The cosmology of John Herschel’s father had been based
on the idea that celestial objects could be classified into
species like plants and animals and that the characteristic
properties of members of each species varied to only a
limited extent.47 Though the younger Herschel was hesitant
to explicitly embrace this assumption, his early work
on double stars indicates that the classification of stellar
objects – in this instance ‘subspecies’ of double stars – still
played an important role in his thought. In 1833, the
assumed bounds on stellar properties allowed him to
speculate on the planetary nature of objects with properties
beyond those bounds. Yet these bounds were even
then in a state of transition and within a few years would
be discarded. By 1846 the astronomer Wilhelm Bessel