On the Use of the Preston Tube in Concentric Annuli

Mr. Lyall's remarks may be answered from the evidence already present in refs 1 and 2 if these are considered objectively. They establish that the ratio of the shear stresses as given by Preston tubes is correct. Evidence on this point is given by the value obtained for rmt from the Preston tube measurement of shear stress ratio and its agreement with the correlation of rmt as a function of radius ratio given by Leung, Kays and Reynolds.