248 
fortunately there are trees growing ata short distance 
from it, which would entirely check the free circulation of 
air about the instruments were the screen set up at the 
usual elevation of about 6 feet above the ground. 
Accordingly the window on the second story of the 
building was selected. It affords a free exposure to the 
north, but is at a level of 41 ft. above the ground, and 
about 87 feet above the sea level. 
This elevation will of course exert a considerable influ- 
ence on the thermometrical observations recorded. 
FALMOUTH.—The establishment of an observatory at 
this station was beset with considerable difficulties ; the 
building in which the Royal Cornwall Polytechnic 
Society holds its meetings was unsuited to the purposes 
of a meteorological station. Accordingly a tower was 
erected at the south-east corner of the bowling green, 
on the top of one of the hills on which the town is 
built. 
The anemograph is on the summit of the tower, well 
exposed on all sides; but from the fact that the ground 
in the neighbourhood is uneven, the hill sloping rapidly 
down to the harbour, it seems probable that the force 
of the wind is not quite true, especially when it is 
easterly. 
The position of the thermograph screen is far from 
being quite satisfactory ; however, a better exposure could 
not be obtained. The screen is attached to the north wall 
of the tower, at an elevation of 11 feet above the ground, 
and about 200 feet above sea level. 
It will be seen that there is the wall of a dwelling house 
at no great distance to the westward, which may possibly 
affect the instrument by radiation, and also interfere with 
the free circulation of the air, 
STONYHURST.—The observatory stands in the centre 
of the college garden, which is on a gentle slope facing 
S.S.E., 381 feet above sea level. The anemograph stands 
on a cylindrical roof 12 feet in diameter and 4 feet 5 inches 
in height. The total height of the cups above the ground 
is 30 feet. 
The country around, including the college grounds, is 
wooded, but not very thickly so, and the trees are in general 
smail, 
The nearest trees whose height could materially influence 
the anemograph are at a distance of about 200 yards, 
bearing from N. by W. to N. by E. 
The main building of the college is placed at the N.W. 
of the observatory, at a distance of 193 yards, its angular 
height above the roof of the observatory being 1° 37’,and 
bearings from N. by W. to W.N.W. 
The nearest hill is the Longridge Fell, whose nearest 
point is about two miles from the college. It extends 
from N. by W. to W. by N., and its highest point is 4° 1’. 
Pendle Hill is at five and a half miles distance E.N.E.; 
height 2° 5’. Between these hills the country is very open. 
To the eastward there are hills at about four miles distance, 
height about 1°. To the S. and S.W, the land is low. 
It will be seen from this that the anemograph is fairly 
well exposed to the different points of the compass. 
The thermograph screen is attached to the north wall 
of the observatory, the bulbs are at an elevation of 7 ft. 
above the ground. The exposure is good. 
Kew.—The observatory is situated in the old Deer 
Park at Richmond. It is a small building, which is well 
exposed to the wind, excepting on the west side, where 
there is a row of trees distant about 150 yards, which 
must materially affect the velocity of the wind. The 
country about is also well wooded. 
The anemograph is placed on the dome. . 
The thermograph screen is attached to the north wall 
of the observatory within ten feet of the west end of that 
wall, at a height of ten feet above the ground, and about 
fifty above sea level. Its exposure is good. 
We hope to take another opportunity of reviewing the 
volume itself. 
NATURE 


a” 
ON THE RECENT SOLAR ECLIPSE* 
(Continued from page 233) 
II.—PoLaRIscoPpic OBSERVATIONS 
V ITH regard to the polarisation experiments, by the kindness of 
Mr. Spottiswoode I am enabled to show you, in a very clear 
way, the raison a’étre of the polariscopic observations made during 
this and former eclipses; but the polariscopic ground is a wide 
one, and it is not my intention to cover it to-night. 
I have had this arrangement of lamp, reflector and prisms made 
so that you may see how the polariscope can determine the per- 
centage of reflected light at different angles, and the direction ot 
reflection. Assume this lamp to represent the sun, let this re- 
flector clese to the lamp represent a particle near the sun, reflect- 
ing light to us, we shall naturally have the light reflected at a 
much larger angle than if the reflector were close to the screen 
representing a particle in our own air. Having this idea of the 
angle of reflection in your minds, and the fact that the larger the 
angle under these conditions the more the polarisation, if you take 
this lamp, as I have said, to represent the sun, and this mirror 
to represent any particle, of whatever kind you choose toimagine, 
it is clear that in order to get the maximum polariscopic effect 
from that particle, you must have it so situated that it will reflect 
light at a considerable angle to the beam coming from this lamp. 
Now it is clear that in order to polarise the beam most strongly, 
I must place the reflector close to our imaginary sun. If I so 
place it as to represent a particle in our own atmosphere, the 
angle will be so small that the polarisation of the light will hardly 
be perceptible. 
Here is our sunlight, which we will polarise at as great an 
angle as we can, by placing the reflector close to the imaginary 
sun, and send it through this magnificent prism which Mr, 
Spottiswoode has been good enough to place at our disposal ; 
and in the path of the beam I will place an object so that you 
determine whether there is polarised light. [Experiment.] You 
see there is considerable brilliancy in those colours; their 
brilliancy depending upon the amount of polarisation. 
Now if, instead of having our reflector close to our imaginary 
sun to represent a particle in the sun’s atmosphere, we place it 
near the screen to represent a particle in our own, in which case 
the angle is extremely small, the brilliancy of the colours will 
entirely disappear. You see it has disappeared. The colours, 
as colours, are distinguishable, but their brilliancy has gone. 
That is the rationale of the polariscopic observations, which 
have been made on the occasion of the last eclipse with more 
elaboration than they ever were before. If we found the corona 
to be strongly polarised, this was held to be a great argument in 
favour of the corona being a real solar appendage, an argument 
strengthened if the polarisation was also found to be radial. At 
present, however, a great many of the observations that have 
been made have not been received, and those that have been re- 
ceived are as discordant as those obtained in former eclipses, and 
therefore my account is an imperfect one, because I have 
not had an opportunity of discussing all these observations, 
Indeed, if I had, I should hesitate to give an opinion: on the sub- 
ject. When Mr. Carrington saw that small corona in 1851, and 
Mr. Gillis saw that small corona in 1855, neither of them traced 
any polarisation whatever ; but when M. Liais saw that large 
corona in 1868, which was invisible to Mr. Gillis, he in his turn 
saw an immense amount of polarisation, which led him to believe 
that the corona was solar, the whole of it, rays and everything 
included, and that we had an indication of a solar atmosphere 
two or three times higher than the diameter of the sun ; that is, 
an atmosphere two or three millions of miles in height. This 
observation is not in accordance with the general conclusions 
from the drawings I have shown you ; and let me add that the 
assumption of reflection at the sun is not without its difficulties, 
and that we have not yet traced reflected sunlight, even when the 
strongest polariscopic effects have been observed. 
TII.—Atry’s AND MADLER’S CONCLUSIONS AS THE RESULTS 
OF THE PRE-SPECTROSCOPIC OBSERVATIONS 
Before passing to the spectroscopic observations, I will state the 
conclusions at which the Astronomer Royal and M. Madler 
arrived after the observations of 1860 had been gathered together. 
The Astronomer Royal, in a lecture delivered before the 
British Association at Manchester in 1861, stated that the assump- 
tion of an atmosphere extending to the moon explained the ob- 
servation of Plantamour, which could, he thought, be explained 
* Lecture delivered at the Royal Institution, Friday, March 17, 1871. 
LYauly 27, 1870 




