Nov. :6, 1871J 



NATURE 



43 



Mieis's "Contributions to Botany" is no less valuable 

 than any of its predecessors as a record of laborious and 

 conscientious devotion to science. A. W. B. 



An Elctncnfaiy Tn-atisc on Statics. By J. W. Mulcaster 

 F.R.A.S., Military Tutor. (London: Taylorand Francis.), 

 This is a good book without any of that attempt at 

 cramming, too common now in our elementary te.xt-books. 

 It is calculated to give the reader a good grasp of 

 the elements of Statics. It goes over the usu d ground, 

 states and proves the principles well and clearly, and 

 contains in each chapter a numerous and excellent series 

 of examples. These examples consist of "graduated and 

 classified groups of problems, each involving distinct 

 statical principles." These, the author says, he finds, and 

 our experience entirely agrees with his, make " an im- 

 pression on the student's mind otherwise not attainable 

 with problems indiscriminately taken.'" We gather from 

 the book that it is the production of a good and practical 

 teacher. J. S. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for ofinioiis expressed 

 by his correspondents. No notice is taken of anonymous 

 communications. ] 



The Aurora Borealis of Nov. 9 and 10 



As llie magnificent display of Aurora on the evening of the 

 loth was witnessed here under very favourable circumstances, 

 and as several of its phases were of unusual occurrence, an 

 abridged account may not be uninteresting. 



The Northern Lights were first noticed at about 7.30 G.M. T.. 

 the appearance being that of a pale white fight, whicli gradually 

 rose from the X.N.W., until it completely enveloped the Great 

 Bear, but was not sutificiently strong to hide even the faint star 

 near Mizar. Towards S.40 the auroral mist assumed the more 

 definite form of three broad white bands, stretching across the 

 sky from E. to W., the uppermost band lying just below Vega 

 and Polhix. 



At the same time a bank of dense black cloud rose from the 

 N. horizon to the height of 7) Ursa?, and shot forth dark streamers 

 as far as the upper arch of light. The streamers E. and W. 

 were brighter than the central part, and waves of light moved 

 slowly and at regular intervals from these brighter parts of the 

 horizon, mingling together at the centre of the arch. 



At 9.10 a very briglit streamer made its appearance. 



Up to this time the display had been colourless, but at 9.20 it 

 assumed a greyish tinge, and had extended by 9.25 as far as /3 

 Cassiopei;^. 



At 9.30 the western extremity of the arch was of a bright red 

 colour, whilst only a slight appearance of redness was visible in 

 theE. 



The aurora then became wonderfully brilliant, and the rapidity 

 of die changes surj^assed anything that had been seen here ior 

 years. Flashes of liglit were succeeded by waves, and these in 

 their turn by small detached cloud?, which travelled rapidly 

 across the sky. At 9.45 the waves and streamers seemed to 

 converge to a point shghtly S. E. of j3 Andromedre. 



In the square of Pegasus a curiously-formed cloud, in the shape 

 of an enormous bird, suddenly appeared and disappeared several 

 times, sending forth each time streams of light E. and W., as if 

 from its outstretched wings. 



At 10 tlie auroral light was strongest, and then the waves, 

 moving rapidly from the N., appeared to return for a short dis- 

 tance on their path when they had passed a few degrees S. of the 

 zenith, like waves breaking on the sea shore. 



At 10.30 two distinct arches of light, the upper one passing 

 through /3 Andromeda', the lower one near Polaris, intersected 

 each other E. and \V. at an altitude of about 20°. 



At 10.40 all colour had disappeared in the west, but a very 

 brilliant red streamer stretched from the E. neariy to the Twins. 

 About this time a thick cloud of elliptic shape was formed be- 

 tween the points N.W. by N. and W. Beneath this cloud was 

 a pale auroral glare, and from its upper side a mass of broad 

 dark streamers rose towards Polaris. At the E. end of the cloud 

 a very broad streamer moved gradually westward, and shortly 

 afterwards a similar streamer formed near the W. and moved in 

 the same direction. 



At 10.45 "■ Arietis was the centre, towards which the new 

 violet-coloured streamers and the waves and flashes tended. 



The last-mentioned cloud was then replaced by another similar 

 in form, but situated farther from the E., its outer streamers of a 

 yellowish green colour meeting in Cassiopeia. 



At 1 1 the only colour visible was the violet in the W. 



At 1 1.5 a point S. of y Pegasi was the centre of motion. 



