March 25, 18 86 J 



NATURE 



483 



musk oxen were met with, and no doubt had the Expe- 

 dition disobeyed instructions and remained at Fort 

 Conger, it would have been saved most of the hardships 

 it encountered, and all the members might have been 

 saved alive Much valuable scientific matter will be 

 found in the appendix — ethnology, botany, ornithology, 

 Medusffi, &c. One of the most striking and instruc- 

 tive features about these handsome volumes is the 

 beauty and accuracy of the illustrations. They are most 

 of them from photographs, and are fine examples of 

 the services which photography can render to science. 

 The texture of rocks and ice in these illustrations is 

 wonderful. 



The narrative itself, though quite unvarnished, is of 

 intense interest ; and the Expedition was in many ways 

 one of the most remarkable ever sent Polewards. 



THE KRAKATAO DUST-GLOWS OF 1883-84 

 Beobachtungen iiber die Ddmmerung insbesondere iiber 

 das Pitrpurlicht und seine Beziehungen zum Bishop' schen 

 So?niL'nri>!g. Habilitationsschrift der philosophischen 

 Facultat der Universitiit Basel vorgelegt von Dr. Albert 

 Riggenbach. (Basel : H. Georg's V'erlag, 1886.) 



THE Krakatab dust-glows of 1883-84 have already 

 created a not inconsiderable literature. To this 

 the pamphlet now before us is a contribution of some 

 value. The writer has not only diligently studied the 

 observations of others, but has added a long series of his 

 own, and has thus acquired a right to an attentive hear- 

 ing on the subject of the remarkable appearances which 

 have given rise to so much discussion. 



Scientific opinion has all but unanimously adopted the 

 volcanic hypothesis of their origin urged with irresistible 

 logic by Mr. Lockyer in the Times of December 8, 1883. 

 It is admitted, though not examined, by Dr. Riggenbach ; 

 whose concern is less with the primary cause of the 

 phenomena than with the minute machinery of their pro- 

 duction. Questions bearing on the general physics of 

 the globe are left untouched, while attention is concen- 

 trated on the intricate optical problems connected with 

 the variegated tints of our skies. 



These, according to our author, result mainly from 

 diffraction. But absorption and reflection also play each 

 an indispensable part. The sunset-sky, it must be re- 

 membered, is illuminated only by a residuum of sunlight. 

 A long journey across the densest strata of the atmo- 

 sphere has robbed it of all its more refrangible con- 

 stituents. The course of the surviving rosy beams is 

 interrupted by encounters with innumerable fine particles 

 of solid matter, always, in greater or less quantity, sus- 

 pended at considerable heights above the earth's surface. 

 These form fresh points of divergence, whence rays which 

 would otherwise have been transmitted unseen, reach the 

 eye, either directly, or after reflections from interposing 

 veils of fine cloud. Thus, the hurling into the air of 150 

 cubic kilometres of volcanic dust in August 18S3, served 

 only to intensify pre-existent conditions for the produc- 

 tion of twilight-pageantry, not to create new ones. What 

 we might almost call the solid constituents of our atmo- 

 sphere were not alone largely increased in amount, but 

 the added dust-supplies were of unusual fineness, conse- 

 quently floated at unusual elevations. Displays of colour 

 hence gained both in splendour and duration. 



The effects of this strange reinforcement from the anti- 

 podes did not, however, manifest themselves at sunrise 

 and sunset only. On September 5, 1883, Mr. Sereno G. 

 Bishop first noticed at Honolulu a peculiar white halo of 

 a pinkish tint encircling the sun (NATURE, vol. xxix. 

 p. 260). The phenomenon had never previously been 

 observed, and is now known as " Bishop's Ring." It was 

 perceived later in Europe, and proved extraordinarily 

 persistent. For fully two years, whenever the air was 

 sufficiently clear, it continued visible, thus long outlasting 

 the twilight-glows, with which, nevertheless, it was most 

 intimately connected. Dr. Riggenbach observed that the 

 rosy illumination began to show after the sun had dipped 

 below the horizon, precisely at the same angular distance 

 from his limb with the maximum intensity of the ring or 

 " corona." And it may be taken as ascertained that the 

 latter was purely an effect of diffraction. The succession 

 of colours was the opposite to that seen in an ordinary 

 halo, the blue lying inside ; while the diameter (measured 

 to the middle of the red zone) was about 28', that of the 

 refraction-halo being 45°. The observed dimensions of 

 the ring gave the means of calculating the size of the 

 particles concerned in producing it ; and they were 

 accordingly found by Prof. Hagenbach to be 0^003 mm., 

 by M. Flogel o'ooi mm. in diameter. Yet, though far 

 finer than the minute vesicles occasioning the dift'raction- 

 rings frequently observed in comparatively close proximity 

 to the sun and moon, their bulk (even adopting the lower 

 estimate) would still be at least one million times that 

 assigned by Sir William Thomson to the ultimate atoms 

 of matter. 



Seen from the Bernese Oberland, or other high ground 

 in Switzerland, during the summer and autumn both of 

 iS84and 1885, this curious aureola presented a striking 

 appearance. A silvery field of diffused radiance extended 

 to about 10° from the sun's limb, and was terminated by 

 coloured circles, the prismatic order of which grew dis- 

 tinct in proportion as the air gained transparency. Below 

 1000 metres of elevation, the whole phenomenon became 

 effaced. It was independent of meteorological conditions, 

 taking its origin in a region of the atmosphere beyond 

 the reach of ordinary disturbances. The invariability of 

 its presence was painfully experienced by Mr. C. Ray 

 Woods during his sojourn on the Rifi"el in the summer 

 of 1SS4. No more effectual obstacle to the work of 

 photographing the sun's proper corona can indeed be 

 imagined than that which, by a linking of causes not 

 difficult to trace, though impossible to foresee, was inter- 

 posed by the memorable eruption two and a half years 

 ago in the Sunda Straits. 



OUR BOOK SHELF 



The Star Guide. By Latimer Clark, F.R.A.S., and 

 Herbert Sadler, F.R.A.S. (London: Macmillan, 1886.) 



Thls is a most useful and carefully planned guide to the 

 best use of small telescopes. It consists of a list of the 

 most remarkable celestial objects visible with such instru- 

 ments, with their positions for every tenth day, and 

 partly serves as an introduction to Webb's " Celestial 

 Objects for Common Telescopes." Very considerable 

 trouble has been taken in the compilation of the table of 

 double-stars. Test objects, lunar craters, shooting-star 

 radiants are also catalogued, and although small apertures 



