io8 



KNOWLEDGE & SCIENTIFIC NEWS. 



[May, 1905. 



ASTRONOMICAL. 



Ne>v Comet 1905ia) Giacobini. 



A TELEGRAM rectived on the 27th March from the Kiel 



CcDtralstelle announced the discovery of a new comet at 



Nice, on the 26th March, by M. Giacobini, for which the 



followirg co-ordinates have beeu furnished : — 



RA. = 86- 3' 30" (5 b. 44 m. 14s.) i_ 1905. March 26 12. Sh.n-8m. 



Decl. = + 10= 56' 56" ) Nice Mean Time. 



A later telegram confirmed the discovery by the comet being 



seen at Lick on March 27 in the position : — 



RA. = 5 b. 48 m. 55s. I 1905. March 27. 7 h. 57 i m. 

 Decl. = + 12° 35' 43" » (Lick Mean Time.) 



The observations indicate that the comet, on discovery, was 

 situated in the North-East of the constellation of Orion, 

 between the stars a and 7, and that it is moving in a north- 

 easterly direction at the following rate: — 



Daily molion in RA. = -f 45' 



Decl. = + 1° 15' 



From the observations obtained on March 26, 28, and 30, 

 the following Ephemeris elements have been computed by 

 Herr E. Stromgren. 



T = 1905, April 3-2098 (Berlin Mean Time). 

 « = 357' 9'49 ) 

 fi = 156- 7'-94 - (1905 o) 

 «' = 4i°37'4« ' 

 log q = o 05232. 



Photoeraphy of the Solar Corona in 

 Daylight. 



For many years astronomers in all parts of the world have 

 been experimenting with various devices in the endeavour to 

 obtain records of the solar corona at ordinary times, hut with- 

 out success. ^L A. Hansky has during the last four years been 

 pursuing this inquiry in the exceptionally favourable atmo- 

 sphere at the summit of Mont Blanc. He found by preliminary 

 trials that the spectrum of the diffused sky light was very 

 feeble in the red region compared with the intensity of the 

 green and yellow portions. It is a fortunate condition that in 

 the solar spectrum the red rays are relatively less absorbed in 

 their passage through our atmosphere than the more refrangible 

 rays ; and as the continuous spectrum of the corona is very 

 intense in the red region, it appeared feasible to attempt photo- 

 graphy of thecorooal structures by meansof these red radiations, 

 obtaining the necessary contrast by passing the light through 

 a screen suitably prepared to cut off all except the red rays. 

 After numerous tests of many aniline dyes in solution, a com- 

 bination was found which completely absorbed all the spectrum 

 radiations from X 6600 to the extreme ultra violet, the colours 

 used being red, orange, malachite green, and gentian violet. 

 The absorbing screens were made by steeping fine grained 

 Lumicre films, previously fixed without development, in con- 

 centrated solutions of the corresponding colours. These were 

 then placed between two glass plates, one with plane parallel 

 faces, the other coated with the usual sensitive emulsion. 



An opaque screen slightly larger than the diameter of the 

 solar image was placed on the outer glass plate, so that the 

 light from the brilliant photosphere was prevented from reach- 

 ing the sensitive plate. 



By the permission of M. Janssen, the photographs were 

 made with the 12-inch telescope of the Mont Hlanc observa- 

 tory. On September 3, 1904, twelve photographs were obtained 

 of the circumsolar regions, with exposures varying from 

 30 seconds to 2 minutes. The positions of the screens were 



changed so as to eliminate any local effects due to them on the 

 plates. The negatives obtained were copied and secondary 

 negatives obtained by intensification, giving increased contrast, 

 which are stated to show remarkable resemblance to those of 

 the solar corona photographed during total eclipses. 



M. Janssen adds a few words in support of the forms thus 

 photographed being truly coronal, and M. Hansky suggests 

 that by a suitable alteration in the colour of the screen used, 

 it may be possible to photograph the images of the prominences 

 in the red light of wave length of the C line of hydrogen. 



In a short criticism of this work of Hansky, M. H. Deslandres 

 suggests that it would be a great improvement if special pre- 

 cautions were taken to eliminate the diffused light in the photo- 

 graphic instrument itself. In the apparatus as used, light 

 would be reflected back from the disc cutting out the sun's 

 direct image to the surfaces of the objective, and from these 

 some light must necessarily be again irregularly reflected 

 towards the photographic plate, where it will tend to produce 

 a diffused glow round the edge of the occulting disc. The 

 direct solar radiation is estimated to be about 200,000 times 

 as intense as that of the corona, and if we assume the irregu- 

 larly reflected and diffused sunlight from the occulting disc 

 and object-glass surfaces to be i-iooth part, it is evident that 

 this would still be far stronger than the corona it is desired to 

 photograph. It is suggested that the occulting screen be 

 placed outside the iuEtrument altogether, at such a distance 

 that it will obscure the sun's disc and also a slight amount of 

 the more intense base of the corona. 



Search Ephemeris for Tempel's Periodic 

 Comet. 1867 II. 



It being probable that the periodic comet discovered by 

 Tempel in 1867, and afterwards observed in 1873 and 1879, 

 may return during the present year, M. K. Gautier has pre- 

 pared a provisional search ephemeris to aid in its identifica- 

 tion. There appears to be evidence that the perihelion dis- 

 tance of the comet has been considerably increased by the 

 perturbations induced by Jupiter, the element being almost 

 double its former value in 1867. This factor will probably 

 cause a great diminution in the intrinsic brightness of the 

 comet. It is hoped, however, that the favourable conditions of 

 the coming apparition may permit of its observation ; perihe- 

 lion passage occurs in the spring, a little before opposition. 

 There is a slight uncertainty of + 12 days in the epoch of 

 perihelion passage, and the ephemeris is therefore given for 

 each of the extreme times in addition to the more probable 

 mean values. The following are the elements on which the 

 ephemeris co-ordinates are based : — 



T = 1905 April 20'5 Berlin mean time. 



fi = 542"-68. 



= 23^42'-o. 



1 = 10" 47''2. 



n = 72'= 4i'7. 



u) = i68' 4o'-3. ) 

 For preliminary purposes until the comet be sighted it will 

 be suflicient to give the positions for every fourth day. 



Ephemeris for Berlin mean MiiliiiglU. 



(mean equinox \ 

 1905. / 



