The part played by major structural strength tests in aeroplane design is well known. Without such tests the standard of safety for aircraft would soon decline and excess weight, as an insurance against structural failure, would become a general rule. Considerable time and effort are expended therefore in the early stages of each new design of aeroplane to check by actual test whether its strength meets requirements. It is clearly reasonable to devote some little further time and effort to the study of methods and technique for strength testing in general.