Mr. Williams remarked that the modern tendency in engineering is to endeavour to heat-treat the existing metals to enable them to withstand the stresses induced by modern design.

Many similar metals are used as in days gone by, but the modern steels are alloyed with other elements to enable them, with particular treatment, to give much higher strength results. For these alloy steels and also for the lighter alloys, special precautions have to be observed in their manufacture, whether they are destined for automobile or aeronautical work, although with aircraft work more precautions are necessary than in any other class of manufacture.