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tracery on a darkened sky, and the remainder of the picture 
quite natural; in some cases again, one half of a photo- 
graph may be correct as a positive, and the other, the 
distance exactly like a paper negative. I bring with me 
for exhibition specimens of these several effects, which 
appear intimately connected together, and deserving of our 
attention. 
The question for us to consider is whether, these effects 
are to be accounted for altogether by the received theories 
of the reversed action of light on iodized plates or paper 
when exposed too long in the camera, in other words, what 
used to be called solarization, or whether to some extent, 
at least, these are not copies of the natural effects as the 
camera sees them, and as we should see them, if we looked 
aright. 
In Tyndalls work on the glaciers of the Alps is a reference 
to a curious phenomenon he saw, where the trees and shrubs 
projected against the sky showed as brilliant white, he says 
this phenomenon is rarely seen by guides or travellers, 
perhaps because they avoid looking towards the brilliant 
sky ; he also quotes a letter from Professor Necher to Sir 
David Brewster, describing the same phenomenon. He says 
he has seen it at different times of the day, and says that 
the appearance of the trees projected against the sky is 
as if they were made most delicately of the purest silver. — 
At pages 180 and 181 are sketches, which, as you will see, 
are wonderfully like the photographs I have to show. 
That some of these effects can be accounted for I am 
well aware, but when taken together there is much that 
is inexplicable, the explanation for one case will not suit 
another. I would, therefore, make the suggestion, that 
in some states of the atmosphere, these bright lines are 
to be found in nature, either visible, or of such actinic 
power as to produce the results you see ; there are certain 
effects in nature, for instance, the streaming light of the 
