The apparatus is illustrated diagrammatically in Fig. 3. Water flows from a constant
pressure bottle through a horizontal glass tube and then through a copper
tube. Bolus flow is produced by injecting air through a hypodermic needle into
the glass tube, thus producing a "train" of alternate air-water boluses. At a given
pressure, the character of the bolus flow, as observed through the glass tube,
remained unchanged for periods up to half an hour.