April 26, 1883] 
wherever plants get free access to the open air above, it was one 
of my own assertions that they must necessarily obtain carbonic 
acid in abundance. It seems to me difficult to understand how 
in a still place, where many plants at once are engaged in deoxi- 
dising a compound which only normally forms 0°03 per cent. of 
the atmosphere, there can always be as much of it left as any of 
them can possibly want. I do not presume to argue with Prof. 
Dyer upon the subject; but as far as my own comprehension 
goes, he has not made this point clear to me. 
May I venture also to suggest that perhaps another danger 
surrounds biology, and especially botany—the danger of becom- 
ing too fechnical and too academic? Now that perfect instru- 
ments, immense collections, and a long technical training are 
neces ary in order to do anything in biology by the regular road, 
does not the science run just a littlerisk of falling into a groove? 
And is it not well from this point of view that there should be 
an outside body of amateurs, who will take occasionally a fresh 
non professional view of the subject, handling their own 
problems in their own way, and publishing their own little 
guesses or glimpses for what they may be worth? No doubt 
they will often go demonstrably wrong ; no doubt the masters 
of the science will usually find numerous blunders of detail in 
their work, and may often see reason to disagree with them alto- 
gether ; and in that case the amateurs ouzht to receive their 
corrections with all humility; but is it not a healthy thing after 
all that the amzteurs should do their best, and try to follow out 
their own lizhts to their own conclusions ? GRANT ALLEN 
Forms of Leaves 
You have recently inserted several letters from Mr, Grant 
Allen on the forms of leave, a question in which I have myself 
been working lately. Mr. Grant Allen’s letters open up a 
number of interesting questions, but for the moment I will only 
refer to his suggestion with reference to the reason why water 
plants so often have their leaves cut up into fine filaments. He 
tells us that this is because the proportion of carbonic acid held 
in solution by water is very small, and that therefore for this 
amount there is a great competition among the various aquatic 
plants. 
The question has already been asked on what grounds Mr. 
Allen makes this statement with reference to the proportionate 
amount of carbonic acid. Without entering on this point, I 
would, however, venture to suggest that the reason for this 
tendency in the leaves of water plants is mechanical rather than 
che nical. 
It is, of course, important for all leaves to present a large sur- 
face for the purposes of absorption with as little expenditure of 
material for purposes of support as possible. Now delicate fila- 
ments such as those of water plants present a very large area of 
surface in proportion to their mass. On the other hand, they 
are unsuited to terrestrial plants, because they are deficient in 
strength and unable to support themselves in air, Take, for 
instance, a handful of the submerged leaves of an aquatic 
ranunculus out of the water, and, as every one knows, the fila- 
ments collapse. This seems to me the real reason why this 
form of leaves is an advantage to water plants. It is perhaps 
for the same reason that low-growing herbs, which are thus pro- 
tected from the wind so often have much diyided leaves. 
April jJouHn Lusppock 
The Fohn 
May I be allowed the space of a few lines to point out a 
defect in the account of the Fohn, given by Mr. Scott in his 
recent work on ‘‘ Meteorology,” and quoted in the review of 
that work which appeared in NATURE, vol. xxvii. p. 575. 
This phenomenon has been fully and clearly explained by Dr. 
J. Hann in a paper entitled ‘‘ Kinfahrung in die Meteorologie 
der Alpen,” published under the auspices of the D. znd O. A/pen- 
verein. Mr. Scott’s account of the Fohn attributes rightly the 
dryness and the cooling of the wind at high altitudes to expan- 
sion ; but he appears to entirely overlook the heating effect due 
to condensation of moisture during the ascent of the wind, 
From observations made in Switzerland, where the Fohn is 
chiefly felt, Hann has established the following rule: the Fohn 
is as many half degrees C. warmer at any place in its de-cent, 
than it is at an equal altitude during its previous ascent on the 
other side, as the place is hundreds of metres below the mountain 
ridge. This he explains by the fact that compression during the 
descent of the Fohn reverses the loss of temperature due to rare- 
NATURE 
605 
faction during its previous ascent ; while the wind brings with 
it over the mountain ridge the heat gained by the liberation of 
latent heat in the condensation of moisture. This latter amounts 
at 15° C. to about half a degree C. foreach ascent of 100 metres 
for saturated air. ‘* Therein,” says Hann, “‘lies the explanation 
of the heat of the Fohn.” A. IRVING 
Wellington College, Berks, April 21 
The Zodiacal Light (?) 
