even this is not the variation there would necessarily be,
were we to adopt the angle of 45 deg. as urged by Daguerre.

Among our principal professors, the beveltop will not be found in use
where the large plates are used. Should any one feel desirous
to test more minutely the effect produced by a bevel top bath,
I would suggest to them to place a frame, so constructed as to hold
three sixth size plates, and fit it to the top of the bath,
and so arrange it with openings that the plates may be placed,
one at the nearest point of the mercury, the second midway,
and the third to the greatest distance, and by placing the plates
over at one and the same time, the experimenter will be enabled
to judge if there exists a difference in the developing.
In speaking of the above, reference is had to baths to the ordinary
heights used by operators.

We will now proceed to examine the effect produced by mercurial
vapor upon the plate at different lengths of exposure.
In some investigations which I have made upon the appearance
of the Daguerreotype impressions when developed over mercury
at 90 deg. C. (194 deg. F.), the following was the result.
Plates, coated and exposed to light in our usual manner
of operating, produced on exposure of

1/2 minute, whole impression, deep blue.

1 minute, ashy and flat; no shadows; linen, deep blue.

1 1/2 minute, coarse and spongy; shadows, muddy; drapery, dirty reddish brown.