28 



NATURE 



[Nov. 8, 1883 



implies a majority which cares nothing for science and 

 much " for the rights of property " and the prospect of in- 

 creased dividends ; nevertheless even the majority is 

 willing to follow the leaders it has chosen, and the leaders 

 will lose nothing if they remember that we have duties to 

 perform towards the past as well as towards the present. 



LETTERS TO THE EDITOR 



[ The Edilor does not hold himself responsible for opinions expressed 

 liy 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 cori espondents 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 interesting and novel facts. '\ 



The Green Sun 



The appearance of a bright gi-een sun for several days in suc- 

 cession seems to be a phenomenon sufficiently rare to deserve 

 notice in your columns, so I send you the following notes on 

 the subject ; — 



On Sunday evening, September 9, the sun for some time 

 before setting appeared perfectly rayless and of a bright silvery- 

 white colour, quite different from anything that I have ever seen 

 before. On the following morning I did not observe it particu- 

 larly, but in the evening I watched it carefully from about five 

 o'clock till sunset. At first it had the same silvery-white 

 appearance as on the previous day, and this continued till 5.30, 

 when it was lost behind a bank of cloud ; on its partial reap- 

 pearance, however, at 5.43, the part visible between the clouds 

 was of a bright pea-green colour. On Tuesday morning it was 

 rather cloudy, but the appearance, when seen at all, was the 

 same as on the preceding night. In the evening, however, it 

 was a magnificent spectacle, and attracted the notice of every 

 one. The silvery sheen was visible early in the afternoon, and 

 the brightness of the sun rapidly faded, till by about five o'clock 

 one could look at it directly without any difficulty. At this time 

 there was a distinct tinge of green in the light when received on 

 a sheet of white paper, while shadows were very prettily tinted 

 with the complementary pink. As the sun sank towards the 

 horizon the green became more and more strongly marked, and 

 by 5.30 it appeared as a bright green disk, with a sharply-defined 

 outline. In fact the definition was so good that a large spot 

 (about I' long) was a conspicuous object to the naked eye. On 

 this occasion the sun was lost in a bank of clouds near the hori- 

 zon, but on another occasion, when I was able to see it actually 

 set, the colour got yellow rather than green close to the horizon. 

 Similar, but less marked, were the appearances both at sunset 

 and sunrise for several days, and before sunrise and after sunset 

 the cloud effects were such as I have never before witnessed 

 here. These cloud effects were chiefly remarkable for the bril- 

 liancy of the colouring and for the length of time that they were 

 visible, being seen for nearly an hour after sunset. The moon 

 and stars, when near the horizon, showed the same green colours 

 as the sun. 



On the 22nd the green sunrises and sunsets began again and 

 continued for three days. I carefully examined the spectrum on 

 every possible occasion with my zodiacal light spectroscope, as 

 well as with a small direct-vision one. The spectrum showed 

 clearly that aqueous vapour played a large part in the pheno- 

 mena, for all the atmospheric lines usually ascribed to that sub- 

 stance were very strongly developed. But in addition to this 

 there was a very marked general absorption in the red. Even 

 an hour before sunset, and often longer, the absorption was 

 complete as far as B, and the dark shade gradually crept up till 

 it reached C,-and at times even that line was invisible, while the 

 absorption was clearly marked up to W.L. 621. At the blue 

 end nothing could be seen beyond W.L. 428, and even that only 

 with a very wide slit, but a photograph showed the lines clearly 

 nearly as far into the ultra violet as on ordinary occasions. The 

 phenomenon was visible over a large area of country, from Ceylon 

 to Vizagapatam, and as far west as Aden. It was not, however, 

 observed at all at the Bombay Observatory. 



I am at present collecting information from various sources, and 

 so do not care to enter into many details at present. 



Most people ascribe the phenomena to the recent great eruption 

 in lava, but there are difficulties in the way of accepting this 



view, which I have not yet been able to get over, and the similar 

 appearance of a blue sun over Europe and America in 1831 

 .'eems to make this explanation unnecessary, besides it is well 

 known that the sun a[ pears green under certain circumstances 

 when seen through steam or even in a mist (Lockyer). On the 

 other hanH, observations referred to in Nature, vol. xviii. 

 p. 155, tend to show that very fine dust might produce the 

 observed effects. 



Can any of your readers refer me to Dr. Schuster's original 

 papers ? 



It may not be without interest to add that on both occasions 

 the green appearance was preceded by abnormal electrical condi- 

 tions of the atmosphere. The potential of the air was strongly 

 negative fir a number of days in succession from about 9.30 

 a.m. to 2.30 p.m., with a clear sky and no rain within 100 

 miles. C. Michie Smith 



Madras, October 10 



I INCLOSE a letter giving an account of the green sun, which 

 may be of interest to your readers. My correspondent is the 

 wife of General Tremenheere, formerly in the Indian army. 

 Warren De La Rue 



73, Portland Place, W., November 3 



Spring Grove, Islrworth, November 2 

 It may interest you to hear that my daughter, writing from 

 Bellary, tells me that a gentleman who was at Ootacamund, in 

 the Neilgherries, was on one of the higher peaks when the 

 phenomenon of the sun took place in September, and he first 

 distinctly saw a green, cloud-like mist pass across the sun, and then 

 oneofa reddish colour, and the sun took thecolourof each of these 

 clouds or mists. People at Ceylon were terribly alarmed at the 

 unusual appearance of the sun. S. S. T. 



Mr. Greaves has the pleasure to forward to the Editor an 

 extract from a letter just received from Mr. Beardmore at 

 Madras, referring to the phenomenon of the green sun now being 

 discussed in Nature. 



Sunhill, Clevedon, November 2 



Harbour Works, Madras, October 10 

 We have had the sun here for some weeks past in the morn- 

 ings and evenings a most curious greenish blue colour, and 

 generally casting a bluish beam of a most pretty tint. Mr. 

 Pogson thinks it due to volcanic dust and sulphurous gases from 

 the great eruption in Java. Another astronomer, Mr. H. Smith, 

 thinks it due to a great amount of aqueous vapour. 



Nathl. Bernard Beardmore 



The Division of the Circle 



Allow me to point out an oversight in Nature (vol. xxviii. p. 

 598), where, in explaining the divisions of a circle the following 

 passage occurs : "In quite recent times it has been suggested 

 that 400 parts should be taken in place of 360, but that is a 

 suggestion which up to the present time has not been acted 

 upon." 



We probably owe our degrees either to the earlier supposed 

 year of 360 days, or to the fact that this number has many 

 divisors, although such divisors afford no practical advantage. 

 When trigonometrical functions were subsequently discovered, it 

 was found that the natural unit is not the circle, but the quadrant 

 or right angle. Our system of numeration being decim.al, it was 

 then most convenient to divide the quadrant decimally, and the 

 circle is thus considered as composed of 4, 40, 400, Sic, parts 

 according to the degree of exactness required. This was pro- 

 posed by Briggs when preparing His logarithms, which are based 

 on decimal-, but unfortunately it was then set aside. Revived a 

 long time after by Lagrange, it was acted upon by Laplace in his 

 " Mecanique Celeste," being thus much more than a mere 

 suggestion. Nowadays decimal divisions of the quadrant are 

 the only ones used by French geodesists. 



Facts are the grand supporters of argument. Will you kindly 

 quote the following ? After grumbling on the nece sity of using 

 the only circle at his disposal because it was divided decimally, 

 a French civil engineer would afterwards employ no other : he 

 found the decimal circle much more convenient. A special ex- 

 periment had been already made in Italy, where two geodesists, 

 carefully interchanged and inspected, had been instructed to 



