Five of Maxwells Papers

Five of Maxwell's Papers

The Project Gutenberg EBook of Five of Maxwell's Papers, by James
Clerk Maxwell (#1 in our series by James Clerk Maxwell)
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Title: Five of Maxwell's Papers
Author: James Clerk Maxwell
Release Date: January, 2004 [EBook #4908] [Yes, we are more than
one year ahead of schedule] [This file was first posted on March 24,

2002]
Edition: 10
Language: English
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*** START OF THE PROJECT GUTENBERG EBOOK, FIVE OF
MAXWELL'S PAPERS ***

This eBook was produced by Gordon Keener.
This eBook includes 5 papers or speeches by James Clerk Maxwell.
Each is separated by three asterisks ('***').
The contents are:
Foramen Centrale Theory of Compound Colours Poinsot's Theory
Address to the Mathematical Introductory Lecture
***
On the Unequal Sensibility of the Foramen Centrale to Light of
different Colours.
James Clerk Maxwell
[From the Report of the British Association, 1856.]
When observing the spectrum formed by looking at a long vertical slit
through a simple prism, I noticed an elongated dark spot running up
and down in the blue, and following the motion of the eye as it moved
up and down the spectrum, but refusing to pass out of the blue into the
other colours. It was plain that the spot belonged both to the eye and to
the blue part of the spectrum. The result to which I have come is, that
the appearance is due to the yellow spot on the retina, commonly called

the Foramen Centrale of Soemmering. The most convenient method of
observing the spot is by presenting to the eye in not too rapid
succession, blue and yellow glasses, or, still better, allowing blue and
yellow papers to revolve slowly before the eye. In this way the spot is
seen in the blue. It fades rapidly, but is renewed every time the yellow
comes in to relieve the effect of the blue. By using a Nicol's prism
along with this apparatus, the brushes of Haidinger are well seen in
connexion with the spot, and the fact of the brushes being the spot
analysed by polarized light becomes evident. If we look steadily at an
object behind a series of bright bars which move in front of it, we shall
see a curious bending of the bars as they come up to the place of the
yellow spot. The part which comes over the spot seems to start in
advance of the rest of the bar, and this would seem to indicate a greater
rapidity of sensation at the yellow spot than in the surrounding retina.
But I find the experiment difficult, and I hope for better results from
more accurate observers.
***
On the Theory of Compound Colours with reference to Mixtures of
Blue and Yellow Light.
James Clerk Maxwell
[From the Report of the British Association, 1856.]
When we mix together blue and yellow paint, we obtain green paint.
This fact is well known to all who have handled colours; and it is
universally admitted that blue and yellow make green. Red, yellow, and
blue, being the primary colours among painters, green is regarded as a
secondary colour, arising from the mixture of blue and yellow. Newton,
however, found that the green of the spectrum was not the same thing
as the mixture of two colours of the spectrum, for such a mixture could
be separated by the prism, while the green of the spectrum resisted
further decomposition. But still it was believed that yellow and blue
would make a green, though not that of the spectrum. As far as I am
aware, the first experiment on the subject is that of M. Plateau, who,
before 1819, made a disc with alternate sectors of prussian blue and

gamboge, and observed that, when spinning, the resultant tint was not
green, but a neutral gray, inclining sometimes to yellow or blue, but
never to green. Prof. J. D. Forbes of Edinburgh made similar
experiments in 1849, with