76 



NA TURE 



\N0V. 22, 1883 



A symmetrical system of ring?, with some attention to simple 

 elegance, would remove the offensive effect produced by the bent 

 bars of mere blacksmith's work which now surround a single 

 column. 



But it is not specially to the state of the Chepstow Bridge that 

 I wish to call the attention of the public. It is to the total want 

 of practical knowlef'ge as to the enduring power of metals, with 

 which this bridge was built, and with which other such bridges 

 must at present be built. We are totally without experiment on 

 the danger of springing or buckling, and on the danger of burst- 

 ing (W'^-K, I believe, for the first time brought forward). And 

 we might perhaps c insider such experiments as well falling 

 within the province of those organised bodies whose union is 

 based on the promotion of the most important determinations in 

 civil engineering. 



The Institution of Civil Engineers (with which body I have a 

 much-valued honorary connection) has lately departed in some 

 measure from the strict subject of engineering to which its atten- 

 tion had been successfully given for so many years. I venture 

 to suggest that this body might well take up the conduct of 

 experiments bearing on engineering. The examination of the 

 effects of force in mere crushing of external surfaces has been 

 admirably prosecuted by American engineers. But the examina- 

 tion of bending and bursting, as the effects of end-pres.'ure, is 

 still open to the engineers of Britain. The funds of the Institu- 

 tion appear to be amply sufficient for such purposes, and the 

 undertaking of them would undoubtedly be considered as honour- 

 able to the body. G. B. AiRY 



The White House, Greenwich, November 17 



Physiology in Oxford 



A PARAGRAPH ajjpeared in i'ae Spectator of Saturday, the loth 

 insf., on the Oxford memorial concerning the University Physio- 

 logical Laboratory. That part of it which affects Magdalen 

 College appears to me to rest upon erroneous information, and 

 is certainly calculated to spread an entirely false and misleading 

 impres-ion of the attitude of this College in the matter, and of 

 the University in general. 



If you will allow me to quote the paragraph, and at the same 

 time give you the ac'ual f.icts, I think you will easily form an 

 opinion on the real state of the case. 



The paragraph states that the signatures were received "from 

 members in Oxford and its suburbs, and the rest from a circle 

 of about fifteen miles round." 



The fact is that the signatures are not drawn exclusively from 

 either the smaller or even the larger area, one of the so-called 

 Ma dalen signatures being that of a member of the Hereford 

 Cathedral choir. 



The paragraph goes on to say : — " We are told that Magdalen 

 men have signed it more numerously than any other College but 

 one, and, in proportion to the size of the College, more numer- 

 ously than any. Now, as Prof. Hurdon Sanderson is ex officio a 

 Fellow of Magdalen, and as Magdalen has for years past had a 

 phy.^iological laboratory of its own, this popularity of the 

 memorial among Magdalen men is highly significant." 



On this I have to rcmaik that the signatures are representative 

 neither of the governing liody of the College, nor of its resident 

 members. 



The governing body of the College consists of the President 

 and twenty-four Fellows ; of these twenty-five three alone have 

 signed the ?nemorial. The re>ident members, as shown by the 

 list of congregation, number twenty-two ; of these twenty-two 

 only six have signed. 



Finally, as regards the last paragraph, it is true that Mag- 

 dalen College has for years past had a physiological laboratory 

 of its own, and il is further true that the University teaching of 

 physiology has been carried on there, previous to the advent of 

 Dr. Burdon Sanderson, for years past under a Government 

 licence with the full and express consent of the whole governing 

 body of the College, a fact which is indeed significant, but 

 hardly in the way in which the Spectator appears to have been 

 informed. Edward Chapman 



Magdalen College, Oxford, November 15 



Green Sunlight 



Mr. G. H. Hopkins' observation that the parting ray at 

 sunset is sometimes brilliant emerald-green brings to my 

 memory a somewhat similar experience. On September 13, 

 1865, watching on the summit of the Rigi for sunrise, I caught 

 the very fir.-.t possible glimpse of the sun's disk as, on a very clear 

 morning, he emerged from behind the sharply-defined outline of 

 a distant mountain. The very first rays, although necessarily 

 proceeding from the comparatively obscure limb of the sun, were 

 dazzlingly brilliant, and of a superb emerald green colour. But 

 almost instantlv, as more of the sun appeared and his light grew 

 sensibly more intense, the green passed away or w as merged in 

 the yellowisli white of ordinary sunlight. 



