The author questioned J. I. Thornycroft's statement made at the thirty-fifth meeting of the Institution of Naval Architects in 1894 that there was not a continuous flow of steam through the tubes of a hard pressed water-tube boiler when pure water was used, and that steam and water followed each other in rapid succession. The author also maintained that even under these favourable conditions the circulation was not rapid, and that with clean pure water it was easily upset.