x^PRIL 13, 191 l] 



NATURE 



223 



I the echelon, the Fabry and Perot interferometer, &c. 



Those workers wishing to learn more of the latest forms 

 I of these special apparatuses should get section B of the 



catalogue, issued separately, in which, in addition to the 

 \ descriptions, figures, and prices, complete bibliographies 

 I concerning them are given. 



We have received the new edition of the " Descriptive 



I List of Photographic Dry Plates, Filters, and Safelight 



Screens " manufactured by Messrs. Wratten and Wain- 



wright, Ltd. (Croydon). The firm have recently installed 



i apparatus for the critical examination of the effect of 



, colour screens upon definition, a matter too often left to 



1 chance. With regard to the plates, &c., prepared specially 



I for all kinds of scientific work, we notice specific state- 



I ments as to those best adapted for photographing various 



' parts of the spectrum, and the " high resolution plates," 



'■ for which a " limiting separation of about 1/ 150th mm." 



is claimed, as against a separating power equal to about 



' Mith mm. for ordinary plates. These special plates are 



panchromatic plates. 



OUR ASTRONOMICAL COLUMN. 



Dktonating Meteor in Messina. — On Monday evening, 

 Ai>ril 10, at 7 p.m., people at Messina noticed a brilliant 

 ', illumination of the sky, succeeded in about three minutes 

 ' by four loud explosions like artillery discharges. The idea 

 was that one of the ammunition magazines in a fort had 

 exploded, but telegraphic despatches from Palermo, 

 Catania, and Reggio di Calabria announce that a similar 

 phenomenon had been remarked there, and that it had its 

 derivation from a large bolide or some other meteoric dis- 

 turbance. The interval of three minutes between the flash 

 and sounds show that the disruption of the fireball occurred 

 at .1 distance of about forty miles from the observer at 

 M- siina. More information is awaited. At other stations 

 tho object may have approached much nearer, if it did not, 

 indeed, shower some of its disintegrated fragments to the 

 ground. April 10 is a rather special date for large fire- 

 balls ; it has furnished many fine specimens in past years. 



Halley's Comet. — Writing to the Astronomische Nach- 

 richten (No. 4489), M. Antoniadi shows that whilst Prof. 

 Eginitis recorded the tail of Halley's comet as being 

 dii'cted towards the sun at 6h. 40m. (G.M.T.) on May 

 20. 19 10, five observers who saw it at various short 

 inirrvais before that time, and five who saw it after, re- 

 corded the tail as directed from the sun ; only twenty-nine 

 minutes separated the times of observation at Sonnwend- 

 stein rind Athens, the former being yh. 9m. (G.M.T.). 

 Mr. Evershed, observing at Kodaik^nal about 2h. (G.M.T.) 

 on May 20, saw no trace of a tail directed towards the 

 sun, although he looked specially for it. 



The same number of the Astronomische Nachrichten 

 conrains a long series of observations of the comet made 

 at Besan(;on (December 10, 1909, to June 29, 19 10) and at 

 Berlin (December 16 to June 10) ; M. Chofardet reproduces 

 a drawing showing the magnificent fan which preceded 

 th sharp nucleus on May 27. 



Circulation in the Solar Atmosphere. — From an 



examination of 3323 prominences shown on photographs 



taken between January, 1904, and December, 19 10, with 



' the Rumford spectroheliograph at the Yerkes Observatory, 



Dr. Slocum has derived some valuable data concerning the 



circulatory currents in the solar chromosphere ; the light 



of the H calcium line was always employed. Of the total 



examined, 1094 prominences, either by their shapes or 



I movements, indicate a horizontal current, and as the 



average height to which these extended was 0-7', or 



30,000 km., the results represent the average poleward 



, components of the solar atmospheric circulation from the 



: lower surface of the chromosphere up to that height. Dr. 



I Slocum finds that in middle latitudes there is a tendency 



for movement towards the poles, and in high latitudes a 



I tendency towards the equator ; near the equator the motion 



■is practically negligible. The contrast between the two 



[tendencies is greater in the northern hemisphere in the 



i ratio of at least 2:1. 



X' >. 



