the altitudes have been taken by Don Juan with that precision which geography requires, may also be in some measure questioned; since we find there was a crack in the instrument employed, the size of which is not mentioned; neither were all the observations repeated.  Even if they had been, it is well known that the observations of those times were by no means so accurate as those made of late years.  After all, however, the observations in this journal appear to have been made with a good deal of care, and they cannot fail to be of great service to geography.

[Footnote 256:  In this edition, which has been taken from that by Purchas, these conjectures of Don Juan de Castro are restored to the text:  but the remarks by the Editor of Astleys Collection are all retained in notes.—­E.]

It is alone by the observations contained in this journal that geographers are able to determine the extent of the Arabian Gulf or Red Sea from north to south[257], as well as the situation of its principal ports on the west side.  The latitude of the straits was verified by the observations of Don Juans pilot.  But as most maps and charts give the situation of Suez, at the northern end of the Red Sea, very different from that marked in this journal, which is 29 deg. 45’ N. it may not be amiss to examine this point.

[Footnote 257:  The modern knowledge of the Red Sea has been much augmented by the labours of Bruce, Nieubur, Lord Valentia, and others, which will be given in a future division of our work.—­E.]

By several very accurate observations made in 1694, M. Chazelles of the Royal Academy of Paris found the latitude of Cairo to be 80 deg. 2’ 20”.  The difference of latitude therefore between Cairo and Suez, will be 17 minutes; which we conceive cannot be very far from the truth, if not quite exact, since the map published by Dr Pocock makes the difference about 20 minutes.  It is true that in Sicards map of Egypt, and in a late[258] French chart of the eastern ocean, Suez is placed only two or three minutes to the southward of Cairo.  But as these authors had no new observations made at Suez to go by, and seem to have been unacquainted with those of Don Juan de Castro, their authority can weigh very little against an express observation, and against Dr Pococks map, which, among other helps, was constructed upon one made by the natives.  Besides this, in his later maps De L’isle regulates the situation of Suez according to the latitude found by Don Juan.  Indeed Sicard places Suez nearly in that parallel, but egregiously mistakes the latitude of Cairo, so that he seems to have given it that position more by chance than design.

[Footnote 258:  It is proper to remark here that the collection of Astley was published in 1745, sixty-seven years ago.—­E.]