不时, 相隔一定距离

Interval \In"ter*val\, n. [L. intervallum; inter between +
vallum a wall: cf. F. intervalle. See {Wall}.]
1. A space between things; a void space intervening between
any two objects; as, an interval between two houses or
hills.

'Twixt host and host but narrow space was left,
A dreadful interval. --Milton.

2. Space of time between any two points or events; as, the
interval between the death of Charles I. of England, and
the accession of Charles II.

3. A brief space of time between the recurrence of similar
conditions or states; as, the interval between paroxysms
of pain; intervals of sanity or delirium.

4. (Mus.) Difference in pitch between any two tones.

{At intervals}, coming or happening with intervals between;
now and then. ``And Miriam watch'd and dozed at
intervals.'' --Tennyson.

{Augmented interval} (Mus.), an interval increased by half a
step or half a tone.