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.
A very large plain without protuberances, is an object not less rare than beautiful; and in those who see it for the first time, it must produce an emotion of wonder. This emotion, however slight, tending to its own gratification, imposes upon the mind, and makes it judge that the plain is larger than it is in reality. Divide this plain into parts, and our wonder ceases. It is no longer considered as one great plain, but as so many different fields or inclosures.
The first time one beholds the sea, it appears to be large beyond all bounds. When it becomes familiar, and raises our wonder in no degree, it appears less than it is in reality. In a storm it appears larger, being distinguishable by the rolling waves into a number of great parts. Islands scattered at considerable distances, add in appearance to its size. Each intercepted part looks extremely large, and we silently apply arithmetic to increase the appearance of the whole. Many islands scattered at hand, give a diminutive appearance to the sea, by its connection with its diminutive parts. The Lomond lake would undoubtedly look larger without its islands.
Furniture increaseth in appearance the size of a small room, for the same reason that divisions increase in appearance the size of a garden. The emotion of wonder which is raised by a very large room without furniture, makes it look larger than it is in reality. If completely furnished, we view it in parts, and our wonder is not raised.
A low ceiling hath a diminutive appearance, which, by an easy transition of ideas, is communicated to the length and breadth, provided they bear any sort of proportion to the height. If they be out of all proportion, the opposition seizes the mind, and raises some degree of wonder, which makes the difference appear greater than it really is.
PART VI.
Of the resemblance emotions bear to their causes.