NOTES. 



ASTRONOMY. 



By A. C. D. Ckommki.in, B..\.. D.Sc, F.K..-\.S. 



THE A.XIS OF MARS.— In "Knowledge" for last 

 October, I described Dr. H. Struve's method of finding the 

 position of the axis of Mars, and its compression, from the 

 motions of the poles of the orbits of Phobos and Deimos. He 

 has now published a revised result, including the observations 

 of 1907 and 1909 (when there were many visual observations 

 at the Lick Observatory, and photographic ones at Pulkowa). 

 He obtains results very near his former ones, but oiititlod to 

 considerably more confidence. — 

 North Pole of Mars at epoch 1880-0— K. A. 317" 4'-4 ; Annual 



Increase 0'-463. N. Dec. 52" 35'-6; .Annual Increase 



0'-239. 

 Obliquity of Mars Equator to orbit, 25' lO'. 

 Polar compression iJir. 



Centre of circle of Poleof Phobos orbit 317° 3'-7. N. 52°36'-0. 

 Distance from Pole of Mars 0° 0'-6. 



Radius of Circle 57' -5. Annual angular motion of Pole 158 . 

 Eccentricity of orbit -017. 

 Centre of circle of Pole of Deimos Orbit 316° I' -2.. N. 



53' 16' -0. 

 Distance from Pole of Mars 0' 55' -5. 



Radius of circle l°44'-0. .-Annual angular motion of Pole (>°- 374. 

 Eccentricity of orbit -003. 



I understand that these values will in future be used for the 

 Ephemeris for Physical Observations of Mars. 



THK I'KILKI-: AND MASS OF U RAX L"S.— Mars is not 

 the only planet for which the satellites give interesting 

 information as regards its figure and the position of its axis. 

 They are particularly valuable in the case of the two outer 

 planets of our system, on whose surfaces it is difficult to detect 

 any marliing. Mr. Marth long ago recognised that the plane 

 of the orbit of Neptune's sateUite Triton was shifting, which 

 is evidently due to the equatorial protuberance of Neptune. 

 The motion is so slow (one revolution taking about five 

 hundred ^nd eighty years) that a longer time must elapse 

 before the position of Neptune's axis is accurately known. 

 A first approximation was given by the present Astronomer 

 Royal and Mr. Edney, in Mon. Not. R.A.S. April, 1905. A 

 more elaborate discussion by .Mr. David Gibb [Proc. Royal 

 Soc. Edinb. 1908-9) indicated that Neptune's North I'ole is in 

 R..'\. 295-6, N. Dec. 42°- 8. Its equator in that case is 

 inclined 21° -2 to the orbit of Triton, and 27' to its own orbit. 

 In view of the probable retrograde rotation of Neptune it 

 might be more proper to call the above Pole its South Pole. 

 In the case of Uranus its nearest sateUitc Ariel, is only half as 

 distant from its primary as Triton from Neptune. There 

 would consecjuently be a nnich more rapid shift of the orbit 

 plane if it differed from the equatorial plane of Uranus. As 

 no such shift has been detected, it is certain that the two 

 planes piactically coincide. This is further shown by the fact 

 that the planes of all the satellites are sensibly the same, l-'or 

 if they were inclined to the equator they would shift at 

 different rates, and their agreement at the present time would 

 be most improbable. Hence we may take the position of the 

 axis of Uranus as known. 



The R.A. of its North Pole for 1900 would be 75°- 81 ; annual 

 increase "- 014: North Dec. 14°-79; annual diminution -"OOl. 

 Orion is therefore the North Polar constellation for Uranus. 

