512 



NA TURE 



\_Sept. 25, i ; 



The glowing sunsets having reappeared, though far less 

 brilliant than in November and December last, I send you a list 

 of the most remarkable of them which have been noticed at 

 Clairvaux, in the Department of Aube. They appeared with 

 the same features as have been so often described in Nature, 

 and were especially glowing on the following days :— November 

 25, 27, 28 ; December 12 ; January 7, 12 ; August 6, 22 (feeble, 

 sky not quite bright), and 23 (more brilliant) ; September 10 

 (feeble, bright sky, beautiful pink coloration in the east) and 

 17 (bright sky, bright pink coloration one hour after sunset). 

 When the sky is bright, the rise of the moon is preceded, for 

 nearly one hour, by a bright illumination of the sky. 



Clairvaux, Aube P. L- 



For the last four evenings, the 15th, 16th, 17th, and iSth, and 

 again to-night, the colour of the sky from 20 to 25 minutes after 

 sunset has taken that deep magenta glow looking very like the 

 effect of a great fire, only lighter in tone. Last night, the 18th, 

 this lasted until after 7 o'clock, and stars were then shining 

 through it as they do through an aurora. 



The reappearance of these glows was to be expected, as the 

 haze and ruddy glow about the sun by day has, so far as I have 

 been able to see, never really been long absent since attention 

 was first drawn to it last autumn. I have now received a letter 

 from Sydney, dated July 24, in which the writer says : " Since 

 we have been in the Southern Hemisphere the sunsets have 

 certainly had more striking colours, and on many occasions I 

 have seen that peculiar magenta or mauve tint in the sky like 

 aurora, only bluer in colour, while the sky has been very white 

 just before sundown." The writer of the above is used to the 

 look of the sun and sky, being an officer on board a mail steamer. 

 I had suspected that absence of colour more or less in the sunsets 

 here during our summer might be owing to the position of the 

 sun rather than to any diminution in the quantity of vapour in 

 the higher atmosphere, and had asked the writer of the above to 

 note as he went south, in their winter, whether there was any 

 increase in the colour of the after-glows, &c, being led to 

 think this might be the case from reading the report of Mr. 

 Neison, Director of the Natal Observatory, in which he speaks 

 of having " first observed these phenomena in February 1883, 

 from which time they increased in intensity until June, after 

 which there was an interruption until the month of August." 

 This led me to expect a return of strongly marked colour in our 

 after-glows in autumn, increasing probably in intensity and dura- 

 tion during our winter months, when the weather is clear enough 

 to see the sky. Robt. Leslie 



Moira Place, Southampton, September 19 



The Diffusion of Species 

 The vast and altogether exceptional assemblage of Salpse men- 

 tioned in Nature (September 11, p. 4° 2 ) bv the Duke of Ar gy H 

 as having been observed by him whilst recently cruising in the 

 Hebridean seas, was due, in all probability, to the exten- 

 sion in a north-easterly direction of the ordinary surface-current 

 of the Atlantic, or to an unusually long continuance of steady 

 south-westerly wind, the effect of which would be to drive the 

 superficial water of the Atlantic before it to the British coasts, 

 and, with the water, the enormous multitudes of Salpoe which 

 are occasionally to be met with in the latitude of the Canaries 

 and Cape Verd Islands. 1 



During voyages to and from Bengal, via the Cape, in the 

 go 3d old days of sailing vessels, I repeatedly came across vast 

 aggregations of these creatures, my attention having been specially 

 called to them whilst engaged as I generally was for many hours 

 by night as well as by day, in using a towing net from the stern 

 ports for the capture of natural history specimens. 



On my last voyage from Bengal in 1857 the ship sailed through 

 some fifty or sixty miles of what the Duke aptly describes as 

 Salpa soup, and which looked exactly like boiled tapioca. The 

 quantity of Salpa: present in a bucket of the sea-water was, at 

 least, equal in volume to the volume of water, but then the 

 bodies of the Salpie themselves consist in reality of more than 90 

 per cent, of water. On the occasion referred to, almost the 

 entire mass consisted of a small species of Salpa about an inch 

 in length, but nevertheless large enough to render the bright 



1 As is well known, 

 occur at the surface 

 of moderate weather. 



yellow digestive cavity of each, which is about the size of the 

 smallest pin's head, distinctly visible. This was invariably full 

 of certain species of oceanic diatoms the endochrome of which 

 imparted the yellow colour. It is worthy of remark that in the 

 case of the Salpa?, as well as many other organisms holding a 

 yet lower position in the animal scale, there undoubtedly exists 

 a selective power which enables them to pick out certain kinds 

 of food in the midst of a superabundance of different kinds. 



