9 
: 
; 
TRANSACTIONS OF THE SECTIONS. i) 
under this impression, a motion is perceived in a direction transverse to the real im- 
pression on the retina; and there is the appearance of lines complementary in the 
same transverse direction. 
On the Aberration of Light. By the Rev. Professor Cuatuts, M.A. 
The phenomenon of aberration was explained by assuming the direction of vision 
to be always coincident with the direction of the propagation of light. A star, ac- 
cording to this supposition, is seen in its proper direction, while an object which 
moves with the spectator is seen in a direction which, with respect to the earth’s mo- 
tion, is behind its true place. Astronomical observation does not determine whether 
aberration affects the apparent position of the wire of the telescope, or of the star. 
Assuming the position of the star to be changed, it follows from this view, that the 
star must be considered to be in advance of its true place as regards the direction of 
the earth’s motion, and this result is in accordance with the principle on which cor- 
rections for aberration are applied in astronomical calculations. 
—— 
On the Aberration of Light. By G. G. Stoxrs, M.A. 
In this paper the author adopts the undulatory theory of light. He supposes that 
the luminiferous ether is displaced by the motion of the earth and planets through 
it, in a manner similar to that in which ordinary fluids are displaced by solids moving 
through them, though not necessarily according to the same laws. He supposes 
that the ether close to the surface of the earth is at rest relatively to that surface, 
being entangled in the earth’s atmosphere. Consequently, experiments on reflexion, 
refraction, and interference, made with the light coming from any particular star, 
will lead to the same result at whatever time of year they are made, conformably 
with experiment. He supposes that light is propagated through the ether in motion 
in the same way that sound is propagated through air in motion; that is to say, he 
supposes that the displacement of a small portion of a wave’s front in a very short 
time is compounded of the displacement which would exist if the zther were at rest, 
and of the displacement of the ether itself, so that in general the direction of a 
normal to that portion of the wave’s front is changed by the motion of the ether. 
The law of aberration which results from this supposition is complicated, so long as 
we suppose the.motion of the zther arbitrary; but if we suppose its motion such 
| thatudx + vdy + wdZz is an exact differential, where u,v, w are the resolved parts 
along the rectangular axes of x, y, 2, of the velocity of the particle of ether whose 
coordinates are x, y, 2, then the law of aberration which is derived from the theory 
coincides with the law which is the result of observation (Philosophical Magazine, 
July 1845). 
On the Caustics produced by two Mirrors in Rotation. By Prof. AnpERson, 
Prof. Anderson exhibited the curves traced on the ceiling by the reflected light 
from the two revolving mirrors placed in a beam of sunlight, and pointed out mathe- 
" matical rules for tracing the curves for the several angles at which the mirrors might 
be set, and the angle which the beam of sunlight makes with the plane of rotation. 
On the Rotation of Minute Crystals in the Cavities of Topaz. 
By Sir Daviw Brewster, F.R.S. L. § E., Hon. M.R.LA. 
This paper is printed in the Edinburgh Transactions, vol. xvi. part i. p. 19. 
On the Condition of Topaz subsequent to the formation of certain Classes of 
Cavities within it. By Sir Davin Brewster, /.R.S. L. § E., M.R.LA. 
This paper is printed in the Edinburgh Transactions, vol. xvi. part i. p, 7-9. 
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