A New Electro‐Sonic Altimeter: An Instrument, on Marine Sounding‐Apparatus Lines, to Give the Pilot His Exact Height

THE principle is not new of measuring the actual height of an aeroplane when within a short distance above the earth by generating sound signals in the machine, directing them down towards the earth and measuring the time taken for them to be reflected back again. It has been used successfully for some years in the field of marine sounding and various instruments working on this principle have from time to time been produced for aircraft. A new height‐measuring instrument on these lines has recently been introduced by Henry Hughes & Son, Ltd. Light weight and operation from a low‐voltage d.c. supply were two important points borne in mind in determining the general plan of this new altimeter, which obtains all its power from a 24‐volt accumulator through a motor‐driven alternator.