The largest angle of vision seems to me the natural measure of space. The eye is the only judge; and in examining with it the size of any plain, or the length of any line, the most accurate method that can be taken is, to run over the object in parts. The largest part that can be taken in at one stedfast look, determines the largest angle of vision; and when that angle is given, one may institute a calculation by trying with the eye how many of these parts are in the whole. Whether this angle be the same in all men, I know not. The smallest angle of vision is ascertained; and to ascertain the largest angle, would not be less curious. But supposing it known, it would be a very imperfect measure; perhaps more so than the natural measure of time. It requires great steadiness of eye to measure a line with any accuracy, by applying to it the largest angle of distinct vision. And suppose this steadiness to be acquired by practice, the measure will be imperfect from other circumstances. The space comprehended under this angle, will be different according to the distance, and also according to the situation of the object. Of a perpendicular this angle will comprehend the smallest space. The space will be larger in looking upon an inclined plain; and will be larger or less in proportion to the degree of inclination. This measure of space, like the measure of time, is liable to some extraordinary errors from certain operations of the mind, which will account for some of the erroneous judgements above mentioned. The space marked out for a dwelling-house, where the eye is at any reasonable distance, is seldom greater than can be seen at once without moving the head. Divide this space into two or three equal parts, and none of these parts will appear much less than what can be comprehended at one distinct look; consequently each of them will appear equal, or nearly equal, to what the whole did before the division. If, on the other hand, the whole be very small, so as scarce to fill the eye at one look, its divisions into parts will, I conjecture, make it appear still less. The minuteness of the parts is, by an easy transition of ideas, transferred to the whole. Each part hath a diminutive appearance, and by the intimate connection of these parts with the whole, we pass the same judgement upon all. The space marked out for a small garden, is surveyed almost at one view; and requires a motion of the eye so slight, as to pass for an object that can be comprehended under the largest angle of distinct vision. If not divided into too many parts, we are apt to form the same judgement of each part; and consequently to magnify the garden in proportion to the number of its parts.