Page:Narrative of a Voyage around the World - 1843.djvu/24

 xviii which has been adopted in our charts, from a circumstantial account in the remark-book of the Fly, within a week after her leaving Bahia, and with chronometer on board. For this purpose it will be proper to run down the parallel of 16° 50 S, (or 16° 55, so as to allow for the northerly current,) and to carry in a chain of deep sea soundings from about the longitude of 35° 30 W., till in 37° 30 W. From thence you may shape an extremely useful course, so as to round Cape St. Thomé and Frio at such a distance, if the wind will permit, as will enable you to intersect some very discordant soundings which have been inserted in the chart, from different but apparently good authorities. One well determined line of genuine depths Avill go far to elucidate all the difficulties.

At Rio de Janeiro, or at Santa Catharina, you will have an important task to perform, and the choice of the two places is of no moment, provided the chronometers enable you to determine their meridian distance with precision. The longitude of the former has been reduced within very narrow limits, by various observers, and a vast number of observations of various kinds, the mean of which gives 43° 8 W., for the little island of Villegagnon; but as every change of a standard meridian is attended with great inconvenience to seamen, it may be hoped that a good series of moon-culminating stars may now put the question at rest, so that no further alteration will be requisite, at least for nautical purposes.

As magnetic phenomena are objects of much scientific interest at present, you should not lose the opportunity of obtaining some careful observations of dip and intensity, at one of the above places, and likewise at one of the high southern positions where it was obtained by Captain P. King. Port Famine would be well adapted to the purpose