it in your pocket, expose a plate according to your table, and in case
the light or plate should not be just in accordance with the conditions
under which the table was prepared, expose other two plates, one a little
less and one a little more than that first exposed. Then note down
everything you have done--kind of view, stop, speed of plate, exposure of
each plate, and length of exposure of actinometer.

When you get home, the first thing to do is to get hold of a paint box
and paint the underside of the glass of your actinometer to match the
darkened paper. Do this by gas light. Then scrape away a little of the
paint, so as to let a strip of the paper be seen below it. After this
develop your three plates with a developer of normal strength, and see
which is best. If you have chosen a really bright spring day, and are
using plates of medium rapidity, you will most likely find that exposed
according to the table just about right.

Now let us see how we can use these aids in our field work. We have
ascertained the correct exposure with a given stop on one class of view,
with light of a given quality, but now suppose all these conditions
altered. Let the view have heavy foliage coming close up to the camera,
the stop be a size larger than that used in our first experiment, and the
day rather dull. The table tells us what the exposure would be with this
stop on this view, on a bright day; and if the actinometer take twenty
seconds to reach the painted tint, then we must double the exposure given
in the table.

You may sometimes find that the actinometer indicates a very different
exposure from what the eye would lead you to expect. For instance, one
day last September I went to Bothwell Castle, to get a picture I knew of
in the grounds. It was one of those strange yellow days we had then, and
the sun, though shining with all his might, was apparently shining
through orange glass. The actinometer indicated an exposure of thirty
seconds where in good light one would be right. I was rather incredulous.
Thirty seconds in broad sunshine! However, I gave this exposure, but for
my own satisfaction I gave another plate fifteen seconds only.

On developing, the latter was hopelessly underexposed while that having
thirty seconds gave a negative which furnished one of my exhibition
pictures.

I have shown you how to reduce the quality of the light to a certainty,
also how to reduce to rule the exposure with different lenses an