2SQ OFTHI EXTERNAL SP.NSIS.

the chairs and tables, for example, in the chamher where we are fitting, with the moft perfectprecifion and accuracy; and if in broad day-lightwe ever ftumble over any of them, it raufi be,not from any error in the Sight, but from fomedeleft in the attention. The precifion and accu-racy of our judgment concerning Inch near ob-jefts are of the utmoft importance co us, andconftitute the great advantage which a man whofees has over one who is unfortunately blind. Asthe diftance increafes, the diftinftnefs of this Per-fpeftive, the precilion and accuracy of our judge-ment gradually diminifli. Of the tangible objeftswhich are even at the moderate dillance of one,two, or three miles from the eye, we are fre--quently at a lofs to determine which is neareft,and which remoteft. It is feldorn of much im-portance to us to judge with precifion concerningthe lituation of the tangible objefts which are evenat this moderate diftance. As the diftance increafes, our judgments become more and more un-certain; and at a very great diftance , fuch as thatof the fixed ftars, it becomes altogether uncertain.The moft precife knowledge of the relative fltua-tion of fuch objefts could be of no other ule tous than to fatisfy the moft unneceifary curi-ofity.

The diftances at which different men can bySight diftinguilh, with fome degree of precifion,the lituation of the tangible objefts which the vi-lible ones reprefent, is very different; and thisdifference, though it, no doubt, may fometimes

depenc: