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 and stops on certain classes of subjects, and it remains with you only to guess correctly to what class the view you wish to take belongs; I can assure you from my own experience that there is enough uncertainty about that point to prevent good negatives ever becoming monotonous.

The only aid I can suggest in this case is the continual use of a note-book.  Note every plate you expose, and when you have a failure be careful to record the fact, and you will gradually find these accumulated notes becoming a great help in cases of doubt.  One hint I can give to beginners is that a great number of the pictures to be met with in this part of the country are intermediate between “Open Landscape” and “Landscape with heavy foliage in foreground;” and it is scarcely needful to say that if you are in doubt, let the exposure be rather too much than too little; you may make a negative of an overexposed plate, but never of an underexposed one.

* * * * *

ISOCHROMATIC PHOTOGRAPHY.

[Footnote:  Read at the stated meeting of the Franklin Institute, March 18, 1885.]

By FRED. E. IVES.

It is well known that the ordinary photographic processes do not reproduce colors in the true proportion of their brightness.  Violet and blue photograph too light; green, yellow, orange and red, too dark.  For a long time it was believed to be impossible to remedy this defect; and even when it became known that bromide of silver could be made more sensitive to yellow and red by staining it with certain dyes, the subject received very little attention, because it was also known that the increase of sensitiveness was too slight to be of practical value in commercial photography.

Dr. H.W.  Vogel, who was one of the first, though not the first, to devote attention to this subject, announced, in 1873, that he had succeeded in making a yellow object photograph lighter than a blue or violet one, by using a silver-bromide plate stained with coraline, and exposed through a yellow glass.  The plate showed no increased sensitiveness to red, and the experiment, although of considerable scientific interest, did not indicate a practically useful process.