SOLAR DISTURBANCES DURING OCTOBER, 1913 



By FRANK C. DENNETT. 



October has proved more interesting to the solar observer 

 than any month since December last. Only one day was 

 missed, October the 5th. On seven days (4, 9 to 11, 13, 21, 

 and 30) the disc appeared free from disturbance, and 

 on nine others (1 to 3, 14 to 18, 22 and 23,) only faculae were 

 visible. It is to be remarked that the greater part of the 

 faculae and the whole of the dark spots were displayed in the 

 northern hemisphere. The longitude of the central meridian 

 at noon on October 1st, was 1° 24'. 



No. 12. — A pretty group of tiny pores first seen on the 6th, 

 which in the afternoon were ranged like segments of two 

 interlocking eclipses. On the 7th only the rear portion was 

 seen, whilst on the 8th only a grey facula-lipped pore 

 remained which was gone next day. Its maximum length was 

 35,000 miles. 



No. 13. — Two pores, the larger preceding, almost in the 

 centre of the disc, only seen on the 12th. 



No. 14. — A small bright facula having two penumbraless 

 pores, one on either side, east and west, seen on the 19th, 

 when the disturbance showed hydrogen flocculi, and the dark 

 D s line of helium with the spectroscope. Next day the facula 

 was still traceable with minute pores but they were not seen 

 after. 



No. 15. — On the 24th a group of pores was visible a little 



within the northeastern limb amid brilliant faculae. The 

 components remained small, and were subject to much 

 change until last seen on the 29th. Its greatest length was 

 72,000 miles. 



No. 15a. — On the 31st there was a dark grey "veiled" 

 spotlet a little north of the area which had been occupied 

 by No. 15. It was not, however, seen afterwards. 



Faculae like tiny bright granules were visible within a few 

 degrees of the North Pole, on October 1st to 3rd, 6th, 15th, 

 16th, 24th and 25th. A small one was noted at longitude 28°, 

 S. latitude 40°, on the 3rd. Faculae were also noted near the 

 south-west limb on the 11th, and the north-east on the 14th. 

 On the 16th a faculic knot was at longitude 217°, S. latitude 

 33°. On the 17th and 18th a faculic knot seen at 87°, 38° N. 

 (near the north-east limb), and a bright streakiness near 77°, 

 25° N. Traces of the former still showed on the 20th, as well 

 as a pale patch within the eastern limb a little north. Pale 

 faculae a little within the eastern, and nearing the south- 

 western limbs on the 22nd. Also within the north-eastern 

 limb, at 351°, 15° N. on the 23rd and 24th. Within the 

 eastern limb a faculic knot was visible on the 31st. 



Our chart is constructed from the combined observations of 

 Messrs. J. McHarg, A. A. Buss, C. Frooms, E. E. Peacock, 

 and the writer. 



DAY OF OCTOBER, 1913 



10 « s 40 so M 70 eo so no it a> bo ko iso m 170 iso i*) aco ao 



210 240 250 240 270 280 30 300 310 320 330 340 350 ■ 



NOTES. 



ASTRONOMY. 



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



DETERMINATION OF RADIAL VELOCITIES OF 

 FAINTER STARS.— It has often been felt that it would be 

 of great importance in advancing our knowledge of the 

 structure of the universe, if spectrograms taken with an 

 objective prism could be used in the determination of radial 

 velocities. The results with the slit spectroscope are 

 splendid in their marvellous accuracy ; but owing to the great 

 loss of light at the slit, and the resulting length of exposure, 

 the method is practically limited to the naked-eye stars, or 

 those not much below this limit. When the method of the 

 prism before the object glass, without any slit, is employed, 

 there is no loss of light, consequently much fainter stars can 

 be reached with a moderate exposure ; also there are many 

 spectra on each plate, so the work of making a spectroscopic 

 Durchmiisterung is rendered possible. In fact, much progress 

 has been made with this at Harvard, but hitherto attention 

 has been paid merely to the type of spectrum, not to motion 

 in the line of sight. Suggested methods of doing this were 

 given by Professor Pickering and others ; these are now 



discussed by Dr. Schlesinger in Proc. Amer. Phil. Soc, 

 Vol. LII, No. 209. He considers two methods practicable for 

 obtaining fairly accurate results. The first consists in 

 measuring the distance between two known lines in each 

 spectrum. With prismatic spectra the effect of velocity in the 

 line of sight is much greater for the violet end of the spectrum 

 than for the red. Hence stars approaching us have their 

 spectra lengthened, those receding have them shortened. 

 Plates are now available that will photograph the red end of 

 the spectrum with moderate exposures. It is desirable to use 

 a Cooke Triple object-glass, or else to have one specially 

 designed to bring the required regions into focus together. 

 The author also recommends the use of a temperature case 

 surrounding the whole apparatus, as change of temperature 

 affects the sharpness of the spectra. He also advises taking 

 check plates every night on stars whose velocity is already 

 known by the slit method. With these precautions results of 

 considerable accuracy may be expected. 



The other practicable method is that of placing a screen of 

 neodymium chloride before the plate. This artificially 

 introduces some absorption lines into the spectrum, one of 

 which, at X 4272, is stated to be suitable as a comparison line. 



460 



