circumnatant

Now if these iron-filings are conceived to be suspended in a fluid, whose specific gravity is similar to their own, and a magnetic bar was introduced as an axis into this fluid, it is easy to foresee that the iron filings would dispose themselves into concentric spheres, with intervals of the circumnatant fluid between them, exactly as is seen in these nodules of iron-earth.

The Botanic Garden A Poem in Two Parts. Part 1: the Economy of Vegetation Erasmus Darwin 1766