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Proceedings of the Royal Society 
crypts, whilst the sub-chorionic lay in relation to the capillaries 
situated beneath the plane of the general uterine mucous surface. 
The amnion formed a continuous bag from one horn of the chorion 
to the other, but did not reach the poles of the latter. In the left 
horn, which contained the foetus, it extended to 2 inches, in the 
right to 9 inches from the corresponding pole of the chorion, its 
free surface was studded with small pedunculated corpuscles. The 
allantois was not so extensive as the amnion. The urachus 
expanded into a large funnel-shaped sac, which bifurcated when it 
reached the chorion and formed a right and left cylindrical horn ; 
the left reached to 7 inches from the left pole of the chorion, the 
right to 21 inches from the right pole. 
2. Note on some Anomalous Spectra. By H. F. Talbot. 
A recent number of Poggendorffs a Annalen contains a short 
but interesting paper by Christiansen, of Copenhagen, in which he 
states that a hollow prism tilled with the alcoholic solution of 
fuchsine produces a highly anomalous spectrum, which, instead of 
proceeding regularly from the red to the violet like the ordinary 
solar spectrum, stops at a certain point, returns backward, then 
stops again and resumes a direct course to the end. This paper by 
Christiansen, kindly pointed out to me by Professor Tait, recalls to 
my memory an experiment which I formerly made more than 
thirty years ago, and which, with the permission of the Society, I 
will briefly describe, premising, however, that I write from memory, 
and without access at present to the original paper which I believe 
I have still preserved. My account may therefore contain some 
inaccuracies, but the general nature of the experiment was as 
follows :—I prepared some square pieces of window glass, about an 
inch square. Taking one of these, I placed upon it a drop of a strong- 
solution of some salt of chromium, which, if I remember rightly, was 
the double oxalate of chromium and potash, but it may have been 
that substance more or less modified. By placing a second square of 
glass on the first, the drop was spread out in a thin film, but it was 
prevented from becoming too thin by four pellets of wax placed at the 
corners of the square, which likewise served to hold the two pieces 
of glass together. The glasses were then laid aside for some hours 
