However, noticing in Capt.  Abney’s article the statement that the bromide of silver should be as nearly as possible in the same state in the paper as in the plate, I thought “Why not Morgan’s paper?” This, of course, is just bromide emulsion on paper, and if, as I suspect from its color, it contains a trace of iodide, why, so do most commercial plates.  A sheet of this paper cut into strips, soaked for ten minutes in a fifteen-grain solution of potassium nitrite, and dried, gives a sensitive paper which darkens with great rapidity to a good deep tint, and keeps indefinitely.  Here is some prepared last summer, which is still quite good.  To use this paper make a little box so that a little roll of it can be stored in one end, and drawn forward as required beneath a piece of glass.

Bearing in mind that your table of exposures is calculated for the best spring light, go to the country some bright day next month with note-book, actinometer, and the necessary appliances for exposing a few plates.  Select, say, an open landscape, and use your smallest stop.  When all ready to expose, get out your actinometer and expose it to the reflected light of the sky for ten seconds (if the sun is shining, turn your back to it, and keep the actinometer in your own shadow); then put 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.