THE 
LONDON, EDINBURGH ann DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE, 
SUPPLEMENT to VOL. XXI. FOURTH-SERIES. 
LXXI. On the Reflexion of Light at the Boundary of two Isotropic 
Transparent Media. By L. Lorenz*. 
AMIN, as is well known, discovered that Fresnel’s formule 
for the intensity of the rays reflected and refracted at the 
boundary of two isotropic transparent media do not perfectly 
agree with experiment, the difference bemg very considerable 
when the angle of incidence approaches to the angle of polariza- 
tion. Cauchy had already proved that, under these circum- 
stances, waves must be produced with longitudinal vibrations ; 
and having assumed that these waves were absorbed very rapidly 
(though not instantaneously, since in that case he would have 
returned to the formule of Fresnel), he now introduced a cor- 
rection into the formule which caused them to agree with ex- 
periment. 
All calculations, however, which have hitherto been made 
concerning the reflexion and refraction of light, have proceeded 
on the hypothesis of an instantaneous passage from one medium 
to the other, and a consequent instantaneous change of the 
index of refraction. Such a passage is, however, a mere meta- 
physical abstraction, which cannot possibly exist in nature; and 
the calculation would be more exact and more satisfactory if a 
gradual passage were admitted between the two media through 
a space which might afterwards be assumed to be as small as we 
please. It is, moreover, a fact that bodies are really surrounded 
by an atmosphere which must produce such a gradual change of 
refraction. 
The object of this paper is to show that Jamin’s experiments 
can only be reconciled with Fresnel’s formule when the calcula- 
tion is made on the above hypothesis. — 
In what follows, the case of total reflexion will not be con- 
sidered. 
If the incident light be polarized in the plane of incidence, 
* Translated by F. Guthrie, from Poggendorff’s Annalen, vol. cxi. p. 460. - 
Phil, Mag. 8, 4. No. 148, Suppl, Vol. 21. 21 
