Aug. 24, 1871 | 
NATORE 
339 

SOCIETIES AND ACADEMIES 
BENGAL 
Asiatic Society, June 7.—‘‘Memorandum on the Total 
Eclipse of December 11 and 12, 1871,” by Lieut.-Col. J. F. Ten- 
nant, R.E., F.R.S. In December of this year we havea Total 
Eclipse visible in Southern India. The duration is short, but in 
some respects the circumstances are very favourable, as the Line 
of central Eclipse passes over the Nilgherry Hills, where, I 
understand, fine weather may be confidentle,expected. In order 
1o be prepared, I have computed carefully the Central Line across 
India, and have added the extent to which errors of the Tabular 
place of the moon may be expected to shift it. I hope to have 
before the Eclipse a knowledge of what errors may be anticipated 
in the Tables, and thus be in a position to choose a central spot, 
if itis worth making a change. The figures, however, show that 
this is not probable, the principal result of an error in Right 
Ascension being to shift the centre of the shadow along its path, 
the deviation from which would be corrected by a small error in 
the declination which could hardly be foreseen. The duration of 
the Eclipse will be small. At the Nilgherries it will be about 
two minutes, but this cannot, so far as I know, be as yet ac- 
curately predicted, from uncertainty as to the real diameters of 
the sun and moon, when free from the enlargement by irradiation. 
If the value of the moon’s diameter deduced by Oudemans from 
Eclipses, be used with that of the sun obtained in the Greenwich 
Transit Circle, then I find the duration in the Nilgherries just two 
minutes. The dataofthe Nautical Almanac give two minutes 
seven seconds, and if I may judge from the result I got in 1868 
the real duration will fall between these. Shortas this time is, 
it is enough with an adequate preparation to produce some re- 
sults of value. It is long enough to allow photographs to be 
taken of the Corona, as to whose structure there is more to be 
discovered. ‘There seems now no sort of doubt that the Corona 
is not only asolar appendage, but is, as I stated in my report on 
the Eclipse of 1868, the comparatively cold atmosphere of the 
sun, This should be further spectroseypically examined. Ob- 
servers have differed about the number and position of the faint 
bright lines they have seen, but it does not seem that any one 
has connected the variations with the position of the part ex- 
amined. ‘To do this appears urgently necessary, and there have 
been additions made to the spectroscope which will allow more 
than one portion of the Corona to be examined, and its lines 
recorded during the short time it is visible. There is another 
subject, too, of spectroscopic examination. Kirchhoff, in his theory 
of the so'ar cons‘itution, supposed it surrounded by an extensive 
atmosphere consisting of metallic and other vapours, as well as 
gases, by the absorption of which the dark Fraunhofer lines were 
produced. It has long been clear that there was no such ex- 
tensive a'mosphere, and some physicists have been satisfied that 
there is none such. Mr, Lockyer and his collaborateurs, though 
they have detected a great number of bright lines at the bases 
of the prominences, have never approached, so far as I know, 
the number of even the conspicuous dark lines, whose 
origin has, therefore, not been satisfactorily made out. At 
the Eclipse of December 22, 1870, however, Prof, Young, at 
the moment of obscuration, and for one or two seconds later, 
saw, as far as he could judge, every atmospheric line reversed, 
and this was confirmed by Mr. Pye. I have but the scant in- 
formation of this po'nt given in the Royal Astronomical Society’s 
Council Report, but it is sufficient to show me why this has not 
been seen before by observers looking out for it, and also to make 
me feel the importance of verifying the observation. To under- 
stand why it has not been seen before, it must be considered that 
the image of a bright object in the focus of a telescope when re- 
lieved aga‘nst comparative darkness is enlarged by a phenomenon 
known as irradiation; the light encroaches on the darkness. 
The sun thus appears larger and the moon smaller than the 
real size. This continues till the real contact of the limbs in- 
ternally ; at this moment the thread of light, which previously 
had considerable width, appears suddenly broken and vanishes in 
a total eclipse ; while in the transit of a planet or annular eclipse 
there appears the ‘* black drop ” of the observers of the Transit 
of Venusin 1769. At page 16, vol. xxix, of the monthly notices 
of the Astronomical Society will be found some figures illus- 
trating this phenomenon in a planetary transit. When we are 
dealing with sothin a stratum surrounding the true photosphere, 
We cannot see it in sunshine, as it is lost in the irradiation (t way 
be partly visible in very large telescopes where the irradiation s 
very small), and we are very ap’ to lose it a th: moment when 
the sun disappears, for it is found only between the places where 

a moment before the sun and moon’s limb appeared, so that the 
observer following either of them might well miss it. In the 
search for and verification of this important observation, the 
duration of total phase can matter little. I have been in com- 
munication with the Home Secretary on the subject of obser- 
vations of this eclipse, and my views, I may say, have been most 
cordially receivd. Iam not yet in a position to submit a pro- 
position officially, but I have great hopes of being able to do so in 
a few days.* | may just mention that in plotting the shadow track 
on a map it is necessary to allow for the error of its zero of longi- 
tude, a precaution often forgotten. The longitudes of the G. T. 
