232 



NATURE 



\yuly 22, 1875 



If the instrument has been so used please to correct me. 



Otherwise permit me to say for myself, that being in Paris on 

 Wednesday July 7, when the great physical and astronomical 

 mathematician of the age, M. Leverrier, stood up in his place in 

 the Academy of Sciences to explain how it had come about that 

 the official predicter of the weather in the Obscrvatoire had 

 announced a fine dry period just before the destructive inunda- 

 tions in the South of France with all their train of frightful 

 national calamities began, — I paid attention to the conclusion of 

 his speech, which wound up with announcing " that all the bad 

 symptoms had now (July 7) passed away, that the barometer 

 was high in England, and that all the probabilities united 

 pointed to a fine time coming." 



Every day after that for a week the weather only became 

 worse and worse, darker and wetter, in the usually gay city 

 of Paris ; and then I transferred myself to London, and 

 was there on the 14th, 15th, and part of the i6th of July, a 

 witness to, if possible, still worse weather, growing darker and 

 wetter all the time. So much, then, for the failure of the ordi- 

 nary methods of prediction, even in able hands; and. let us 

 be lenient to them, for who would or could have expected such 

 deluges of rain with a high barometer, and in the month of 

 July? 



Now, however, comes an indication of where the spectroscope 

 seems capable of saying something meteorologically useful : for 

 in all that dark and wet weather in London a pocket spectro- 

 scope showed me from every part of the sky a broad dark band 

 on the less refrangible side of D, and partly in the place of it. 

 This band was so intense as to be the chief feature of the whole 

 spectrum; and though no doubt "telluric" in its origin, was 

 very different from the standard telluric effects seen at sunset in 

 ordinary weather. 



I feared at the time that this grandly dark spectral band might 

 be of base artificial origin, such as an absorption effect by London 

 smoke ; and when journeying northward by rail on July 16, it 

 was certainly charming to find that in proportion as we left 

 London the rain ceased, the dark spectral band decreased, the 

 clouds (amongst which, by the way, there M'ere some remarkable 

 counter-motions chiefly from north to south) diminished, and by 

 the time we reached York fine weather prevailed. The ground 

 there was dry, the rivers low, and the sky spectrum not only 

 presented no dull bands, but the true D line was seen exquisitely 

 fine and neat, as the thinnest imaginable spider-line in a tele- 

 scope's illuminated field : so thin, fine, and clear indeed, as to 

 offer a delight to the eye, such as none but an earnest spectro- 

 scopist can have any idea of. 



Thus far, it is true, we have only had oark nebulous bands in 

 place of fine sharp lines as accompaniments of rain, London rain 

 too, with a high and steady barometer in the pleasant month of 

 July. But mark, if you please, what follows. 



The morning of the 17th of July, in Edinburgh, was glorious 

 with pure blue sky, transparent atmosphere, delicious tempera- 

 ture, and light N.E. Wind. So, too, it continued all the day 

 through, to the delight of thousands upon thousands in the 

 streets. No smoke either was issuing from any of the factory 

 chimneys, for there was a half-holiday or something more, and 

 the usually working population was enjoying itself in the open 

 air. The only clouds were a few briUiant and picturesque cur- 

 rents along the northern horizon, giving something like Alpine 

 mountain snowy tops to the lovely undulations of the Scottish 

 hills. 



Simply beautiful were those bright cloud forms as an artistic 

 feature in the general landscape ; but in the spectroscope— why, 

 good gracious ! 1 could only say, what is the meaning of this ? 

 It was only a little pocket spectroscope, remember, without 

 scale, and with small dispersion ; but there was the D line ap- 

 pearing in seven times its usual strength, and with the London 

 smoky band, too, beginning on its less refrangible side. Of the 

 utterly abnormal intensification of D (or rather of some peculiar 

 telluric lines so very near D as not to be separable from it in so 

 small a spectroscope) in the light reflected from those clouds, 

 there could not be the slightest doubt ; for whenever the spectro- 

 scope was applied to a higher altitude than these clouds, there 

 was little or nothing of the kind ; only the usual Fraunhofer 

 lines, fine and clean as generally seen in fine weather. The 

 effect, too, was very different, both in spectrum place and distri- 

 bution, from what is characteristic of a low sun ; while the sun 

 was at the time not low, no sunset colouis had visibly begun, 

 the clouds which gave the black intensification of the D line 

 were almost absolutely white, and it was as yet only two o'clock 

 on a fine bright July afternoon. 



So I merely made comparative drawings of the spectrum given 

 by these low white clouds, and that afforded by the general sky 

 above them in the Polar neighbourhood, inked them in, and 

 then waited to see what would follow. 



And it was this. At 10 p.m. of that very fine day, and with- 

 out any sensible falling of the high barometer, the sky clouded 

 over completely. At 11 p.m. settled rain began. At 1.30 a.m. 

 it was still raining, and I have reason to believe that it continued 

 all night. It was certainly still raining in the morning of the 

 next day, Sunday, and continued more or less all that day and 

 all that night ; while this morning, Monday, July 19, after a 

 heavy thunderstorm, fog and heavier rain began and have 

 proved the order of the day. All this with a barometer still 

 nearly uninfluenced in its serene height and steadiness,* but not 

 so the spectroscope, for, excepting the E line, all the other lines 

 have disappeared in dull bands which occupy their places very 

 nearly, and the London band on the less refrangible side of, and 

 over D, is the main characteristic of all the visible spectral range, 



15 Royal Terrace, Edinburgh, Piazzi Smyth 



July 19 Astronomer Royal for Scotland 



OUR ASTRONOMICAL COLUMN 



The Triple-Star, South 503.-111 Astron. Nachr., 

 No. 2,045, Baron Dembowski has published measures of 

 this star made in 1873-75, which exhibit large changes in 

 the relative situation of the components, as compared 

 with the measures of Sir James South early in the year 

 1825. Thus we have for A and B : — 



South i825"i Position I34°T Distance 39"'94 



Dembowski. i873*8o ,, 120 "3 ,, 8 '24 



„ i875'2i ,, 118 -8 ,, 7 -07 



And for A and C :— 



South iS25'i Position 337° -3 Distance 201" -76 



Dembowski. i875'2i ,, 335 -4 ,, 232 "04 



Lalande observed A and C on Jan. 23, 1798 ; Bessel 

 observed all three components on March 6, 1823 ; and 

 Argelander has an observation of B on Feb, 16, 1856, 



On inspecting the above measures there will arise at 

 first sight a suspicion that the change of distance 

 between A and C and in both elements between A 

 and B may be caused by proper motion of A nearly in 

 the line joining A and C, To put this to the test we may 

 take a mean between South's measures of 1825 and the 

 angle and distance of A and C deduced from Bessel's 

 meridian observations in 1823, and compare it with the 

 mean of Dembowski's measures of A and C in 1875. 

 Assuming the differences to be due to proper motion of 

 A, we find for the annual values : — 



P.M. in R.A + o"-389 



P.M. in Decl — o •461 



And, if with this proper motion we reduce Dembowski's 

 mean of measures of A and B in 1875 to the epoch of 

 South's observations there results : — 



For 1825-1 Position i36''-5 Distance 36"-5 



Considering that the P.M. adopted is only an approxima- 

 tion, there appears to be little doubt that the changes to 

 which the Baron Dembowski has drawn attention in his 



Meteorological Journal at Royal Observatory, Edinburgh, foi 

 I P.M. ea'-k day. 



