Catalogue Raisonné. 155 
south, but that in accordance with climate, successive shoals approach the 
coasts for the purpose of spawning ; and this view he supports by some 
interesting facts. ‘I'he nets of Hastings are always cast north and south, in 
order that they may drift with the ebbing and flowing of the tide, which 
takes the direction of east and west in that part of the British Channel ; 
and it is curious, that while those fish which are encumbered with roes, 
are caught in great numbers on the east side of the nets, they are not 
met with in a greater proportion than one in about one hundred withr 
_ Out roes on the west side. 
_ The mackerel which are met with off Hastings, appear to be of a different 
_. __ Species from those caught off Mount’s Bay in Cornwall. 
‘The fishermen of Cornwall, under the impression that the mackerel moved 
eastward along the coast, have endeavoured repeatedly, on their return, 
_ to meet them off the Praul Point, Portland Race, and off the Isle of 
Wight, without success. With respect to the mackerel, his ideas do 
not appear to be very definite, and he questions whether they may not 
move north. 
On the Reflection and Decomposition of Light at the separating surfaces of 
media, of the same, and of different Refractive Powers. By Davip Brews- 
TER, LL.D. F.R:S. L. & E.— Edin. Journ. of Science, No. II. N.S. p. 209. 
A detail of the important discoveries laid before the Royal Society of Edin- 
burgh in 1816, and announced in the Quarterly Journal for July—Oc- 
tober of that year. 
The experiments are divisible into two classes. 
I. Those which (in opposition to the opinion of Herschel) establish the ex- 
_istence of reflecting forces at the confines of media of the same refractive 
power ; and, peel 
II. Those in which periodical colours are produced at the confines of par- 
.. ticular kinds of glass, and various fluids, and soft solids, of the same, and 
of different refractive powers. 
From the first of these classes of facts, the following conclusions are drawn: 
1. The reflective and refractive forces, in media of the same refractive 
power, do not follow the same law,—which is directly opposed to the as- 
sertion of Herschel. 
2. The force which produces reflection, varies according to a different law 
in different bodies. 
The reflective forces in the solid and fluid, may be conceived to decrease in 
various ways. 
a. They may extend to different distances from the reflecting surface, and 
decrease according to the same law. 
6. They may extend to different distances, and vary according to a diffe- 
rent lane 3 Or, 
‘ys peney may extend to the same distance, and vary according to different 
aws. 
It seems highly probable that the law of the refractive force also varies in 
different bodies ; and if we take for granted the mutual dependence of 
the refracting and reflecting forces, (which there seems to be no method 
of determining,) these experiments will establish a variation in the law 
of the refracting forces of different media. Rei 
In the undulatory system, these new facts may be explained, by supposing 
that the density or elasticity of the ether varies near the surface of dif- 
ferent bodies,—an opinion which has been already adopted, to explain 
the loss of part of an undulation in several of the phenomena of interfe- 
rence. 
Speaking of the second class of phenomena, Dr. Brewster remarks, “ Al- 
though there ean be little doubt that periodical tints are more or less de- 
veloped in every combination of solids and fluids of the same refractive 
power, yet their production in combinations where there is much un- 
compensated refraction, is influenced by certain changes on the surface 
of the solid, the nature and origin of which I have in vain attempted to 
discover...... That some unrecognized physical principal is the cause of 
all these phenomena, will appear still more probable when I submit to 
_ the Society a paper on the very same periods of colour produced at simi- 
lar angles of incidence, by the surfaces of metals and transparent solids 
when acting singly upon light.” i 
