532 



NA TURE 



[August 4, 1904 



OUR ASTRONOMICAL COLUMN. 



The Red Spot on Jupiter. — This object exhibited a 

 slackening motion during the years from 1878 to 1900. It 

 then became decidedly accelerated, so that the rotation 

 period, which in 1899 and 1900 was gh. 55m. 41-75., de- 

 creased in 1901 to gh. S5m. 40-65., and in 1902 to 

 gh. 55m. 39-os. In igo3 the spot again became retarded, 

 and the rotation period increased to gh. S5m. 41-os. This 

 retardation has now in turn given way to another acceler- 

 ation of speed. In January last the longitude of the spot 

 was 35°, whereas at the present time it is only 30°, so 

 that the rotation period during the first six months of igo4 

 has been about gh. 55m. 39-55. It is difficult to explain 

 these curious oscillations in velocity. Some extensive dis- 

 turbances have, however, affected the south temperate region 

 of the planet in recent years, and a large dusky patch has 

 been visible since igoi rotating with a rate of gh. ssm. 18-75., 

 or about 22 seconds less than that of the red spot. The 

 motion of the latter may possibly have been affected by 

 disturbances occurring in the same latitude, but this can 

 only be fully determined by further observations. In the 

 meantime, both the red spot and the south temperate spot 

 are being attentively watched as to their motions and appear- 

 ances. The two objects were in conjunction in July, igo2, 

 and June, igo4, and in the spring of igo6 the event will be 

 repeated if the south temperate spot should remain visible 

 until that time. As to the red spot and its surroundings, 

 they appear to form features of remarkable permanency, and 

 are likely to continue perceptible for an indefinite period. 



X'.^RUHLE R.^Di.-\L Velocity of a Andro.med.e .and Four 

 OTHER Stars. — Whilst engaged in line-of-sight work with 

 the Lowell spectrograph Mr. V. M. Slipher discovered 

 the variable radial velocities of a Andromedre, a Libra;, 

 0- Scorpii, X Sagittarii, and t Capricorni. 



The velocities of a Andromedje were obtained from 

 measurements of (he H7 and 4481 magnesium lines, the 

 helium 4472 line also being measurable. They range from 

 -)-20 (February 11) to —45 km. (March 4), but are un- 

 certain to a few kilometres. The observations indicate a 

 period of about 100 days and a very eccentric orbit. 



The measurements of the a Librae spectrograms give a 

 range between —60 km. on May 24 and -I-20 km. on July 6, 

 and suggest that both components are bright. The velocities 

 of a Scorpii range between -I- 25 (June 25) and —25 km. 

 (June 18). Only two plates were measured for X Sagittarii, 

 which is a visual variable having a period of seven days, 

 and these gave -f- 1 and —22 km. on June ig and 22 re- 

 spectively- A range of from —45 km. (September 7, igo3) 

 to 4-6 km. (July 6) was obtained for the radial velocity of 

 e Capricorni (Lowell Observatory Btdletin, No. 11). 



Various Cl.asses of Silicium Lines and their Occur- 

 rence IN Stellar Spectra. — In a communication to 

 I'Acad^mie des .Sciences (Paris), M. de Gramont de- 

 scribes some results he has obtained during a series of 

 experiments on the effects of various amounts of self-induc- 

 tion in the spark spectrum of silicium. His observations 

 led him to form two main classes of silicium lines : — 

 (i) those which are not affected or are strengthened by 

 self-induction amounting to 003 henry ; (2) those of which 

 the intensities are reduced by self-induction and which dis- 

 appear entirely with 0006 henry. 



He further divides them into eight groups (a-ri), and, in 

 a table showing their individual characteristics in the spark 

 and in various stellar spectra, he shows their connections 

 with the four temperature groups (silicium i.-iv.) named 

 by Sir Norman Lockyer in his temperature classification of 

 the stars. From this table he draws the following con- 

 clusions : — (i) Only the spectra of the first class, i.e. 

 hydrogen and helium stars, show the lines which disappear 

 under the action of self-induction, those of helium, e.g. the 

 Orion stars, exhibiting as strong lines those which are first 

 to disappear (Lockyer's silicium iii.), whilst the hydrogen 

 stars, e.g. Sirius, present the lines which are the last to 

 disappear (silicium ii.). Stellar spectra of the second class 

 (solar type) and the " flash spectrum " contain the lines 

 which appear in both arc and spark, and resist self-induc- 

 tion, e.g. \ 3905 7 (silicium i.). As the lines belonging to 

 Sir Norman Lockyer's group iv. are near oxvgen and 

 nitrogen lines, and always disappeared from the spectra with 

 the air lines, and as oxygen and nitrogen have been shown 



NO. 18 14, VOL. 70] 



to exist in the absorbing atmospheres of the stars the spectra 

 of which show this group (e.g. Crucis), M. Gramon! 

 suggests that these lines are attributable to air {Comptes 

 reiidus, No. 3, vol. cxxxix.l. 



