Page 365

IAA TURE
              "Chameleon Barometer"
 IN my first communication (vol. xi. p. 307) upon this subject, I
stated that the actual temperature had apparently no effect upon
the colour of the paper. Since then I have had reason to change
my opinion. During the late severe weather I have had better
opportunities of studying the behaviour during frost, and I have
observed that though in summer the paper will remain red for a
difference of 3' between the thermometers, in very cold weather
it is only red when that difference falls to o', or perhaps .50.
This seems to agree with the fact that cold air cannot dissolve so
much aqueous vapour as warm air.     A. PERCY SMITH
  Rugby, March 6
        OUR ASTRONOMICAL COLUNAI
  TOTAL SOLAR ECLIPSE OF 878, OCTOBER 29.-In a
communication to the Times in August 1872, this eclipse,
in the days of King Alfred, was pointed out by the Rev.
S. J. Johnson, of Upton Helions, Devon, as having been
probably total in London. In the Saxon Chronicle it is
merely stated that " the sun was eclipsed one hour of the
day," without reference to any phenomena of totality ; the
Clironicon Scotorum records "a dark noon;" in the
Annales 1-uldenses we read: "Sol quoque in 4 Kal.
Novembris post horam  nonam  ita obscuratus est per
dimidiam horam, ut stella in ceelo apparent et omne-
noctem sibi imminere putarent." This night-like appears
ance of nature clearly indicates that the eclipse was total
at Fulda (Hesse-Cassel), and if our calculations assign
elements for the eclipse, which show totality at this spot,
it may fairly be assumed that they will give very nearly
the true phase for London. Correcting the arguments of
Damoiseau's Lunar Tables of 1824, so as to bring them
into agreement with Hansen for moon and Le Verrier for
sun, and taking the minor equations from the Tables, we
find the following elements for 878, Oct. 29:-
  Conjunction in R.A., oh. 5 tIM. 24S. M. T. at Greenwich.
    R.A.   ................. 218 6 10
Moon's hourly motion in R.A  ..      37 25
Sun's        ,,        ,,                2 29
Moon's Declination  ... ... ... ... 14 6 44
Sun's             , ... ... ... ... 15 4 40
Moon's hourly motion in Dec] .I... ...  8 25
Sun's                                    0......     48
Moon's horizontal parallax  ... ..   60 35
Sun's      ,,       ,,                   0......     9
Mocn's true semi-diameter  .. ..     i6 31
Sun's      ,,       ,,       ... ...    x6 12
S.
S.
S.
S.
  Assuming the position of Fulda to be in longitude
oh. 38m. 415. E., and latitude 500 33'7, we find by direct
calculation from the above elements a total eclipse,
totality commencing at 2h. 9m. 32S. local mean time, and
continuing Im. 415. with the sun at an altitude of 190.
The partial phase began at oh. 56m. and ended at
3b. 24m. The Fulda annalist has "post horam nonam"
for the time of the eclipse, but the times we have found
cannot be very much in error. The sun rose at Fulda on
this day at 7h. 12m. apparent time, or at 6h. 57m. mean
time, so that the ninth hour from sunrise would be 4 P.M.
To reconcile this difference, Dr. Hartwig, of Leipsic (who
calculated the eclipse in 1853 from the best data then avail-
able, without finding it quite total at Fulda), conjectured
that the author of the Chronicle might have reckoned his
time from the commencement of twilight at the beginning
of the month. However this may be, our elements, which
may be cxpected to be pretty near the truth, have indi.
cated a vexy measurable duration of totality at Fulda.
Calculatirg now for London (St. Paul's), we again find a
total eclipse commencing at ib. 16m. 20S. mean time, and
ending at ih. i~m. ios., cr with a duration of im. 50s.
If any reader should have the curiosity to examine the
track of totality further, the following folmule will assist
365
him. Putting I for the geocentric latitude of place, and
L for its longitude from Greenwich, reckoned positive
eastward, t for Greenwich mean time-
COsjm= x36'55co - [2W3760] sin. 1+ [270924] cos. ?, cos.(L + x55'31'7)
_ 1-1. 17m. I5S. F [1'76o81] sin. w - [3-32433] sfl. I
               -[391281] cos. /, cos. (L + log lo04)
Upper sign for beginning of totality, lower one for ending;
the quantities within the brackets are logarithms.
  The Rev. S. J. Johnson found no other total eclipse in
London during the long interval from 878 to 1715, and
we are able to confirm his inference that there is not
likely to be another one visible in the metropolis for five
hundred years from the present time. Less than seven
years after the eclipse of 878, or on June i6, 885, a very
great eclipse passed over Scotland and Ireland. By a
similar accurate computation to that detailed above, it is
found to have been total not far from Nairn, and the
duration of totality was little less than five minutes, a
most unusual length for so high a latitude. In Chronicon
Scotoztemn we read, " The stars were seen in heavens."
  ENCKE'S COMET.-The ephemeris of this comet for the
present appearance, communicated by Dr. von Asten, of
Pulkova, to the St. Petersburg Academy, not having been
yet transferred to the Astronoznische Nachriclhten, where
such matters are commonly looked for, we continue our
reduction of the places to 8 P.M. Greenwich time for the
period when the comet is likely to be most easily found
in these latitudes:-
                  R.A.      N. P.D.   DISTANCE
                h. n. 0.              from Earth.
    March 20    1 19 27     75 0 0     1 433
          22    1 25 58    74 32-8
       ,, 24    1 32 43     74 6-7     1350
       ,, 26    1 39 41     73 423
          28    1 46 50    73 204      I-258
       ,30     1 54 8      73 2-1
    April i    2 1 28      72 40-8     I-156
       ,,  3    2 842       72 424
       ,,  5    2 15 37     72 45-3    1-042
       ,,  7    2 2153      73 0o5
           9    2 27 1      73 319     o-9i8
The distance from the earth is expressed, as usual, in
parts of the earth's mean distance from the sun.
  VARIABLE STARs.--Next week we shall give the times
of maxima and minima of the better known variable stars
for two or three months in advance, calculated from the
elements in Prof. Schbnfeld's last catalogue. It does not
appear that an ephemeris for 1875 has been circulated as
in several previous years.
THE FREANCH TRANSIT EXPEDITION TO
                NEW CA LEDONVIA
W     E have received the following interesting communi-
       cation from a correspondent:-
  The French Transit of Venus Expedition to New
Caledonia was the result of an after-thought on the part
of the French Academy, which only took a definite form
in the shape of active preparations for the great event in
May last, months, if not years, after the other stations
had been fixed on and the construction of the necessary
instruments commenced. The New Caledonian ob-
servers were consequently at a great disadvantage, being
obliged to complete all their arrangements within the
short space of ten weeks, and to start for this Ultinza
Tihule of civilisation in the middle of July. Everything,
however, was got in readiness at home with so much care
and despatch that nothing of the slightest importance,
either in the astronomical or photographic department of
the expedition, has been found wanting. The observatory
has been fitted up and the observations made with as
much completeness as if the centre of France, and not a
convict settlement at the very opposite extremity of the
March i r, 1 875]
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