Nov. 23, 1882 | 
NATURE 
77 
analysis, without being convinced that this hypothesis is nothing 
but a delusion and a snare, and that the quicker it is thrown 
aside and abandoned the better it will be for geological science” 
(American Fournal of Science, vol. xxiii. p. 287). 
I take this opportunity of pointing out a mistake in my book. 
At page 156 the number 1127 ought to be 1734; and consequently 
the number 0996 ought to be 0'965, The argument will still 
hold. O, FISHER 
Harlton, Cambridge, November 9 
P.S.—Since forwarding the above I have observed a note at 
p. 912 of Dr. Geikie’s ‘Text Book of Geology,” in which he 
says that I have ‘‘endeavoured” to show that the secular 
contraction of a solid globe through mere cooling will not 
account for the phenomena. ‘The word ‘‘endeavoured,” does 
not express the attitude of my mind upon the question. 
Forty-twoyears ago the contraction theory occurred to myself inde- 
pendently. Iremember that in my youthful joy at what I thought 
thought a discovery, I forthwith vaulted over a gate! In 1868 
I read my paper on ‘‘The Elevation of Mountains by lateral 
Pressure,” fully believing that I was elucidating the cause which 
had prodaced them in the contraction through secular cooling. 
In 1873 I began my paper on ‘The Inequalities of the earth’s 
Surface viewed in connection with the Secular Cooling,” while 
still under the same impression. I first of all estimated the 
actual elevations, and, this done, I calculated the amount of those 
which would be formed upon Sir William Thomson’s view of 
the mode of solidification. To my excessive surprise, the 
reult showed the utter inadequacy of the contraction hypo- 
thesis. I thought I must have made some error in the 
calculations, but could find none. I still, however, adhered 
to the original idea of contraction, and suggested, towards the 
end of that paper, a fluid condition of the interior at some for- 
mer period, thinking that sufficient contraction might be perhaps 
obtained by that means; for I had not yet dared to question 
Sir Wm, Thomson’s dictum of the fresen¢ complete solidity of 
the earth. It was not until about a year ago, when I wrote the 
chapter in my book about the ‘‘ Amount of Compression,” that I 
perceived that even the condition of a liquid substratum would 
not give the necessary degree of contraction to produce the com- 
pression. I have thus been driven from the contraction hypo- 
thesis step by step, and have by no means been endeavouring to 
support a preconceived opinion against it.—O, F. 
Shadows after Sunset 
HAPPENING by chance to look into ‘‘ Loomis’s Meteorology,” 
after reading M. Dechevren’s account of the blue, white, and red 
bands visible before sunrise and after sunset at Zikawei, I noticed 
under the above heading the following account of shadow-bands, 
which not only appear to be very similar to those observed by 
Dechevrens, but are explained in identically the same way 
(‘* Loomis’s Meteorology,” p. 107): ‘A similar phenomenon [to 
the water-bands described in the preceding paragraph] is fre- 
quently noticed about fifteen minutes after sunset, when the 
shadows of clouds near the horizon are projected upon the 
western sky in the form of radiant beams diverging from the sun. 
These beams are parallel lines of indefinite length, but from the 
effect of perspective they seem to diverge from the sun, and if 
they could be traced entirely across the sky, they would for the 
same reason converge to a point directly opposite to the sun. 
Such cases are sometimes, though not very frequently noticed. 
Similar shadows are sometimes seen in the morning before sun- 
rise, and form a conspicuous feature of the morning twilight. 
This effect is sometimes noticed in nearly every part of the 
world. It must have attracted the attention of the ancient Greeks, 
and is thought to explain that poetic expression ‘‘the rosy- 
fingered dawn.” 
M. Dechevrens appears to think the phenomenon does not 
occur in Europe or temperate latitudes generally, but from what 
Loomis says, one would infer that he may be mistaken in this, 
and that to a modified extent it may be visible in Europe and 
America, Perhaps some of your readers who are in the habit 
of observing the face of the sky will be able to verify this sup- 
position. For my own part I have not remarked it in England, 
but have occasionally witnessed it in Bengal during the rains, 
very markedly. ‘The explanation offered by M. Dechevrens 
seems the only reasonable one under the circumstances, but he 
hardly seems to lay sufficient stress upon the fact that when the 
sunis below the horizon his rays can only illuminate a shallow 
stratum of partially condensed vapour in the upper atmosphere. 
Any obstruction of his rays will consequently shut off the whole 
of the reflected light from this stratum, and cause the blue sky 
to appear through the shadow, all the more cerulean by contact 
with the whitish or rosy colour of the adjacent portions which 
still bask in the solar rays. E. DouGLaAs ARCHIBALD 
An Abnormal Fruit of Opuntia Ficus-Indica 
THE accompanying figure represents a fruit of Opuntia Ficus- 
Indica, which is wholly inclosed in one of the well-known 
flat branches of this plant; normally the fruits appear as 
exserted obovate bodies on the margin, or on either side, of the 
branches. The figure is exactly half natural size ; the fruit is 
therefore full grown. There is no interruption in the ascending 
curves of spinous tubercles, only they are somewhat smaller on 
the fruit, which has also a less wrinkled skin than the remainder 
of the branch. It is of rather uncommon occurrence, nobody 
having seen here anything alike in the extensive ¢uma/les or 
Indian fig-plantations of our neighbourhood ; nor have I been 
able to find any mention of such a case in the books at my dis- 
posal, It is evidently an instance of non-development of 
peduncle, a special case of suppression of axile organs (Masters, 
‘¢Teratology,” p. 393). But I think it throws also some light 
on the nature of what generally is taken to be the pericarp of 
the Opuntia fruit, which, after all, seems to be a slightly modi- 
fied branch, bearing the ovary of the flower in a cavity on its 
- Abnormal Fruit of Opuntia Ficus-Indica from Caracas. 
upper end. A similar view is held forth by Dr. Noll ina paper 
published in the Aznaal Report of the Senkenbergische Gesell- 
schaft (Frankfurt, 1872, pp. 118-121, with two plates), where he 
describes and figures two abnormal fruits of Opuntia coccinelli- 
fera from the Cavary Islands, with branches growing from the 
exterior part of the fruits. Their apparent pericarp is therefore 
an axile organ of a certain order, say of the order 7, whilst the 
additional branch is of the next order, +1. The case which 
forms the object of the present note is quite the reverse of those 
mentioned by Dr. Noll, as the branch of order #, or the exterior 
part of the normal fruit, is not developed independently, being 
represented by its parent-branch of order, 7 —I. 
If this view be correct, there can no longer be any reason for 
speaking of an exserted ovary in Opuntia (Hooker and Bentham, 
“Genera plantarum,” I., $51), as this organ is wholly sunk in 
the interior of a branch, just as it happens in other Cacteze with 
an ovarium immersum. A, ERNST 
Caracas, October 4 
