What is "anaclastic glass"

Anaclastic \An`a*clas"tic\, a. [Gr. ? to bend back and break; to reflect (light); ? + ? to break.]

1. (Opt.) Produced by the refraction of light, as seen through water; as, anaclastic curves.

2. Springing back, as the bottom of an anaclastic glass.

   Anaclastic glass, a glass or phial, shaped like an inverted funnel, and with a very thin convex bottom. By sucking out a little air, the bottom springs into a concave form with a smart crack; and by breathing or blowing gently into the orifice, the bottom, with a like noise, springs into its former convex form.

n. A glass or phial, shaped like an inverted funnel, with a very thin convex bottom that can be made concave or convex by sucking out or blowing in air.