In the tropical Atlantic and Indian Oceans also I have seen, 

 during calms, immense numbers (though not to be compared 

 with the gatherings of the smaller Salpse) of the larger chain 

 Salpa:. These sometimes attain a length of from 8 to 10 inches, 

 and have stomachs as large as a good-sized marble or hazel-nut. 



But the most interesting assemblage of the lower forms of 

 pelagic life was noticed by me about 200 miles from Ceylon, 

 .luring a dead calm of four days' duration, when the sea wasas 

 smooth as a mirror, and undisturbed save by its never-ceasing 

 majestic swell. Deep down, as far as the eye could penetrate, 

 were to be seen numbers of brightly coloured water-snakes, deli- 

 cately tinted " Venus's girdles," "Velelke," and countless 

 multitudes of those more minute living things which, though 

 barely visible as mere specks to the unaided vision, are full ot 

 beauty and interest when observed under the microscope. Such 

 a calm is a veritable pandemonium to the "skipper, —to the 

 naturalist it is a paradise. CI. C. Wallich 



September 14 



I AM specially interested in the Duke of Argyll's letter on the 

 above subject (p. 462), being a resident during nearly half the year 

 in the most southern of the Hebrides. His Grace is so competent 

 a naturalist, and so accurate an observer, that I assume at once 

 he had evidence which satisfied himself that an adder swam from 

 Mull to Iona. Still I must be pardoned if I say that your 

 readers have not been supplied with the proofs which have satis- 

 fied his Grace. A boy and girl in Iona, who, I presume, had 

 never seen an adder in their lives, killed a creature in the sea 

 there. Might it not have been an eel ? 



As regards distribution of species I may mention the follow- 

 ing In this island (Islay) we have multitudes of stoats but not 

 a single weasel, while I am informed on trustworthy authority 

 that in the neighbouring island of Colonsay there are many 

 weasels but not a single stoat. R. Scot Skirving 



Sunderland House, Islay, September iS 



Shifting of the Earth's Axis 



In the very interesting address of Prof. Young (Nature, 

 September 18, p. 501) he refers to the variability of the earths 

 axis, and states that a change of 1" per century has been detected 

 at Pulkowa, but that " the Greenwich and Pans observations do 

 not show any such result." Now only last year, in the " Pyra- 

 mids and Temples of Gizeh," I had (p. 126) noted that the 

 Greenwich observations did appear to show a change, and that 

 a change of the same amount and same direction as is stated by 

 Prof Young for Pulkowa ; the observations of this century show- 

 ing a decrease of 1" of latitude per century, or with those of 

 Maskelyne a decrease of 1" 38 per century. 



This change I adduced as corroborating the result shown by 

 four very accurate orientations of the earliest buildings, the Gizeh 

 pyramids. These structures, whose errors are but a few seconds 

 of angle, agree in standing as much as 4' or 5' to the west of the , 

 present north. This would imply a change of about 5 or 6 per 

 century in the direction of long. 120° ; a result quite comparable t 

 to the motion of 1" or l"'4 per century in long. 0° and 30°. Such 

 a change might be effected by causes which are beyond our 

 observation ; as, for instance, unbalanced ocean circulation equal 

 to a ring of water only 4 square miles in section moving at a mile 

 an hour across the poles. If this motion of 6" per century in 

 Ion". 120 is still in action, we might now expect to find a change 

 of about 5" in the meridian determined at the beginning of the 

 Ordnance Survey, a ground of observation which should not be 

 neglected. W. M. Flinders Petrie 



Bromley, Kent 



1st assemblages of Salpa; and kindred forms a instantly 

 Arctic and Subarctic seas, during the prevalence 



Salmon-Breeding 



Mr Francis Day's interesting communication last week (p.. 



48S) on this subject is likely to attract more attention from biologists 



and pisciculturists than any other recently-ascertained fact in the.; 



natural history of the Salmonidx, and it opens the large ques- 



