126 
NATURE 
[Dec 15, 1870 

a mistake in stating the relation of Momentum to Energy or ws 
viva, and will endeavour to rectify it. 
In quoting a dictum of the late Dr. Boole, Prof. Tait styles 
him the greatest logician the world has produced, or is likely to 
produce, for many a long day. In dissenting from this super- 
lative, I do not refer to the men most widely known in recent 
years as logicians—Whately, Hamilton, Mill, Mansel ; I con- 
sider that the comparison of them with Boole fails through the 
dissimilarity of the matters compared ; his Logic was but to a 
very small extent the Logic of any one of these writers. 
only person who cultivated Logic in the manner of Boole was 
another noted mathematician, the veteran De Morgan. 
without undertaking to say which of these two had the greater 
genius, I donot scruple to affirm that the labours of De Morgan, 
in their common department, if only through longer continuance | 
in time, resulted in a much larger number of contributions to the 
science than can be credited to Boole. The two men were 
friendly co-operators, not rivals; and they will, I have no 
doubt, be mentioned together as often as reference is made to the 
Algebraic extensions of Formal Logic. 
Aberdeen, Dec. 9 A. BAIN 

The Spectrum of the Aurora 
THE brilliant displays of the Aurora Borealis observed in 
England on the 24th of September and the 14th of October, 
1870,* were also generally observed in this country. The fact 
may be worthy of record in your journal, as indicating the un- 
usual extent of the phenomena. As the newspapers in different 
parts of the United States contained full descriptions of these 
displays, a detailed account need not here be given, I may re- 
mark, however, that they were generally regarded as the most 
brilliant displays we have had since 1859. Fine auroras were 
again witnessed on Monday morning, October 24th, from 5 to 
6.30 A.M., and on the evening of the same day, from 6 to II 
pM. At 9 P.M. (on the evening of the 24th) an auroral 
arch passed very nearly through the zenith from the eastern to 
the western horizon, or rather from a point a few degrees south 
of east, to another somewhat north of west. An extraordinary 
number of more feeble auroras have been noticed during the last 
two months. DANIEL KIRKWOOD 
Bloomington, Indiana, Nov. 9 
Can Aurora be Seen in Daylight? 
I VENTURE to believe of, in spite of circumstantial accounts 
to the contrary, and I ground my belief on the following consi- 
derations :—1. No description of a daylight aurora that I have 
ever seen will beara critical examination. Take that published 
in the last number of NATURE. Here two arcs of faint white 
lines are said to have been seen in a direction ‘‘almost due east,” 
and certainly the illustration given is not very unlike the appear- 
ance that auroral arcs sometimes present. But auroral arcs, so 
far as I know, never appear in the east, and the conclusion, 
therefore, is unavoidable that the object observed was nothing 
more than a remarkably symmetrical form of cirrus cloud. In 
another instance, lately published, although the thing described 
is called a daylight aurora, I fail to see in the description anything 
more than an account of the appearances presented when a high 
canopy of cloud clears off bodily from the sky with a sharp, 
straight edge, which by perspective becomes anarch. In the 
case referred to, the clouds clearing off from the direction of 
magnetic north, the arch corresponded in position with that of 
an aurora, and hence was set down as auroral. Ina third ac- 
count of a’ daylight aurora, it is expressly mentioned that the sky 
was hazy, and a solar halo visible, a condition of things which, 
while it would make the occurrence of aurora-like cirrus ex- 
tremely probable, would be specially unfavourable to the visi- 
bility of a true aurora ; for certainly if so delicate and phospho- 
rescent a light as that ofan aurora is to be seen at all in the day- 
time, it can only be under circumstances the most favourable as 
regards clearness of the lower atmosphere, 
2. A comparison of the auroral light with the light of other 
objects whose visibility can be more easily measured, tends 
strongly to confirm the view I have advanced. No one who re- 
members Donati’s comet at its brightest will hesitate to allow 
that for intrinsic brilliancy that object surpassed the most vivid 
aurora, Yet Donati’s comet at its brightest could not be detected 
* Nature, Nos. 49, 50, and 51. 
The | 
Now, | 



