74 



NATURE 



[September 27, 1917 



OUR ASTRONOMICAL COLUMN. 



A New Comet. — A Copenhagen telegram announced 

 an observation of Encke's comet by Dr. Max Wolf 

 on September 14. At 1311. 5i-3m., Konigstuhl Mean 

 Time, the position of the comet was R.A. 6° 24', de- 

 clination + 13" 16'. The Morning Post of September 

 26 states that an observation made on September 21 

 proves the object to be a new comet, and not Encke's 

 comet, as first supposed. 



An Empirical Law of Planetary Distances. — An 

 interesting empirical law connecting the distances of 

 the planets from the sun is discussed by G, Armellini 

 in the Observatory for September. The law is ex- 

 pressed by the simple formula -^,i,= i-53", where 1-53 

 represents the distance of Mars from the sun, and n 

 takes the values —2, —1,0, i . . . for the planets 

 Mercury, Venus, Earth, Mars . . . The numerical 

 values given by the formula are compared with the* 

 true values, and with those given by Bode's law, in 

 the appended table : — 



Formula True distances Bode 



Mercury .. 1-53- - = 0-427 ... 0-387 ... 0-4 



Venus" ... I -53" '===0-054 •-• 0723 ••• 0-7 



Earth ... 1-53'' =1-00 ... i-oo .., i-o 



Mars ... 1-53^ =1-53 ... 1-52 ... i-6 



Asteroids ... | ^'53' ==2-34 ... ' ... 1 ^.g 



Jupiter ... 1-53* =5-48 ... 5-20 ... 5-2 



Saturn ... 1-53-' =^-3^ ••• 9-54 ••• 10-0 



(Vacant place). 



Uranus ... i'53^ =19-46 ... 19-2 ... 19-6 



Neptune ... i-53« =29-76 ... 30-1 ... 38-8 



It will be seen that the formula has a marked advan- 

 tage over Bode's law in the representation of Neptune. 

 Moreover, since the two distances given for the aste- 

 roids are comprised within the limits of the asteroidal 

 zone, there is only one vacant place, whereas Bode's 

 law, if written in the form .t„ = o-4 + (o-3 x 2«), presumes 

 the existence of an infinite number of small planets 

 between Mercury and Venus. It is considered possible 

 that the vacant place between Saturn and Uranus may be 

 occupied by small planets which have not been detected 

 on account of their great distances. 



Eclipsing Variables. — Photographic light-curves of 

 the eclipsing variables, TT Lyrae and Y Camelopar- 

 dalis, obtained at Harvard, have been utilised in a 

 discussion of the orbits of these stars by Martha B. 

 Shapley {Astrophysicai Journal, vol. xlvi.,'p. 56). The 

 periods derived from the new observations are respec- 

 tively 5243708 days and 3-305568 days. In the case : 

 of TT Lyrae the observations give positive evidence of 

 a shallow secondary minimum and of a variation of 

 light due to the ellipsoidal form of the components. 

 There is also an unusually large "reflection" efTect, 

 which is attributed to inter-radiation, and on this 

 interpretation the hemisphere of the faint star which I 

 faces the bright component is eleven times as bright as 

 the other. Since only a small part of the light of the 

 blight star remains visible at principal minimum (the 

 variation being 2^ magnitudes), a large proportion of 

 the total loss of light at that time is due merely to 

 rotation of the unequally illuminated faint companion. 

 Y Camelopardalis has also a large range of variation, 

 losing 78 per cent, of its light at principal eclipse. The 

 two systems are closely similar in many respects, and 

 are estimated to be more than 3000 light-years distant 

 from the earth. 



Similar observations and determinations of orbital 

 elements have been made at the Laws Observatory 

 in the case of the eclipsing variables Z Vulpeculae, 

 TV Cassiopeise, and u Herculis (Laws Observatory 

 Bulletin, 26, 27, 28). The elements of the eclipsirtg 

 systems TV, TW, TX Cassiopeiae, and T Leonis 

 Minoris have been investigated by R. J. McDiarmid 



(Dissertation, Princeton University). The brightness 

 of TX Cassiopeiae is estimated to be 1400 times that 

 of the sun. 



