[ III ] 
XII. An Account of the Trigonometrical Operation, whereby the 
Difance between the Meridians of the Royal Obfervatories of 
Greenwich and Paris has been determined. By Major-general 
William Roy, F. R. S. and A. S. 
Read February 25, 1790* 
I NT RODUCTION. 
T HE trigonometrical operation which becomes the fubjeCt 
of the prefent Paper, had its commencement, as will 
be remembered, in the meafurement of a bafe on Hounflow- 
Heath in 1784, an account of which was given to the Royal 
Society in the following year. 
On the completion of that firft part of the bufinefs, it was 
little expected, that nearly three full years would have elapfed 
before, even in this country, an inftrument could be obtained 
for taking the angles ! 
In the fpring of 1787, there were indeed appearances, that 
Mr. Ramsden would have enabled us to embrace the early 
part of the feafon, by proceeding with the execution of the 
main defign ; and therefore Sir Joseph Banks had opened 
(through the official intercourfe of his Majefty’s Secretary of 
State, the Marquis of Carmarthen, with the Ambaflador 
at the Court of France) a correfpondence with the Academy of 
Sciences, regarding the co-operation expected on their part* 
for connecting the triangles which we were now preparing to 
2 extend 
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