ON FINDING THE TIME At Sea. Leeds, 7th Feb., 1838. MR. EDITOR, I have reason to suppose that it is a prevailing prejudice amongst practical men,* * that it is necessary to reduce all time observations to mean time, in order to procure a correct determination of the difference of longitude; and, in the opinion that such an erroneous impression exists, I am rather confirmed by the example given by Mr. Tonkin, at page 121, of your February number. When an observation of apparent noon by chronometer, is obtained, the method of reducing the corresponding Greenwich mean time, (as found by chronometer,) to Greenwich apparent time, is much more theoretically correct, than the converse method of reducing apparent noon at ship to mean noon at ship as has been done by Mr. Tonkin. To prove this, I shall, with your permission, repeat the example given by him at page 121; reducing the observation to apparent time, instead of to mean time, and I shall then briefly point out in what respect the former mode is more correct than the latter, leaving its superior conciseness to speak for itself. EXAMPLE. 24th Dec. 1835, daily rate of chronometer, 2.53s. daily change of equation―30.03s. Equation, at Greenwich mean noon... +2076s+ 0 0 16-81 4 15s Greenwich apparent time at ship's apparent noon ......... This last being ship's west longitude in time. +3 19 36-96 [*Surely our correspondent is venturing on a libel on "practical men" who, if they know anything at all of the matter, must know that apparent time is obtained from the sun, and mean time from the chronometer; it is immaterial what time is used for the longitude as long as it is the same in kind, and this the equation applied to either in a different manner will effect.-ED. N. M.] Now, it is evident, that in reducing Greenwich mean time, to Greenwich apparent time, no reference to longitude is at all necessary; but that, on the contrary, in reducing apparent noon at ship, to mean noon at ship, a longitude must be assumed for the purpose of calculating the change in equation; and, as this assumed longitude must, in the first place, be only an approximate one, (since the correct one is not known until the completion of the process,) therefore, although the difference may be inconsiderable in practice, yet, theoretically speaking, the former method is the more correct. In the original example, before referred to, at page 121; the accumulated rate is put down (unavoidably) with the sign + (plus); although the rate is (minus); this, of itself, causes some obscurity, although I scarcely know whether the fault be that of the method or of the arrangements; in the example given by me this apparent contradiction is avoided. I have the honour to be, Sir, Your obedient servant, NAUTILUS. THE BLOSSOM'S VOYAGE.-CAPTAIN BEECHEY'S REFUTATION OF CAPTAIN DUPERREY'S REMARKS. Her Majesty's Surveying Vessel, African, DEAR SIR,—In the Journal de la Marine (No. 6, 1837) there is a letter from Captain Duperrey addressed to you, in which the propriety of identifying Prince William Henry Island, of Wallis, with L'Ostange, so named by Captain Duperrey, and Clermont de Tonnere with the Island of Minerva seen by Mr. Bell, is somewhat hastily discussed, and in which my longitudes of various parts of the Pacific are questioned. As you have honoured my geographical positions with a confidence which is very complimentary to me, I cannot do less than reply to that letter, so far at least, as to give you my reasons for classing these islands as I have done, and to offer for your information a few remarks upon my longitudes in general. As regards the identity of the above-mentioned islands, Captain Duperrey begins his letter by declaring it wholly impossible for Wallis to have committed an error of fifteen miles in his latitude, and by maintaining that Prince William Henry Island still exists to the southward of L'Ostange, and will yet be found in the latitude assigned to it by its discoverer. In paying this compliment to Wallis, in general so justly due to that navigator, Captain Duperrey must surely be ignorant of the fact of my having examined the vicinity of this island in order to ascertain whether Wallis was mistaken in his latitude or not; and yet he might have concluded from what I published upon this subject in the narrative of my voyage, as well as from the nature of my instructions, that such an examination must have been made. I believe I need not state to you that this was done, and that I took the most effectual method of ascertaining that the islands I visited were really those discovered by Wallis, by first comparing my longitudes with those of Wallis at such of his discoveries, as from some peculiarity described in his voyages, admitted of no doubt of its identity. Had I not done this, I might have fallen into the error of Bellinghausen who supposed Cumberland Island to have been Prince William Henry Island, from its true situation agreeing so nearly with the place assigned to the last mentioned island by Wallis. Whitsunday and Queen Charlotte Islands, lying within sight of each other, are happily situated for the purpose above-mentioned, there being no other islands so circumstanced within several degrees of them. I there ascertained the amount of Wallis's error in longitude; and then ran down the parallels of his