Oct. 23, 1884] 



NA TURE 



607 



volvesan acquaintance with Gauss's discoveries in regular 

 polygons without the information having been given to 

 the student. The proofs of i. 9 and iii. 35 appear to us to 

 admit of improvement, the first by the familiar addition 

 of "on side remote," &c, and the latter might advan- 

 tageously be curtailed. These are small faults in a work 

 of such extent, and we instance them to show how little 

 we find not to our liking in an admirable text-book. We 

 notice that Dr. Casey has adopted the convenient terms 

 " circum-circle," " circum-centre," &c, first introduced, 

 we believe, by W. H. H. H. in these columns. He also 

 calls a certain well-known locus by the name of " Simson's 

 line," following the practice now usually adopted by 

 geometers in this country, we do not know on what 

 authority ; that well-informed writer in the history of the 

 subject, Mr. J. S. Mackay, states in his edition of Euclid, 

 recently reviewed in these columns, that he had not met 

 with the property in Simson's writings. 



Prof. Henrici in his article on " The Axioms of Geo- 

 metry " (Nature, I.e.) does not approve of Dr. Casey's 

 treatment of the Fifth Book (the Algebraic), and criticises 

 adversely Hamilton's quaternion proof of Euclid i. 32, 

 given by our author in an appendix (cf. also NATURE, 

 vol. xxix. p. 573). Dr. Casey prints the article as in the 

 first edition, and takes no notice of the criticisms we refer 

 to. A very large and well-selected collection of exercises 

 (upwards of 800 we think), with the addition (now) of 

 numerous examination questions, complete a work every 

 way worthy of the reputation of the great Irish geometer. 



LETTERS TO THE EDITOR 



[ The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



[The Editor urgently requests correspondents to keep their letters 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insure the appearance even 

 of communications containing inter esting and novel facts, \ 



The Sky-Glows 



On reading Prof. Herschel's letter in Nature for October 2 

 (p. 536), in which he so vividly describes the sunset of Sept. 20, 

 I was so forcibly reminded by its similarity, especially with 

 regard to the "diverging beams," to one which I lately witnessed 

 during an excursion to the White Mountains (New Hampshire), 

 that I send you a short account of it. It occurred on the evening 

 of September 9 while we were staying at Twin Mount House, at 

 a short distance from which is an elevated wooden erection, 

 commanding splendid views of the neighbourhood. We had 

 been watching the shadows creeping over the hills, the evening 

 light reflected on a bend in the river below, had seen the sun go 

 down behind the soft gray outlines of Mount Agassiz, and revelled 

 in the glorious tints, such as Prof. Herschel describes, when, on 

 returning to the hotel and stepping out on the balcony to take a 

 last look, we saw, from the point where the sun had lately disap- 

 peared and where the fiery glow still lingered, these remarkable 

 " diverging rays," so distinct in their character and so sombre in 

 their dark (though slightly greenish) shadow-like line — there were 

 not many of them — that I involuntarily exclaimed that I had never 

 seen anything like them before, and that surely the climate must 

 have something to do with their striking appearance and unusual 

 definition. I may mention that the day-glow was also con- 

 spicuous at times on that continent, notably at Quebec on 

 August 25 last. 



Since writing the above, I find that your correspondent, Mr. 

 J. E. Clarke (September 18, p. 4S8), also refers to dark bars at 

 sunrise and sunset, and the radiating character of the latter. 



Further Barton, Cirencester, October 17 E. Brown 



That Mr. Backhouse is right in thinking the day-glows were 

 entirely fresh in November of last year, the following extract 

 from my diary confirms. As ordinary meteorological phenomena 

 are entered upon a daily chart, my note-book only refers to what 



is unusual. Those whom I called to notice the sky thought it 

 quite strange. " 1883, xi. 25. — Sky colouring at 2.45 to 

 3 p.m. of a pale rosy-pink tint to the blue, giving a greenish- 

 gray cast to cirro-cumuli where it shone through. Formed circle 

 round sun extending from about 10° to 25° or 30° away. Inside 

 the 10° sky yellowish. Can this have anything to do with the 

 green sun seen in India, and therefore with the Java eruptions ? 

