TRANSACTIONS OF THE SECTIONS. 7 
plane perpendicular to the plane of incidence. When a drop of water 
or oil was introduced between the films, the phenomena of polarization, 
as well as of colour, instantly disappeared. 
The preceding paper was illustrated by coloured drawings. 
On the Cause of the Increase of Colour by the Inversion of the Head. 
By Sir Daviv Brewster. 
“Tt has been long known to artists and tourists that the colours of ex- 
ternal objects, and particularly of natural scenery, are greatly aug- 
mented by viewing them with the head bent down and looking back- 
wards between the feet, that is, by the inversion of the head. The co- 
lour of the western sky and the blue and purple tints of distant moun- 
tain scenery are thus beautifully developed. The position of the head, 
however, which I have described, is a very inconvenient one, but the ef- 
fect may be produced nearly to the same extent by inverting the head so 
far as to look at landscapes backwards beneath the thighs or under theleft 
arm. It is not easy to describe in any precise language the degree of in- 
crease which the colours of natural scenery thus receive, but an idea may 
be formed of it from the fact, that the colours of distant mountains which 
appear to me asif of a French-gray colour when viewed with the head 
erect, appear of a brilliant blue or purple tint with the head inverted. 
Upon inverting the landscape by reflexion I found that no increase of 
colour took place. Ithen viewed the inverted landscape with the head 
inverted and found the colour to be increased as before. Hence it ap- 
pears that the increase of colour is not owing to the simple inversion 
of the object and to our viewing it under unusual circumstances. That 
the augmentation of tint is not owing to the impression falling upon a 
part of the retina not so much accustomed to receive such impressions, 
is obvious from the fact that the tint is the same upon whatever part of 
the retina the image falls, and it is easy to see that the very same part 
of the retina is affected whether we look at an object with the head up- 
wards or downwards, or in any other position, provided we look at it 
directly. In order to acquire some information on this subject, I re- 
quested a friend who was unacquainted with any theoretical views that 
had been advanced, to make some observations on the change of colour 
of distant mountains. The result of these was to convince him that 
the increase of tint arose from the protection of the eye from lateral 
light, owing to the position of the head when inverted. On submitting 
this opinion to examination, I found that the tint was not increased by 
protecting the eye from lateral rays, even to a much greater extent than 
is done by the inversion or inclination of the head, and therefore that 
this could not be the cause of the increase of colour. In this perplexity 
about the cause of the phenomenon in question, I had an opportunity 
of observing the great increase of light which took place in an eye in a 
state of inflammation. This increase was such that objects seen by the 
sound eye appeared as if illuminated by twilight, while those seen by 
the inflamed eye seemed as if they were illuminated by the direct rays 
