Of the houses of a town, in which the divisions between the houses may be distinguished by the light which fall on the mist at the bottom. If the eye is above the houses the light seen in the space that is between one house and the next sinks by degrees into thicker mist; and yet, being less transparent, it appears whiter; and if the houses are some higher than the others, since the true [colour] is always more discernible through the thinner atmosphere, the houses will look darker in proportion as they are higher up. Let _n o p q_ represent the various density of the atmosphere thick with moisture, _a_ being the eye, the house _b c_ will look lightest at the bottom, because it is in a thicker atmosphere; the lines _c d f_ will appear equally light, for although _f_ is more distant than _c_, it is raised into a thinner atmosphere, if the houses _b e_ are of the same height, because they cross a brightness which is varied by mist, but this is only because the line of the eye which starts from above ends by piercing a lower and denser atmosphere at _d_ than at _b_. Thus the line a _f_ is lower at _f_ than at _c_; and the house _f_ will be seen darker at _e_ from the line _e k_ as far as _m_, than the tops of the houses standing in front of it. 467. OF TOWNS OR OTHER BUILDINGS SEEN IN THE EVENING OR THE MORNING THROUGH THE MIST. Of buildings seen at a great distance in the evening or the morning, as in mist or dense atmosphere, only those portions are seen in brightness which are lighted up by the sun which is near the horizon; and those portions which are not lighted up by the sun remain almost of the same colour and medium tone as the mist. WHY OBJECTS WHICH ARE HIGH UP AND AT A DISTANCE ARE DARKER THAN THE LOWER ONES, EVEN IF THE MIST IS UNIFORMLY DENSE. Of objects standing in a mist or other dense atmosphere, whether from vapour or smoke or distance, those will be most visible which are the highest. And among objects of equal height that will be the darkest [strongest] which has for background the deepest mist. Thus the eye _h_ looking at _a b c_, towers of equal height, one with another, sees _c_ the top of the first tower at _r_, at two degrees of depth in the mist; and sees the height of the middle tower _b_ through one single degree of mist. Therefore the top of the tower _c_ appears stronger than the top of the tower _b_, &c. 468. OF THE SMOKE OF A TOWN.