pulsations in our souls, if we have an
intellectual pendulum and escapement. Most persons can keep tolerably even
time with a second-hand while it is traversing its circle. The light is
pretty good at this time, and we count only as far as thirty, when we
cover the lens again with the cap. Then we replace the slide in the
shield, draw this out of the camera, and carry it back into the shadowy
realm where Cocytus flows in black nitrate of silver and Acheron stagnates
in the pool of hyposulphite, and invisible ghosts, trooping down from the
world of day, cross a Styx of dissolved sulphate of iron, and appear
before the Rhadamanthus of that lurid Hades.

Such a ghost we hold imprisoned in the shield we have just brought from
the camera. We open it and find our milky-surfaced glass plate looking
exactly as it did when we placed it in the shield. No eye, no microscope,
can detect a trace of change in the white film that is spread over it. And
yet there is a potential image in it,--a latent soul, which will presently
appear before its judge. This is the Stygian stream,--this solution of
proto-sulphate of iron, with which we will presently flood the white
surface.

We pour on the solution. There is no change at first; the fluid flows over
the whole surface as harmless and as useless as if it were water. What if
there were no picture there? Stop! what is that change of color beginning
at this edge, and spreading as a blush spreads over a girl's cheek? It is
a border, like that round the picture, and then dawns the outline of a
head, and now the eyes come out from the blank as stars from the empty
sky, and the lineaments define themselves, plainly enough, yet in a
strange aspect,--for where there was light in the picture we have shadow,
and where there was shadow we have light. But while we look it seems to
fade again, as if it would disappear. Have no fear of that; it is only
deepening its shadows. Now we place it under the running water which we
have always at hand. We hold it up before the dull-red gas-light, and then
we see that every line of the original and the artist's name are
reproduced as sharply as if the fairies had engraved them for us. The
picture is perfect of its kind, only it seems to want a little more force.
That we can easily get by the simple process called "intensifying" or
"redeveloping." We mix a solution of nitrate of silver and of pyro-gallic
acid in about equal quantities, and pour it upon the picture