In my case I do not douljt the phenomenon was purely 

 subjective, for before sunrise the sky was all lit up of a magni- 

 ficent crimson hue. Every one must have noted how the moon 

 when surrounded with bright crim;on clouds looks more or less 

 decidedly green. 



A very striking effect of this sort, like the others an example 

 of the well-known visual phenomenon of "accidental colours," 

 may be artificially obtained, any time the moon shines, by 

 burning an ordinary "blue" signal light. After my eye had 

 been intensely excited by such a light close at hand, I have seen 

 the moon, near or at its full, of a deep plum colour, by which I 

 mean the colour of the bloom on a black plum or on a well 

 coloured Hamburg grape. Or, in place of these, the vioLt 

 of my friend Prof. Piazzi Smyth's exquisite chart of colours in 

 his "Madeira Spectroscopic," or the blcti violet of Chevreul's 

 chromatic circle. I recommend the experiment as easy of per- 

 formance and exceedingly beautiful in its effects. Possibly a 

 small blue light would suffice. But, on the occasion to which I 

 have referred, certainly not less than thirty ounces of nitre, ten 

 of sulphur, and five of black antimony sulphide were employed. 

 These, mixed in fine powder, may be burned in a case about six 

 inches high and four in diameter ; of course in the open air, and 

 where no mischief may accrue from an intensely hot and volu- 

 minous flame. 



In a communication made to the Royal Society of Edinburgh 

 in 1S52 (Trans, vol. xx. pp. 445-471), I adduced evidence to 

 prove that a continuous thin layer surrounds the sun's photo- 

 sphere, of which upturned portions form the red protuberances 

 seen at total solar eclipses ; and I then showed that if the well 

 known darkening of the sun's limb be due to absorption in his 

 atmosphere, it can only be caused by such a thin envelope. 

 The existence of this envelope, the sun's chromosphere, is now 

 fully established. If, from the red colour of its upper portions, 

 we may infer the resultant tint emitted by the whole to be red, 

 then, by a well known law, the discolouration of the sun's limb 

 due to its absorption should be of a greenish hue. But such an 

 effect would necessarily be but slight, and could not explain the 

 brilliant green \\'itnessed on the Kigi. Nor do I recollect any 

 instance where the first emerging rays of the photosphere at the 

 end of a total eclipse have been observed to be green. 



William Swan 



Ardchapel, Dumbartonshire, November 8 



A LETTER from Barinas, Venezuela, states that on September 

 2, from daylight until noon, and from 3 p.m. to sundown, the 

 sun appeared like a globe of burnished silver. Between noon 

 and three o'clock it was of a bluish-green colour. This appear- 

 ance in the western hemisphere seems to dispose of the sug- 

 gestion of the Java eruptions as the cause of green suns in India. 



Hyde Clarke 



Mangrove as a Destructive Agent 



As I have never seen the mangrove mentioned but as a con- 

 servative or productive agent as regards geological change, it 

 may be interesting to readers of Nature to hear of its acting 

 in a contrary direction. 



In several parts of eastern tropical Africa, where the shores 

 are mostly of upraised coral limestone, I have noticed the effect 

 of mangrove in eating away this rock, but nowhere have I seen 

 it so v\ ell marked as in the Island of Aldabra, some two hundred 

 miles to the north-west of Madagascar, and which I surveyed in 

 187S. 



Aldabra is an upraised atoll about twenty-two miles long, and 

 presents low cliffs of about fifteen to twenty feet of solid coral rock 

 to the sea and also to the lagoon, which is, at low water, nearl y dry 



