, by consent of the parties, finally proceeded with before the judge
_as arbitrator_. In the court of chancery it is the practice to hear in
private cases affecting wards of the court and lunatics, family disputes
(by consent), and cases where a public trial would defeat the object of
the action (_Andrew_ v. _Raeburn_, 1874, L.R. 9 Ch. 522). In an action
for infringement of a patent for a chemical process the defendant was
allowed to state a secret process _in camera (Badische Anilin und Soda
Fabrik_ v. _Gillman_, 1883, 24 Ch. D. 156). The Court of Appeal has
decided that it has power to sit in private; in _Mellor_ v. _Thompson_,
1885, 31 Ch. D. 55, it was stated that a public hearing would defeat the
object of the action, and render the respondent's success in the appeal
useless. In matrimonial causes, the divorce court, following the
practice of the ecclesiastical courts under the provisions of the
Matrimonial Causes Act 1857, s. 22, hears suits for nullity of marriage
on physical grounds _in camera_, but not petitions for dissolution of
marriage, which must be heard in open court. It was also decided in
_Druce_ v. _Druce_, 1903, 19 T.L.R. 387, that, in cases for judicial
separation the court has jurisdiction to hear the case _in camera_,
where it is satisfied that justice cannot be done by hearing the case in
public.

CAMERA LUCIDA, an optical instrument invented by Dr William Hyde
Wollaston for drawing in perspective. Closing one eye and looking
vertically downwards with the other through a slip of plain glass, e.g.
a microscope cover-glass, held close to the eye and inclined at an angle
of 45 deg. to the horizon, one can see the images of objects in front,
formed by reflection from the surface of the glass, and at the same
time one can also see through the transparent glass. The virtual images
of the objects appear projected on the surface of a sheet of paper
placed beneath the slip of glass, and their outline can be accurately
traced with a pencil. This is the simplest form of the camera lucida.
The image (see fig. 1) is, however, inverted and perverted, and it is
not very bright owing to the poor reflecting power of unsilvered glass.
The brightness of the image is sometimes increased by silvering the
glass; and on removing a small portion of the silver the observer can
see the image with part of the pupil while he sees the paper through the
unsilvered aperture with the remaining part. This form of the instru