2163, VOL. 86] 



Among the earlier plates there were few which afforded 

 data from which the velocities of the motions could be 

 determined, but during the past 3ear suitable plates for 

 this purpose have been taken regularly. There is some 

 difficulty in determining which of the observed movements 

 may be ascribed to systematic circulation and which to 

 local explosive outbursts, but ten selected cases give veloci- 

 ties of from 0-5 km. to 10 km. per second for the com- 

 ponent of the circulatory movement which is perpendicular 

 to the line of sight ; one detached cloud, floating at an 

 elevation of 442", or 320,000 km., showed a velocity of 

 50 km. per second. Dr. Slocum points out that these 

 results are not necessarily a contradiction to those obtained 

 by Dr. St. John, who failed to detect any currents of 

 appreciable velocity parallel to the solar surface ; the two 

 researches deal with different levels in the solar atmo- 

 sphere. He further suggests that as his results depict the 

 movements at an average height of 30,000 km., they prob- 

 ably apply to an upper current analogous to terrestrial 

 anti-trades ; a later discussion to deal with the different 

 levels is promised (Astrophysical Journal, vol. xxxiii.. 

 No. 2, p. 108). 



The I^opularisation ok Astronomy. — From Tlie York- 

 shire Weekly Post for April 8 we learn that the excellent 

 idea of out-of-door astronomical talks has also been sug- 

 gested by Mr. J. H. Elgie as a useful item in the pro- 

 gramme of the Leeds Astronomical Society. For the past 

 three weeks the society has been waiting, in vain, for a 

 favourable sky so that they might hold the proposed 

 Saturday evening meeting. Such meetings, open to the 

 public, might easily be organised, and would probably do 

 a great deal to dissipate the lamentable ignorance concern- 

 ing the stars which is so frequently displayed by the 

 general public. 



The Antwerp Astronomical Society. — Among the many 

 interesting matters recorded in the sixth annual report 

 (19 10) of the Antwerp Astronomical Society, it is of interest 

 to learn that the society's observatory is being very gener- 

 ally used by a large number of students in the local schools, 

 who, under the guidance of their tutors, visit the observa- 

 tory and have the equipment, &c., explained to them. A 

 new communal observatory is to be placed on the top of a 

 school which is in course of erection in the city. An 

 analysis of the observing weather during 19 10, made by M. 

 Felix de Roy, is also of interest. Of the 365 days in 1910, 

 observations of the sun were possible on 269 days, and 

 night observations were possible on 142 ; for 1909 the 

 figures were 292 and 151 ; in 1908 there were 156 good 

 nights ; in 1907, 145 ; and in 1906, 102. 



Si'ECTROscopic Binaries. — The Journal of the Royal 

 Astronomical Society (Canada, vol. iv., No. 6) contains 

 the orbits of the spectroscopic binaries 93 Leonis and 

 e Ursa; Minoris as determined by Messrs. J. B. Cannon 

 and J. S. Plaskett, respectively, from plates taken at the 

 Dominion Observatory, Ottawa. 



Mr. Cannon made two determinations, using micrometer 

 measures in the first and the comparator in the second, 

 and, judging from the probable errors of an average plate, 

 there is but little difference between the two methods ; 

 fainter spectra may be measured with the micrometer than 

 in the comparator, but with poor lines for measurement 

 the latter instrument probably affords a better agreement 

 among the measures. The period of 93 Leonis is found 

 to be 71-7 days, and the eccentricity of the orbit is very 

 small. 



For € Ursae Minoris Mr. Plaskett finds a period of 

 39-482 days, a range of velocities of 63 km. per sec, and 

 a small eccentricity ; tlv volority of tho system is 

 — 11-398 km. per sec. 



EXPERIMENTS WIT If dWI. DUST IN 

 ERENCH €01. 1 II'.RIES. 

 C()()\ afhr the dangers due to ili' piMMice of coal dust 

 "^ l)('gan to be realised in this cuuniiy, and, as a con- 

 sequence, regulations regarding the composition and 

 methods of employing explosives in dusty mines had been 

 added to the .Statute-book, the number of great explosions 

 occurring within a given time underwent such a remark- 

 able diminution that for several years it seemed almost as 

 if they were about to cease altogether. But a partial 



