500: BARON VON WREDE ON THE ABSORPTION OF LIGHT 
I have already made the preparations necessary in order to prove by 
experiment the identity of the phenomena of absorption and those 
which must result from the hypotheses assumed by me for their expla- 
nation. The formule which are required for such an experiment I will 
now analyse. I have already proved that when light of all wave- 
lengths traverses a medium which causes a retardation e, all species of 
light whose half wave-length is 
Ge Ver # c c - 
Ry a Bee Qm—1’?.2m+1  — 
become minima. Now in order to derive from this a formula for the 
minima which must arise, in consequence of the retardation c, in a 
spectrum whose external limits are a (the greatest) and 6 (the small- 
c 
2m — 1” 
est), I designate this number by s, and suppose that 1 az 
c 
ae ;> further puz. 
but ta 7 
stil 1 BU anes, 
2m EyeE ee (m+s)+1 
Hence we have 2m —14 2° and 2m + 172% orm z£ + yand 
a = 
c a : ia en 
pratt 4, and consequently m = the entire number in — + Le 
R 
In the same manner we have m + s Z 3 + 2 and 73 — 4, conse- 
quently s= entire numb. in (4 si +) — entire numb. in (< —1 ) (ily 
If on the contrary we assume the pheenomenon of absorption as known, 
and search for the magnitude of the retardation which causes it, we 
must first determine in one manner or the other the wave-lengths of 
the species of light which represent any two minima. If I call these a! 
and , and the number of the intermediate absorptions s — 1 (i. e. s de- 
signates the ordinal number of the minimum whose length of undulation 
is B', reckoned from that whose length of undulation is a’), and suppose 
yO EE cre] hee eee ee 
ey UW are 2(m' +s)—1 2B 
we have 
oie (»'~3) = p' ((m! +8) 3) 
thence 
m! = git » 
and consequently 
sper Be oe \> see nbey arte eee 
