Height and magnitude

The question before us relates to the height, and not to the general magnitude of the object, these being separate considerations; because the eye is capable of surveying more in breadth than in height; but it is also capable of seeing much farther below its axis than above it, as shewn by the following profile [fig. 44]. From hence it appears, that the projection of the forehead and eyebrow causes great difference betwixt the angle A B and the angle A c, and that the line parallel to the horizon A, which I shall call the axis of vision, does not fall in the centre of the opening betwixt the extreme rays B and c.