Question

when the barometer is thoroughly unsettled there may be light local currents, perfectly imperceptible to man, yet felt by cows and sheep.
in this sentence, currents means:
flows of air in one direction
vibrations at the earth’s surface
low continuous indistinct sounds
processes of separation

Explanation:

The context mentions a barometer being unsettled and local currents that animals can feel. In meteorological - related contexts, when a barometer is affected, it often relates to air - flow changes. "Flows of air in one direction" is the most appropriate meaning as it is consistent with the idea of something that could be related to barometer changes and be imperceptible to humans but felt by animals.

Answer:

A. flows of air in one direction