with the naked eye until about half an hour after sunset, and then 
only the head could be seen. 
3. The modifications of cirrus cloud are so infinitely diversified, 
and sometimes so very remarkable, as to offer a great temptation 
to the observer to invest them with the mysterious attributes of 
the aurora. Moreover, they do occasionally present a very 
striking resemblance to pencils of auroral light, differing, how- 
ever, essentially in the character of fixity which they possess, as 
well as in the absence of any determinate relation to the mag- 
netic pole or zenith. 
On the grounds now stated I venture to refer daylight auroras 
in general to the large class of ‘‘ errors of observation.” 
Clifton, Dec. 13 GEORGE F. BurbDErR, M.D. 
The North London Naturalists’ Club 
THE Secretary of the North London Naturalists’ Club desires 
the Editor of NATURE to correct an incorrect statement which 
appeared in the last number of that journal. The North London 
Naturalists’ Club is not broken up, it is not six years old, nor 
has it ever met on a Monday. Its last meeting was on Thursday, 
Nov. 24, at Myddelton Hall. Three subjects were then exhibited 
and explained, viz. ‘‘The Structure and Growth of the Yeast 
| Plant,” ‘* The Structure of the Gastric Teeth in the Lobster,” 
” 
and ‘The Anatomy of Amphioxus.” The meeting was thinly 
attended, but that is no alarming phenomenon for societies of 
this kind. The previous meeting on Oct. 27 was a very full one, 
owing to a paper read by a deservedly well-known member of 
the club on the highly interesting subject of ‘‘Spontaneous 
Generation.” It must be confessed that the club is not so 
vigorous as when first started, but these facts show that it is 
by no means defunct. J. SLADE, 
Hon. Sec. N.L.N.C. 
Browning’s Spectroscope 
In the last number of NATuRE there is a description by Prof. 
Young of a spectroscope, in which the prisms are made to alter 
their positions relatively to each other by bending backwards 
and forwards the metal work to which they are attached. I 
should of course not wish to offer any opinion on the efficiency 
or otherwise of this arrangement. 
My reason for writing is that in the course of the article Prof. 
Young goes out of his way to remark that, in attaching bars at 
right-angles to the bases of the prisms in my Automatic Spec- 
troscope, I have adopted a plan of Mr. Rutherford’s. Will 
you kindly permit me to state that I began my Automatic Spec- 
troscope in the year 1862, and that, so far as publication consists 
in exhibiting anything to a large number of persons, I had pub- 
lished it in the year 1863. I have reason to believe that M. 
Duboscq also attached bars in a similar manner to the bases of 
prisms with the intention of obtaining a minimum deviation 
adjustment, about the same time as myself, or soon afterwards. 
I do not know at what time Mr. Rutherford may have contrived 
his plan, but, as I have never read any description of his instru- 
ment, I must disavow having adopted any plan of his. At the 
same time I must remark that it is a small step towards obtaining 
the complicated movement required to produce an automatic 
minimum deviation adjustment, and it seems to me that itis a 
step every person would be likely to take who wished to obtain 
the adjustment by a mechanical motion. 
111, Minories, Dec. 12 JouNn BROWNING 

Evolution of Light 
Your correspondent, who describes in the number of NATURE 
of the 17th ult. a faint light observed by him on tearing strips 
from a woven fabric in the dark, may be interested to know that 
a similar phenomenon is noticed by Mr. Grove in his ‘* Correla- 
tion of Physical Forces,” as occurring with indiarubber water- 
proof cloth (4th ed. p. 48). 
Mr. Grove ranks it under phenomena of heat and light, rather 
than of electricity. Cy ee 

Fungi 
It is very unfair that the mushroom amily should lie under a 
ban, because Locusta, at the instigation of Agrippina, employed 

