The engineering designer is always limited by the properties of available materials. Some properties are critically affected by variations in com- position, in state or in testing conditions, while others are much less so. The engineer must know this if he is to make intelligent use of the data on properties of materials that he finds in handbooks and tables, and if he is to exploit successfully new materials as they become available. He can only be aware of these limitations if he understands how pro- perties depend on structure at the atomic, molecular, microscopic and macroscopic levels....