3H 



NATURE 



[June 20, 19 18 



OUR ASTRONOMICAL COLUMN. 



Nebulosity in Star Clusters. — In a lc4ter to 

 the Observatory for June Dr. Harlow Shapley states that 

 the appearance of nebulosit)- which has sometimes been 

 noted in visual observations of star clusters has not 

 been confirmed by the Mount Wilson photographs. In 

 the case of the cluster No. 361 of Dreyer's Index Cata- 

 logue, the photographs show stars fainter than i8th 

 magnitude, but there is no trace of nebulous matter. 

 The cluster N.G.C. 6760^ which has also often been 

 observed visually as nebulous, appears purely stellar 

 on the photographs. The actual connection between 

 luminous nebulosity and star clusters seems to be 

 limited to stellar groups of little condensation and rich- 

 ness, where the brighter stars are mainly of type 

 A or B. In these cases the nebulosity becomes 

 visible because of direct reflection of the light of the 

 surrounding stars, and partly on account of selective 

 secondary radiation. Thus the frequent association 

 of diffuse nebulosity with blue stars of high tempera- 

 ture does not necessarily indicate immediate evolu- 

 tionary relationship. There is at present no certain 

 evidence of luminous nebulosity in globular clusters. 



Interpretation of Stellar Types.- -In a com- 

 munication to the National Academy of Sciences, 

 Washington, March, 1918, Prof. C. D. Perrine makes 

 the interesting suggestion that the spectral class of 

 a star is in part dependent upon the amount of 

 cosmical matter in its neighbourhood and the relative 

 velocity, of the star and matter. Many of the A, B, 

 and O stars, the gaseous nebulse, the novae, and 

 possibly the Cepheid variables, on this hypothesis, are 

 confined to the galaxy because there the energy derived 

 from the matter swept up is in excess of that lost by 

 radiation. The direction of spectral change under 

 such conditions will be towards the nebulae. In 

 regions where there is little or no cosmical matter the 

 energy gained from external sources is not sufficient to 

 compensate for the loss of radiation, and the direction 

 of change will be towards the later types. Upon this 

 hypothesis the stars are probably all pursuing one 

 definite course of very slow change towards extinc- 

 tion, but each individual star will be pursuing a course 

 which may have many whole or partial cycles due to 

 varying external causes. 



The Strathmore Meteorite. — ^This remarkable 

 meteorite fell on December 3, 1917, at 1.18 p.m. 

 Though in full sunshine, its brilliance was compared 

 with the limelight, and it left a trail. It was seen so 

 far away as Hexham, 120 miles from the earth-point. 

 Prof. R. A. Sampson gives an interesting account of 

 it in the Proceedings of the Royal Society of Edin- 

 burgh (vol. xxxifiii., part i.. No. 10). He fixes the 

 explosion point as twenty miles above Collessie, Fife. 

 Four fragments have been found, one penetrating a 

 roof near Coupar Angus; the largest, weighing 

 22^ lb., fell at Easter Essendy Farm, near Loch 

 Marlee; it made a hole 20 in. deep, the rubbish being 

 piled to the north-west, showing the direction of 

 •motion, which agrees with other indications. The 

 fragments did not fall until some minutes after the 

 sounds of explosion were heard, showing how much 

 the speed (which must initially have been some miles 

 per second, to account for the brilliancy) had been 

 reduced by atmospheric resistance. Prof. Sampson 

 explains the heating of meteors by supposing that the 

 air in front of them -has not time to escape, so is 

 rapidly compressed. Assuming probable figures for 

 mass and velocity, he shows that a temperature of 

 2000° might be produced. The meteor is of the stony 

 class, to which many people assign a volcanic origin. 

 In view of the difficulty of understanding how it 

 could have escaped from our atmosphere without rup- 

 NO. 2538, VOL. lOl] 



ture, if expelled from a terrestrial volcano, Prof. 

 Sampson suggests a lunar origin. In this case it 

 might either describe an orbit within the earth-moon" 

 system, or, with a higher speed, a planetary orbit about 

 the sun. The latter would seem the more likely, Mr. 

 Denning having shown that it probably came from a 

 known radiant in Sagitta, which is active early in 

 December. The lunar origin ^vould then imply that a 

 large shower of fragments was expelled from the 

 moon during a single eruption. 



THE SOUTH-EASTERN UNION OF 

 SCIENTIFIC SOCIETIES. 



'pHE twenty-third annual congress of th 

 ■'■ Eastern Union of Scientific Societies Wc 



the South- 

 as held at 



Burlington House, in the Linnean Society's rooms, 

 on May 29 and three following days, under the 

 presidency of Sir Daniel Morris. The presidential 

 address was entitled "The Geographical Distribution 

 of Plants," and was, to some extent, concerned with 

 the various means of dispersal of seeds and the manner 

 in which geographical distribution was effected. The 

 destruction of the flora of the Island of Krakatoa by 

 volcanic eruption and the comparatively rapid growth 

 of a new flora gave valuable evidence as to the manner 

 and time required for replacing a destroyed flora. 

 Transport by water-currents, through a powerful 

 agent, would be assisted by the agency of birds, and 

 meteorological agencies must not be wholh' left out of 

 the reckoning. Many seeds reach our own shores 

 fr6m tropical America by the agency of the Gulf 

 Stream, but these have not been known to germinate 

 in a natural state after transportation. 



Mr. Percy Webb's paper on " Romano-British 

 Mints " was an excellent summary of the subject. 

 Mr. Webb pointed out that it was probable that the 

 province of Britain, accustomed to use and strike 

 coins for nearly two hundred years before the Roman 

 invasion, kept its mints in some operation even under 

 Roman rule. There is no clear identification of 

 mints owing to the system of inint-marking not com- 

 mencing until a late period. Claudius struck types 

 of coins relating to Britain, but they were no doubt 

 issued and used in Rome. Hadrian issued bronze 

 pieces on which appears the seated figure of Britannia, 

 her first appearance in history. These coins, and 

 others of the same type issued by Antoninus Pius, 

 suggest in their less accurate mintage, and from the 

 fact that they have come to light in numbers in British 

 finds, that they are of colonial origin. From Carausius 

 and Allectus we have indisputable British issues, 

 the former the founder of the short-lived first British 

 Empire, the latter defeated and slain by the Romans 

 on Wolmer Common, near Liss, where his military 

 chest was exhumed in 1873, having been buried before 

 battle with its contents of nearly 30,000 coins. 



The subject of "Mosquitoes in England " was intro- 

 duced for discussion by Sir Ronald Ross, and amongst 

 those who took part in the discussion were Col. 

 Buchanan, of the Local Government Board; Capt. 

 MacDonald, and Mr. A. J. Grove. Sir Ronald Ross 

 pointed out that malaria had formerly been prevalent 

 in Britain, but had afterwards died out. Anophelines, 

 however, continued to exist in certain low-lying parts, 

 and recently evidence has been found to suggest that 

 malaria has really continued all the time to be endemic 

 to a very small degree in parts of Kent. Last year 

 some cases undoubtedly occurred, in this country. 

 Certain alarmists are seriously perturbed by the possi- 

 bilities of its greater prevalence. Sir Ronald came to 

 the conclusion that the spread of malaria in a com- 

 munity must depend upon about fifteen different 

 factors. " Of all the millions bred in a locality, pos- 



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