PROFESSOR LUDWIG MOSER ON LATENT LIGHT. 473 
I only wish to accommodate myself to the general manner of 
speech; properly I ought to substitute duration of oscillation, 
which, however, would be of but little use, as we do not know 
the function of that duration on which the action of light on 
bodies depends. 
If we also add the proposition, that the length of action of a 
particular class of rays is an equivalent for their inferior refran- 
gibility, so that, for instance, a more continued action of yellow 
light produces the same as the shorter action of the violet rays, 
then we shall easily understand all the phenomena of the so- 
_ ealled “ continuation ” (Fortfiihrung). If an iodized silver plate 
be exposed for a short time to the ordinary rays in a camera 
obscura, then the red rays alone are capable of producing a visi- 
ble image; the green and yellow rays certainly will not cause 
its appearance. If the visible rays had acted longer, then we 
might suppose that, if rays of a greater refrangibility than the 
violet or the dark rays lying at the end of the spectrum had 
commenced the action, the green and yellow would continue 
the formation of the image which was begun, and would render 
it visible. I may pass over practical proofs of this, as they are 
contained in my former paper. If, moreover, the invisible rays 
have begun an image, and have only acted a short time, then the 
blue, and even the green rays will possess a continuing power, 
but the violet ones will not. If they have been acting for a long 
time, then the violet rays will have the same effect, &c. &c. 
In order to render the preceding, which is practically so im- 
portant, more visible at a glance, I will adjoin the determined 
proportions of refraction to the several rays, viz. to the 
Invisible Rays. Blue Rays. Yellow Rays. Red Rays. 
NN(i—n). N(i—2n). N(1—3n).. N(1—4n). 
If the blue rays acted for a short time, then the action is car- 
ried on by the red ones, i. e. rays which differ in the refracting 
proportion 2nN. If the invisible rays acted for a short time, 
then the blue ones continue the action, the difference being 2 n N 
as before. If the blue rays have acted for a long time, we may 
suppose it as if rays of a still greater retrangibility had acted, for 
instance, the invisible rays with an index of refraction N (1 —2), 
and in that case the yellow rays can continue the action. No 
more value must be attached to this exemplification than it was 
meant to possess, namely as a means of showing the connexion 
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