Mason and Dixon [720] Source query

[Peter Nockolds]

I've just joined the list and whilst I don't think this is much of a
spoiler I'll leave a few blank lines.












9th November 1769 - 1999

I'm new to Pynchon too so please excuse any implied ignorance in this
question.  

To save a possibly inconclusive trip to London libraries can anyone tell me
if Maskelyne's letter to Mason dated 9th November 1769 exists or existed or
is an invention of Pynchon's imagination?

Thanks in advance

Peter Nockolds
Independent Scholar
Astronomy, Art and Literature
Richmond
Surry
UK