Artificial intelligent assistant

hemispherule

hemiˈspherule Obs.
  A half spherule; a small hemispherical lens.

1696 W. S. Gray in Phil. Trans. XIX. 281, I was wont to Grind them [glasses] and Polish them on a brass Plane, and so reduce them to Hemispherules. 1756 T. Amory J. Buncle (1770) II. 81 They have them [microscopes] of all kinds, of one and more hemispherules.

Oxford English Dictionary

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