Preface

Understanding the basic structure of matter and measuring this structure in detail have long presented a challenge to philosophers and scientists. In the fifth century B.C., the Greek philosopher Democritus described the ultimate structure of matter as discrete rather than continuous and is reported to have said that “The only existing things are atoms and empty space; all elsei s mere opinion.” This atomistic theory became a cornerstone of the philosophy of Epicurus and was described much later by Lucretius in his didactic poem De Rerum Natura. According to this philosophy, the properties of material objects were considered to be determined solely by the sizes, shapes, positions, and motions of the atoms of which the material was constituted.