Line of Sight Constants i-or so.me Orion Type Stars. 

 —In No. 3, vol. xix., of the Astrophysical Journal, Miss 

 E. E. Dobbin gives a list of line-of-sight constants for 112 

 stars of the Orion type, computed for the reduction of the 

 Bruce spectrograph observations. 



Dr. Schlesinger's formula.', as employed in his " Line-of- 

 Sight Constants for the Principal Stars," were used, and 

 the name, magnitude, position, and constants are given for 

 each star. The longitude is given for igoo, and therefore 

 requires the 50" precession correction for each year since 

 then. 



The Tails of Borrelly's Comet (1903) and Light- 

 pressure. — Mr. S. .\. Mitchell, of Columbia University, has 

 calculated the value of the repulsive force due to light- 

 pressure which acted on the several tails of Borrelly's comet. 

 Using the values for the angle between the radius vector 

 of the comet's path and the tail, as determined by Prof. 

 Albrecht, he found somewhat discordant values for the 

 principal tail, which gave, in the mean, the value for the 

 light pressure as iS-47 times gravity. For the secondary- 

 tail the values were much more consistent, and gave a mean 

 of I S24 times gravity ; the last four lines given in this table, 

 which were derived from measures of the angle on August 

 13, 14, 15, and 18, give a mean for the repulsive force of 

 1-460 times gravity, and therefore appear to indicate the 

 existence of a third tail, which the photographs obtained on 

 August 12 and 15 corroborated. 



In a second table Mr. Mitchell compares the values of the 

 angles between the tails and the radii vectores as obtained 



(1) by calculation from the repulsive forces given above, 



(2) by direct measurement. The results agree fairly well 

 considering the uncertainty of the measures of such ill- 

 defined objects as the tails. The differences between the 

 observed and calculated values for the principal tail as the 

 comet approached the sun indicate the presence of some 

 other repulsive force in addition to that caused by light 

 pressure, and Mr. Mitchell believes that part of this, at 

 least, is real. The size of the particles forming each of 

 the three tails, as determined from the above repulsive forces, 

 was o-i/i, /I, and i-33/t respectively {.'Istrophysical Journal. 

 No I, vol. XX.). 



Survey of India, igoi-2. — .\ volume of " Extracts from 

 Narrative Reports of the Survey of India, igoi-2," pub- 

 lished at Calcutta (1904), contains accounts of the work done 

 by several parties of surveyors in connection with the 

 triangulation of Upper Burma, latitude operations, the 

 magnetic survey of India, tidal and levelling operations, and 

 the topography of Upper Burma, Sind, and the Punjab. 



During the latitude operations some puzzling anomalies 

 were discovered between the observed and calculated values, 

 the difference O-C preserving its positive character to a 

 point much further north than might be expected. 



The latitude results obtained, using stars from Newcomb's 

 catalogue and from the (_ireenwich ten-vear catalogue for 

 1880, show the same probable errors, but there is a note- 

 worthy consistency of sign and amount (about -I- 03") in the 

 value Newcomb-Greenwich, 



.\n interesting account of the practical details of the 

 magnetic survey, and of the instrumental equipments at 

 Dehra Dun, Kodaikanal, Calcutta, and Rangoon are given 

 in part iii., where the principles of several new and modified 

 instruments are also fully described. 



THE BRITISH MEDICAL .iSSOCI.lTION IN 

 OXEORD. 

 'T'HE seventy-second annual meeting of the British Medical 

 Association, which was held in Oxford last week 

 (July 26 to 2g), was beyond question one of the most 

 successful meetings in the memory of members of the 

 association, as it was in point of numbers much the largest 

 yet recorded. 



It was remarkable also for the persistence and enthusiasm 

 with which, in spite of all the counter-attractions of that 

 ancient and glorious seat of learning, and of the diversions, 

 entertainments, and receptions arranged both by the 



