An even more simple demonstration might be made by having an Eskimo stand in a particular spot and marking the length of his shadow as cast on a level stretch of ice or snow. Just twelve hours later let the Eskimo stand at the point where a mark had been made to indicate the end of the shadow, and it would be found that his present shadow--cast now, of course, in the opposite direction--would reach exactly to the point where he had previously stood. The only difficulty about this simple experiment would result from the fact that the sun is never very high as viewed from the pole and therefore the shadow would necessarily be long. It might therefore be difficult to find a level area of sufficient extent on the rough polar sea. In that case another measurement similar in principle could be made by placing a pole upright in the snow or ice and marking on the pole the point indicated by the shadow of an Eskimo standing at any convenient distance away. At any interval thereafter, say six or twelve hours, repeat the experiment, letting the man stand at the same distance from the pole as before, and his shadow will be seen to reach to the same mark. Various other simple experiments of similar character may be devised, any of which would appeal to the most untutored intelligence as exhibiting phenomena of an unusual character. Absolutely simple as these experiments are, they are also, within the limits of their accuracy, absolutely demonstrative. There are only two places on the globe where the shadow of the upright pencil would describe a circle, or where the man's shadow would be of the same length at intervals of twelve hours, or would reach to the same height on a pole in successive hours. These two regions are of course the poles of the earth. It may reasonably be expected that explorers who reach the poles will make some such experiments as these for the satisfaction of their untrained associates, to whom the records of the sextant would be enigmatical. But for that matter even an Eskimo could make for himself a measurement by using only a bit of a stick held at arm's length--as an artist measures the length of an object with his pencil--that would enable him to make reasonably sure that the sun was at the same elevation throughout the day--subject, however, to the qualification that the polar ice was sufficiently level to provide a reasonably uniform horizon.