9 
of Edinburgh, Session 1866 - 67 . 
the sky towards the zenith that the light can be obtained, and in 
this case part of it might be advantageously thrown into a window 
by expensive reflectors ; but in streets and lanes open at both ends, 
where a narrow strip of the sky is visible from one point of the 
horizon to the opposite point, no aid whatever can be obtained 
from reflectors, and in such cases the method we are about to 
describe is peculiarly effective. 
If in a very narrow street or lane, we look out of a window with 
the eye in the same plane as the outer face of the wall in which 
the window is placed, we shall see the whole of the sky by which 
the apartment can be illuminated. If we now withdraw the eye 
inwards, we shall gradually lose sight of the sky till it wholly 
disappears, which may take place when the eye is only six or eight 
inches from its first position. In such a case the apartment is 
illuminated only by the light reflected from the opposite wall, or 
the sides of the stones which form the window; because, if the 
glass of the window is six or eight inches within the wall, as it 
generally is, not a ray of light can fall upon it. 
If we now remove our window and substitute another in which 
all the panes of glass are roughly ground on the outside, and flush 
with the outer wall, the light from the whole of the visible sky 
and from the remotest parts of the opposite wall, will be introduced 
into the apartment, reflected from the innumerable faces or facets 
which the rough grinding of the glass has produced. The whole 
window will appear as if the sky were beyond it, and from every 
point of this luminous surface light will radiate into all parts of 
the room. In order to explain the superior effect of roughly 
ground glass, let us suppose that the ordinary window is replaced 
with a single sheet of the best glass inserted flush with the outer 
wall. The whole of the light from the visible portions of the sky 
will fall upon its surface, but at such an obliquity that four or five 
sixths of it will be reflected outwards, and the other two or one 
sixth, which is transmitted, will fall on the floor or on the shutters, 
and be of no value. 
In aid of this method of distributing light, the opposite sides of 
the street or lane should be kept white-washed with lime, and for 
the same reason the ceilings and walls of the apartment should be 
as white as possible, and all the furniture of the lightest colours. 
VOL. VI. 
B 
