From frequent observation of the difference between seeing an object with and without moving the head, I am inclined to believe, that, by the latter, the mind grasps the whole idea at once; but, by the former, it is rather led to observe the parts separately: hence are derived many of those ideas of apparent magnitude or proportion which induce us to pronounce, at the first glance, whether objects are great or small. I should, therefore, answer the question, "At what distance does any object appear at its greatest height?" by saying, when the spectator is at such a distance, that the line drawn from his eye to the top of the object, forms an angle of not less than twenty-eight degrees with the axis of vision; and thus, supposing the eye to be five feet six inches from the ground, the distance will be according to the following diagram [fig. 45].
The scientific observer will always rejoice at discovering any law of Nature by which the judgment is unconsciously directed. At a certain distance from the front of any building, we admire the general proportions of the whole: but if the building can only be viewed within those angles of vision already described, it is the several parts which first attract our notice, and we generally pronounce that object large, the whole of which the eye cannot at once comprehend.
