a. 不稳定的, 无定向的

[医] 起立不能的

[ adj ]
not static or stable
<adj.all>

Astatic \A*stat"ic\, a. [Pref. a- not + static.] (Magnetism)
Having little or no tendency to take a fixed or definite
position or direction: thus, a suspended magnetic needle,
when rendered astatic, loses its polarity, or tendency to
point in a given direction.

{Astatic pair} (Magnetism), a pair of magnetic needles so
mounted as to be nearly or quite astatic, as in some
galvanometers.