466 

NATURE 
[ Oct. 12, 1871 

glass. Any two of these form an opaque combination—that is 
to say, the first glass stops all the rays which could pass the 
second, and the second stops all that pass the first. Buta green 
and a blue glass do not form an opaque combination, but pass 
the green rays. If we place the red, the green, and the violet 
glasses in a row close to each other, with the green in the centre, 
place a piece of yellow glass so as to overlap the junction be- 
tween the red and green glasses, and a piece of blue glass to | 
overlap the junction between the green and violet glasses, and 
arrange the combination so that white light can pass through it, 
it will be seen that the yellow glass passes the red and green rays, 
and the blue glass passes the green and violet rays ; and that the 
only effect of the yellow and blue glasses is to deepen the colours 
when the light passes through them. 
Darrock, Falkirk, Sept. 23 JoHN AITKEN 
Anthropology and M. Comte 
PERHAPS you will allow me to state that your report of my 
paper ‘‘On the Anthropology of Auguste Comte,” read before 
the British Association at Edinburgh, is wreng in two essential 
particulars. First, I did #o/ attempt to ‘* expound the views of 
M. Comte according to the principles laid down by Mr. Darwin.” 
Comte’s views on man and his relation to the animal kingdom 
were published upwards of twenty years ago ; Mr. Darwin’s re- 
cently. Second, I did of ‘‘ maintain that Auguste Comte’s 
worship of humanity would be the great doctrine of the future.” 
I may, and do believe this, but I made no reference to it what- 
ever in the paper which you have so correctly mis-reported. 
The Positive religion was not the subject of discussion, and I 
limited myself to what my paper implied. J. KaINEs 
3, Osborne Road, Stroud Green Lane, N., Sept. 22 

A Plane’s —— ? 
would not the word asfect meet Mr. Wilson’s requirements? In 

reference to those important planes of every-day life, garden | 
walls or house fronts, its use is well established ; and there would 
be no violence to either custom or language in applying it to 
geometry. J. K. LauGuron 
[Another correspondent suggests the term “slope.” —Ep.} 
Meteorological Phenomenon 
AMONGST some old memoranda I find the following, which I 
copy verbatim :— JosEPH JOHN MURPHY 
Old Forge, Dunmurry, Co. Antrim, Sept. 18 
“Monkstown, near Dublin, about 3.10 P.M. 25th of July, 
1858, saw, about opposite the sun, an appearance like 
the rainbow, but horizontal, and extending along a few 
degrees of the horizon. The red was above the sea- 
horizon, and the green below. I could not make out beyond 
the green, but this might be because the blue was blended with 
the colour of the sea. As I did not see it commence, I cannot 
say how long it lasted. It faded gradually but rapidly, without 
any other change in the sky that I saw. The day was alternate 
sunshine and heavy showers ; the sun was shining at the time. 
«*This note has been made within half an hour after its disap- 
pearance.” 
Lunar Rainbow 
It seems probable, froma discussion of former observations, 
that the polarisation of the sky is altogether changed during 
totality, and that instead of being radial to the sun as at other 
times, its plane is perpendicular, or nearly perpendicular, to the 
horizon. This appears at all events to be the case overa very 
large area about the eclipsed sun. = 
In passing along a parellel to the horizon through the sun’s 
centre, we should expect to find, at some little distance fiom the 
limb, the pure atmospheric polarisation unaffected by any com- 
ponent due to the corona. 
At such a point an observer using a Savart might therefore 
expect to find the bands disappear at an angle of 45° to the 
horizon. Having carefully turned out all trace of the bands upon 
the centre of his field, let him now pass onward towards the sun’s 
limb (directing his attention all the time to the centre of his field 
only), whenhe there perceives the firsttraceof bands. He will know 
that the plane of polarisation has changed. If, on going bick- 
wards, the bands disappear again, while in passing onwards they 
continue to increase, he will know that that change is due to a 
component introduced by the corona; and he will be able to 
estimate the distance from the moon’s limb at which such a com- 
ponent first became visible. 
I feel disposed to think that by this method he will be able to 
trace the corona further than he could by the unaided eye ; forit 
will be somewhat equivalent to making the corona shine upon “a 
perfectly black back ground of sky ; and much more than equiva- 
lent to accomplishing this with a Nicol only, for the Savart will 
detect less than one-eighth of the polarisation detectable by the 
Nicol. 
The visible outer border of the corona is where our eye first 
distinguishes a difference between 
The light of the sky 
an 
The light of the sky + the light of the corona, 
Ir is perhaps answering somewhat at cross purposes, but | while by this method the visible outer edge of the corona will 
r ‘ ‘ 
be where we first distinguish a difference between an area of no 
polarisation and polarisation due to the corona. 
In using a Savart with a large field, the central portion of the 
field might well be marked by fixing in the common focus of the 
telescope a plate of glass with a small circle etched upon it corre- 
| sponding say to 8’ or 10’ of diameter in the field of view. 
A very perfect lunar rainbow was seen here last night. I | 
noticed it first at 9.42. At that time the northern portion of it only 
was visible, but its intensity steadily increased, and by 9.45 the 
there was a peculiar glare, extending upwards about 20°, the 
apex of the arch being remarkably clear and well-defined. The 
rainbow faded away as rapidly as ithad been developed, and at 
about 9.50 had entirely disappeared, At the time of the occur- 
rence the western portion of the heavens was very clear, and 
the moon about 8° above the horizon. Temperature cold, with 
a biting wind from W.S. W. R. 
Hinderton, Neston, Cheshire, Sept. 23 

The Corona 
May I suggest a method of observation which would possibly 
be a more delicate test than that which our own sight affords for 
ascertaining the outer limits of the corona? 
arch was complete. Both at the northern and southern extremities | quarter of an hour on an endless roll of paper. 
A, C, RANYARD 

A Rare Moth hI 
A FINE specimen of the rare moth Deiofeia pulchella (crimson 
speckled footman) was captured by R. Beck on the Moors near 
Scarborough on the 11th inst. Could any of the readers of 
NATURE inform me whether it has eyer been taken so far north 
before ? W. E. WALLER 
Oliver’s Mount School, Scarborough, Sept. 22 
Meteorology in America 
Tue writer of the article on this subject may be interested in 
hearing that a meteorograph, similar in some respects to that 
invented by Prof. Hough, was sent to the International Exhi- 
bition just closed in London, It was invented and constructed 
in Sweden, and one similar is said to have been performing satis- 
factorily for nearly three years. In the Swedish, as in the 
American instrument, the height of the mercury in the barometer, 
and the wet and dry thermometers, is felt by steel wires descend- 
ing the tubes ; but in the Swedish instrument the levers to which 
these wires are attached are acted on by very fine screws, the 
revolutions of which, translated by a series of wheels into the 
language of barometers and thermometers, are printed every 
The whole 
apparatus is set in motion bya galvanic battery, which even 
winds up the clock which regulates its own action. The 
barometer is tapped before it is registered, but there is no cor- 
rection for temperature. The price is 350/. 
The barometer invented by Prof. Wild seems to bear some 
resemblance to the barograph invented by Mr. King, and now 
used at the Liverpool Observatory. W. R. 
Ruined Cities of Central America 
In the summary of the proceedings of the late meeting of the 
British Association, in the issue of NATURE for August 31, 
is an abstract of a paper by Captain L. Brine, R.N., Ox the 
Ruined Cities of Central America. The gallant captain is wrong 
in stating that the existence of these ruined cities was unknown 