 Have noticed once or twice of late unusual sunset-colouring 

 very late. At 4.30 strange ruddy or bright red tint on brick 

 houses in Bootham. At 5.30 the west ruddy, as from glare of 

 fire ; still signs visible of this up to six. Sunset at Green- 

 wich at 3.58; therefore here at 3.38. Notice also various 

 newspaper reports and also in Nature of striking appearances 

 after sunset, ascribed to auroras, &c." J. Edmund Clark 

 Bootham, York, October 19 



Cole's Pits 



In reference to the subject of the " Cole's Pits," respecting 

 which a notice from Mr. A. Irving appeared in Nature for 

 Oct. 9 (p. 560), I find that as early as 1784 these pits, or rather 

 perhaps some of them, were investigated by the Hon. Danes 

 Harrington. And a paper appears on the views entertained by 

 him regarding them in Archaologia, vol. vii. p. 236, under the 

 head of " An Account of Certain Remarkable Pits, or Caverns, 

 in Berkshire." Although Mr. Barrington expresses some doubts 

 as to his conclusions, he nevertheless leans to the opinion that 

 they are the winter dwellings of a pre-Roman people, the entire 

 series constituting perhaps an ancient British town. He esti- 

 mates them at about 273 in number, and covering a space of 

 about 14 acres. In depth they vary from 7 to 22 feet, and are 

 40 feet and upwards in diameter, the largest being not in all 

 instances the deepest. They extend in regular series, and are 

 placed rather closely to each other. They are referred to a 

 period anterior to that of Stonehenge ; and it is conjectured that 

 if each pit contained five occupants the entire community would 

 have numbered something like a population of 1400 souls. As 

 suitable for the residence of uncivilised people stress is laid on 

 the fact that the place is entirely of the dried sand on the rich vale 

 of the White Horse. The dwellings are supposed to have been 

 entered by climbing down a nide ladder or notched pole after 

 the manner adopted by the natives of Kamchatka in reaching 

 their underground habitations. It is remarkable as bearing on 

 the theory that these pits are abandoned quarries, that no objects, 

 such as pottery, indicative that they (the pits) were used as 

 dwellings, were found by Mr. Barrington. There can be no 

 doubt that the pits are simply the sites of shafts dug for the 

 purpose of obtaining the underlying ironstone. Indeed, Mr. 

 Godwin-Austen appears to have set the matter at rest many years 

 ago ; and although lam not able at the moment to state in what 

 paper on the subject the opinion occurs, I am in possession of a 

 note in which Mr. Godwin- Austen, with the keen perception of 

 the skilled geologist, observes that although "the Faringdon 

 tradition points this spot out as the site of the castle of King 

 Cole, whose memory is preserved in a well-known fragment of 

 popular poetry, geology can countenance no fictions except its 

 own, and Cole's Pits are evidently the remains of the open 

 workings for the ironstone underlying the mass of sand." 



Reading, October 10 Joseph Stevens 



Circular Rainbow 



H The circular rainbow mentioned by Mr. Marshall seejrs to 

 be similar to what may be seen at the Niagara American Falls 

 by persons who are fortunate enough to have taken the trip 

 under a portion of that Fall at the right time. When coming 

 out into the front of the Fall, if the sun be shining and in a 

 favourable position, each observer is surrounded by a rainbow of 

 which his eye is the centre, and which accompanies him while 

 in front of the Fall like the halo of a saint of old, but larger. 



Before railroad days, when travelling by coach from Bristol to 

 Bridgwater, I once saw a complete circular rainbow resting on 

 the vale below the Leigh Woods, just out of Bristol. 



Barnstaple, October 20 W. SYMON5 



P. S.— One morning, as the sun was rising over the Southern 

 Atlantic, the sea being moderately rough, I saw each white 

 crested wave drowned with the prismatic colours, causing a 

 dancing play of glorious colour never to be forgotten. 



