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480 PROFESSOR LUDWIG MOSER ON LATENT LIGHT. 
greatest degree of refrangibility. In this case also they justify 
the character which has been given to them, and consequently 
the process of levelling furnishes us with a means of determining 
the relative refrangibility in cases where the methods employed 
with the ordinary rays are of no avail whatever. As the most 
refrangible rays are capable of levelling the image while it is in 
the Daguerrian state, the invisible rays will also be abie to effect 
it. In order to prove this I allowed several iodized plates to 
remain so long in the camera obscura that they would have pro- 
duced the images with great accuracy if afterwards treated with 
mercurial vapours. I then placed these plates on pure silver, 
gold, copper, mirror-metal, iodized silver, and porcelain, either 
in such a manner that a contact (although only partial) took 
place, or else so that they could not touch each other on account 
of the interposition of strips of mica. When the plates had 
lain a considerable time in the dark the images were for the most 
part completely levelled ; in some cases a trace of them was made 
visible by the mercurial vapours, but even then only on certain 
parts of the plate. ‘(he invisible rays had in this case levelled 
the images produced by the visible rays; they are capable of 
doing the same with images produced by their own means, if 
they are still in their earlier stages of development. Bodies of 
silver, gold, iron, and horn were laid upon an iodized plate of 
silver and kept there for an hour, so that their images were 
formed. However, after a plate of silver and iron had lain upon 
them for several hours, the images were completely levelled 
and could not be rendered visible by any means; but if the 
image produced by the invisible rays is in a more advanced 
state, then it cannot be destroyed by others of the same kind, of 
which fact I have convinced myself by a number of experiments. 
The visible rays, on the other hand, are in no case capable 
of levelling an image produced by invisible light, and by this it 
is evident that the latter consists of rays more refrangible than 
those of the ordinary prismatic spectrum. It would be useless 
to adduce proofs oi this statement, because I am indebted for 
the knowledge of the identity in the action of light on all bodies, 
and the extension of Daguerre’s discovery to all vapours, to the 
circumstance that visible rays are not capable of destroying 
images produced by those which are invisible. 
As may be seen, the levelling by rays of different refrangi- 
bilities provides us with a very desirable means of distinguishing 
