490 



NATURE 



[August io, 191 6 



of horizontal rocks. The question is, of course, a 

 technical one for geographers to decide, and Prof. 

 Johnson's short paper is worth consideration. 



In recent years the intercorrelation of meteoro- 

 logical data in different parts of the world has sug- 

 gested important results which promise to have con- 

 siderable economic value. Dr. G, T. Walker, Direc- 

 tor-General of Observatories in India, has published 

 a memorandum regarding the probable amount of 

 monsoon rainfall in 1916 (Simla: Government Press; 

 8 annas). Data from South America, the Indian 

 Ocean, and Ceylon, as well as from India, are briefly 

 considered, and the result is to lead Dr. Walker to 

 suggest that the outlook for the general monsoon 

 rainfall of India is on the whole unfavourable this 

 year, and that the rainfall is likely to be in slight or 

 moderate defect, at any rate in the earlier part of the 

 season. The deficiency is likely to be most marked 

 in north-west India, while conditions appear to be 

 favourable in Lower Burma, Assam, Malabar, and 

 south-east Madras. Forecasting of this nature is still 

 in its infancy, but Dr. Walker's attempt is most 

 interesting, and promises to grow in value year by 

 year. 



The August " Catalogue of Books in Standard 

 Literature " of Mr. F. Edwards, High Street, Maryle- 

 bone, contains many works dealing with general 

 natural history, botany, conchology, ornithology, mam- 

 malia, entomology, and ichthyology. 



OVR ASTRONOMICAL COLUMN. 



The August Meteors. — Mr. Denning writes : — 

 "There is every indication that the Perseid display of 

 igi6 will be of rather unusual activity. The shower 

 was quite rich on July 31, August i and 5, and 

 evidently increasing. Some fine meteors were ob- 

 served, and especially on July 26, loh. 7m., August 2, 

 iih. 41m., August 3, gh. 44m., and August 5, gh. 14m. 

 That on the latter date was a fireball, and it formed a 

 brilliant spectacle as seen from Bristol, falling from 

 Cygnus to Ophiuchus. 



"The maximum of the shower will probably be 

 attained on Friday, August 11, but there will be many 

 meteors visible also on August 12. The display is 

 one noted for its long duration, but the really active 

 phase of the phenomenon is included within one or 

 two nights. 



"The average height of the Perseids is from 81 to 53 

 miles, and their velocity 38 miles per second. Their 

 flights are directed from the north-eastern sky, the 

 radiant at 44° + 57° in Perseus being situated in that 

 quarter of the heavens. 



"The time of maximum should be carefully deter- 

 mined, and the horary numbers ascertained during 

 the nights of August 11 and 12. The moon, however, 

 being very nearly full, will prevent many of the smaller 

 meteors being observed. 



"The more brilliant objects should be especially 

 noted, and their paths among the stars recorded as 

 accurately as possible. The phosphorescent streaks 

 which are generated along the courses enable the direc- 

 tion to be exactly registered on a star map or celestial 

 globe. These Perseids furnish many fine meteors, and 

 fireballs frequently occur among them. In the case 

 of one of the streaks or afterglows remaining visible 

 for several minutes, its drift amongst the neighbour- 

 ing stars should be noted as precisely as possible." 



July Meteors. — Mr. Denning writes: — "The very 

 fine summer weather prevailing during the latter half 

 of July enabled a large number of observations to be 

 obtained. The first Perseids were detected on July 8, 



NO. 2441, VOL. 97] 



but the shower was not very prominent until July 3 

 and August i. A splendid meteor was seen from it 

 or possibly from a contemporary display in the sam 

 region, on July 2b, at loh. 7m. 



"There was a very active radiant of slow and bril 

 liant meteors from the point at about 302° -8° fron 

 July 7 to the end of the month, and it was still visibli 

 on August 2. Twenty of its meteors were recorded a 

 Bristol, and many others were seen by Mrs. Fiam 

 metta Wilson at Totteridge. Six of the meteors wen 

 doubly observed, and their real paths have been com 

 puted. 



"During the last week of the month the Aquaric 

 shower came actively into play from 338°— 11°. Thi; 

 stream has been only scantily visible in the past few 

 years, but its return in 1916 showed it to have re 

 covered its old-time prominence. The chief radiant! 

 seen were : — 



"Observers — Mrs. Fiammetta Wilson, Totteridge; 

 Miss A. Grace Cook, Stowmarket ; and the writer, 

 Bristol." 



A Sun-spot ix High L.atitude. — In the course of 

 the heliographic work at Greenwich, it has been found 

 that photographs of the sun taken at the Cape Ob-i 

 servatory on December 26, 1915, show a srriall, but un- 

 mistakable, spot in the extraordinary latitude 59-6° S ' 

 This is considerably above that of the spot observe 

 by Peters in 1846, the latitude of which was 50-4°, an 

 is apparently the highest yet recorded (Journal B.A..'\. 

 vol. xxvi., p. 292). 



Lowest effective Power of a Telescope. — It hr 

 usually been considered that the lowest power whi( 

 can be employed on a telescope, while retaining fu 

 illumination, is one of five to each inch of apertur< 

 this estimate being based on the assumption that tl. 

 average diameter of the pupil of the eye is one-fift 

 of an inch. Mr. W. H. Steavenson has investigate 

 the diameter of -the pupil by flashlight photograph} 

 and has found that while one-fifth of an inch may b 

 a fair estimate of the aperture in daylight, one-thir> 

 of an inch is much nearer the aperture at night. A: 

 interesting application of this result has been mad 

 by Naval Instructor M. A. Ainslie, R.N., in connec 

 tion with the 72-in. mirror of the Rosse reflector, tio\ 

 included in the collections at the Science Museun^ 

 The "original" eyepiece of the great telescope ha 

 been found to have an equivalent focal length c 

 77 in., giving a magnifying power of 84 and a 

 emergent pencil of 0-855 i"- diameter. It follows th? 

 the effective aperture of the speculum, when thi; 



