In my little box of drawing-tools was a small brass protractor--a semi-circle divided into one hundred and eighty degrees, with half-degree marks. This would be convenient in the work I was about to do, though not absolutely necessary, as in its absence I could have easily constructed one that would answer my purpose. The first thing to do was to establish a true north and south line. That night the stars shone brightly, and I easily found the pole star by the pointers in the Great Bear, or “Dipper.” In the sand at the north cape I drove an upright stake made of a stout cane. Then taking another straight piece I placed it in a notch on top of the upright and sighted along its length adjusting it until it pointed straight at the north star. To secure it in this position I drove a short notched stake at the butt of the inclined cane and tied the cane firmly to both. I was now sure that the two uprights were in a true north and south direction from each other, and the work for that night was finished, as the remainder could be better done by daylight.
The next thing I wanted was a standard of measurement; unfortunately my drawing instruments did not contain the usual ivory rule. But this did not occasion me much uneasiness, as I hoped to be able to deduce the standard inch by a comparison of my belongings. If I once got the true inch it would be easy to get from that the foot, the yard, the rod, the mile. I had my photograph plates as one guide; these I had every reason to suppose were cut quite accurately to the dimensions of five inches by seven. Then there was the brass protractor. It is true there were no inches marked on this; but the workman who made it would naturally follow some standard, and the chances were very great that the diameter of this instrument would be found to be an exact multiple of the inch, and as I conjectured, exactly four inches. To test this matter I laid the protractor on the short side of one of the plates, and taking the difference between the two found, as I had expected, that this difference was one fifth of the width of the plate, and one seventh of its length. This proved satisfactorily to my mind that the plate was accurate in dimensions, that is to say, five by seven inches, and that the difference between the length of the straight side of the protractor and the width of the plate was the standard inch. From this starting-point I constructed a foot measure, and cut me a light pole exactly a rod in length.