PROFESSOR LUDWIG MOSER ON LATENT LIGHT. 48] 
the group of the invisible rays from that of the ordinary ones, 
and it is no longer necessary to make our experiments on the 
rays of the first kind in so-called dark chambers and at night, 
in order to remove any possible objection. The two kinds of 
rays are so easily distinguishable, that I might proceed to the 
solution of the question as to whether or not there are any rays 
in day- and sun-light which possess the refrangibility of the in- 
yisible ones. That there are none such present in the camera 
obscura, is evident from the fact that every image which is in 
the Daguerrian state, or even a little more developed, is destroyed 
by means of the blue and violet rays. But this might possibly 
arise from the lens having the power of absorbing these invisible 
rays, which I will again remark must not be confounded with 
Ritter’s dark rays. It was necessary then to act with pure sun- 
light, and for that purpose I placed a figured screen over and at 
a sufficient distance from an iodized plate of silver, and exposed 
the whole for one or two seconds to the sun. On being now 
placed in the sun under a blue glass, no image was produced. 
In order to render this negative result more positive, I exposed 
the plate with its screen to the sun for three seconds, and during 
the eclipse of the 8th of July for fourteen seconds, so that a very 
clear picture of the excised part was rendered visible. The plate 
was then laid in the sun under a blue glass, and in a very short 
time the image was completely levelled and destroyed. Images 
of this kind were much more plainly formed under red, yellow, 
and green glasses. It has hereby been proved, that among the 
various rays of the sun the invisible ones are not present. Nor 
are they to be found in daylight, a fact of which I have con- 
vinced myself by several experiments. 
If these rays, which are emitted by every body considered as 
self-luminous, are wanting in the sun, the cause of it may be, 
that they are absorbed during their passage through the atmo- 
sphere. But in respect to this other opinions are possible, de- 
pending upon the motions of elastic bodies, but which must not 
be mentioned here, more particularly as the experiments which 
I have made, with a view of establishing one theory or the other, 
have as yet yielded no positive result. 
It is now possible to determine the latent colour of some va- 
pours, and I will first direct my attention to that of mercury. 
Its latent colour is not blue or violet, for these colours level the 
images that are in the Daguerrian state, while the vapours of 
