Vacillate

Its [the barometer's] normal register in the Paumotus [the Tuamotus] was 29.90, and it was quite customary to see it vacillate between 29.85 and 30.00, or even 30.05; […]

Courageous, patriotic, yet vacillating, many of the noblest principles and the purest intentions, men of large possessions and ancient names, under the afflicting circumstances of the times, failed to render service to their unhappy country, but involved themselves in irremediable ruin.

Though it is vital to be alert for circumstances which require a change of plan, it is fatal to vacillate.

On the streets of Berlin, Ruth and her compatriots vacillated "between hope and despair."