NO. 2500, VOL. 100] 



THE EGYPTIAN OIL FIELDS 

 'T'HE Egyptian oilfield occurs along the western 

 ■■■ coast of the southern end of the Gulf of Suez, 

 and, being- beside a great ocean highway, is in a most 

 convenient position tor an oilfield, and where mining 

 operations should throw light on some interesting 

 geological problems. Dr. Hume writes on this field 

 with high authority and intimate knowledge; his in- 

 formation and conclusions are, however, often in- 

 definite, and his report has that air of detachment 

 from practical applications which has been responsible 

 for much of the distrust of geology felt among mining 

 engineers. The author is no doubt wise to avoid 

 unnecessary trespass on the field of the engineer, and 

 his report is on the region and not on the oilfield 

 alone. It would, however, have been even more useful 

 if it had included statistics of the oil yields and informa- 

 tion as to the quality of the oil, and if the author had 

 not declined to express any opinion on the future of 

 the field. 



_ His geology is also cautious. He states that the 

 oil is mostly derived from a cavernous dolomitic lime- 

 stone, which he regards, however, as merely a reser- 

 voir. He attributes the source of the oil to deeper 

 . beds of Globigerina marl. This suggestion may be 

 due to the influence of Prof. Mrazec, who accomp/inied 

 Dr. Hume on a visit to the field, has contributed the 

 cross sections to the report, and is probably responsible 

 for the suggested comparisons with the Rumanian oil- 

 fields. The Egyptian oilfield appears to have much 

 more in common with that of Persia than with that 

 of Rumania. In the fields beside both the Gulfs of 

 Persia and Suez the chief oil horizon is a thick series 

 of gypsum beds which Dr. Hume regards, doubtless 

 correctly, as lagoon deposits ; they overlie a Mid-Miocene 

 (Helvetian) coral limestone, and lie below a limestone 

 containing a fossil oyster, Alectryonia virleti, which 

 is characterrstic of the Upper Miocene (Tortonian). 

 Dr. Hume refers this bed to an indefinite " Mio- 

 Pliocene" horizon, which he places above the Lower 

 Pliocene. The remarkable resemblance in the general 

 succession of the Egyptian and Persian oilfields favours 

 the correlation of the virleti beds with the Upper 

 Miocene, and the origin of the oil from the gypsiferous 

 deposits. 



The Egyptian oilfield structurally consists of a band 

 of sedimentary rocks which has sunk between the 

 granitic masses of Sinai and south-eastern Egypt. It 

 thus resembles the Alsatian oilfield which has been 

 lowered between the Archean masses of the Vosges and 

 the Black Forest. By this movement the beds have 

 naturally been folded and faulted. But it is not clear 

 from Dr. -Hume's account whether, in the Egyptian 

 field, the folding was the primary movement, or, as in 

 the Alsatian field, was secondary to the faulting. He 

 attaches most stress to folding, but he includes therein 

 movements that would generally be regarded as fault- 

 ing; for the upraising of a mass of old granite into 

 overlying sediments, which are thereby disturbed and 

 brecciated along the contact, he includes as folding. 



The report is well illustrated by numerous photo- 

 graphs and an excellent map by Dr. Ball, and though 

 the text leaves us wishing that the author out of the 

 fullness of his knowledge had given more information 

 on some branches of the subject, we are grateful for 

 a valuable addition to both Egyptian and economic 

 geology. J. W. G. 



1 Ministry of Finance, Egypt. Report on the Oilfields Region of Egypt. 

 By W. F. Hume, Director of the Geological Survey of Egypt. Pp. viji-f- 

 103 + 23 plates. (Cairo: Government Press, 1916.) 



