Navigating the Lower Saint Lawrence in the 19th Century.
Quebec Mercury #41, Page 241. Tuesday, May 22, 1827. | ||
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Mr. Editor: Several of the ships coming up the Gulf and River
this spring, after having had a good departure from the Bird
Isles, suddenly made the land about Cape Rosier, and as far south
as Malbaie (to the southward of Gaspé), when they expected they
were in a fair way between the Island of Anticosti and the south
land. This deserves the serious attention of all nautical men
using this trade. And it is also their duty, if possible, to
point out the cause of such error in their courses steered. The causes appear to me to be, first; the strong southeast current which runs down this river in the spring of the year, at the rate of 3 or 3« knots; which current, as soon as it rounds Cape Rosier and Gaspé, sets directly to the southward with equal force. Secondly, it would be well that all ships at every opportunity should try experiments on the variation of the compass. I am fully of opinion that it does, and has increased. Since my first coming up the St. Lawrence, and very lately from experiments made, I found six degrees more variation than ever I expected, of my courses steered. Thirdly, the remarks and experiments of the late truly scientific officer, Captain Matthew Flinders, of the Royal Navy. Those who may be in possession of his work on this subject, will excuse my transcribing them, for those who have them not. His experiments seems to me to be simple, and many a master, I think, would amuse himself with them, if in possession of his rules, &c. He clearly convinces every nautical man that the ship itself has a certain local attraction on the compasses, and that, that attraction is always greatest, when the ship's head is near or at the east and west points of the compass. He says, "When the head was east, the variation differed from the true, and always on the same side, while the ship remained in the same hemisphere. 2nd; When the head was west, the difference was equally great, but a contrary way. 3rd; The head being north or south made no difference in the variation, and it was then a meridian between what was found at east and west. 4th; At the intermediate points between the magnetic meridian and east or west, the difference from the true variation bears a proportion to the angle made by the ship's head with the meridian. If the head were on the western side, the difference was of the same nature as that when the head was west; if on the east side, as at east. 5th; The proportion at the intermediate points, obeyed the following law. As the radius is to the difference at east or west (for 8 points), so is the sine of the angle between the ship's head and magnetic meridian, to the difference for that angle. Or if the number of points which the head was to the right or left of the meridian were taken as a course, and difference for eight point reduced to minutes, taken as the distance; then the difference for the number of point was found in the departure column of the traverse tables." And he says, "that these differences were of a contrary nature in the southern, to what they were in the northern hemisphere". And that "the causes of all these changes in a compass on shipboard, and the modes by which they may be obviated, I have endeavoured to explain, in the account of the experiments drawn up, by order of the Admiralty. And to obtain further proofs, it is desirable that the differences should be observed in as many ships and as accurately as possible, in the following manner: The azimuth compass to be used should be a good one. The card traversing freely, and, if possible, the needle should be retouched, with magnetic bars, before the observation is made. A low stand, or stool must be prepared, so that when the compass is placed upon it, it may be of the same height with that by which the ship is steered. The binnacle being then taken away, substitute the stand and azimuth compass; or if the sun cannot be then seen all round, fix the stand as near to the situation as it can be seen, let it be clear of any iron, and exactly amidships. Let the azimuth be taken, using both sides of the vane, and this as often as convenient, and with the ship's head in various directions; but more particularly, at as near east or west, noting the direction of the head to the nearest quarter point. These observations should always be made with the same instrument and in the same place, and be entered in a table of ten columns under the following heads: 1. Time. 2. Latitude. 3. Longitude. 4. Dip of the needle, if an instrument is on board. 5. Altitude of sun's centre, corrected for dip, refraction, and semidiameter. 6. Azimuth observed, being the mean of three or four sights, with each side of the vane. 7. By whom made. 8. Ship's head, mean of what it was at the beginning and end. 9. Variation. 10. Circumstances specifying, if at anchor or under sail, also if the ship was steady or at anchor. A number of such experiments carefully made, and particularly when lying steadily at anchor, would show whether the difference at the binnacle is usually so great as to cause much error, and consequently, how far the discovery of them is of importance to ordinary navigation. But more specially to the navigation of the Gulf and River St. Lawrence. As many of the masters in this trade will have time, and perhaps take pleasure in making the above experiments, by their joint abilities, they would correctly ascertain the true variation to be allowed both coming up and going down this river, and in time prevent any such error in the compass as that now complained of. Taking all these causes into consideration, I am of opinion that a local attraction added to the increase of variation, have been the cause that so many ships found themselves so much farther to the southward than they thought themselves, and it appears in many instance, very fortunate that daylight appeared so soon or they might have incurred much serious danger. The chief courses steered seem to have been north northwest by west, and north northwest. Which courses everyone would think fair courses, according to the distance from the Bird Rock, but it proved erroneous. Therefore, if a ship in future should not be certain of her distance from the Birds, she may safely, in my opinion, steer northwest « north, and northwest, particularly in the spring and fall of the year, but the courses down from Cape Rosier may be used as usual; say one point of the compass difference from the opposite point steered upwards. | ||
| A Marine. | ||||
| Quebec, May 21, 1827. | ||||
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G.R. Bossé©1998. |
Posted Nov. 1, 1998. |
Updated Nov. 20, 1998. |