A homemade exposure meter. This meter comes from a 14-drawer cabinet found in the Herschel family home in the 1950s. The contents of this and a similar cabinet seem to suggest that they were used by successive generations of the family to store specimens, material and apparatus for carrying out experiments.

A number of the Herschels were interested in photography (from John Frederick William Herschel's very early involvement with the invention of photography in the first half of the 19th century onwards). It is likely this exposure meter along with other photography related material belonged to one of his 12 children, probably William James his eldest son who was a member of a photography society towards the end of the 19th century.