June 4, 1908] 



NA TURE 



1 1 1 



OUR ASTRONOMICAL COLUMN. 



Astronomical Occurrences in June :— 

 June 6. 5h. 37111. to gh. 20m. Transit of Jupiter's Sat. III. 

 (Ganymede). 

 7. 4h. 2401. Conjunction of Mercyry and Mars. Mercury 



o' 19' N. 

 ,, I3h. om. Mercury at greatest elongation, 23° 5S' E. 

 13- 9h. 57f". to I3h. 39m. Transit of Jupiter's Sat. III. 



(Ganymede). 

 14. loh. 13m. to nil. 24m. Moon occults 4 Sagittaiii 



(mag. 4-6). 

 19. Ilh. lom. Minimum of Algol (S Persei). 



21. Sh. igm. Sun enters Cancer and Summer commences. 



22. Sh. 32m. Venus in conjunction with Mars, Venus 



2° 4' S. 

 2S. Eclipse of the Sun partially visible at Greenwich. 

 Begins 5h. 14m. : Middle $h. 3Sm. ; Ends 6h. 2m. 

 Magnitude (Sun's diameter =1) o'o65. At the 

 time of greatest obscuration nearly one-fifteenth of 

 the Sun's southern limb will be occulted. 



The Return of Encke's Comet. — A telegram from the 

 Kiel Ccntralstelle announces that Encke's comet was found 

 by .Mr. Woxidgate, of the Cape Observatory, on May 27. 

 Its position at I7h. 491T1. (Cape M.T.) on that date was 

 R..\. = 2h. 59-3111., dec. = 7° 29' S. This is situated about 

 half a degree north of p Eridani, and is, at present, un- 

 observable in these latitudes. 



The Radi.al Velocity of Algol. — No. 22, vol. ii., of 

 the Mittcilungcn der NikoJai-Hatipsteruwartc zu Pitlkoivo 

 contains a very full discussion by Prof. BelopolsUy of the 

 radial-velocity observations of .Mgol made at the Pulkowa 

 Observatory during the years 1905-7. The results obtained 

 from each line on each spectrogram are discussed in detail, 

 and the following elements are finally derived : — 

 a 42°.5+i°.35, £ = 00476 + 0-0037, T = 2-509 + 0-00019 days, 

 a = 1,693,523 + 100 km., and 1 = 90°. 



The Radial Velocity of € Urs^ M.ajoris. — From two 

 spectrograms obtained at Potsdam in 1889, Profs. Vogel 

 and Scheiner found the radial velocity of e Ursas Majoris 

 to be —30-4 km., the measurements being made on the 

 Hy line. But from nine very consistent plates, secured 

 with the Bruce spectrograph in 1902-3, Prof. Adamt, 

 derived the value —9-4 km., and in 1903 this was con- 

 firmed by measurements of seven plates obtained at Pots- 

 dam, the mean value being —9 km. Vogel and Eberhard 

 then re-measured the original plates, and confirmed the 

 first value. The comparison of these results suggested 

 that, possibly, the radial velocity of e Ursa; Majoris is 

 variable. That the star is of peculiar interest is shown 

 by the fact that its spectrum is given as type I. a 2 in 

 X'ogel's classification, as VIII. P. in the Harvard classifi- 

 cation, and that Sir Norman Lockyer, whilst classing it 

 as " Sirian," has pointed out that it has several well- 

 marked peculiarities. 



For these reasons Messrs. Baker and Schlesinger, of 

 Allegheny Observatory, obtained — during Marcli and April, 

 1007 — and the former measured, seven spectrograms taken 

 with the Mellon spectrograph, which gives a measurable 

 spectrum of 21 mm. in length between X 3925 and \ 4750. 

 The resulting mean value was —7-1 km. +0-46 km., and 

 as this agrees so closely with that obtained by Prof. 

 Adams and with the later value of Prof. Vogel, the matter 

 must still be considered as requiring further investigation 

 (Publications of the Allegheny Observatory, vol. i.. No. 4, 

 i'- 25)- 



Oeserv.-\tions of Jupiter's S.vtellites. — Some interest- 

 ing observations of eclipses and occultations of Jupiter's 

 satellites are recorded by M. S. Kostinsky in No. 4249 of 

 the Astronomische Nachrichten (p. 14, May 20). On 

 April 3 photographic and visual observations of a partial 

 eclipse of J. ii. by the shadow of J. i. were secured; the 

 brightness of J. ii. was diminished about 0-3-04 magni- 

 tude according to the eye observations, and the minimum 

 brightness occurred at iih. 52-3m. (Pulkowa M.T.). On 

 February 24 an occultation of the second satellite by the 

 first was observed at loh. 45.5m., and on March 27 and 30 

 two series of photographs of the second and third satellites 

 were secured during their eclipse by the planet's shadow^ 



NO. 2014, VOL. 78] 



-■\ partial eclipse of the second by the tlTIrd satellite 

 was observed by Herr Fauth at the Landstuhl Observa- 

 tory at 8h. 17m. 55s. CM.E.T.) on February 20. 



