592 



NATURE 



[August 7, 191, 



(vol. Ixxxix.. p. 435). The Proceedings of the con- 

 vention have now been published for the University 

 of London Press, Ltd., by Messrs. Hodder and 

 Stoughton. The handsome volume runs to 359 large 

 pages, and contains the inaugural address of the 

 president, Prof. S. P. Thompson— extracts from which 

 were published in Nature of the date mentioned— and 

 the papers read at the convention. The papers are 

 chiefly of a technical description, largely directed to 

 the issues of technical inquiry, and a few are devoted 

 to the details of manufacture. Among the contents 

 of the volume of more general interest may be men- 

 tioned the report of Prof. Turner's lecture on the 

 great observatories of America, and Prof. Stirling's 

 popular lecture on optical illusions. A table of con- 

 stants for calculating spherical aberration forms an 

 appendix; this comprises a selection of logarithms of 

 use in some of the more laborious calculations which 

 the designers of lens combinations have to make. The 

 price of the volume is 10s. net. 



The National Academy of Sciences of the United 

 States of America was founded in 1863, and 1913 

 sees completed the fiftieth year of its existence. It 

 was decided in 1909 to have prepared for publication, 

 in connection with this semi-centenary of the academy, 

 a volume containing as complete an historical sum- 

 mary as could be brought together in the time avail- 

 able. A committee was appointed to take charge 

 of the matter, and in the summer of 1910 the services 

 of Dr. F. W. True were secured as editor. The 

 result of the labours of this committee is seen in the 

 " History of the First Half-Century of the National 

 Academy of Sciences, 1863-1913," a copy of which 

 has reached us from Washington. It was hoped that 

 a list of the scientific communications presented to the 

 academy since its foundation, some two thousand in 

 number, might be added to the volume, but it has 

 been found impossible in the time available to compile 

 the necessary data. The completion of the under- 

 taking is deferred until a later date. The present 

 handsome volume runs to some 400 large pages, and 

 gives exhaustive information as to the founding of 

 the academy, its annals, and its work as scientific 

 adviser of the U.S. Government. Biographical 

 sketches of the incorporators of the academy add in- 

 terest to the work, while the numerous appendices 

 provide most useful lists of members, medallists, 

 officers, and so on. 



Mr. Francis Edwards, 83 High Street, Marylebone, 

 London, W., has published the August issue of his 

 catalogue of second-hand books in all classes of litera- 

 ture. The volumes listed include a number from the 

 library of Mr. Thomas Pennant, the antiquary and 

 naturalist. 



OUR ASTRONOMICAL COLUMN. 



August Meteors. — The most interesting and im- 

 portant season of the year for meteoric work has now 

 arrived. The Perseids return regularly in August, 

 and always repay observation, though there are 

 marked variations in their annual displays. 



During the last few years this shower has scarcely 

 justified expectation, but the conditions have not been 



xo. 2284, VOL - 91] 



very favourable. At the ensuing return possibly the 

 meteors may return in their old-time abundance, but 

 there will be a little interference from moonlight 

 before midnight. This need not, however, materiallv 

 affect the character of the displav, for on the nights 

 of August 11 and 12, when the maximum will occur, 

 our satellite will be only just past the first quarter, 

 and will set on August 11 at nh. 13m., and August 12 

 at i.'h. qm. p.m. 



It seem- desirable to watch the phenomenon closely 

 every year for several reasons. Its period is not ye't 

 exactly ascertained, and we are not sufficiently well 

 acquainted with its annual variations. The hourly 

 number of meteors visible should be determined, and 

 the time of their maximum abundance. It is also 

 important to record the apparent paths of such bril- 

 liant meteors as may be visible. 



In the case of fireballs the lingering streaks give 

 evidence of rapid currents in the upper atmosphere, 

 and should be specially watched. It will be useful to 

 note the position of the streaks amongst the stars and 

 to record the rate and direction of their drift, at short 

 intervals, during the period of their visibility. The 

 streaks are usuallv from sixtv-five to fifty-five miles in 

 height. 



Directly a streak is seen a telescope or field-glass 

 should be directed towards it. A streak which remains 

 visible to the naked eye a few seconds can sometimes 

 be watched for five or ten minutes with a glass. 



It is astonishing how many of the meteors of the 

 August stream are destroyed every year by collision 

 with the earth's atmosphere. Basing calculations on 

 observed facts, it is probable that between 80 and 100 

 millions of these meteors are encountered every year. 

 This great annual expenditure might be thought to 

 have a perceptible effect in diminishing the visible 

 numbers, but when we remember that Prof. H. A. 

 Newton computed the number of meteors in the 

 August system as 300,000,000,000,000, it is certain 

 that any apparent falling off in the richness of the 

 shower would only become sensible after many 

 thousands of years. 



Displacement of Spectrum Lines of Metals due 

 to Impurities. — An important piece of research work, 

 chiefly interesting to spectroscopists, is that recentlv 

 communicated by M. Keivin Burns to the Comptcs 

 rendus for June 30 (vol. clvi.. No. 26, p. 1976). M. 

 Burns finds that the presence of a large proportion of 

 luminous vapour in an arc of iron or mercury dis- 

 places the spectrum lines of those metals contained in 

 a small proportion in the arc (such as barium, man- 

 ganese, cadmium) in relation to the positions they 

 would occupy if the metals which produced them were 

 predominant. He suggests that this displacement 

 mav be the result of numerous particles in a special 

 condition where they emit light and not of ordinary 

 molecules or atoms ; the displacement is not explained 

 by a pressure effect. He points out that the existence 

 of this displacement does not render it prudent to use- 

 such lines of impurities as standards in attributing the 

 wave-lengths found from measures made under other 

 conditions. 



Circulation in the Solar Atmosphere. — Anyone 

 who has closely studied a number of photographs of 

 solar prominences photographed on the limb of the 

 sun would have the idea of solar currents brought to 

 his mind. 



A systematic study of a large number of such photo- 

 graphs becomes therefore of extreme interest from the 

 solar circulation point of view, and such a studv has 

 been undertaken by Prof. Slocum, of the Yerkes Ob- 

 servatory, from spectroheliograph photographs he has 

 taken with the large Yerkes refractor. His second 