 We cannot, as in the case of Mars, obtain the oblateness of 

 Uranus from the shift of the orbit planes of the satellites, for 

 no shift appears to exist. Dr. Oesten Bergstrand, Director of 

 the Upsala Observatory, has endeavoured to determine it from 

 the motion of the peri-uranium of the inner satellite Ariel. He 

 has utilised the observations made at Lick Observatory since 

 1894, The orbit is so nearly circular that we cannot place 



great confidence in the result. He finds eccentricity of .Ariel's 

 orbit -007, annual movement "f peri-nranium 15°; the cor- 

 responding results for Umbriel ari^ -008, 4° or 5". The 

 value of the compression depends on the distribution of 



dcusitv in the globe of Uranus. 



Rotntion Pcrioil. 

 Hours. 



If Uranus is homogeneous the compression is ib ... — 

 If it is arranged like Jupiter, the compression is ■}« •■• 17-6 

 If it is arranged like Saturn, the compression is i\i ... 11-3 



Value adopted as most probable rro ... 13 



It would seetn, then, that Uranus takes distinctly longer to 

 rotate than Jupiter and Saturn do, and the same appears to be 

 the case with Neptune from the figures given above. It is 

 perhaps not surprising, from the fact that they are intermediate 

 in size between the giant planets and the terrestrial ones. 



ROTATION OF VENUS.— M. Belopolsky has recently 

 published another spectroscopic determination of the period 

 of rotation of Venus, which he again finds to be not very 

 different from one day. It will be remembered that Professor 

 Lowell's spectroscopic determination favoured the long period. 

 Mr. Scriven Bolton has contributed a series of drawings to The 

 Journal of the British Astronomical Association, which 

 lead him to a period of 2i^' 28"". Mr. McEwen adds a note 

 reconnnending that too Tuuch weight be not given to this 

 determination, owing to the extreme delicacy of the markings 

 on ^■enus. 



I'.OTANV. 



By Professor F. Cavers, D.Sc, F.L.S. 



CVCAD STEM-STRUCTURE.— The Cycadaceae, as the 

 lowest group of Gymnosperms, and therefore of F'lowering 

 Plants, now living, are of such importance in the evolution of 

 plants that every new detail discovered regarding their 

 structure is of interest. In a recent paper. Chamberlain 

 iBot. Gaz.. 1911) has described the structure of adult stems 

 of species of Zainia. Ccratozamia. and Dioon, and has 

 considerably supplemented the information given by earlier 

 writers. In Dioon spitiiilosiim the wood zone in a plant six 

 metres in height reaches a width of ten centimetres, far 

 exceeding the extent of the wood zones previously described 

 for any Cycad. This species shows a remarkable resemblance 

 in detailed stem-structure to the Cretaceous fossil Cycad, 

 Cycadeoidea, one of the members of the extinct family 

 Benuettitales which were in some respects more primitive than 

 the Cycads, and formed a link between this group and the 

 remarkable Cycadofilicales or fern-like seed-plants. No 

 groulh rings (" annual rings ") were found in the wood of 

 /Cauua ftoridana or Ccratozamia mcxicana ; Dioon 

 spinulosum and /). cdide have growth rings, which in the 

 former species answer to the periods of activity which result 

 in the formation of crowns or cones, but which in D. cdnle do 

 not correspond to such periods. The protoxylem, or first- 

 formed wood, consists of scalariform tracheids, from which 

 there is a gradual transition to the tracheids with bordered 

 pits, the latter forming the chief part of the wood. Scalari- 

 form tracheids are also found in the large medullary rays. 



INK-CAP TOADSTOOLS. — The small toadstools belong- 

 ing to the genus Coprinus are remarkable in that the cap 

 with its gills after a few days becomes converted into a black 

 semi-fluid mass. The biology of these curious toadstools has 

 been studied already by Buller in his brilliant " Researches on 

 Fungi," but Weir {Flora, N.F. Band 3. 1911) has made a 

 very extensive investigation of the genus Coprinus and dis- 

 closed many new and interesting facts in the physiology of 

 these plants, and his long paper may be summarised as 

 follows. In addition to the differentiation of the tissue mto 

 central conducting filaments and strengthening outer tissue, 



