The lines are as fine as they are straight. As a rule, they are of scarcely any perceptible breadth, seeming on the average to be less than a Martian degree, or about thirty miles wide. They differ slightly among themselves, some being a little broader than this; some a trifle finer, possibly not above fifteen miles across. Their length, not their breadth, renders them visible; for though at such a distance we could not distinguish a dot less than thirty miles in diameter, we could see a line of much less breadth, because of its length. Speaking generally, however, the lines are all of comparable width.
Still greater uniformity is observable in different parts of the same line; for each line maintains its individual width, from one end of its course to the other. Although, at and near the point where it leaves the dark regions, some slight enlargement seems to occur, after it has fairly started on its course, it remains of substantially the same size throughout. As to whether the lines are even on their edges or not, I should not like to say; but the better they are seen, the more even they look. It is not possible to affirm positively on the point, as they are practically nearer one dimension than two.
On the other hand, their length is usually great, and in cases enormous. A thousand or fifteen hundred miles may be considered about
