When we cannot form an idea of distance, by the knowledge of the intermediate space between us and any particular object, we endeavour to distinguish the form of that object, in order to judge of its size; but when we cannot perfectly distinguish the figures, and at the same time behold a number of objects, whose forms are correspondent, we conceive those which are most brilliant are most proximate, and those most obscure are most remote; a notion which is not unoften the source of very singular mistakes. In a multitude of objects disposed in a right line, as the lamps upon the road from Versailles to Paris, of which, as we cannot judge of the proximity or remoteness but by the quantity of light they transmit to the eye, it often happens that when examined at the distance of the eighth of a league, we see all the lamps situated on the right hand instead of the left, on which they are in reality situated. This fallacious appearance is produced from the above-mentioned cause, for as the spectator has no evidence of the distance he is from the lamps, but by the quantity of light they emit, so he conceives that the most brilliant lamps are those which are the first and the nearest to him. Now if some of the first lamps happen to be dull and obscure, and any one of the others particularly bright, that one would appear to be first and the rest behind, whatever was their real situation; and this seeming transposition would be solely owing to the supposed change of their situation from the left hand to the right; for to conceive to be before what is actually behind in a long file, is to see on the right what is situated on the left, or on the left what is situated on the right.