May 3, 1883] 



NA TURE 



tions of the zodiacal light, or to " Chambers's Astronomy," 3rd 

 edition, p. 92, where a short chapter is devoted to the subject. 



Speaking from my own experience, the zodiacal light is best 

 observed in this neighbourhood during the clear evenings of 

 February or March, in the late twilight, and of course in the 

 absence of moonlight. 



On referring to my copy of the Astronomical Register for 

 1875, v0 '- *"'■ P- I0 -6> I fi n d a letter from Mr. T. W. Backhouse 

 in reply to a previous communication from Canon Beechey in the 

 same volume, p. 174, describing what appears to have been a 

 much finer display of this sunset phenomenon as seen by the 

 rev. gentleman from Downham, Norfolk, than either your cor- 

 respondent or myself witnessed. 



Mr. Backhouse states : "It is purely an atmospheric pheno- 

 menon ascribed to the sun shining on particles of water or ice." 



May I ask if the above explanation is an established fact or 

 only a theory ? 



I shall be glad if you receive and can make room for the 

 accounts of other observers, as I cannot think the appearance is 

 a very common one — at least not in this neighbourhood. 



Hull, April 24 William Lawton 



Referring to the letters in your columns on this subject, I 

 beg to forward two photographs of the sun, which show distinct 

 horns of light on each side of the disk. They were taken — the 

 sun high in the heavens at the time — some two months ago in a 

 simple camera, without any special arrangement, except a rapid 

 shutter, but the development was undertaken with some care, 

 and arrested as soon as the light fleecy clouds around made their 

 appearance. H. B. P. 



Blackheatb, April 27 



[We have received the photographs, which are certainly very 

 remarkable if our correspondent can certify that the strange 

 prolongations which appear on them are special to them, and 

 not in any way dependent upon any possible reflection from the 

 lenses employed. — Ed.] 



The phenomenon described on pages 580 and 605, under the 

 heading "The Zodiacal Light (?) " was that generally known as 

 a "Sun Pillar." I send herewith an engraving of one seen 

 from Sidmouth in 1871, full descriptions of which were given in 

 the Meteorological Magazine for May, June, and July of that 

 year. 



Sun Pillar seen near Sidmouth, April 4, 1871. 



I believe that it is merely a portion of a halo passing verti- 

 cally through the sun ; in the recent case, that portion of the 

 halo which was above the sun was alone seen, soiietimes the 

 portion below it is seen alone, and occasionally both are visible, 

 together with a parhelic circle (or parts of one), and then of 

 course we have the rare phenomenon of the sun as the centre of 

 a luminous cross. I have called this complete phenomenon of 



the solar cro s rare, for I know of only three occasions of its 

 being seen, and even these I have not verified in the originals, 

 but those interested may search in Hugenii Ofuscula poslhuma, 

 ii. 48, (or the details of the phenomenon seen in Cassel in 

 January, 1586, by Roth; and in the Mem. de t Acad, des 

 Sciences for 1693 and 1722, for descriptions by Cassini and 

 Malezieu. G J. Symons 



62, Camden Square, N.W. 



The curious luminous projection after sunset on the 6th inst., 

 noticed by several of your correspondents, was also seen for 

 some time very soo 1 after sunset in Herefordshire. Its shape 

 was somewhat like a vertical pillar of soft, hazy, vellowish, 

 luminous light, about the width of the solar disk, 10° in height 

 above horizon, and finishing rather abruptly with a conical 

 termination in a clear sky. R. P. Greg 



Coles, Buntingford, Herts, April 29 



Allow me to call the attention of such of your readers as are 

 interested in the above phenomenon, to a communication from 

 Mr. J. J. Murphy of Belfast, in your issue of July 13, 1876, and 

 to another from myself, a f jrtnight later, describing a sun pillar 

 seen in the north of Ireland on June 27, 1876. R. V. D. 



Beragh, co. Tyrone, April 28 



Mock Moons 



The mock moons mentioned in your last week's issue (p. 606), 

 by Mr. Mott, were seen here. The circle subtended an angle of 

 50 . When first seen, a line drawn through the mock moons 

 passed through the moon itself. At 11 p.m. such a line was 3" 

 above the moon. At I a.m. the appearance was as at first. 

 This change of level of the refracting cloud is what Mr. Mott 

 alludes to when he says it "seemed to be unaccountably out of 

 place." I was not aware that there was any fixed place for the 

 brighter portions of the halo. Sm. 



Temple Observatory, Rugby 



The Freshwater Medusae 



It may interest some of your readers to know that the little 

 freshwater Meduje (Limnocodium Sowerbi), which appeared in 

 the Victoria Regia Tank here on June 9, 1880, for the first time, 

 again on June 12, 1881, and not at all during 1882, appeared again 

 in the tank on Saturday morning, April 28, many of them being 

 full grown individuals. The tank, which remains empty during 

 the winter, was filled with water on March 8. 



April 30 W. SowERBY 



The Circles of a Triangle 



Cannot the method of "portmanteau" words be advan- 

 tageously applied ? I beg leave to suggest the following names : 

 circumcircle, incircle, excircle, and midcircle ; these are for 

 speech, in print or writing they might appear C0.I0, E0, M©. 



April 28 W. H. H. H. 



Flight of Crows 



In watching crows as they fly overhead, I often think they 

 are not flying straight forward, but have the line from head to 

 tail at an angle of about fifteen degrees with the line of flight. 

 Can this be corroborated? I do not like to trust my own 

 observing powers in such a matter. Joseph John Murphy 



Old Fo>-ge, Dunmurry, co. Antrim, April 24 



METAMORPHIC ROCKS OF SCANDINAVIA 

 AND SCOTLAND 



MUCH interest attaches to the researches of the 

 Swedish geologists among the older crystalline 

 rocks of Scandinavia. In the year 1873 Mr. A. E. 

 Tornebohm published an important paper in which he 

 showed that in the high grounds of Sweden Lower Silu- 

 rian rocks, with recognisable fossils, pass up conformably 

 into a vast overlying series of quartzites, schists, and 

 gneisses. These metamorphic rocks were divided by 

 him into two groups— the Seve group, composed mainly 

 of quartzites and schists, and the Koli group, consisting 



