February 22, 1906] 



NA TURE 



401 



that observatory during the total solar ellipse of August 30, 

 1905, and the days immediately preceding and following it. 



Extraordinary deviations from the normal diurnal curves 

 were registered in all three elements, and these are plainly 

 shown on the photographic copy of the records which 

 accompanies Father Cirera's communication. 



Observations of Jupiter. — Major Molesworth's report 

 of his observations of Jupiter, made at Trincomali, Ceylon, 

 during 1904-5, appears in No. 3, vol. lxvi., of the Monthly 

 Notices R.A.S., and records the times of rotation of, and 

 the changes in, most of the Jovian features. 



One especially remarkable observation was that the 

 following and preceding ends of the large mass of dark 

 matter, known as the Great S. Tropical Dark Area, 

 appeared, on comparing the observations, to have crossed 

 the whole Red Spot bay simultaneously. As it seems 

 impossible tli.it there could be any such instantaneous trans- 

 ference of material, Major Molesworth explains the pheno- 

 menon by the suggestion that the movement of the dark 

 area into the belt following the bay caused the extrusion 

 of an equal amount of dark material from the belt pre- 

 ceding the bay. 



GRANULATIONS ON THE SOLAR SURFACE. 



A N interesting research which promises fair to lead us 

 to an increased knowledge concerning the nature of 

 the sun's photosphere has recently been instituted by Prof. 

 Hansky at the Pulkowa Observatory. On examining the 

 splendid collection of photographs of the solar surface 

 obtained by Prof. Janssen at Meudon, Prof. Hansky was 

 not able to satisfy himself that the whole of the reseau 

 seen on the negative was actually of solar origin ; it seemed 

 probable that some parts of it were produced by waves 

 in our atmosphere, and on no two consecutive negatives, 

 nor even on two taken simultaneously, could the same 

 granules be recognised. For this reason he attacked the 

 problem at Pulkowa, bringing into operation the astro- 

 graphic telescope in order to obtain photographs on a large 

 scale. 



The solar image at the focus of this instrument has a 

 diameter of 3 cm., which by the use of a concave lens 

 was increased to about 54 cm. (i.e. 213 inches). With 

 this apparatus numerous photographs were obtained during 

 May and June, 1905, and showed many of the finer details 

 of the granulations which cover the solar surface; but 

 oven on this scale it was impossible to recognise the same 

 features on successive photographs. A further improve- 

 ment was then made, so that the intervals between the 

 exposures might be appreciably shortened — in no case had 

 it been less than five minutes — and with the new arrange- 

 ment adapted to the astrograph it became possible to take 

 eight consecutive photographs with intervals of fifteen to 

 thirty seconds' duration. These showed the changes taking 

 place in the sizes and relative positions of the granules 

 very plainly, and from them the author has chosen six for 

 reproduction in his circular. Fig. 1 is a copy of one of 

 these reproductions, and shows the general nature of the 

 photographs which Prof. Hansky is obtaining, and from 

 which he hopes to derive valuable results. The scale is 

 such that the solar diameter would measure about 06 m., 

 or 235 inches. The large black portions represent parts 

 of sun-spots which came within the region photographed. 



Although on this scale obvious changes in the size -mi! 

 arrangement of the granules took place in twenty-five 

 seconds, it was impossible to measure their magnitude, so 

 Prof. Hansky intensified the photographs by successive 

 copying, and finally obtained positives showing, portions of 

 the disc on such a scale that the length of the solar 

 diameter would be about 6 m. (19-7 feet), that is to say, 

 1 mm. = o".32, or 233 km. on the solar surface. 



An examination of these positives showed that the 

 primary desideratum had been attained ; the same granules 

 were recognisable on successive photographs, and the scale 

 was large enough to enable measurements of the granules 

 themselves and of their movements to be made. The dis- 

 placements were measured with the stereo-comparator, 



and were referred to a neighbouring small spot, movement 

 towards the spot being indicated by the negative, and 

 away from the spot by the positive, sign. The diameter 

 of the actual sun was taken as 1,400,000 km., and on 

 June 21 this gave i" = 740 km. The mean variation of any 

 two settings on the same object was + o"-i2, and the 

 probable error for the relative displacement ±o"-IO. 



The displacements of the granules during the twenty-five 

 seconds which elapsed between two successive photographs 

 taken on June 25 were very diverse. In that interval live 

 of the granules had moved — o"o, — o"-55, ~o"-y/, — o"-48, 



H 



1 " Photographit 

 ,ky. 



de la Granulation solaire faites a Poulkou 



PyA. 



and — o"-So respectively, which in the mean gave — o''--o, or 

 — 51S km., i.e. about —21 km. per second. Another group 

 gave —38 km. per second, whilst for a third the com- 

 paratively low velocity of —14 km. per second was 

 recorded. 



Comparisons of other photographs showed that some 

 granules were moving away from the spot with various 

 velocities, and, as shown by the following figures, it 

 appeared that the periodic movement of the granules 

 materially affected the size of the spot. The diameter of 

 the spot is given for different times on June 25 : — 



NO. 1895, VOL. J3~\ 



4h. 17m. 15s., 2 "-64 ; 4IL 17m. 40s., 2"-25 ; 5V). 3m. 15s., 

 V'03; 5h. 4m. 15s., i"-35 ; 5b. 5m. 50s., 2"-7o; 

 5I1. 6m. 20s., 2"'88. 



On consecutive photographs taken with an interval of 

 one minute the same granulation was recognised with 

 difficulty, whilst with a three-minute interval the whole 

 riseau was practically re-arranged beyond recognition, 

 although in one or two cases it was possible to trace a 

 granule after this interval, and in two cases it was re- 

 marked that gemination had taken place. 



The dimensions of the granules varied greatly between 



