Jan. 5. 1888] 



NA TURE 



221 



rich in ammonia. The guano dust is carried by the pre- 

 vailing west winds far into the country, and would fall into 

 the mother-liquor lakes, where, on exposure to the air at 

 a warm temperature, it would gradually oxidize to nitrate, 

 and, acting on the sodium carbonate, would form sodium 

 nitrate (Chili saltpetre). 



The "caliche" (crude saltpetre) is most variable in 

 appearance and in the percentage of nitrate which it 

 contains. The various substances, other than sodium 

 nitrate, which are found in the Tarapaca and Atacama 

 deposits are described at length by the author, who com- 

 pares them with those which are found at Stassfurt, and 

 he traces in the comparative prominence of the more 

 soluble salts in the Chilian deposits a further confirma- 

 tion of his theory that the nitre-beds are formed from 

 mother-liquor salts. 



The boo'c is well indexed, and is supplied with a map 

 and several sections of the district described. 



J. I. W. 



OUR BOOK SHELF. 



Tenerife, and its Six Satellites. By Olivia M. Stone. 

 In Two Vols. (London: Marcus Ward, 1887.) 



A GOOD book on the Canary Islands, which have been of 

 so much service to many an invalid, has long been 

 wanted ; for, as Mrs. Stone says, many parts even of the 

 best-known islands of Tenerife and Gran Canaria are 

 untrodden ground to English people, and are but little 

 known to persons of any other nationality. Mrs. Stone 

 supplies all the information that can be needed by the 

 most exacting visitor to the islands, or by persons who 

 may wish to read about them at home. As she has 

 already shown in her "Norway in June," she has ex- 

 cellent powers of observation, and knows how to give a 

 clear and effective account of all that she sees in her 

 travels. In the present work her descriptions are all the 

 more vivid because they were written " on the spot," 

 when everything she wished to set down in her narrative 

 was still fresh in her mind. To the Island of Hierro, to 

 which she and her husband seem to have been the first 

 English visitors, she devotes a good deal of attention ; 

 and what she has to say about that " solitary, happy, 

 singular" island is full of interest, and would alone have 

 justified her, if justification had been necessary, in making 

 her travels in the Canary Islands the subject of a book. 

 In an appendix she presents a useful epitome of all 

 necessary expenses connected with her tour. 



Through Central Asia. By Henry Lansdell, D.D. 

 (London: Sampson Low, 1887.) 



This is a popular edition of the author's well-known 

 " Russian Central Asia, including Kuldja, Bokhara, 

 Khiva, and Merv." He has omitted many whole chapters 

 and most of the notes, thinking it best that the present 

 edition should consist chiefly of a personal narrative. 

 Any student who may desire fuller information regarding 

 Central Asia is referred to the original work, in which Dr. 

 Lansdell gives 4300 species of fauna and flora in about 

 twenty lists with introductions, adds a bibliography of 

 700 titles, and treats more or less fully of the geography, 

 economy and administration, ethnology, antiquities, 

 history, meteorology, geology, zoology, and botany of all 

 parts of Russian Turkistan, Kuldja, Bokhara, Khiva, and 

 Turkmenia, down to the frontier of Afghanistan. To the 

 new and abridged edition he has added an appendix on 

 he delimitation of the Russo- Afghan frontier. 



LETTERS TO THE EDITOR. 



[TAe 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 mamiscripts. No notice is taken of anonymous 

 communications. 



[The Editor urgently requests correspondents to keep their 

 letters as short as possible. The pressure on his space 

 is so great that it is impossible otherwise to insure J he 

 appearance even of communications containing interesting 

 and novel facts. 



The Star of Bethlehem. 



Referring to the hypothesis in your last week's issue, that 

 the star of Bethlehem was Venus, I would point out that 1180 

 synodical periods of Venus {i.e. ilSo x 583*92 = 689,025 mean 

 solar days) take us back from October -28, 1887 — when Venus 

 was at her maximum brilliancy as a morning star — to only 

 May 3 of the year i A.D. instead of December 25 of the year 

 I B.C. For the number of days from October 28, 1887, to 

 December 25, i B.C., is 689,155 (viz. 1887 x 365*2425 = 689,213 

 - 64 -I- 6 = 689,155). This would appear to show, either that 

 the birth of Christ took place about May 3, or that Venus 

 at her maximum brilliancy as a morning star was not the star 

 (f Bethlehem. I should be glad of your remarks on this. 



John T. Nicolson. 



20 Thirlestane Road, Edinburgh, December 26, 1887. 



I INFER from the article entitled "The Star of Bethlehem " 

 (Nature, December 22, 1887, p. 169) that the writer supposes 

 the craze he deals with did not exist until Venus became a 

 morning star. It was equally prevalent here when, early in the 

 year, she was an evening star, as the following fact will show. 

 On May 21, 1887, a lady wrote me as follows : — " Will you 

 kindly tell me what people mean about 'a ivonderful star^l 

 All our servants are talking about it. . . . Some call it ' the 

 star of Bethlehem.' ... I hear it is ' wonderfully bright l'"" 



Torquay, December 26, 1887. Wm. Pengelly. 



In regard to the so-called "star of Bethlehem," Prof. C. A. 

 Grimmer, in " Life from the Dead," No. 69 (August 1879), 

 p. 267, wrote: — " It will be seen in 'Cassiopeia's Chair,' and 

 will be accompanied by a total eclipse of the sun and rrioon. 

 The marvellous brilliancy of the ' star of Bethlehem ' in 1887 

 will surpass any of its previous visitations. It will be seen even 

 at noonday, shining with a quick flashing light the entire year, 

 after which it will gradually decrease in brightness, and finally 

 disappear." E. CuATHAM. 



January 2. 



On some Apparent Contradictions at the Foundations 

 of Knowledge. 



In Chapter III. of Mr. Herbert Spencer's "First Principles" 

 (p. 47, under heading, " Ultimate Scientific Ideas "), are treated 

 the subjects of space and time. Here contradictions and diffi- 

 culties of an apparently insuperable character are encountered in 

 the attempt to define the nature of space and time, and the ex- 

 istence of these difficulties is frankly acknowledged. But with 

 all the respect that is here due, it appears difficult to admit that 

 these apparent contradictions are necessary, and in regard to 

 space, in the first place, it will be my object here to suggest a 

 remedy. 



I will first quote some passages from the " First Principles " 

 (5th edition) relating to this question, viz. as follows : — 



"Thus as space and time cnnnot either be nonentities, nor 

 the attributes of entities, we have no choice but to consider them 

 as entities. But while on the hypothesis of their objectivity, 

 space and time must be classed as things, we find on ex- 

 periment that to represent them in thought as things is 

 impossible " (p. 47). 



It will be observed here that we encounter the apparent con- 

 tradiction that those are classed as things which it is found 

 impossible to represent in thought as things.^ 



' Experiment wo li then in Erectly say that srace and time were not 

 things. 



