The influence of the air on the going of time-keepers has naturally been the subject of much discussion, particularly in reference to time-keepers used by astronomers. On pendulums the air acts in two ways :—by its buoyancy it lessens the downward tendency of the parts, and so lengthens the time of the oscillation; and it opposes resistance to the motion. On the chronometer balance, the latter action alone is felt; to this action we shall confine our remarks.