FirstEdition DUE TO THE necessity to save weight and materialin the design ofmodern structures and machines, stability problems have become increasingly im- portant. The classicalengineering approach to this type of problem has been characterized by the tacit assumption that structures are nongyroscopic conservative systems,that is, bythegeneraladoptionofthemethodsdeveloped for this particular case. During the last decades numerous stability problems of a more complicated nature have become important, and it has therefore become necessary to correlate the various types of problems with the ap- proaches to be used in their solution. The principal object ofthis little bookisthis correlation between the systems to be investigated and the methods to be used for this purpose, In other words, our main concern is the choice of a correct approach. It is evident that this idea renders it necessary to distinguish between the various types of problems or systems.At the same time the similarities and the connections between apparently quite different problems will become obvious, and it will be evident that there islittle differencebetween, say, the buckling of a column, thecritical speed of a turbine shaft, and the stability of an airplane, a control mechanism, or an electric circuit.
