264 



KNOWLEDGE. 



July, 1913. 



A pair of the photographs are reproduced in 

 Figures 268 and 269 enlarged about two and a quarter 

 times, one degree answering to two millimetres in 

 the photographs. The time is Central European 

 time and reckoned from h to 24 h , h answering to 

 12 noon. 



With a prism-objective we succeeded in taking 

 some photographs simultaneously with the auroral 

 photographs, on which are seen stellar spectra and 

 some views of the aurora lying side by side, 

 answering to various spectral lines. The prism had 

 an angle of 60°+ and was placed in front of the 

 kinostigmatic objective, on the principle already 

 mentioned in my " Bericht." A systematic 

 employment of this method will be of great 



importance to the study of the highest strata of the 

 atmosphere. 



Most of the cinematograph attempts were failures, 

 as the film (Lumiere) was not as a rule affected by 

 an exposure of less than two seconds. It was only 

 with very intense aurora that we succeeded in 

 getting good photographs with an exposure of about 

 one second and with about two seconds' interval 

 between the photographs. Two or three such 

 series were taken, thus proving the utility of the 

 cinematograph both for taking photographs and for 

 registering rapid changes. 



The working-up of the matter collected during 

 the expedition will be the subject of a subsequent 

 detailed account. 



t With regard to the kind of glass that would be best for the purpose. I received valuable information from Dr. Slipher 



when visiting the Flagstaff Observatory in the summer of 1912. 



NOTES. 



ASTRONOMY. 



By A. C. D. Crommelin, B.A., D.Sc, F.R.A.S. 



PROLONGED OBSERVATIONS OF TEMPORARY 

 STARS. — Professor Barnard has put the Yerkes 40-inch 

 refractor to a very useful piece of work in following the 

 temporary stars of recent years long after they have become 

 invisible to ordinary telescopes. He notes that in at least two 

 cases — T Coronae of 1866 and Nova Geminorum (2) of 1912 — 

 the Nova was identical with a previously seen or photographed 

 star. His study was made partly in the hope that he might 

 find some peculiarity in the aspect of faded Novae. In this 

 he was disappointed : a few of them show longer focus than 

 ordinary stars, and the more recent ones show slight variability, 

 but otherwise they are indistinguishable from ordinary stars. 

 T Coronae was a B.D. star of magnitude 9-5 before the out- 

 burst, and is now at practically the same magnitude and 

 apparently colourless. 



Nova Cygni of 1876 is now of magnitude 15, perhaps 

 slightly variable : its appearance is hazy and the focus longer 

 than usual. In these respects it resembles Nova Aurigae of 

 1891, which is a magnitude brighter, and Nova Sagittarii of 

 1898, which is of magnitude 15. 



Nova Persei of 1901 is now of magnitude 12$, well defined 

 and colourless, of ordinary focus. According to Professor 

 E. C. Pickering this star existed before the outburst as a star, 

 photographed as far back as 1890, whose light fluctuated 

 between magnitudes 13 and 14. 



Nova Lacertae of 1910 also existed before the outbreak as 

 a star of magnitude 13$ ; it is now of magnitude 12$, having 

 the appearance of a small bluish-white nebula ; focus five 

 millimetres greater than usual. 



Nova Geminorum of 1912 existed before the outbreak as a 

 13-5 magnitude star. It fluctuated in brightness last winter, 

 and was of magnitude 8? last January. On February 8th, 

 1913, "with good seeing and at the proper focus, the Ha 

 image was clearly seen. It was small, sharp, and intensely 

 crimson, surrounded by a greenish - blue halo 3" or 4" in 

 diameter. The normal focus, however, was not different from 

 that of an ordinary star." 



Nova Geminorum of 1903 is now of magnitude 16$ and still 

 fading. The Nova of the Andromeda nebula (1885) is now 

 invisible; this may be partly from the bright background. 



Professor Barnard also gives a diagram of the small stars 

 in the region of Tycho's Cassiopeia Nova of 1572. There are 

 several stars shown, but none of them appeared in any way 

 peculiar. 



SATURN'S NINTH SATELLITE.— Another interesting 

 paper of Professor Barnard's describes his visual observations 

 of Phoebe with the 40-inch. Now that Saturn is far north 

 of the Equator he finds the satellite quite an easy object, at 

 least as bright as magnitude 14 (it had previously been 

 supposed to be of magnitude 16). The positions were in 

 practically perfect agreement with the American ephemeris, 

 which uses Dr. F. E. Ross's elements. As these were pre- 

 pared several years ago, and as the perturbations are very large, 

 this agreement is most creditable to him. 



PARALLAX OF THE ANDROMEDA NEBULA.— Astr. 

 Nachr. No. 4650 contains a determination of the parallax of 

 one of the small companion nebulae of the great one, made by 

 M. Gustaf Strbmberg at Stockholm. He obtains for the 

 parallax 0"-073 with a probable error of 0"'055. Some 

 previous determinations had given 0" ■ 171, 0"-132, and 

 0" -070 for the parallax. As the nebula is a difficult object 

 for precise measurement it can only be claimed that the 

 results give some slight probability to the conclusion that it 

 has a sensible parallax, which of course if proved would 

 negative the idea of its being an external universe. 



THE STAR POLARISSIMA.— Astr. Naehr. No. .4650 

 has an article by L. Courvoisier on this faint star, which is of 

 magnitude 9-3. It is only 10' from the North Pole, and thus 

 is always within the range of the field of view of a meridian 

 instrument ; also it is bright enough to observe on a clear 

 night with a partially illuminated field, so the writer suggests 

 that it might with advantage be used for obtaining the 

 azimuth error of the instrument. For this purpose an 

 accurate knowledge of its place and proper motion is 

 required. These are investigated in the article. The proper 

 motion is given as about 3" per century with a probable error 

 of one-third of itself. The star's right ascension this year 

 is 14 h 12™, diminishing 5" each year. 



VARIATION IN THE SUN'S RADIATION.— Astr. 

 Nachr. No. 4656 contains a paper by Messrs. Abbot, Fowle 

 and Aldrich on the simultaneous measures of the Sun's 

 radiation at Mt. Wilson and at Bassour, Algeria. The mean 

 value after correcting for atmospheric absorption, and so on, is 



I -929 calories per square centimetre per minute. It appears 

 to increase 0-07 calorie for an increase of 100 in Wolfer's 

 sun-spot numbers. There is also an irregular variation of 



II per cent, which is concluded to be really in the Sun, from 



