You may wish to refer to an author’s idea, model or dataset but have not been able to read the actual chapter containing the information, but only another author’s discussion or report of it. Similarly you
may refer to a primary source, e.g. an author’s letters or diary, or a government report, that you have only ‘read’ as cited or reproduced within another author’s text. In both cases you should acknowledge the use of a secondary source.
"The model of Mitchell (1996) (cited in Parry and Carter, 2003, p.160) simulates the suppressing effects of sulphate aerosols on the magnitude of global warming."
In this example ideally you should list both the Parry and Carter (2003) and Mitchell (1996) sources in your reference list but many schools will accept the listing of the secondary source (i.e. Parry and Carter) only.