been going on, and we are now ready to take the glass plate out of the
nitrate-of-silver bath. It is wholly changed in aspect. The film has
become in appearance like a boiled white of egg, so that the glass
produces rather the effect of porcelain, as we look at it. Open no door
now! Let in no glimpse of day, or the charm is broken in an instant! No
Sultana was ever veiled from the light of heaven as this milky tablet we
hold must be. But we must carry it to the camera which stands waiting for
it in the blaze of high noon. To do this we first carefully place it in
this narrow case, called a _shield_, where it lies safe in utter darkness.
We now carry it to the camera, and, having removed the ground glass on
which the camera-picture had been brought to an exact focus, we drop the
shield containing the sensitive plate into the groove the glass occupied.
Then we pull out a slide, as the blanket is taken from a horse before he
starts. There is nothing now but to remove the brass cap from the lens.
That is giving the word Go! It is a tremulous moment for the beginner.

As we lift the brass cap, we begin to count seconds,--by a watch, if we
are naturally unrhythmical,--by the 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