The Congo Rovers: A Story of the Slave Squadron

by Harry Collingwood

I assented.

“Very well, then,” continued Smellie. “Be so good, Mr Mildmay, as to draw a line south-south-east from that pencil-mark which represents the Daphne on your chart.”

The master took his parallel ruler and did so.

“So far, so good,” resumed the second lieutenant. “Now my sketch shows that the outer extremity of Shark Point bore from the tree north-west ¼ west. In other words, the tree bears from Shark Point south-east ¼ east. Lay off that bearing, Mildmay, if you please.”

“Very good,” he continued, when this second line had been drawn. “Now it is evident that the point where these two lines intersect must be the position of the tree. But, as a check upon these two bearings I took a third to that sharp projecting point at the mouth of Banana Creek,” indicating with the pencil on the chart the point in question. “That point bears north-west by north; consequently the tree bears from it south-east by south. Mark that off also, Mildmay, if you please.”

The master did so, and the three lines were found to intersect each other at exactly the same point. “Capital!” exclaimed Smellie, in high good-humour. “That satisfactorily establishes the exact position of the tree. Now for the next step. The slave fleet bears north-west ¼ west from the tree; and the western entrance to the creek (that by which we shall advance to the attack to-night) bears exactly north-west from the same point. Let us lay down these two bearings on the chart—thus. Now it is evident that the slave fleet and the entrance to the creek are situate somewhere or other on these two lines; the question is—where? I will show you how I ascertained those two very important bits of information if you will step to my cabin and bring me the telescope which you will find hanging against the bulkhead.”

Intensely interested in this valuable practical lesson in surveying I hurried away to do his bidding, and speedily returned with the glass, a small but very powerful instrument, which I had often greatly admired.

Taking the telescope from my hand he drew it open and directed my attention to a long series of neat little numbered lines scratched on the polished brass tube.

“You see these scratches?” he said. “Very well; now I will explain to you what they are. When I was a midshipman it was my good fortune to be engaged for a time on certain surveying work, during which I acquired a tolerably clear insight of the science. And after the work was over and done with, it occurred to me that my knowledge might be of the greatest use in cases similar to the present. Now I may tell you, by way of explanation, that surveying consists, broadly, in the measurement of angles and lines. The angles are, as you have already seen, very easily taken by means of a pocket-compass; but the measurement of the lines bothered me very considerably for a long time. Of course you can measure a line with perfect accuracy by means of a surveyor’s chain, but I wanted something which, if not quite so accurate as that, would be sufficiently correct, while not occupying more than a few seconds in the operation of measurement. So I set to work and trained myself to judge distances by the eye alone; and by constant diligent practice I acquired quite a surprising amount of proficiency. And let me say here, I would very strongly recommend you and every young officer to practise the same thing; you will be surprised when you discover in how many unexpected ways it will be found useful. Well, I managed to do a great deal of serviceable work even in this rough-and-ready way; but after a time I grew dissatisfied with it—I wanted some means of measuring which should be just as rapid but a great deal more accurate. I thought the matter over for a long time, and at last hit upon the idea of turning the telescope to account. The way I did it was this. You have, of course, found that if you look through your telescope at an object, say, half a mile away, and then direct the instrument to another object, say, four miles off, you have to alter the focus of the glass before you can see the second object distinctly. It was this peculiarity which I pressed into my service as a means of measuring distances. My first step was to secure a small, handy, but first-rate telescope—the best I could procure for money; and, provided with this, I commenced operations by looking through it at objects, the exact distances of which from me I knew. I focused the glass upon them carefully, and then made a little scratch on the tube showing how far it had been necessary to draw it out in order to see the object distinctly; and then I marked the scratch with the distance of the object. You see,” pointing to the tube, “I have a regular scale of distances here, from one hundred yards up to ten miles; and these scratches, let me tell you, represent the expenditure of a vast amount of time and labour. But they are worth it all. For instance, I want to ascertain the distance of an object. I direct the telescope toward it, focus the instrument carefully, and find that I can see it most clearly when the tube is drawn out to, say, this distance,” suiting the action to the word. “I then look at the scale scratched on the tube, and find that it reads six thousand one hundred feet—which is a few feet over one nautical mile. And thus I measure all my distances, and am so enabled to make a really satisfactory little survey in a few minutes as in the case of this afternoon. You must not suppose, however, that I am able to measure in this way with absolute accuracy; I am not; but I manage to get a very near approximation to it, near enough for such purposes as the present. Thus, within the distance of a quarter of a mile I have found that I can always measure within two feet of the actual distance; beyond that and up to half a mile I can measure within four feet of the actual distance; and so on up to ten miles, which distance I can measure to within four hundred feet.

“And now to return to the business in hand. My telescope informed me that the slave fleet was anchored at a distance of eighteen thousand three hundred feet (or a shade over three nautical miles) from the tree, and that the western entrance to the creek is twenty-eight thousand nine hundred feet (or about four and three-quarter nautical miles) from the same spot. We have now only to mark off these two distances on the two compass-bearings which we last laid down on the chart: thus,”—measuring and marking off the distances as he spoke—“and here we have the position of the slavers and of the entrance to the creek; and by a moment’s use of Mildmay’s parallel ruler—thus—we get the compass-bearing of the entrance from the Daphne. There it is—south-east by east; and now we measure the distance from one to the other, and find it to be—eight miles, as nearly as it is possible to measure it. Thus, you see, my rough-and ready survey of this afternoon affords us the means of ascertaining our course and distance from the Daphne to a point for which we should otherwise have been obliged to search, and which we could not possibly have hoped to find in the impenetrable fog which now overspreads the river.”