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288 pages, Hardcover
Published February 19, 2019
In coming down the river this afternoon, I observed the slope of a particular part of the wall and made an estimate of its altitude. While at supper, I noticed the same cliff from a position facing it, and it seemed steeper, but not half so high. Now lying on my side and looking at it, the true proportions appear. This seems a wonder, and I rise to take a view of it standing. It is the same cliff as at supper time. Lying down again, it is the cliff as seen in profile, with a long slope and distant summit. Musing on this, I forget "the morrow and the canyons to come"; I have found a way to estimate the altitude and slope of an inclination, in like manner as I can judge of distance along the horizon. The reason is simple. A reference to the stereoscope will suggest it. The distance between the eyes forms a base line for optimal triangulation.