February i8, 1909] 



NATURE 



469 



to the present been the McLeod gauge, the accuracy of 

 which was called in question by the work of Sir William 

 Ramsay more than a dozen years ago. In the January 

 number of the Verhandltmgen der deutschen physikalischen 

 Gesellschaji, Drs. K. Schecl and W. Heusc, of the 

 Reichsanstalt, describe a manometer they have constructed 

 which allows them to measure small dilTerences of pressure 

 to an accuracy of about oooooi millimetre of mercury. 

 The instrument consists of two metal reservoirs of small 

 volume separated from each other by a membrane of copper 

 26 centimetres diameter and 003 millimetre thick, which 

 bends under any difference of pressure in the two reservoirs 

 by an amount proportional to the difference. The move- 

 ment of its centre is measured by the aid of a Fizcau 

 interferometer. By means of this instrument the authors 

 have verified Boyle's law for air down to a pressure of 

 0000 1 millimetre of mercury, and have shown that the 

 McLeod gauge will give trustworthy results at these low 

 pressures. 



The Watkins Meter Co., of Hereford, has published a 

 fourth edition of the useful " Watkins Manual of Exposure 

 and Development," by Mr. .Mfred Watkins. The little 

 book, which contains an abundance of practical informa- 

 tion, is sold at !5. net. 



The fifth annual issue of M. Max de Nansouty's 

 " .Vctualitfe si'ientifiques " has been published by MM. 

 Schleicher Frires, of Paris. The volume contains a series 

 of essays on scientific subjects of current interest, which 

 range over the whole field of natural knowledge. It would 

 be difficult to imagine a more interesting way for the 

 student of science to keep up his knowledge of French, and 

 at the same time revise and extend his acquaintance with 

 recent work in his own particular subject of study. The 

 price of the volume is 3.50 francs. 



The Dorset Natural History and Antiquarian Field Club 

 offer the " Cecil " silver medal, and prize of the 

 approximate value of 5^., for the best paper on " The Dis- 

 covery of Radium : its Probable Origin, Present Develop- 

 ment, and Possible Future Use." The competition is open 

 to any person who was between the ages of eighteen and 

 thirty on May 12, 1908, and was either born in Dorset or 

 resided in the county for twelve months previous to that 

 date. Papers should be sent by March i to Mr. Nelson M. 

 Richardson, of Montevideo, near Weymouth. 



OUR ASTRONOMICAL COLUMN. 



Interaction of Slx-si'ots. — In a paper publislud in 

 No. I, vol. xxix., of the Astrophysical Journal tp. 40, 

 January), .Messrs. P. Fox and G. Abetti discuss a number 

 of observations which lead to the conclusion that in many 

 individual cases, if not in general, there exists a physical 

 connection between different groups of sun-spots. 



A preliminary examination of Carrington's and of 

 .Spoerer's results showed that the coincidences of longitude 

 in spots of different latitudes were no more numerous than 

 would be called for by the probability of chance coincidence. 



An examination of the Rumford spectroheliograms, 

 taking into account, not only the coincidences of spots 

 with spots, but also of spots with disturbed, fiocculic, areas, 

 showed that the coincidences were rather more numerous 

 than demanded by chance, but the result was still in- 

 definite. 



However, when individual cases were considered, it at 

 once became evident, from an examination of spectro- 

 heliograms, that separate spots, in about the same longi- 

 tude but in opposite hemispheres, were physically connected. 

 One example, illustrated by reproductions, shows the 

 development of a spot (Greenwich, No. 6185) as a northern 

 companion of a southern spot (Greenwich, No. 6184) 

 between May 6 and May 13, 1907. 



NO. 2051, VOL. 79] 



A more striking interaction is shown by a series of Ha 

 spectroheliograms taken on September 10, 1908, on which 

 violent eruptions are shown in connection with two spots 

 in opposite hemispheres, these eruptions culminating in the 

 gap between the spots being bridged over. Visual observa- 

 tions made during the four hours in which the whole of 

 the display took place showed violent eruptions of hydrogen 

 in the neighbourhood of the spots. Measurements of posi- 

 tion indicated that between September 8 and 12 the 

 northern spot advanced 3°-3 in longitude and i°-7 in lati- 

 tude towards the southern spot, the latter remaining 

 stationary. 



Distribution of the Stars. — A result having an 

 important bearing on questions relating to the distribution 

 of stars is announced by Prof. E. C. Pickering in Circular 

 No. 147 of the Harvard College Observatory. 



An analysis of the Revised Photometry is now being 

 carried out at Harvard, and among other results already 

 obtained the following is held to be of sufficient importance 

 to call for immediate publication. 



If the stars were infinite in number and distributed at 

 random throughout space, the number, N, in any given 

 class brighter than magnitude, M, should be given by the 

 formula N = aM + b, where a = o-6o, and b_ is another 

 constant. A previous determination of a, considering 4000 

 bright stars, gave the value 052, and the deficiency was 

 attributed to the absorption of light by some interstellar 

 medium. , . , u 



In the present investigation the stars brighter than 

 magnitude 6-50 were divided into six magnitude-groups, 

 and then into two divisions. The one division included the 

 spectral classes A and F (Type i.), the second included the 

 classes G K, and M (Tvpcs ii. and iii.), and it was found 

 that whilst for the first a = 060, for the second its value 

 was onlv 0-5 1. From this result it is obvious that in any 

 study of stellar distribution it is essential that the stars 

 must first be classified according to their spectra. 



Jupiter's Seventh and Eighth Satellites.— In No. 4300 

 of the .Istroiwmischc Nachrichten (p. 63, February 2) Sir 

 William Christie publishes an ephemeris for J vui. com- 

 puted from the elements previously published by Messrs. 

 Cowbell and Crommelin. This ephemeris gives the distance 

 Satellite viii.— Jupiter, in R.A. and declination, for every 

 fourth dav between January 2 and March 19, the values 

 given for February 19, for example, being -7m. 34-85. and 

 -4' 46". Two photographs taken at Greenwich on 

 January 16 gave the correction -l-io-3S., +2' 40 ; a 

 second photograph was secured on January 19. 



No photograph of J vii. has yet been obtained, every 

 available opportunity having been employed to photograph 

 the more recently discovered satellite. It is understood 

 that an ephemeris for J vii. will appear in the second 

 edition of the American N..'\., 1909. 



The Anomalies of Refraction.— In determining time by 

 their circumzenithal apparatus, MM. Fr. NuU and J. J. 

 Fric found a discordance which they attributed to per- 

 turbations of the atmosphere lasting over an appreciable 

 period. Whilst the small evanescent anomalies of refrac- 

 tion affected their observations to some extent, it was_ found 

 that there was a superimposed anomaly the period of 

 which would amount to seconds. . 



By an ingenious application of photography to their 

 method, they have now succeeded in demonstrating the 

 existence of 'this second anomaly, and find its period to be 

 of the order of twenty seconds, whilst the amplitude of the 

 movement it causes is about i" of arc. 



The results, and the methods by which they were 

 obtained, are discussed and illustrated in No. 13, 1908, of 

 the BiiUfiiii international dc I'.icadcmie dcs Sciences dc 

 Boht'nic. 



The Storv of the Telescope. — In view of the tercen- 

 tenary of the telescope, Mr. Mce has issued a very interest- 

 ing li'ttle brochure, in which he reviews the more important 

 events in the development of the instrument. He also adds 

 useful lists of observatories, large telescopes, astronomical 

 societies. S.C., and tabulates the chief astronomical events 

 since the death of Copernicus in 1543. This work can be 

 obtained from the author, Llanishen, Cardiff, price 6d. 



