Jan. lo, 1889] 



NATURE 



247 



OUR BOOK SHELF. 



Questions and Examples on Elementary Experimental 

 Physics. By Benjamin Loewy. (London : Macmillan 

 and Co., 1888.) 

 This book contains some 470 questions and exam- 

 ples in elementary physics, selected from the various 

 papers set by the author for the examinations of the 

 College of Preceptors. The questions are arranged 

 under the four sections, sound, light, heat, and electri- 

 city and magnetism, and are further subdivided in each 

 section into groups of five or six, with the suggestion 

 that each group should form the subject of an ordinary 

 school lesson. Problems involving a knowledge of 

 mathematics beyond elementary arithmetic and geometry 

 are avoided ; in other respects the general standard of 

 the questions is about that of the advanced stage of 

 the Science and Art Department's examinations. The 

 questions are well selected, and free from ambiguity or 

 repetition. We notice under Heat, ix., i, the question: 

 " In the process of graduating a thermometer, why must 

 the freezing-point be determined before the boiling- 

 point ? " This is the order of operations as usually given 

 in the text-books, but it has been shown in the elaborate 

 report of the Bureau des Poids et Mesures that the interval 

 between the freezing and boiling points is most constant 

 when the freezing-point is determined as soon as possible 

 after the boiling-point. 



We can recommend this little book to the attention of 

 those teachers who have to prepare pupils for the public 

 examinations in elementary physics. For success in 

 such examinations it is not sufficient that the pupils 

 should possess the requisite amount of knowledge : they 

 must also acquire the power to express their knowledge 

 clearly and concisely on paper, and such power it is one 

 of the functions of such a book as this to impart. 



H. H. H. 



The Unknown Horn of Africa. By F. L. James, F.R.G.S. 



(London: G. Philip and Son, 1888.) 

 This is an extremely interesting record of an exploration 

 from Berbera to the Leopard River, undertaken about 

 four years ago. Various attempts had been made, before 

 Mr. James's journey, to penetrate to the interior of 

 Somali Land, but without success. Mr. James and his 

 companions, more fortunate, or more skilful, than their 

 predecessors, contrived to push their way to the goal for 

 which they started ; and the result is that the present 

 volume is accompanied by a map embodying much new 

 information regarding a district of considerable extent 

 and importance. Some of the difficulties encountered 

 by the party were formidable, but courage and persever- 

 ance enabled the travellers to overcome every obstacle. 

 Mr. James has much to tell us about the flora and fauna 

 of the country, as well as about its physical features ; and 

 he has many lively and instructive passages describing 

 his relations with the natives, whose peculiarities he 

 seems to have thoroughly understood. The story is itself 

 so interesting, and is told in so bright and pleasant a 

 style, that the book ought to be one of the most popular 

 of recent works of travel. It is illustrated by a number 

 of excellent coloured plates, and by various effective pic- 

 tures, composed from photographs of natives and native 

 scenery taken on the spot. 



Seas and Skies in Many Latitudes. By the Hon. Ralph 



Abercromby. (London: Edward Stanford, 1888 ) 

 This is not an ordinary book of travels. It has been 

 written mainly for the purpose of calling attention to such 

 phenomena of the sky and weather as Mr. Abercromby 

 has observed in various parts of the world. The opening 

 chapter describes the author's experiences in Canada and 

 the United States in the year 1865. Then he gives an 



account of a voyage round the world, beginning with 

 what he saw in Egypt, and passing on to descriptions 

 relating to Australia, New Caledonia, Fiji, New Zealand, 

 Cape Horn, and Rio Janeiro. Mr. Abercromby next 

 takes his readers within the Arctic Circle, and afterwards 

 he tells of a long journey, in the course of which he was 

 at the Cape of Good Hope, Mauritius, Ceylon, the Hima- 

 layas, Borneo, Manilla, San Francisco, and Washington. 

 He by no means confines his narrative to matters specially 

 attractive to meteorologists. He takes interest in many 

 different classes of subjects, and has something more or 

 less memorable to record about almost all the places 

 he has visited. It is, however, meteorology that he keeps 

 chiefly in view, and we need scarcely say that on this 

 subject, which he has so long and carefully studied, his 

 book is always fresh and instructive. The value of the 

 work is increased by good maps and illustrations. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 take to return, or to correspond with the writers of, 

 rejected manuscripts intended for this or any other part 

 of Nature. No notice is taken oj anonymous communi- 

 cations. '\ 



Alpine Haze. 



With the caution of a true man of science, Prof. Tyndall 

 has given this name to a phenomenon observed by him in the 

 Alps. Does not W. Clement Ley beg the question by calling 

 it "dust-haze"? I should translate his nebula arida by 

 " dry haze." 



Two hundred years ago, Ludclf gave the best definition of 

 q>har by translating it : " opacitas aeris qualis solet esse tempore 

 fervidissima: its tat is. " 



In my last letter I quoted several names of it, in order to 

 show that the vulgar eye has long distinguished this pheno- 

 menon. I have since learnt that, in the Basque dialect of 

 Gipuzkoa, its proper name is bisuutsa, but that seafarers call it 

 lur-autsa, i.e. "earth-haze," laiioa, meaning common fog. The 

 Ethiopic name, qobar, comes from qa'diara, a root extant also 

 in Hebrew and Arabic, and meaning to bury. Qobar hides the 

 landscape, and conceals stars of the third magnitude, even in 

 the zenith. Gasparin observed it on Mount Venlouk, where he 

 crossed a thick cloud which made no impression on his hygro- 

 meter. Humboldt, viewing qobar in Peru, says, "Quelle est 

 cette vapeur qui est visible et qui ne mouillepas?" but leaves 

 his question unanswered. 



While travelling in Spain, Willkomm remarked qobar at a 

 distance of 3 of 4 miles, yet, on reaching the actual spot, he 

 saw nothing. He clearly distinguished it from the laiidrauch 

 ascribed to smoke caused by turf burning in Westphalia, and 

 thinks, like Spaniards, that callina increases with solar heat. 

 Several German authors have spoken of this phenomenon as 

 smoke, but Egen is the only one who has followed it up from 

 place to place through an extent of 200 kilometres, and rendered 

 it probable that it then covered a space of more than a thousand 

 square myriametres. It seems, however, that particles of smoke 

 should attract moisture, if there were any in the air, and then 

 form real clouds or otherwise fall to the ground by increase of 

 weight. 



Bravais saw qobar on the Faulhorn, when his hygrometer was 

 at 51, air saturated with moisture marking ico. In Ethiopia, 

 where I have observed it so low as 20, the hygrometer's mean 

 reading was 41 when qobar was conspicuous. Above 72 it 

 disappeared. These figures apply to the place of observation. 

 Conclusions can be safely drawn only when the air's nr.oisture 

 shall have been measured in several places along the line of 

 sight up to the spot where qobar prevails, or, better still, in that 

 spot itself when recognized from a distance. 



Since I published my first account of qobar, Martins, who 

 observed it in Auvergne, Switzerland, and from Mount Canigou, 

 is the only author who has specially described it. He says 

 that the Swiss call it lu'ilc, and that he saw none of it in 

 Lapland. In spite of Kaemtz's remark that, moisture being the 

 essence of all fogs, a " dry fog " is an expression not less un- 