The Orbit of o Andromed.e. — The following elements 

 for the orbit of a .'\ndromediE are published by Mr. Baker 

 in vol. i., No. 3, of the Publications of the Allegheny 

 Observatory (pp. 17-22) : — P = 96-67 days, 6 = 0-525, 

 T = i9o7 November 2-40, w = 76°-2i, K = 3o-75 km.» 

 7= — 11-55 km., .\ = 34-6o km., 6 = 26-90 km.,' and 

 a sin 1 = 34,790,000 km. The discussion of the orbit was 

 based on the measures of eleven lines between \ 3933-789 

 and \ 4481-437 on ninety-four plates obtained with the 

 Mellon (single-prism) spectrograph, and the results are 

 compared with those previously obtained at the Lowell, 

 Lick, and Potsdam observatories. 



The United States Naval Observatory. — The annual 

 report of the United States Naval Observatory for the 

 fiscal year ending June 30, 1907, gives the usual data re- 

 garding the time-service, publications, &c., and a brief 

 summary of the observations made with each set of instru- 

 ments. The observation of each star in Sir David Gill's 

 Zodiacal Catalogue of 2798 stars was nearly complete, 

 but a few more observations remained to be made in the 

 autumn of 1907. More than 3000 observations were made- 

 by difl'erent observers with the new self-registering transit 

 micrometer installed in October, 1906, and the results 

 again prove the efiiciency of this instrument. Bad weather 

 limited the number of photoheliograms obtahied, records 

 being secured on only 150 days ; spots were shown on the 

 negatives on 148 days. There are now 1455 solar negatives 

 in hand, and in order to minimise the labour of reducing 

 these it is proposed that a heliomicrometer, as devised by 

 Prof. Hale, be installed. 



ON THE SHAPES OF EGGS, AND THE CAUSES 

 WHICH DETERMINE THEM.' 



T^HE eggs of birds and all other hard-shelled eggs, such 

 as those of the tortoise and the crocodile, are normally 

 simple solids of revolution, but they differ greatly in form 

 according to the configuration of the plane curve by the 

 revolution of which the egg is, in a mathematical sense, 

 generated. Some few eggs, such as those of the owl or 

 of the tortoise, are spherical or very nearly so ; a few,, 

 such as the grebe's or the cormorant's, are approximately 

 elliptical, with symmetrical or nearly symmetrical ends ; 

 the great majority, like the hen's egg, are ovoid, a little 

 blunter at one end than the other ; and some, by an 

 exaggeration of this lack of antero-posterior symmetry, are 

 blunt at one end but characteristically pointed at the other, 

 as is the case in the egg of the guillemot and puffin, the 

 sandpiper, plover, and curlew. 



Various theories, based upon the principles of natural 

 selection, are current and are very generally accepted to 

 account for these diversities of form. The pointed, conical 

 egg of the guillemot is generally supposed to be an adapta- 

 tion advantageous to the species in the circumstances under 

 which the egg is laid ; the pointed egg is less apt than a 

 spherical one to roll off the narrow ledge of rock on which 

 this bird lays its solitary egg, and the more pointed the 

 egg so much the fitter and likelier is it to survive. The 

 fact that the plover or the sandpiper, breeding in very 

 different situations, lays eggs that are also conical elicits 

 another explanation, to the effect that the conical form 

 permits the many large eggs to be packed closely under 

 the mother-bird. ' The round egg of the tortoise and the 

 elongated egg of the crocodile have been supposed to be 

 developed in conformity with the shape of the creature that 

 has afterwards to be hatched therein. \Vhatever_ truth 

 there be in these apparent adaptations to existing circum- 

 stances, it is only by a very hasty logic that we can accept 

 them as a vera causa or adequate explanation of the facts ; 

 and it is obvious to my mind that, in attempting to de.al 

 with the forms assumed by matter, whether in the organic 

 or the inorganic world, we ought first to attempt to deal 

 on simple physical lines with the forces to which it has 

 been subjected, that is to say, the intrinsic forces of growth 



1 A p.^per read before the Zoological Society of London on .\pril 28 by 

 Prof. D'Arcy Wentworth Thompson, C-R. 