At n . 1 5 the dark streamtrs were sharply defined, but extended 

 only a few degrees above the cloud. Ten minutes later the stars 

 below Vega and Ursa minor were completely hidden, and then 

 from 11.25 to 12.15 'he aurora gradually died away, leaving only 

 a faint white glare on the N.W. horizon. S. J. Perry 



Stonyhurst College Observatory 



On Friday evening, Nov. 10, I was fortunate enough to wit- 

 ness a brilliant display of the Aurora Borealis, which, if it did not 

 surpass, certainly rivalled, that of Oct. 24, 1870. 



At gh. 2om. G. M.T. the whole sky was literally covered with 

 auroral streaks to within 30" of the southern horizon, all appa- 

 rently converging to a pomt near a Andromedae. The streaks 

 were of a white colour, having a slightly blueish tint (probably 

 caused by the mass of intervening air), and their form, to within 

 15^ of '-he point of convergence, was perfectly straight. The 

 radial point was shown by an irregular mass of auroral light, 

 from whicli bright streaks were spread out in every direction, 

 those to the south being much shorter than the streaks to the 

 north or west. The appearance of the sky at the time was that 

 of the outstretched wing of an enormous bird. At gh. 22m. a 

 rich crimson glare was visible in the .S.W., dividing the constel- 

 lations Pegasus and Cygnus, and at 9h. 25m. a resplendent beam 

 of white light 2' in width was conspicuous in the N. E. ; its length 

 was about 50°, and it was nearly parallel in direction with a line 

 joining the stars a. CapcUa and /3 jVuriga;, but 3° to the left of 

 them. It remained visible for 5m. 



At gh. 25m. 30S. a white luminous meteor (apparently one of the 

 " Leonides ") shot swiftly across the constellation Pisces, having a 

 brightness = Sirius, duration 0'5sec., and length of path 10', left 

 no train or sparks. 



At gh, 32m. the constellation Perseus was overspread by a 

 luminous glare of a reddish colour (known to dyers by the appel- 

 lation of " ruddy brown,") and which did not disappear for about 

 lom. At gh. 34m. the crimson glow reappeared in the S.W. 

 between Cygnus and Pegasus, thereby completing a gorgeous 

 arch about 15° in width, extending from the S.W. to the N.E. 

 horizon, passing over the constellations Cygnus, Lacerta, 

 Perseus, Auriga, and Orion. This crimson belt divided the sky 

 into two halves, that on the north being full of auroral streaks, 

 two columns of which were very conspicuous in the north, pass- 

 ing over Ursa Major and extending nearly to the zenith. A small 

 dark cloud lying horizontally across them divided them into two 

 parts, each of which was distinctly visible. 



At gh. 40m. the streaks had entirely disappeared, being replaced 

 by a diffused auroral glare, similar in appearance to the sky be- 

 fore dawn ; but at loh. the streamers reappeared with equal bril- 

 liancy. The radial point had now moved to 2' below /3 Andro- 

 meda;, and was now clearly pointed out by an irregular curve, or 

 hook, about 4° or 5° in diameter, which, although observed at 

 different times during the evening, was never completely formed, 

 as go' or 120' were always wanting to form a complete circle. 



At loh. 23m. a curious phenomenon presented itself. A small 

 irregular patch of crimson light, about twice the diameter of the 

 moon, appeared over /3 Triangulii, which slowly, and gradually 

 expanded, but after a lapse of about 30s. (when about 15° in 

 diameter), its colour changed to the ordinary bluish white of the 

 aurora, the phenomenon lasting altogether about 2m. At 

 loh. 25m. a h'cod.di greenish white band appeared in the N.E. 



By this time the centre of convergence had reached /3 Trian- 

 gulii, thus showing apjiarent progressive motion towards the 

 cast at the rate of about 15" per hour (which is the rate of the 

 rotation of the earth upon its axis). It is worthy of notice that 

 in tlie auroral displays of October 1870 the same stais formed the 

 radiant, and its motion was in the same direction. 



At loh. 37m. a beautiful crimson beam appeared in Auriga 

 (in the same position previously occupied by the white streak at 

 gh 35m.) Its length was about 40°, and at loh. 5oni. a gorgeous 

 triple streak was visible in the same position, which presented the 

 appearance of a broad crimson ribbon, with a border of K'/rAon 

 each side. In about five minutes it faded out of sight. 



At 1 1 o'clock the auroral light was again diffused over the 

 whole northern sky, bounded on the south by si bright milky 