THE same ‘‘ peculiar appearance in the western sky ” as that 
described by your correspondent, ‘‘J. W. B.,” was observed 
here by me on the same evening, April 6. At 7h. om. G.M.T., 
or fifteen minutes after sunset, I noticed a bright, golden- 
coloured column of light, well defined, about 4° in length and 
slightly more than 1° in width, and inclined towards the south. 
“J. W. B.” says it ‘rose vertically from near the horizon” at 
his station, Bath. Here it was decidedly inclined to an angle of 
about 15° towards the south. At 7h. 20m. no traces of it were 
visible. 1 have not seen any similar appearance since. 
W. H. KoBiInson 
N.B.—In the observer’s book this observation is entered as 
“« Bright zodiacal light (?), seen at 7h. om.” E, J. STONE 
Radcliffe Observatory, Oxford, April 20 
REFERRING to the letter of your correspondent, ‘J. W. B.,” 
Bath, in your last issue (p. 580), allow me to say that this pecu- 
liar ray of brilliant light was seen here by myself and many 
other people at about 6.40 p.m. on Friday, April 6. The 
sunset was brilliant and cloudless, but from the horizon to about 
25° in height immediately above the spot where the sun had 
disappeared there appeared a ray of light of great beauty and 
extreme brilliancy ; its centre, a delicate rose colour, graduating 
to the edges into the purest gold. This single ray was perpen- 
dicular, and appeared to be little, if at all affected, in its bril- 
lianey by the approaching dusk of evening, but continued to 
exhibit itself with little-diminished brilliancy for nearly half an 
hour, finally disappearing with the twilight. 
ROBERT DWARRIS GIBNEY 
Glan-y-dwr, Crickhowell, South Wales, April 21 
WHAT your correspondent, ‘‘J. W. B.,” saw after sunset was 
not the zodiacal light, which is easily distinguishable by its great 
extent of area, lenticular shape, and invisibility during strong 
twilight, but it may be not incorrectly termed a sun column. I 
find the following entry in an old journal, of a similar appear- 
ance :—‘‘ 1868, April 17.—Sun column, continuing half an hour 
after sunset, which was perfectly bright, without clouds.” Per- 
haps some of your readers may be able to explain the cause 
of it. E, BRowN 
Further Barton, Cirencester, April 21 
THE phenomenon observed on the evening of Friday, the 6th 
inst., in Bath, by your correspondent J. W. B, (vol. xxvii. p. 
580) was seen at Dolgelly by the writer when on a tour through 
Wales. On his pointing it out to a companion and some of the 
townsfolk, all agreed it was quite unique in their experience. 
A bright, slender pillar of light, hazy toward the edges, rose 
majestically from the western horizon, in a cloudless sky, and so 
continued for about three-quarters of an hour after the sun had 
set. To one long habituated in meteorological observation it 
was of a character differing /ofo ca/o from the path of sunbeams 
through a cloud-rift, which is invariably divergent in appearance, 
as if from a focus. The ‘‘pillar” was uniform in width, per- 
fectly vertical, and straight, the centre lime alone brilliant. 
The height was, however, greater than your correspondent 
indicates. 
Having fortunately with me a pocket-compass, with plumb- 
bob for ‘‘dip” measurements, I determined (1) the light-pillar 
was exacily vertical ; (2) the height, which scarcely varied during 
visibility, was 20°, dying out faintly at that elevation; (3) the 
azimuth 25° north of west. By terrestrial bearings there was an 
appearance or a slight movement northward, but smallness of 
the compass dial (1 inch diameter) precluded any reliable 
angular determination of azimuthal change. 
Further, the evening was very cold, and a continuous easterly 
wind had during the day obscured the hills, which still showed 
many unmelted snowdrifts upon their summits and flanks. First 
observed at 7 p.m., the strange appearance faded out at 7.30 p.m. 