Survey require a correction of 3’-2°7", and those of the Atlas of 
India one of 4’-11" to adjust them to the accepted longitude of 
Madras, 
The President was very glad to learn from Colonel Ten- 
nant that the Government is likely to sanction a scientific ex- 
pedition to the Nilgherries 01 the occasion of the total eclipse 
in December next. The objects to which Colonel Tennant pro- 
posed to direct observation were, he need hardly say, of very great 
scientific interest and importance. The spectroscop'c analysis of 
the Corona, so far as it had yet been, effected, hal been pro- 
ductive of no very certain results. The matter could not, how- 
ever, be in better hands than those of Colonel Tennant. He 
only wished to suggest that those members of the Society, who 
might have the requisite leisure and opportunity, should, even 
with the unaided eye, endeavour to observe as carefully as pos- 
sible the exact apparent shape and characteristics of the Corona. 
He believed that data of very considerable value might be thus 
obtained by persons who knew how to observe. Later in the 
evening Colonel Tennant kindly consented to draw up some 
short direct‘ons which might serve as a guiie to members of the 
Society who might visit localities of the total eclipse. 
Paris 
Academie des Sciences, Aug 7.—M. Faye in the chair. No- 
tice was given of the death o: M, Lecocq, a correspondent living in 
Clermont Ferrand, the author of valuable pamphlets and 
papers on the geo’ogy of Central France. M. Lecocq was, 
however, a very active and clever physici-t, and started many 
theories of his own. He wasa Professor in the University, and his 
loss will be very deeply felt by his friends. —Two different papers 
were sent describinga bolide which was seen on the 15thof August, 
and which is most extraordinary, as it was visible during twenty 
minutes by Marseilles observers. The course was most irregular 
and zig-zag. Leverrier supposed that two different bolides might 
have been seen at Marseilles and at the other stations, as the de- 
scriptions do not agree. The fact of remaining visible during so 
long a time at Marseilles is astonishing, and M. Leveriier is at a 
loss to account for it. The phenomenon will be more fully investi- 
gated. This is also the case with a paper sent by M. W. de Fon- 
vielle, describing the fall of a thunder-bolt on August 3, 3 19”, 
on the kitchen of a convent situated in Paris, at 250 yards from 
the National Observatory, where the astronomers felt a great 
shock. A gas-burner was lit under very curious circumstances. 
The explosion was very long and very strong, and it is supposed” 
the lightning was shaped like a sphere falling from the clouds. M. 
Dumas showed the interest of elucidating a phenomenon of so 
much importance for public safety, as ignition of gas may be the 
secret cause of many fires. The committee is composed of M. 
Dumas and M. Jamin, professor to the Sorbonne. Special 
experimeats and inquiries will be made at the expense of the 
Academy. M. Fonvielle will be an auxiliary member of the 
committee.—-M. Delaunay read a paper on the Observatory 
during his administrati n, and showing that observations of small 
planets will be made with greater zeal than on former years. —A 
letter was read from M. Angstrom, the Swedish physicist, main- 
taining that each gas has its own spectrum in spite of the 
differences exhibited by previous experiments. ‘lhe learned 
physicist shows that in each case where differences were found, it 
is pcssible to explain it by extraneous matters, mixed with the sab- 
stance submitted to the experiment. The importance of this memoir 
is obvious.—M. Bert, who was formerly the Prefect of the North 
during the investment of Paris, sent a paper on the death of 
fishes living in fresh water when immersed in sea water. These 
fishes are literally suffocated by a singular effect of desiccition, 
the exosmose is very active, principally when their skin is clothed 
with large scales. The phenomenon is quite extraordinary when 
observed on fioxs, which lose the greater part of their weight, 
and are almost as much dried up esif they had been salted ave. 
* This has since been done. 
