be managed with very little
training: all it would need is the ability to tell one star from another.

George.

True George, the link I provided does not mention equal altitudes - it is just a brief descriptive piece which I linked to because it gives a photo of the device.

However, for a fuller explanation of its design and intended use, have a look at an article by Andre Danjon - who did much to develop the modern precision astrolabe - in "The contribution of the impersonal astrolabe to fundamental astronomy" MNRAS, Vol. 18, Page 411-31, (1958). Or see Chandon and Gougenheim, "Instruments for observing equal altitudes in astronomy (Gauss's method generalised)" Hydrographic Review, Vol. 12, No. 1, (1935). Or see an article about Danjon by J.

Kovalevsky,  "A Great French
Astronomer",  Sky & Telescope, Page 347 (June 1967). Danjon
developed the precision astrolabe so that latitude could be determined to
0.06 arc seconds and time (so longitude) to 4 milliseconds. That gives
circle of uncertainty small enough to spit out of!

Geoffrey Kolbe



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