The visible air
We observe the breath, or rather the sensations caused by breathing, in order to bring a moment-to-moment concentration. This calms the heart-mind because it is a neutral object. There are various places where people feel the sensations of breathing more acutely—at the nostrils or upper lip, at the rising and falling of the chest, and in the abdomen. All of these places are valid in terms of vipassana meditation. The Mahasi, however, favoured the abdomen as a place of observation.