decreasing distance between lines

I have some old graphic illustrations for the 1800's and they use a blend-like series of lines, but the distance between steps decreases as the pt of the line gets smaller.

Is there a straightforward way to do this in Illustrator. Like I said, it's blend-like, but I couldn't find an option to makes steps in distance. A nice thing about this technique is that it looks like a gradient by having a solid color underneath and an opaque series of lines simultaneously increasing in density and decreasing in pt size.

Thanks!