Author's previous Experiments.—In the paper read by the author on the “Flow of Water in Curved Pipes,” before the Royal Society on June 2, 1910, it was shown that even a small curvature in the length of a cylindrical pipe affected the quantity of flow of water through the pipe. The effect at velocities below the critical velocity for a straight pipe was most remarkable, inasmuch as the experiments showed that in coiled pipes there was apparently no critical velocity region, whilst in less pronounced curves, where the critical velocity is not entirely absent, a very slight sinuosity of the pipe lessened the flow. This was shown by the increase in the value of the index n in the formula, s = Kvn/m from n = 1, for perfectly straight pipes, to n = 1·1 to 1·2 for pipes slightly curved or sinuous. Here s or h/l is the hydraulic gradient, v is the velocity of flow, m is the hydraulic mean radius, and K is a constant. In an attempt to discover the cause of this departure from the law of flow in straight pipes, the author had tried Prof. Osborne Reynolds’ colour-band test in a coiled glass tube, but the arrangements were of a primitive character and the results obtained were not decisive. At the suggestion of Sir Joseph Larmor the colour tests have been repeated with specially made glass tubes, in which the stream motion could be traced by the introduction of coloured water through capillary nozzles.