Aug. 31, 1871] 

NATURE 
347 

85th and rosth, and finally that between the 115th and 14oth 
degrees. But the intensity of colour must vary inversely to the | 
breadth of the stripes, and the three stripes left between the red | 
ones be filled with a pretty vivid blue. This hemisphere | 
placed upon a table with its southern pole pointing towards | 
sunset will atford a tolerable portrait of the aspect of the sky as | 
it appeared immediately after sunset, and continued unchanged | 
for more than a quarter of an hour. Thestripes were not visible | 
near the horizon, but were very distinct at an altitude of about | 
fifteen degrees, and almost disappeared about the zenith. No 
cloud was seen during the occurrence of the phenomenon. 
These stripes were certainly parallel in reality, and their ap- 
parent divergence may be accounted for by perspective. The 
reddish stripes may owe their colour to sunlight reflected back 
from the particles scattered in the atmosphere. But why did 
the celestial vault show so distinct a blue colour in the inter- 
vening bands? Yet, ‘probably, this phenomenon is more easily to 
be explained than the infinite variation of evening colourings that 
want a valid explanation to this day. 
Magdeburg, August 19 
A. SPRUNG 

THE AURORA 
eS was a very fine display of aurora here on the 
night of the 21st. It commenced to be visible 
about 9.30 P.M., reached its maximum about 11, and faded 
suddenly away about 11.30, In appearance it was of a 
| and lost themselves in sheets of white light. 
silvery white, without a trace of that rose colour which 
characterised the three great displays of last autumn, 
The main portion of the light was in the north-western 
quarter of the heavens, and it was sufficiently strong to 
see large print by. Extending from the north-west and 
reaching the north-eastern horizon arose three luminous 
arches concentric with each other, the 1st about nis 
altitude, the 2nd about 25° altitude, and the 3rd about 
40° altitude. These were connected by radial tongues of 
light which were ever changing their height. There was 
another marked and isolated nucleus about and around 
a Lyre. 
At about 10.45 P.M. there were most curious rays shot 
| up from the arches in the north, and concentric with them 
These shooting arches, if 1 may call them so, had at the 
horizon an apparent angle of about 150° to 180", but as 
they approached the nucleus in Lyra, they contracted 
On applying 
the spectroscope I found one bright line visible all over 
| the heavens excepting on the south horizon for an altitude 
apa 
of about 25°. ‘The spectrum obtained on the north-west 
gave five bright lines, of which I send a drawing. 
From want of convenient measuring apparatus I had 
resource to the method of superposed spectra. The light 
I chose for comparison was that of a tallow candle, from 
which I got the bright lines of sodium and carburetted 

COMPARISON: SPECTRA OF SUN, AURORA, AND CANDLE 
Sun Z 
CANDLE. . . 
AURORA, . 
hydrogen. The instrument I used was one of Browning’s 
direct vision spectroscopes—an instrument that gives 
the best results with the minimum amount of light. Of 
the bright lines, two were strong, one was medium, two 
were very faint. In the accompanying map I have put 
the solar spectrum at the top and carried the chief lines 
down for comparison, In putting numbers to the lines I 
have been directed by their degrees of intensity. 
No. 1 is a sharp, well-formed line, visible with a very 
narrow slit. 
No. 2. A line very slightly more refrangible than F. 
The side towards D is sharp and well-defined, while on 
the other side it is nebulous. 
No. 3. Slightly less refrangible than G, is a broad ill- 
defined band only seen with a wide slit. 
No. 4. Aline near E, woolly at the edges, but rather | 
sharp in the centre. This should be at or near the | 
position of the line 1474 of the solar corona, 
No. 5. A faint band coincident with 4, extending 
equally on both sides of it. 
The barometer stood at 29'574 in. ; the thermometer at 
613. A gentle wind was blowing from the south-west, 
and the sky was free from clouds. 
Observatory, Dun Echt, Aberdeen 

LINDSAY 
FRUIT CLASSIFICATION * 
D® DICKSON referred to the confessedly unsatisfactory 
state of fruit-classification, and to the very unnecessary ex- 
tent of the existing terminology, which is further complicated by 
a considerable amount of variance among botanists as to the pre- 
cise application of several of the terms employed. He was of 
the opinion, which he believed to be a growing one among 
botanists, that the most convenient method of classification was, 
in the first place, rigorously to restrict the definition of a “ fruit ” 
to the mature or ripe pistil, excluding from that definition the 
modifications of accessory parts or organs, which, in many cases, 
are correlative therewith ; and, secondly, to base the primary 
classification upon the general character of the modification un- 
dergone by the parts of the pistil in ripening, treating as of minor 
importance the characters involved in the description of the 
flower, such as the superior or inferior position of the ovary, &c. 
The classification which Dr. Dickson suggests for the con- 
sideration of botanists approaches most nearly to that indicated 
by Schacht in his ‘‘ Grundriss,” of which, indeed, it may be 
viewed as a modification and expansion. Schacht grouped fruits 
under three heads— (1) Capsular fruits which dehisce to allow 
the seeds to escape ; (2) splitting fruits or Schizocarps, which 
Dickson, M.D., 
Read before the 
* “Suggestions on Fruit Classification. By Alex. 
Regius Professor of Botany in the University of Glasgow, 
British Association, 1871. 
