ALTHOUGH it is common knowledge that a steel beam may be replaced by a geometrically similar duralumin beam, with a resultant saving in weight, it is not so generally known that such a procedure invariably involves the use of an unnecessarily large quantity of the light‐alloy, and is, therefore, wasteful. The reason for this is that adherence to geometrical similarity, when changing from steel to duralumin, accords the same proportional increase in thickness to all parts of the beam, thus giving uneconomical distribution of metal. It seems, therefore, that some notes showing how more efficient metal distribution may be achieved by departure from geometrical similarity may perhaps prove of interest.