30 
NATURE 
| NOVEMBER 12, 1903 
the centre indicated by four photographic determinations 
of the radiant, the relative places being :— 
Radiant Point 
. From eye observations one 149°-7+22°-7 
From photographic trails 151°-5+22°-2. 
Though there are now some hundreds of eye-estimated 
radiant points of this shower available for comparison, the 
resulting average place is not likely to be as accurate as 
the few positions obtained by photography. But even the 
centres derived from the latter method do not exhibit abso- 
lute agreement, the difference amounting to more than one 
degree in two of the cases. 
It is hoped that the shower will be specially looked for 
on the mornings of November 15 and 16 if the atmosphere 
is favourable. W. F. DENNING. 
Leaf Decay and Autumn Tints. 
Tue leaves of our forest trees at the period of the 
autumnal fall are not similar as respects the condition of 
vitality which they then have reached; that is to say, while 
some still retain their green colour and drop off, as it were, 
mechanically, the majority exhibit a change of coloration 
and are apparently dead or more or less decayed. The 
relation between these stages of vitality or decay and that of 
the particular colour (red, yellow, or brown) which the 
autumn leaves assume may be so far demonstrated by a 
critical scrutiny of certain constituents of the mineral 
matters (ash), especially the silica and lime, which they 
enclose at the very moment when this special and character- 
istic colour is displayed. In order to present to view this 
order of thought, the following tables of ash analyses are 
drawn up, the percentages being calculated on the red, 
yellow, or brown leaves with their petioles dried at 100° C., 
and on the ash minus charcoal :— 
Leaves which become Red in Autumn. 
| Constituents of the ash 
Percentage | 
of ash 7 
SiO. CaO 
| | 
Norway Maple ... ... «.. 10°5 So7a mah aaa 
Wild Cherry soe boo. 5 3 323i. fl 3533 
Rowan ty <cbeett sce ceseallesse | 2070 3°4 41 4 
Scarlet Oak ( Quercets coccinea) 48 3 51 
Dogwood! %,) 2.0 tev see 113 9°3 45°5 
IGE sce cea Aca son 13°7 4°5 29°9 
Leaves which become Yellow or Brown in Autumn. 
Constituents of the ash. 
Percentage 
of ash 
SiO, CaO 
Wych Elm .., son OC 16'8 28°8 40°8 
SV CAMOXE! | feecteia-ti eset eat I2'1 20°7 41°9 
Oak (Quercus robur) .. 6°35 13 44 
Beech Boot anrs PCtO bk AO 63 23 326 
ILEHe aod Ado @ dod) coo) tec 4°6 19°4 27 
Weeping Willow... ...  ... 10°3 10'9 37°5 
Poplar dda a Gen coe 97 23 352 
Fiormbeamy cee erg ras, lene 12'5 42°2 24°4 
Linden ... 89 22'2 35 
Assuming that a heavy ratio of total ash and of silica 
therein is an indication that the life of the leaf is practically 
exhausted and its physiological energy at an end, we may, 
in view of the foregoing tables, consider two cases :—(1) 
where the percentage of silica is under 10 per cent., and 
(2) where the percentage of silica is 10 per cent. or 
more. It will be at once observed that every one of the 
leaves which turn red in autumn belong to the former 
category, while all those exhibiting yellow or brown tints 
and shades belong to the latter. This state of affairs would 
seem to hold good universally, provided only that the other 
conditions of the phenomena are equal. Hence a few other 
examples, such as the birch, the leaf of which, generally 
NO. 1776, VOL. 69] 
yellow, is occasionally dashed with red, or the ash-tree, the 
leaf of which has a small percentage of silica but a high 
percentage of ash, are omitted from the lists. Once upon 
a time I found some hazel leaves, which were almost as red 
as those of a wild cherry, to contain only about 9 per cent. 
of silica in the ash (whereas, according to De Saussure, it 
holds even as early as September 20, 22 per cent. silica). 
With regard to the exceptional instance of the yellow and — 
never red ash-tree leaf, every plant analyst is aware how 
prone its tannic chromogen is to be, in certain circum- 
stances, the precursor of a very dark brown shade, such 
as no other tree of our woodlands (except, perhaps, the 
holly) ever approaches. Eminently interesting and instruc- 
tive is the contrast shown in the tables between the two 
maples as well as between the scarlet oak (Quercus 
coccinea), the magnificently tinted denizen of the American 
forest, and our own British oak (Q. robur), yellow and 
russet in autumn. It is known that the leaves of American 
maples, &c., cultivated in Europe do not exhibit such 
marked changes of colour, i.e. to rich deep scarlet, orange 
scarlet, deep rich purple, rich orange, dark crimson, &c., 
as they do in their own country. The causes of this differ- 
ence are now pretty much made manifest. The soft, mild 
and yet glowing climatic conditions of the American wood- 
lands sustain the vitality of the deciduous leaf to a degree 
not possible with us; we are rarely blessed with an Indian 
summer in the fall. The mineral matters flowing to the 
dying leaf flow in a quantity directly proportionate to the 
decay of its vitality. There is a drainage of substances 
(especially of silica) from the living portions of the arboreal 
organism to the dead and dying parts thereof. In such of 
our leaves as can resist the rigorous climatic severity, 
their vitality is so far sustained that the normal process of 
de-assimilation (the development of coloured pigment from 
tannic chromogen) is not impeded, though never so com- 
plete and splendid as in the glorious forests of New England. 
Patterdale, Westmorland. P. Q. KEEGAN. 
Variation of Atmospheric Absorption, 
Wirtn regard to Prof. Langley’s letter on the abnormal 
atmospheric absorption (p. 5) some observations of a 
different nature may be of interest. 
Both this year and last I was photographing in Switzer- 
land, using a Wynne meter for timing my exposures. In 
1902 I found that the time required to darken the sensitive 
paper on a sunny day, at an elevation of 11,000 feet, was 
one second. This year the time, under exactly similar con- 
ditions, and using the same batch of paper, was three 
seconds. That the difference was not due to the paper 
being stale is shown by the negatives being equally good 
in the two cases. 
The maximum sensitiveness of the paper is for blue light ; 
yellow and orange do not affect it; it was exposed under 
a glass plate about 3 mm. thick. J. Tavsor. 
Harrow-on-the-Hill, November 7. 
Rocket Lightning. ; 
Mr. J. Ewen Davinson (98 Banbury Road, Oxford) ha 
directed my attention to his letter in Nature, vol. xlvii. 
p- 582, describing auroral appearances associated with a 
thunderstorm witnessed by him in Queensland, of which he 
was reminded by the letters headed *‘ Rocket Lightning ”’ in 
your issue of October 22, p. 599. Comparison of the two 
accounts is interesting, but the phenomena appear to me 
not to have been identical. Mr. Davidson says what 
struck him most in the recent account was the description 
of a misty cloud above the low bank of thick cloud. In his 
own case there was a very thin misty condensation over the 
thunderstorm, extending to an altitude of 40° or 45°, and 
‘* the rosy light phenomenon and the streamers only shot up 
to the upper edge of this misty condensation.’’ He says, 
‘“T did not mention the misty condensation in my letter to 
Nature, as I did not then connect the two, but thought it 
was a mere coincidence, the one slightly veiling the other ; 
but that there is a connection is now evident.’’ ‘‘ Both 
observers were practically looking upon the upper edge of 
a thunderstorm at a distance, and in both cases there was 
the misty appearance above it, with the comparatively slow 
upward moving light phenomena.”’ J. D. Everett. 
11 Leopold Road, Ealing, W., October 29. 
e 
