Dead reckoning is the most basic form of navigation for pilots and navigators. Weems' own words allude to that by his noting that Ms. Earhart and the other lady were no doubt familiar with it.
Weems also points out here that dead reckoning has severe limits over open water or clouds whereas there is no means by dead reckoning alone to fix one's position: dead reckoning over land in clear air allows one to use landmarks; over water, only recognizable islands or ships in known positions, etc. could do that. Which leads to Weems' emphasis on radio and celestial navigation as skills to gain so as to overcome the hazard of depending only on dead reckoning over water.
It is very interesting that Weems offers this emphatic advice and encouragement to 'go to school' scant days before Earhart's next attempt. Perhaps few knew of that, including Weems - so perhaps it was innocent and because of not being in loop. I believe she did begin the second attempt in secrecy as it wasn't revealed until she arrived in Miami, first leg complete, so either Weems was not in the loop of people who knew, or was attempting to cool her intent until she could become better prepared as he saw it.
Further, was Weems not aware that Noonan was firmly aboard already? Noonan, by the way, would have had no problem with 'dead reckoning', be assured. Maybe not - maybe Weems was that much 'out of the loop' -
Or, as has been wondered, what of the chain of events / discussions that may have brought this about? Was there concern about Earhart's dependency on Noonan, and some urging from some quarter (Weems himself or perhaps someone else encouraging him to intervene) for Earhart to learn so as to back herself with these skills? Not sure that is knowable.
The letter is a very interesting glimpse into the dynamics of Earhart's efforts at the time and how the many tiny teeth within that clockwork inched along for better or worse. Isn't it interesting - if tragic, to see the outcome of all that machinery ticking along - some of it engaged, other gearworks disengaged by the lady and ignored (and did GP share things like this with her anyway). Weems was not the only one she politely eschewed as to advice - Hooven noted Earhart's less-than enthusiastic willingness to work more to better grasp radio navigation skills as well.
Interested in Marty's take on the import of Weems' sending this 'c/o George Putnam'. My own thought is that at face value that may have been a simple expedient as how to get something into Earhart's hands rapidly, which may have been a problem by direct mail - she may have been quite mobile at the time - I don't know for sure. Putnam may simply have been the more reliable route. Conversely, was there a hope that Putnam would take the letter to heart and reach into Earhart's head better than others had done, historically? That seems possible. Or was there some realization that all things had to go through Putnam as a gatekeeper? That too is possible. One also wonders how many decisions GP effectively made in the planning - might he have ignored this and not passed it on to Earhart's consideration, believing things were already covered by having Noonan aboard, etc.? It is interesting - as I see it there are definite elements here and there among the events of this flight where ambiguity appears to exist as to who was really in control.
The most telling thing toward a 'fit' with her disappearance as I see it is that Weems had focused on an observed weakness: Earhart lacked the world-class radio and celestial navigation skills that might have saved her. Yes Noonan was aboard and should have filled the void in terms of celestial navigation, so we might reasonably discount that concern. But the radio was an obvious gap, and Weems' had a point; and here we are still looking...