other discoveries and determined their true positions. I found them all correctly placed as to distance from each other, and, with the exception of Cumberland and Prince William Henry Islands, in latitude also, but their longitudes were all about forty miles too far east. In searching for Prince William Henry Island, I ran down the parallel of 19° 00' S. in which Wallis had placed it, for thirty miles from Cumberland Island, or until I had overrun Wallis's distance several miles, and at noon observed in 19° 4' S. Having then nothing in sight from the mast-head, which commanded a view of ten miles more, I hauled to the northward, and immediately discovered an island which is the one in dispute. This island agreed exactly as to distance from Queen Charlotte Island with that of Prince William Henry, but its latitude was 15' too far north, and thinking with Captain Duperrey, that this was too great an error for Wallis to have committed, I stood again to the southwest into 18° 58′ S. until I commanded a view of sixty miles from Cumberland Island, and had overrun Wallis's distance thirty miles. In short, until I had proved that had the island existed where Wallis placed it, either in latitude and longitude, or in distance from Queen Charlotte Island, I must have passed over it without seeing it. In order to show you how nearly Wallis's distances agree with mine by observation, and to remove from your mind all doubt of the identity of these islands, I beg to direct your attention to the following tables. Queen Charlotte 19 18 19 17 138 04138 42 38 Egmont Egmont Gloucester 19 20 19 23 138 30 139 12 42 Gloucester 19 1119 08140 04140 41 37 Cumberland Cumberland 19 18 19 12 140 36 141 09 33 Prince W. Henry. Prince W.Henry. 19 00 18 14 141 06141 43 37 The Figures are given in round numbers. miles. miles. I trust, Sir, this explanation will be satisfactory to you, and likewise to Captain Duperrey, who I hope will do me the justice to believe that I fully considered these facts, and carefully examined the vicinities of the islands as placed by Wallis, before I ventured to deprive M. Duperrey of what he imagined to be his own discovery. In justice to Captain Wallis, who has placed Prince William Henry Island fifteen miles too far south, it should be known that he saw this island at daylight, at a distance " far to windward," and as he had no observation on that day, he of course deduced its position from his run by the log from the preceding noon, at which time he appears to have been six miles in error in his latitudes,* and this was not a direct run, as he lay to during the dark part of the night, and of course his reckoning was more liable to error. With regard to the identity of Minerva Island and Clermont de Tonnere, I must observe that, at the time I published my voyage, my authority for the situation of Minerva Island was contained in the foot notes (pages 287, 288) of your Hydrographical Memoir, copied, I believe, from the Asiatic Journal: in the last mentioned page that island is stated to be " 45' west of Serle Island," and in the first to be "12° 44' west of Otaheite or 15 east of Serle Island." It was evident from the tenor of this passage that, although there was some confusion between east and west, Mr. Bell had seen Serle Island on his route, or else why is his longitude in both cases reckoned from the meridian of that island, or why is that island mentioned at all? Upon the supposition, therefore, that it was seen, Minerva Island was of necessity identified with Clermont de Tonnere, as being the only island either east or west of Serle Island, within the limits of the above mentioned distances, and the propriety of this arrangement derived additional strength from the circumstance of the first mentioned difference of meridians, forty-five minutes, agreeing so nearly with the actual distance of Clermont de Tonnere from Serle Island. But if we take the other difference of meridians, viz., 12° 44′ east of Otaheite, which is most favourable to Captain Duperrey's case, * See the latitude he gave to Cumberland Island on this day. we shall find the imaginary injustice done to him is not so great; for instance : So that had I taken this difference of meridians, Minerva Island would have been as near to Clermont de Tonnere as to Serle Island; which of these data is to be preferred, I am even now at a loss to know, as I have no other means of ascertaining whether Mr. Bell saw the island in question or otherwise, upon which the whole question hinges, than by consulting what has been published on the subject; the matter must, therefore, here rest, as far as I am concerned, and in truth, as Captain Duperrey justly remarked, it is not worth the trouble of further investigation. I come next to the subject of my longitudes, which Captain Duperrey states to be in general 15' too far east. He here again does me an injustice, and if he examines the matter a little closer he will find that he is mistaken. If, for the sake of argument, we take the longitudes according to his own determinations and those of Bellinghausen and Kotzebue, whom he quotes as very respectable authorities, he will find that with one or two exceptions we agree as nearly as could be expected; for instance :— * Kotzebue's longitudes are, on an average, 3' east of Bellinghausen's: |