March ii, 1875] 



NA TURE 



365 



■ Chameleon Barometer " 



In my first communication (vol. xi. p. 307) upon this subject, I 

 stated that the aclual lempcrature Iiad 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 belter 

 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 ihermometers, in very cold weather 

 it is only red when that difference falls to 0°, or perhaps ■5°. 

 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 COLUMN 



Total Solar Eclipse of 878, October 29.-111 a 

 communication to the Times in August 1872, tliis 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 

 Chronicon Scotoriim records " a dark noon ; " in the 

 Aniialcs Tiildciiscs we read : " Sol quoque in 4 Kal. 

 Novembris post horam nonam ita obscuratus est per 

 dimidiam horam, ut stellffi in ccelo 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. 51m. 24s. ivL T. at Greenwich. 



R.A 



Moon's hourly motion in R.A. 

 Sun's „ ,, 



Moon's Declination 



Sun's ,, 



Moon's hourly motion in Deck 

 Sun's ,, „ 



Moon's horizontal parallax 

 Sun's „ „ 



Mocn's true semi-diameter 

 Sun's „ ,, 



.. 218 6 10 

 37 25 

 2 29 

 .. 14 6 44 S. 

 .. 15 4 40 S- 

 8 25 S. 

 o 48 S. 

 60 35 

 o 9 

 16 31 

 16 12 



Assuming the position of Fulda to be in longitude 

 oh. 3Sm. 41 s. E., and latitude 50" 33"7, we find by direct 

 calculation from the above elements a total eclipse, 

 totality commencing at 2h. gm. 32s. local mean time, and 

 continuing im. 41s. with the sun at an altitude of 19'. 

 The partial phase began at oh. 56m. and ended at 

 3h. 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 1S53 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 

 lin-iC from the con.menctment of twilight at the beginning 

 of the month. However this may be, our elements, which 

 may be expected to be pretty near the truth, have indi- 

 cated a veiy measurable duration of totality at Fulda. 

 Calculating now for London (St. Paul's), we again find a 

 total eclipse commencing at ih. i6m. 20s. mean time, and 

 ending at ih. i8m. los., or with a duration of im. 50s. 

 If any reader should have the curiosity to examine the 

 track of totality further, the following foimulas will assist 



him. Putting / for the geocentric latitude of place, and 

 L for its longitude from Greenwich, reckoned positive 

 eastward, / for Greenwich mean time — 



Cos. 11'= 136-55^0 - [2137C0] sin. /+ [1-70924] COS. /, cos, (^ -|- 155" 31-7) 

 /=ih. 17111. 15s. T [1-76081] sin. ju - [3-32433] sin. / 



- [3 91281J COS. /, cos (L + 109° io'-4) 



Upper sign for beginning of totaiity, 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 171 5, 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 16, 885, a very 

 great echpse 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 Cliroiiicon 

 Scotorum 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 Astronomisclie Nachriclitcn, 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 : — 



N.P.D. 



DISTANCE 

 from Earth. 



I '433 



March 20 i 19 27 75 o-o 



,, 22 I 25 58 74 32-8 



„ 24 I 32 43 74 6-7 1-350 



„ 26 I 39 4t 73 423 



,, 28 I 46 50 73 204 1-258 



„ 30 I 54 8 73 2-1 



April I 2 I 28 ■ 72 4b -8 I -156 



1, 3 2 8 42 72 42-4 



„ S 2 IS 37 72 45-3 1-042 



■ ,72 21 S3 73 0-5 



,,9 2 27 I 73 31-9 0-918 



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. Schcinfeld's last catalogue. It does not 

 appear that an ephemeris for 1875 has been circulated as 

 in several previous years. 



THE FRENCH TRANSIT EXPEDITION TO 

 NEW CALEDONIA 



WE 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 fi.xed 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 Ultitna 

 Thiile 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 depaiiment 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 



