NavList:

Roger E., you wrote:
"for us mere mortasls and neophytes on this journey, could you please detail how two altitudes guarantee a latitude."

I shoot an altitude of one star, let's say Sirius, and record the exact GMT/UT. Then I turn and shoot an altitude of another star, let's say Procyon, and record the exact GMT/UT. That's two sights of known objects so of course I get a fix, right? It's just two standard circles of position. Yes, there's some momentary ambiguity since two circles cross in two places, but that's not a real problem in practice, right?

So now suppose you remove on detail above. I don't have the exact GMT/UT, and more than that I don't even know the date. So now what? We still have exactly the same fix, but the longitude is indeterminate! Latitude? No problem. How do you find that latitude?? Many ways, but the easiest is just to feed in any old arbitrary date and GMT. Get your fix. Toss the longitude. 

See? Easy.

Frank Reed

Frank I think you are describing the double chronometer method.  In the late 19th century Mr AC Johnson of "Cloudy Weather" fame described how the latitude could be calculated by this method:

Take two time sights separated by a suitable time period. Then calculate  two longitudes using an aaumed latitude. Finaly calcuulate a latitude correction  

     correction for latitude = d long/ d C. where C is the C from the A B C tables. In Johnson's book   "C" was called table II.   C/II was originated  by Johnson.

As I understand it there were at least two uses for the method. First if  a noon latitude was different from that used for reducing the morning time sight (for longitude)  it was a relatively simple task to correct the longitude. Secondly, and I think this was the use promoted by Johnson, was that it did not matter if the noon sun was obscured by cloud - hence his nickname.

This may not be on topic for this thread but I believe that it  is relevant to the ABC meassage  I posted a week or so ago.

David C

PS A few years ago I  worked a sight by this method. At The time I liked to think that I was the first person to do this in nearly a century !!!!!