There are no optical illusions more extraordinary than those shown
in the exhibition of Dissolving Views. The effects of the changes in
the diorama are only such as are seen in nature, the same scene being
represented under different circumstances, and the marvel in that case
is that such beautiful and natural effects can be produced on the
same canvas. But Dissolving Views set nature at defiance, and exhibit
metamorphoses as great as can be conceived by the wildest fancy.
Whilst, for instance, the spectator is looking at the interior of a
church, he sees the objects gradually assuming different appearances.
The columns that support the vaulted roof begin to fade away, and their
places are occupied by other forms, which gradually become better
defined and stronger, and a tree, a house, or, it may be, a rock,
thrusts the columns out of view, and the roof dims into blue sky,
chequered with clouds. The original view thus entirely disappears, and
the scene is changed from the interior of a church to open country, or
to a rocky valley. This is done, not by changing at once one scene
into another, but by substituting different individual objects, which
at first appear like faint shadows, and then, becoming more and more
vivid, at length altogether supplant their predecessors on the field of
view, and will, in their turn, be extinguished by others.
It sometimes happens that some strongly marked object resists
apparently the efforts made to dispossess it, and in the midst of a
mountainous scene will be observed the form of a chandelier or of a
statue, that occupied a distinguished place in the church that has
just vanished. In a short time, however, these relics disappear, and
the mountain, the valley, and the lake are freed from the incongruous
images of the former scene.
[Illustration]
[Illustration]
These effects are produced in a manner as simple as they are
extraordinary. All that is requisite is to have two magic lanterns
fitted on to a stand, with their tubes inclined towards each other, so
that both discs of light may exactly coincide, and form on the screen
a single disc. If paintings on glass, representing different views, be
then placed in each lantern, with the lenses adjusted to bring the rays
to a focus on the screen, the two images will be so mingled together
as to present only a confused mixture of colours. Suppose one of the
views to be the interior of a church, and the other to be a mountain
scene;--the pillars of the church will be mingled with trees and rocks,
and in the midst of the confusion there may perhaps be discerned
a strongly painted chandelier or an altar piece. When an opaque
shade is placed before the lens of either of the lanterns, to prevent
the light from reaching the screen, the previous confusion becomes
instantly clear and distinct, and the church or the landscape is seen
without any interfering images. If the opaque screen be gradually
withdrawn from one lens, and at the same time drawn in an equal degree
over the other, the different objects will again be mingled, and those
in the one scene will predominate over those in the other in proportion
to the relative quantities of light permitted to issue from each
lantern to the screen. The two first of the accompanying drawings are
thus blended together in the third, when the screen is half withdrawn
from each.
[Illustration]
It is usual to fix the opaque shade, which alternately covers and
exposes the two magic lanterns, on to a central pin, so that it may be
moved vertically up or down. The shade is so arranged, that in raising
the end to cover the lens of one lantern, the farther end descends,
and exposes, in an equal degree, the other lens. During the time that
either of the views is altogether concealed, the painting is changed;
and in this manner an unlimited number of metamorphoses may be effected.
It requires no expensive apparatus to show the effect of Dissolving
Views on a small scale. Two common magic lanterns are quite sufficient
for the purpose of private exhibition, and the angle at which they
should be fixed on their stand may be readily ascertained after a few
trials. To make the transformation more extraordinary, a man's face may
be painted on one glass and a landscape on the other; and, when the
change is made from the face to the landscape, a strongly painted eye
or nose may be seen occupying the centre of the view, long after the
other features have disappeared, until all the rays of light from that
painting have been excluded. The change from youth to age, from beauty
to ugliness, may also be shown with striking effect.
It will be observed that the principle, on which the metamorphoses
of Dissolving Views depend, is similar to that which produces the
variations in the diorama. In both cases there are two paintings on
the same space, either of which may be shown at pleasure by different
dispositions of the light; the chief difference between them being
that the Dissolving Views are seen altogether by reflected light,
whilst in the diorama the paintings at the back and front are shown
alternately by reflected and by transmitted light.