Published online by Cambridge University Press: 14 August 2015
In addition to its traditional roles of checking theories and applying them, observation also plays an important role in guiding theory and indicating the form that it should take. This paper reviews types of observation, types of stellar system (omitting the highly flattened ones), and the relations between them. Observational limitations are indicated, as well as places where observations of particular sorts are needed, either for guidance of theories or for their application.