Unpublished paper, 'Experiments on the heating power of the prismatic rays' by Baden Powell Powell recounts his experiments using a photometer to compare the heating power of separate primary rays of solar light with the heating power of the same rays when united to form a white ray. Powell provides his experimental results in tables. Ink inscription top left of first page reads 'To be returned to the author if required'. A red ink inscription to the right of this reads 'JFWH [John Frederick William Herschel] (51)'. A pencil inscription below title reads 'Powell on heating powers of Rays'. Ink corrections and deletions appear throughout paper. Subject: Physics [early 19th century]