28 



NATURE 



[September i, 192 i 



to the climate and the country will be so great 

 and varied that "it would be hard to put any 

 limits "on them. The evidence for these esti- 

 mates is not convincing. That the influence of irri- 

 gation must be to increase the precipitation to some 

 extent is not likely to be questioned ; but the extent of 

 the influence is uncertain. Mr. Quayle claims that 

 irrigation has increased the rainfall during the past 

 ten years. This period is, however, too short to give 

 any trustworthy evidence of a permanent change, as 

 are also the statistics quoted from 1885. Similar pre- 

 dictions have been made from other areas where ex- 

 tended irrigation happened to coincide with the wetter 

 part of a climatic cycle. The absence of any increase 

 of rainfall beside the irrigated areas of Egypt sug- 

 gests caution in reliance on records for so short a 

 period as are available in Victoria, especially as it is 

 in a situation where irregular long-period variations 

 in weather are so likely to occur. 



Messrs. Longmans and Co. are to publish in the 

 autumn vols, i and 2 of "A Comprehensive Treatise 

 on Inorganic and Theoretical Chemistry," by Dr. 

 J. W. Mellor, which work will consist of six volumes 

 in all. Vol. i will to a large extent be historical and 

 introductory, and give a general survey of chemical 

 research and discovery from the earliest times to the 



present day. This volume will also deal in detail 

 with hydrogen and oxygen in their many forms and 

 compounds. Vol. 2 will cover the whole range of the 

 following elements and a systematic range of related 

 compounds : — Fluorine, chlorine, bromine, iodine, 

 lithium, sodium, potassium, rubidium, and caesium. 

 The same publishers also promise a new edition^the 

 fourth— of Dr. E. J. Russell's "Soil Conditions and 

 Plant Growth." 



Messrs. W. Heffer and Sons, Ltd., Cambridge, 

 have in the press " Notes and Examples in the 

 Theory of Heat Engines," by J. Case. The book is 

 intended as a companion to lectures to enable the 

 student to see at a glance the essential points of the 

 subject and to help him with his revision for examina- 

 tions. The engineer who has to deal with the ele- 

 mentary thermodynamics of steam and other heat 

 engines should find the work of value, as all the 

 important formulae he may require are printed in 

 heavy type and easily found. 



A USEFUL catalogue (No. 89, August) of nearly two 

 thousand second-hand books dealing with entomology, 

 ornithology, general zoology, and botany has just 

 been issued by Messrs. Dulau and Co., Ltd., 34 Mar- 

 garet Street, W. i. It is obtainable upon application. 



Our Astronomical Column. 



Large Meteors. — Mr. W. F. Denning writes: — "A 

 considerable number of unusually brilliant meteors 

 were observed at about the period of the recent Perseid 

 display. On August 11 at gh. 28m. G.M.T. a very fine 

 object was recorded at Bristol and at various places in 

 South Wales. Near the end of its flight it illuminated 

 the firmament so strongly that people at first mistook 

 it for a flash of lightning. The meteor fell from 

 a height of from 75 to 53 miles, and its path was 

 over the region from Swansea to Barnstaple Bay. 

 It was directed from the usual radiant point in 

 Perseus. 



"Another meteoric fireball appeared at loh. 42m. 

 G.M.T. on the same night. It passed over Berkshire 

 at a height descending from 78 to 45 miles at a 

 velocity of about 30 miles per second. This was also 

 a Perseid, and it was observed from Bristol and Wim- 

 borne, Dorset. 



"Another fireball was seen on August 15 at qh. 46m. 

 G.M.T. As viewed from Nuneaton, Warwickshire, 

 by the Rev. Ivo Carr-Gregg, it crossed a Ursae Majoris 

 in a direction from Serpens and Scorpio. Only one 

 observation has come to hand of the latter object, 

 and a duplicate record of the path would supply the 

 necessarv data for computation of the fireball's real 

 course in the air." 



Ancient Eclipses. — Dr. J. K. Fotheringham was 

 the Halley lecturer this year, and chose ancient 

 eclipses as his subject. He noted the appropriate- 

 ness of the choice, since Dr. Halley had been the first 

 to announce the secular acceleration of the moon's 

 motion from his study of the old eclipses. 



Dr. Fotheringham expresses surprise that Dr. E. W. 

 Brown in his new tables of the moon adopts the value 

 6" per century which arises from the change in the 

 eccentricity of the earth's orbit; the ancient eclipses, 



NO. 2705, VOL. 108] 



as discussed by Drs. Fotheringham and Cowell (mis- 

 printed " Cavell " on p. 25 of the lecture), make it 

 tolerably certain that the actual value is 4" or 5" 

 greater, and that the sun has also an acceleration of 

 at least 1-5", presumably arising from a retardation 

 of the earth's rotation. 



One of the most definite records of eclipses is that 

 of Thucydides (August 3, 431 B.C.); it has hitherto 

 been inferred that, since " some stars became visible," 

 Athens must have been close to the central line, but 

 Dr. Fotheringham shows that a magnitude of \o\ 

 digits suffices. In the eclipse of last April Venus, 

 Mercury, Capella, Vega, Arcturus, and Aldebaran 

 were seen at places in the British Isles where the 

 magnitude did not exceed io-6. 



In addition to their application to astronomy, the 

 lecture shows the great value of several of these 

 eclipses from the chronological point of view ; in fact, 

 their combination with Ptolemv's - and the Assyrian 

 eponym canons determines dates back to the tenth 

 century b.c. 



Calendar Dates in Meteorology. — M. Jean Mas- 

 cart contributes a paper to Compies rendus of July 11 

 in which he points out the desirability of dating 

 meteorological phenomena by the sun's longitude in 

 place of the calendar date. Owing to the odd frac- 

 tion of a dav that occurs in the length of the tropical 

 vear, the same calendar date corresponds with dif- 

 ferent solar longitudes. There is, of course, no ques- 

 tion that M. Mascart's contention is sound in theon,' ; 

 but since it is almost inevitable that the observations 

 should be taken at fixed hours of the solar day, it 

 would involve considerably more labour to re-arrange 

 them in accordance with the sun's longitude, and it is 

 verv doubtful whether there would be any adequate 

 compensation for such extra work. 



