Looking at an enlarged view of Sorcha's enlargements, especially in the sky area, the texture shows as regularly spaced dashed lines, of constant width, straight and parallel, with the light/darkness from variations in the "length of the dashes." This implies the use of a "graver's wheel," as would have been used to engrave a plate for an etching.

Such tools were - at least according to descriptions I've seen - commonly used in engraving such plates; but I haven't heard of much use of similar tools in pen and ink drawing, although similar ones did exist and are/were fairly commonly used e.g. in mapmaking where regular "dashed lines" are wanted.

Usually a tool of this kind had a "marking point" coupled to a wheel that rolled on the surface. As the wheel rotated it raised and lowered
the point to produce a mechanically precise line of dashes. Different wheels produced different ratios of dash to gap. To allow for "overstriking" some varied the dash/gap length, maintaining constant ratio between the two. (Sharp edges and too precise mechanical rendering produces objectionable "edges" and "periodic patterning" in a textured area.)

Since the line width is close to the apparent pixel dimension in Sorcha's images, some care must be taken to avoid taking pixellation for graver's lines; but the sky lines, where such a tool would be most likely used are pretty distinct here, while the dome areas, where "freehand scratching" would be more likely don't show the same kind of texture.

Based on this "clue(?)" the picture is most definitely an engraving - but an opinion from someone more intimately familiar with reproduction processes of the era than I am would be most welcome.

John