PRACTICAL MICROSCOPY by George Davis, 1889:
Collins' " Harley " binocular is now constructed on the
Jackson model. The base is large and made in one piece, the limb
carrying the body, stage, substage, and mirror is in one piece also,
with a machine-planed groove from end to end. A rackwork of six inches
in length is attached to the body so that very low power objectives can
be used. The fine adjustment is placed between the tube and the limb.
The stage is circular in form and with concentric rotation, with a
simple arrangement for adjustment should it get out of the centre. It
has a clear aperture underneath, of three inches, when the apparatus
plate is removed, and consequently very oblique illumination can be
obtained by means of the mirror alone.