fuly 24, 1884] 



NA TURE 



If we suppose an acceleration of four days in the time of 

 perihelion passage, the effect on the geocentric position is — 



On August 16, in R.A. + 15'L in declination + 2 1 

 On „ 28, „ + 16-7, „ + 1 41 



The theoretical intensity of light expressed in the usual manner 

 would be 0-92 on August 16, and I '40 on September I. 



During the above period, with the places assigned, the comet 

 would rise at Greenwich from 2I1. 10m. to 2h. 20m. before the 

 sun. In 1873, when the circumstances approached nearest to 

 those of the return in the present year, the comet was detected 

 at Marseilles on the morning of September 2, the distance from 

 the earth being ro2, and that from the sun 0-94, the intensity 

 of light I'oS. At its last appearance in 1879 it was seen by 

 Tempel at Arcetri, on January 14, when the intensity of light 

 was only 0-13, an exceptional case, since at no previous appear- 

 ance had it been observed under a less value than 0-33. 



From the first discovery of the comet in 1846 by Brorsen, an 

 astronomical amateur at Kiel, the period of revolution has gra- 

 dually diminished from the effect of the planetary perturbations ; 

 subjoined are the times of perihelion passage in those years when 

 the comet has been observed, and the sidereal periods corre- 

 sponding to those times : — 



Days 



1846 February 25-37 G.M.T 2034'! 



2022-7 



2002-4 



I999'4 



i994'9 



From its unfavourable position the comet was missed at its 

 returns in 185 1 and 1862. It is well known that the present 

 orbit is due to the action of the planet Jupiter in 1842 : at the 

 perijove passage at 6 p.m. on May 27 in that year the comet's 

 distance from Jupiter was 0-0547 of the earth's mean distance 

 from the sun ; consequent upon this near approach, the inclina- 

 tion of the orbit in which it previously moved was diminished 

 nearly 15° according to the calculations of Dr. Harzer, who has 

 very fully investigated the circumstances It is probable that 

 there had been a great perturbation of the elements from the 

 same cause in 1759-60, and that in 1937 (according to D'Arrest) 

 this may again occur. 



The Binary-Star j8 Delphini. — Dr. Dubjago, of the Ob- 

 servatory at Pulkoua, has published a first orbit of this star, the 

 duplicity of which was discovered by Mr. Burnham in 1S73 ; 

 more than lSo° of the orbit have been described since that year. 

 The period found is 26-07 years, the periastron passage at 

 1882-19. After that most rapid of all the known revolving 

 double-stars 5 Equulei, to which Mr. Burnham attributes a 

 period of only io'S years, there is only one, 42 Coma; Berenicis, 

 that has a shorter revolution attached to it, and /3 Delphini may 

 be eventually proved to have the less period. In 1873 Mr. 

 Burnham estimated the distance of the components o" '7 ; they 

 have since closed until the star has been beyond the powers of 

 any but the largest telescopes. Dr. Dubjago's elements assign 

 for lS84'6 position 2I9°'4, distance o""28. 



RED SUNSETS* 

 'T'HE equatorial diameter of the earth is 7901 miles and the 

 circumference is 24,825, and as she revolves once on her 

 axis in twenty-four hours, a place on the equator moves through 

 1034 miles in an hour : but at any depth beneath the surface the 

 velocity is less in proportion to that depth ; in like manner, if 

 we look on the atmosphere as part and parcel of the earth, at a 

 certain height the velocity is greater in proportion to that height. 

 The whole world has been greatly interested during the last 



1 Paper read by Alexander Ringwood at an ordinary meeting of the 

 Canterbury Philosophical Institute, New Zealand, on May 1, 1884. 



seven or eight months with the beautiful phenomena of coloured 

 suns and brilliant sunsets ; and the liveliest interest has been 

 exhibited as to their origin. Lockyer was the first, I believe, to 

 point out the fact of the phenomenon of coloured suns appearing 

 first in the east and then gradually shifting to the west. He 

 traces them to Panama, and speaks of them as having been seen 

 on a north-south line ; but it strikes me that after leaving Panama 

 the phenomenon passed still further westward, was seen on 

 September 3, 4000 miles west of Panama, and at Honolulu on 

 September 5, and struck India and Ceylon on the 8th, thus per- 

 forming more than a complete circuit of the globe ; moreover, I 

 am of opinion that it may be traced still further westward, where 

 it was seen in lat. 24° 6' N., long. 140° 29' W., by Capt. 

 Penliallow of the barque Hops, on September 25, having then 

 performed 2 : { revolutions of the globe. 



All the information that I have collected, and from which I 

 have compiled the following tables, has been obtained from 

 Nature. The time column has been deduced from the time 

 and date of the phenomenon appearing at the different stations, 

 reduced to Krakatoa time ; in some instances great difficulty has 

 been experienced, especially in reference to the time at Maranham 

 in Brazil, and at Trinidad, and it has been concluded that at those 

 stations the times are late, because it was seen at Panama before 

 the time given at them, which we suppose to be an error. Like- 

 wise in the case of the Gold Coast, in one place the date given 

 is August 30, and in another September 1, but from the general 

 result it would appear to have reached that locality about mid- 

 night August 30-31. 



The tables, I trust, are sufficiently clear ; the first column of 

 miles represents the mean diurnal velocity that the cloud travelled 

 at between Krakatoa and the different localities en route ; and in 

 the subsequent columns are given the same from each station in 

 rotation. Of course it will be understood that a small error of 

 an hour or two in the time at the stations comparatively close to 

 the eruption would make a large difference where we show the 

 diurnal velocity ; and as I have had only a week's notice to 

 prepare this paper, I trust that any errors that may be hereafter 

 found will be treated with that consideration. 

 Table I. — Showing the Mean Diurnal Velocity in English 



Milts of the Phenomena of Coloured Suns and Brilliant 



Sunsets in the Northern Hemisphere 



1 for Northern He 



.j.lu- 



105 miles per day. 



The true mean of the first column, viz. that under the head of 

 Java, is obtained by adding the distance between Krakatoa and 

 each separate station together, and dividing the aggregate by the 

 gross total number of days. The way by which the distance 

 between any two stations is derived is by multiplying the differ- 

 ence in degrees of longitude by the value of a degree in English 

 miles for the mean latitude of the two places. It must be re- 

 membered that between India and the last-named locality on the 

 list the dust cloud is supposed to have performed over a revolu- 

 tion and a half of the earth. 



I place great confidence in the result obtained from the obser- 

 vations deduced from India, because there there are scores of 

 trained meteorological observers whose duty it is to immedi ttely 

 report any phenomena that may take place, and such as that 

 concerning which I speak could not have escaped their immediate 



