3i6 



NATURE 



[November 4, 1920 



These photographs showed that the spectrum 

 "was practically identical with that of the 

 star o Cygni — that is, it was practically an ab- 

 sorption spectrum. This star is noted for ex- 

 hibiting fine, sharp lines representing metals at 

 :i very high temperature, these lines being en- 

 hanced when passing from the temperature of the 

 arc to that of the spark. Two nights afterwards, 

 when the nova attained its maximum brilliancy, all 

 the lines became broad and fuzzy, and bright com- 

 ponents to the lines began to show up at the red 

 end of the spectrum. More recent work at the 



a Cygni do not fit those in the nova is that, 

 owing to the great velocity in the nova, these lines 

 are displaced towards the left — i.e. towards the 

 violet. From measurements made, the velocity 

 in the line of sight works out at about 400 to 

 900 km. per sec, depending on the date on which 

 the photograph was taken. In this particular 

 case — namely, August 26 — the velocity was about 

 900 km. per sec, and was actually the maximum 

 velocity attained. 



At a late stage in their career novae begin to 

 exhibit the nebular lines. The first indication of 



I. d Cygni. 2. Nova Cygni, August 26. 



Fig. 2.— The spectrum of Nova Cygni on August 26, showing the typical nova spectrum. The contiparison spectrum is that of a Cygni, 



which the nova closely resemtled on August 22. 



Hill Observatory has shown that at later stages 

 all lines became more diffuse, a larger number 

 of bright components appeared, and the continu- 

 ous spectrum began to dim. 



The stage when the nova showed a typical nova 

 spectrum is illustrated in Fig. 2. It will be 

 noticed that amongst others all the dark hydrc^en 

 lines have bright components on the right-hand 

 side. For the sake of comparison, a spectrum of 

 the star a Cygni is placed above the nova spec- 

 trum, and the line Hj3 is made to fit the dark H;8 

 in the nova. 



The reason why the other hydrogen lines in 



this stage having been reached in the present nova 

 was recorded on a photograph taken at the Hill 

 Observatory, Sidmuuth, on October 22. The 

 stage might have been reached at possibly an 

 earlier date, but no records were available between 

 October 2 and the date mentioned above. 



As a rule, new stars are far more scarce than 

 comets, but Mr. Felix de Ray points out the interest- 

 ing fact that for a couple of years novae have 

 been more plentiful than comets, and that at the 

 present time no fewer than four novae, including 

 Nova Aquilae III., Nova Lyrae, and Nova Ophiuchi 

 IV., can be observed with small apertures. 



Obituary. 



Dr. Hermann Struve. 

 T^R. KARL HERMANN STRUVE, who died 

 -*— ' on August 12 at the age of sixty-six, be- 

 longed to a family famous in astronomy, being 

 the son of Otto Struve, and the grandson of 

 F. G. W. Struve. All three were gold medallists 

 of the Royal Astronomical Society, this being a 

 unique case of hereditary distinction in the annals 

 of that body. 



K. H. Struve was born at Pulkova in 1854, 

 being the third of the four sons of Otto Struve, 

 who was then director of Pulkova Observatory. 

 He studied at Dorpat University, where he showed 

 special aptitude in physics and optics. Apparently 

 it was the acquisition of the 30-in. refractor at 

 Pulkova that tempted him to devote his life to 

 astronomy. It was with this instrument that he 

 made the splendid series of observations of 

 Saturn's satellites for which his name will be 

 chiefly remembered. He adopted the plan of com- 

 paring the satellites with each other, instead of 

 with Saturn, which led to a great increase in 

 accuracy. His discussion of the observations 

 NO. 2662, VOL. 106] 



gave greatly improved values of the masses of 

 primary, ring, and satellites, and of the positions 

 of Saturn's equator and the orbit planes; it also 

 revealed some interesting librations in longitude. 

 For this work Struve was awarded the R.A.S. 

 medal and the Damoiseau prize of the Paris 

 Academy. A similar investigation on the system 

 of Mars gave the position of Mars's equator, the 

 amount of its oblateness, and the rate of motion 

 of the nodes. 



Other astronomical work included double-star 

 measures, star parallaxes, micrometer measures of 

 Eros, and drawings of Jupiter ; moreover, in 1874 

 Struve took part in the Russian expedition to 

 Port Possiet, Eastern Asia, to observe the transit 

 of Venus. 



In 1895 Struve became professor of astronomy 

 at Konigsberg, and director of the observatory, 

 for which he obtained a 32-5-cm. refractor. In 

 1904 he succeeded Dr. W. Foerster as director of 

 the Berlin- Babelsberg Observatory, retaining this 

 post until his death. So late as 1916 he made 

 further observations on Saturn's satellites with 



