ii4 



NATURE 



[April 



191, 



The book does not give any of the scientific 

 results of the expedition, which will no doubt prove 

 to be valuable from an observer of such wide arctic 

 experience as Captain Mikkelsen. The book is 

 illustrated by many instructive photographs, 

 which are arranged haphazard, and by a map 

 which is the most inconveniently placed that we 

 remember to have seen. 



CORONAL, GLORIES, AND 

 HEILIGENSCHEIN. 



DURING May and June, 1912, several corre- 

 spondents described a number of optical 

 phenomena, principally solar haloes, which they 

 had observed just before the commencement of the 

 remarkable haze which covered the sky in the 

 northern hemisphere during the summer months 

 of iast year, and a short article dealing with the 

 simpler haloes and mock suns appeared in Nature 

 (vol. lxxxix., p. 377). Recently attention has been 

 directed to certain less generally known and less 

 majestic phenomena (possibly also less ominous), 

 which are described as (1) coronae, (2) glories, 

 Ulloa's rings, anthelia, or Brocken spectres; 

 (3) haloes, or more strictly Heiligenschein or dew 

 glories, and a note on these may supplement the 

 earlier article. 



Coronse are luminous rings around the sun or 

 moon, usually, although not necessarily, smaller 

 than the smallest halo properly so called, which 

 has a radius of 22°. The order of their colours is 

 opposite to that of haloes, red being outside and 

 blue inside for each ring. Inside the first ring is 

 the aureole of a peculiar pale-tinted blue near the 

 luminary, with brownish-red next to it. Sometimes 

 the aureole alone is visible. 



Coronas are produced by diffraction either by 

 small drops of water or possibly by ice-needles, 

 although Dr. Simpson, from observations in the 

 Antarctic with a party led by Captain Scott in 

 September, 191 1, and from theoretical considera- 

 tions, concluded that coronae there were not 

 produced by ice-crystals, but by super-cooled 

 drops of water, and drew the very important de- 

 duction that "liquid" water exists in the atmo- 

 sphere at temperatures far below the ordinary 

 freezing point. The more uniform the size of the 

 drops in the cloud producing a corona, the more 

 brilliant is the phenomenon. The angular 

 radius of a coronal ring is proportional to the 

 wave-length A of the colour of the ring and 

 inversely proportional to r, the radius of the 

 drops, but a small correction is necessary on 

 account of the fact that the sun or moon is not 

 a point-source of light, but has a definite dia- 

 meter. Observed radii 8 must be diminished by 

 16' before they are used in the formula 

 sin0 = cA/V, where c is roughly o'8, 1*3, i"g for 

 the first, second, and third rings. The intensity 

 of the light in the rings is of the order of 1/100 

 of the intensity of the direct light from the 

 source. The diameter of the drops in clouds pro- 

 ducing coronae varies from about o'oi to 0-04 

 millimetres. 



Glories are luminous rings seen around the 

 NO. 2266, VOL. 91] 



head of the shadow of the observer upon a cloud. 

 They are specially frequent upon mountains, 

 hence the name Brocken-spectre. Antonio de 

 Ulloa, the Spanish captain who took the French 

 scientific expedition to Peru in 1735 and explored 

 the Andes with Bouguer and Condamine, shares 

 with Bouguer the honour of having first given a 

 precise description of the phenomenon which is 

 sometimes associated with his name. Scoresby, 

 the arctic explorer, observed glories frequently in 

 polar regions, with clouds rising from the sea, by 

 climbing the mast of his ship. On one occasion 

 he saw as many as four coloured rings. 



Accounts of glories occur on almost every page 

 of the logbook kept by the observers on Ben 

 Nevis, and on one occasion, November 23, 18S4, 

 they saw as many as five together, varying in 

 radius from less than 2 to more than io°. 

 According to Pernter, glories are coronae produced 

 by reflected light. They are consequently much 

 less intense than direct coronae, and are usually- 

 seen by sunlight. Out of nearly 200 glories 

 described by the Ben Nevis observers, only three 

 were seen by moonlight. Mascart, however, 

 attributes glories to diffraction of the inci- 

 dent light in the same way as if it were travel- 

 ling in the opposite direction, and against this 

 explanation the objections which Miss A. Everett 

 quotes (January 23) from Prof. Richarz would 

 not hold. 



Haloes or glories around the shadow of the 

 head thrown on dewy grass in early morning or 

 evening have been called " Heiligenschein " to 

 distinguish them from haloes of the ordinary type. 

 The " Heiligenschein " is a real phenomenon which 

 can be photographed, and it extends some dis- 

 tance from the edge of the shadow. It is not to 

 be confused with the apparent brightness around 

 the shadow thrown on a flat surface, which is a 

 purely subjective phenomenon. This latter may- 

 explain the brightness along the shadow of an 

 overhead tram-wire mentioned by Mr. Merrick in 

 a letter. The Heiligenschein is most clearly seen 

 in meadows where the grass is more or less uni- 

 form in length and orientation, and is covered 

 with small drops of dew. The height of the sun 

 should be such that the length of the shadow 

 is 40 ft. or more. The phenomenon is attributed 

 to the light reflected from the spherical dew- 

 drops both directly and after two refractions and 

 one or more internal reflections. These effects 

 give a maximum intensity in the direction of the 

 incident light, the intensity falling off continuously 

 without alternation of colour. It is, therefore, 

 quite distinct from haloes, coronas, and glories. 



The halo on ruffled water described by Prof. 

 Worthington in Nature of February 13 (p. 647) 

 appears to be akin to Heiligenschein, although 

 the condition of slight turbidity which he postu- 

 lates suggests that the turbid constituents may 

 act in a similar way to fog particles. 



In addition to the letters already published in 

 Nature, several others have been received. Mr. 

 T. S. Patterson, of Glasgow University, refers 

 to Benvenuto Cellini and the consolation which 



