340 



NATURE 



[May 13, 1920 



Our Astronomical Column. 



Conjunction of Mars with Spica. — Interesting, 

 though not extremely close, approaches of Mars to 

 the bright star Spica Virginis will occur on May 22, 

 when Mars will be situated 2^ degrees north of the 

 star. On that night the planet will pass the meridian 

 at 9.21 G.M.T. at an altitude of about 30 degrees. 

 On succeeding nights Mars will be observed to the 

 N.N.W. of the star, but on June 2 will become 

 stationary, and thereafter move slowly eastwards. On 

 June 12 he will again be in conjunction with Spica 

 Virginis, and about \°y]' N. of the star. Mars will 

 cross the S. meridian 10 minutes before sunset on 

 the latter night, and a good view will not be obtain- 

 able of the planet and star until 9 p.m. G.M.T. and 

 afterwards. Mars will be much the brighter of the 

 pair, and visible at an earlier time than the star. The 

 two conjunctions will form attractive and striking 

 configurations. 



The Duplicity of v Geminorum. — ^There is an article 

 on this star by Dr. Bernewitz in Asir, Hach., 5041. 

 The orbit as a spectroscopic binary was investigated 

 in the Publications of Ottawa Observatory (vol. iv., 

 No. 19). The period is 9-6 years, and the value of 

 asint is 1,400,000,000 km. This large value suggested 

 that it might not be impossible to detect the duplicity 

 visually. It has been examined with the 65-cm. 

 refractor at Berlin-Babelsberg Observatory by Dr. 

 Bernewitz, Dr. Bottlinger, Prof. Guthnick, and Mr. 

 F. Pavel. All agree that the image is distinctly 

 elongated. Neighbouring stars of similar magnitude 

 app>eared perfectly round, so that it is concluded that 

 the effect is not instrumental. On examining 

 V Geminorum through increasing thicknesses of a dark 

 wedge it was found that before it disappeared it 

 became round ; they conclude from this that the com- 

 panion is about I rnagnitude fainter than the primary. 

 This difference removes uncertainty as to the quadrant. 

 Dr. Bernewitz and Mr. Pavel each measured the pair 

 on five nights, and their respective results are : 



Date P. A. Distance. 



0-14 



o-i6 



1920-208 Il6-2 



1920-205 124-3 



They state that the spectroscopic results indicate that 

 the star is now near elongation. If measures can be 

 obtained over a sufficient arc of the orbit, it will be 

 possible to deduce the parallax and mass. The spec- 

 tral type is B5, so that a mass-determination would 

 be of particular interest. 



KODAIKANAL OBSERVATIONS OF PROMINENCES. — Vol. i., 



part 2, of the Memoirs of Kodaikanal Observatory 

 has lately been distributed. It contains a full descrip- 

 tion, with numerous photographs, of the prominence 

 observations made by Mr. and Mrs. Evershed, and a 

 discussion of their distribution and motion. Their 

 preponderance at the sun's eastern limb, which many 

 observers have noticed, is difficult to explain except 

 as an earth effect. It will be remembered that Mr. 

 Evershed has recently noticed another sign of an 

 earth effect in the distribution of line-of-sight velocities 

 in the photosphere. 



It is pointed out that besides the principal promin- 

 ence zones, which coincide with those of sunspots, 

 there are also high-latitude zones. The prominences 

 in these are less active than the equatorial ones ; they 

 frequently appear as pyramids, or rows of round 

 patches. Their wave of activity begins in latitude 50°, 

 soon after sunspot maximum; it travels poleward, 

 reaching the oole about the next maximum and dying 

 out there. It is suggested that the change in the 

 corona round the poles, which takes place in the 



NO. 2637, VOL. 105] 



sunspot cycle, may be connected with this prominence 

 fluctuation. 



The rotation of the prominences has been studied 

 at Kodaikanal ; it is found to be more rapid than that 

 of the photosphere. Line-of-sight velocities and disc 

 observations of long-lived prominences agree in sup- 

 porting this. It is concluded that the prominences are 

 so tenuous that the free path of the atoms is infinite. 

 Their luminosity " is due to the internal energy of the 

 atoms, perhaps derived mainly from absorption of the 

 intense solar radiation." 



Leonardo da Vinci.^ 



By Edward McCurdy. 



WITH the list of war inventions may be numbered 

 Leonardo's researches in aviation. He pursued 

 this subject for many years. His studies range from 

 the consideration of the primary causes of flight in birds 

 and other winged creatures to the invention of a screw 

 propeller and the consideration of its applicability to 

 aerial navigation. He also made an actual attempt. 

 Jerome Cardan, the physician who made a horoscope 

 for Edward VI., in his work "De Subtilitate " refers 

 to an unsuccessful attempt at flight made by Leonardo 

 da Vinci, and adds somewhat dryly, " He was a great 

 painter." A sentence on the cover of Leonardo's 

 manuscript, " Sul Volo degli Uccelli," written in 1505, 

 has been interpreted as referring to this attempt. 

 "The great bird," it runs, "will take its first flight 

 uppo the back of the great swan, filling the whole 

 world with amazement, and filling- all records with 

 its fame ; and it will bring eternal glory to the nest 

 where it was bom." 



This enigmatic utterance may be somewhat more 

 comprehensible if it is remembered that cecero is the 

 Italian word for swan, and "the back of the great 

 swan " may therefore be interpreted as a reference to 

 Monte Ceceri, a hill to the south-west of Fiesole, from 

 which it is believed the flight took place. 



From the meagre records of the attempt we pass to 

 researches in theory and construction. 



Tlie material falls naturally into two groups, the 

 first being a series of investigations of the laws which 

 g^overn the power of flight as manifested in Nature by 

 birds and other winged creatures, the second consisting 

 of deductions from these principles in the construction 

 of a mechanism which should be capable of sustaining 

 and being worked by man. The interdependence of 

 the two parts of the inquiry is stated with _ great 

 succinctness in a passage in the Codice Atlantic© : 



"A bird is an instrument working according to 

 mathematical law, which instrument it is within the 

 capacity of man to reproduce with all its movements, 

 but not with a corresponding degree of strength, 

 though it is deficient only in the power of maintaining 

 equilibrium. We may therefore say that such an 

 instrument constructed' by man is lacking in nothing 

 except the life of the bird, and this life must needs 

 be supplied from that of man. 



"The life which resides in the bird's members will, 

 without doubt, better conform to their needs than will 

 that of man, which is separated from them, and 

 especiallv in the almost imperceptible movements 

 which preserve equilibrium. 



"But since we see that the bird is equipped for 

 manv obvious varieties of movements, we are able 

 from' this experience to deduce that the most rudi- 

 mentarv of these movements will be capable of being 

 comprehended bv man's understanding: and that he 

 will to a great extent be able to provide against the 



1 From a discourse delivered at the Royal Institution on Friday, March 19. 

 Continued from p. 3og. 



