The Honourable Committee of the Hudson's Bay Company obliged us with sundry observations, made, and tabulated, by their own Captains.
James Bradley, D. D. Regius Professor of Astronomy, and F.R.S. favoured us with several observations made at the Royal Observatory at Greenwich.
John Hyde, Esq; F.R.S. communicated a sett of useful observations, extracted from two journals kept on board the Triton and Britannia East Indiamen.
A correct journal kept on board the Delawar East Indiaman was handed to us by a gentleman unknown.
Capt. George Snow furnished a considerable number of observations, made with care and accuracy by himself, in several successive voyages to, and from Barbadoes and Virginia; together with several remarks upon the subject: One, which we apprehend to be material, we beg leave to insert, as it meets with some confirmation by the tables annexed; viz. “At Barbadoes the variation seems at a stand very near; for in the road, 1752, I observed 5 degrees east; and by Mr. Halley's draught, in the year 1701, 5½ degrees: in 1747, at Port Royal keys, Jamaica, I observed the variation 7° 20' E.; and on the coast of Carthagena the same week, off the high land of Sancta Martha, 7° 45' E. nearly south of Port Royal: Therefore these curves are not much altered; and the curve at Jamaica is nearly at a stand, as tho' tied; and the south part of them, with the rest, dropping to the westward.”
Mr. Mungo Murray, author of a treatise on ship-building, presented us with several observations taken on board the Prince Edward and Chesterfield East Indiamen, and his Majesty's ship the Neptune.
For all these favours we return our sincere thanks.
No observations made upon land have been received, except Dr. Bradley's aforesaid; which has frustrated our intentions of continuing the curves from sea to sea.
By collecting, comparing, and adjusting, all these materials, we have been enabled to construct variation-curves upon Dr. Halley's mercator-chart, adapted to the year 1756; which will soon be in readiness to present to this Royal Society.
As a work of this kind requires much time, and a multitude of observations, both by sea and land, to render it more perfect and general; we hope the ingenious in all nations will lend their assistance: By this means every periodic review will be productive of improvement.