In the recent paper by Warren a summary was made of current data on two-dimensional bow shock wave detachment distances. It was shown that the experimental results of Griffith and Alperin, as well as the detachment distances computed by Vincenti and Wagoner, could be collapsed into a single curve by using Spreiter's Transonic Similarity Parameter. This has been confirmed by the present authors who have found that the experimental results for wedges obtained by Bryson also correlate favourably with the curve given by Warren (Fig. 3 of Ref. 4).

The results of the foregoing workers have been for steady flow conditions. However, it has been noted by Lilley et alia that a steady shock wave pattern can be established in free flight only after steady motion has been maintained for a considerable (infinite) time. In general, the locus of detached bow shock waves depends on the time history of the motion whenever a body is accelerated from subsonic speed.

An instrument is described which measures the time duration of a specified number of complete cycles of an oscillation over the frequency range OT cycles per second to 500 cycles per second. The accuracy of the reading is dependent on the frequency measured and the number of cycles taken; but, in most cases, an accuracy better than 01 per cent is obtainable. The construction of the instrument is described and circuit diagrams given.

An exact solution of the streamlines of the slow viscous motion inside a cylinder with partially moving walls has been obtained and verified experimentally. This problem has been treated by H. B. Squire for high Reynolds numbers.

The design of the exhaust ports of a two-stroke cycle engine is mainly based on the area required to reduce the cylinder pressure at the end of the expansion stroke to scavenge air pressure in the minimum practicable time. The flow through the exhaust ports is both sonic and subsonic; in the former case the flow is independent of the exhaust pipe conditions but not in the latter case. In the first stage of the design, however, the exhaust pipe conditions may be assumed to be constant when calculating the port area, subsequent calculations of the pressure drop allowing for the pipe size may then be made by the methods suggested by Wallace, Cole, or Benson. In the following Note formulae are developed for estimating the port area neglecting the exhaust pipe size.