21.   The pipes were placed at regular intervals.

22.   The prison is inspected at regular intervals by government health officers.

23.   The rest, six in all, have come at regular intervals since.

24.   The stage was illuminated by a stroboscope, a light which flashed at regular intervals by means of a rotating shutter.

25.   There are stations where runners can get water at regular intervals throughout the Marathon.

26.   These women were given blood tests at regular intervals for a year.

27.   They believed the celestial motions are performed with exacting regularity, just as the harmony of musical sounds depends on regular intervals.

28.   They operate rather like bank deposit accounts, where the interest rate is credited at regular intervals.

29.   They started at a particular time, and at regular intervals another dorm would go in.

30.   They would have to field candidates for a variety of offices at regular intervals or risk being closed.