1882.] 
Analyses of Books . 
167 
is taken in the usual manner, on developing the plate there appear 
occasionally other forms in addition to that of the sitter. These 
forms are often recognised as the similitudes of deceased friends 
or relatives. The conditions of these singular phenomena are 
not definitely enumerated in Miss Houghton’s book. As far as 
we gather from various passages the presence of a medium is 
essential, but it does not appear necessary that the sitter should 
possess mediumistic powers. It is also requisite that the sitter 
should be in a calm, unruffled frame of mind. Even when these 
conditions are carefully fulfilled success is by no means uniform, 
or rather, it is decidedly exceptional. The additional figures 
appear generally draped in wide, flowing robes, like the white- 
sheeted ghosts of ancestral tradition, but the head and face, 
according to the specimens given in illustration, are often clearly 
and distinctly human, and might admit of recognition. In some 
cases the entire figure is reproduced with but scanty drapery, 
and sometimes a trunk has appeared without a head. Persons 
not endowed with mediumistic power see on such occasions 
nothing save the sitter and the furniture of the room. We have, 
then, the hypothesis that objects may exist which refledt only 
light capable of adting upon a prepared plate, but invisible to the 
human eye. That there are such rays of light, the so-called 
ultra-violet rays, is admitted. The human eye is only susceptible 
to a certain part of the spedtrum. The ultra-violet rays, further, 
are able to set up chemical adtion of various kinds. But the 
novelty here involved is the supposition that objedts exist which 
refledt such rays, and such only. We have no right to pro- 
nounce, a priori , that no such objedts are possible. But we are 
here brought in contadt with one of the limits of our perceptions. 
Whatever does not refledt rays of light which affedt our retina 
is for us simply invisible, and, for anything we can show to the 
contrary, there may be such objedts. Questions here naturally 
arise which can only be decided by varied and prolonged photo- 
graphic experimentation. 
The genuine charadter of the figures obtained is, of course, 
liable to be questioned, or rather denied. Having never come 
in contadt with jugglers, or studied their modes of adtion, we 
are not entitled to say with authority what is within and what is 
beyond their power. But a very considerable number of precau- 
tions for the prevention or discovery of fraud have been adopted. 
The cameras have been carefully examined and exchanged for 
others. Private marks have been put upon glass plates brought 
to be operated upon lest they should be exchanged for others 
previously prepared whilst in the dark room. The entire studio 
has been searched, as we understand, not merely by amateurs 
but by experienced pradtical photographers, but the “ trick,” if 
trick it be, has not come to light. We read : — “ Neither Mr. 
Hudson nor Mr. Herne knew who we were. Mr. Herne I never 
saw before. I shut him up in the recess at the back of the 
