The apparatus used in these experiments consisted of a wind tunnel, a fan for producing a current of air in the tunnel, a balance for measuring the force on various rods mounted in the wind tunnel, and a Pitot tube and tilting gauge with which to determine the velocity of the air.

It will be unnecessary in this communication to give details of the arrangement of the wind tunnel and fan or of the balance used, as these have been fully described by one of the writers previously in this Journal; but before proceeding to an account of the actual experiments, particulars of the tilting pressure gauge and Pitot tube and the exploration of the velocity of air in the tunnel must here be given.