Appraises current explanations of how visual processing occurs. Highlights the basics of simultaneous and serial levels of processing. Discusses the results of a series of experiments on visual-search tasks and also on the role of prior knowledge in processing. (ML)

Discusses the development of the concept of atomicity and some of the many which can be used to establish its validity. Chemical evidence, evidence from crystals, Faraday's law of electrolysis, and Avogadro's number are among the areas which show how the concept originally developed from a purely philosophical idea. (JN)