The San Francisco call., 1896-03-22

Georges d'Infreville, distinguished elec-
trical expert OF this city, says the New
York Sun, who has perfected an apparatus
by which it is possible to see in complete
darkness. Mr.. lnfrevilie also succeeded
several years ago in taking photographs In
darkness. His researches and their re-
suits have been known for a long time to a
number of well-known scientific men in
this city, but not until few weeks ago did
he make public the principles of his re-
markable process.
When the news of Rontgen's discovery
first reached this country Mr.. d Infreville
announced in the Electrical Engineer that
he had several years ago succeeded In pho
tographing and seeing in darkness, but he
did not describe his method. A recent ar
ticle in the same journal contains, how
ever, an account from his own pen of the
theory and application of the process.
He does not use vacuum tubes or any OF
the complicated electrical apparatus
needed for the generation of the x ray.
On the other hand, his apparatus is ex-
tremely simple. His process consists of
two operations. First he casts on the OBJ
ject to be seen or photographed ultraviolet
rays, which are invisible to the human eye.
Secondly, he renders visible the objecl
thus illumined.
The ultraviolet rays of the spectrum, as
is known to all versed in the first princi-
pies of light, are found beyond the violet.
They are the most refrangible or easily
bent rays in light; have the shortest wave
length and most rapid vibrating period,
and so do not affect the human eye They
extend beyond the violet of the solar spec
trum several times as far as the length of
the visible spectrum.
These invisible rays can, however, be
made visible. Plates washed with bisul-
phate of quinine, an alcoholic solution of
stramonium or barium platino-cyanide,
Immediately duoresce when placed in the
spectrum beyond the violet. This change
to the visible is due to diminution in the
refrangibility of the ray which is ordinarily
too refragible to affect the eye.
The accompanying cut shows Mr.. d In
freville's method of casting these rays on
the object and then making them visible
The figure B represents tightly closed
box having at a window with sliding
shutter From the point l. light falls on
the prism at and is there decomposed
into various colors OF the spectrum, which
are visible on the side A. The prism is of
quartz which does not absorb the ultra
violet rays to any great extent. The shut
ter at B is opened and adjusted SO as to
allow only the ultra violet rays to pass out
into the darkness and fall upon the object
at d. The figure is telescope. having
at o an objective of quartz or other SUBJ
stance which will refract ultraviolet rays
without absorbing them. In the telescope
at f is plate coated with fuorescent
substance and transparent. The rays that
strike the object and are not absorbed by
ii are reflected to the objective of the tele-
scope and pass through it to the plate at F
where the image is formed. TIE image
can be seen from the other side by means
of an ordinary convex ocular glass, which
is shown at n.
To photograph the object in darkness q
finorescent plate is used to obtain the
proper focus. Then plate sensitive to
the actinic effects of the ultraviolet rays
is exposed and the picture thus formed on
it.
In his first article in the Electrical En-
gineer on the subject Mr.. d Infreville said:
II will state, SO as not to mislead any
one, that photographing or seeing in dark
ness does not give the same result as in