Dickinson, as with all poets, is renowned for her ability to make her readers see things in new, varied and fascinating ways with the comparisons that she uses. This poem is no exception as women's clothing and then a mountain range are compared to the "thought" that exists beneath a film:
THE THOUGHT beneath so slight a film
Is more distinctly seen,—
As laces just reveal the surge,
Or mists the Apennine.
Dickinson here uses two images then that are very different but similar in what she is using them to compare - as mists can just reveal the peak of a mountain or laces reveal the "surge" of a woman, so the "thought" beneath a film is revealed in a subtle, tiny and imperceptible way. The connection between these two very different images therefore is that both help us to understand the comparison that Dickinson is making by being images of items that are revealed gradually and imperceptibly.