412 



NATURE 



{Feb. 28, r 



again ; how much information this will convey to a 

 student we leave our readers to judge. The answers to the 

 various questions which are asked on the sextant are far 

 better than the definitions, as are also the answers to the 

 questions on cyclones. The questions on the deviation of 

 the compass, for masters' certificates, are also fairly well 

 answered, although a little further explanation of Napier's 

 diagram, which forms the frontispiece, might have been 

 given with advantage. 



For reference to the questions given, the book will no 

 doubt be very useful to intending candidates, but the 

 answers given are good examples of the system of cram- 

 ming for examinations, which cannot be too strongly 

 condemned. 



Giiatetnala ; The Land of the Quetzal. By William T. 

 Brigham. (London : Fisher Unwin.) 



Mr. Brigham, an American author, has made three 

 journeys in Guatemala, and in the present volume he has 

 brought together all that seemed to be important in the 

 notes written during his travels. The work is one of 

 great interest, and ought to be not less welcome to the 

 general reader than to persons who have special reasons 

 for studying the subject. Mr. Brigham is a keen observer, 

 and records his impressions clearly, simply, and effec- 

 tively. No one who, in imagination, attends him in his 

 course across the continent to Coban, from Coban to 

 Quezaltenango, from Quezaltenango to the Pacific, will 

 fail to be attracted by what he has to say about the 

 physical features of the country and about the manners 

 of its inhabitants. There are also excellent chapters on 

 Guatemala city, and on Esquipulas and Quirigua. A 

 sufficiently full account is given of the vegetable and 

 animal productions of Guatemala, and of its earthquakes 

 and volcanoes. In an introductory chapter, Mr. Brigham 

 has something to tell us about Central America generally, 

 and it may be worth noting that these regions will one 

 day, in his opinion, be "the garden and orchard of the 

 United States, not necessarily by political annexation, 

 but by commercial intercourse." Great care has been 

 taken to secure the accuracy of the illustrations, most of 

 which are dirett reproductions from negatives. 



LETTERS TO THE EDITOR. 



[ The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents . Neither can he undertake 

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

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications. ] 



Weismann's Theory of Variation. 



I THINK it may be reasonably objected to Mr. Cunningham's 

 ingenious reductio ad absnrdum of Weismann's theory, that 

 because we cannot exactly state what happens in the mysterious 

 fusion of sperm- and germ-nucleus, it by no means follows that 

 such fusion does not largely account for the observed variation. 

 I say largely, because Prof. Weismann's more recent paper, 

 " Ueber die Zahl der Richtungskorper und iiber ihre Bedeutung 

 fiir die Vererbung" (Jena, 1887), completes in a most important 

 manner the paper quoted and criticized by Mr. Cunningham. 



The argument is briefly as follows. The expulsion of the 

 second polar body by sexual eggs is the removal of half the 

 ancestral germ-pla-ms in order to make room for those which 

 are added in fertilization. For this reason we must suppose 

 that an equivalent reduction of the sperm-nucleus also takes 

 place. If this reduction did not occur, the number of germ- 

 plasms would be doubled in each sexually-produced generation 

 — an unthinkable result. 



If there were only one kind of germ-plasm in each nucleus, 

 and sexual reproduction commenced, there would be 1024 distinct 

 germ-plasms in each of them at the end of ten generations. 

 But the number of generations must be so vastly in excess of 

 ten that the number of ancestral germ-plasms in each sperm- and 



germ-nucleus must be considered to be infinite, or at any rate so 

 large that the expelled halves would never be the same. It 

 therefore follows that no two sperm- or germ-nuclei can be alike, 

 and individual variation must follow. A little consideration 

 also shows that while the children of the same parents must 

 differ, they must also resemble each other more than the children 

 of other parents, and while they must differ from their parents 

 they must also resemble them more than the parents o>f other 

 children. 



The occurrence of atavism may be explained as a direct 

 consequence of an unusual predominance of ancestral germ- 

 plasms ; the fact that atavism is a rare exception also follows 

 from the fact that the expulsion of half the germ-plasms in 

 each generation will nearly always prevent such predominance. 



It is impossible to carry the subject further in the scope of a 

 letter, or one might refer to the evidence for the absence of 

 variability in parthenogenetic species, in which the second polar 

 body is not expelled from the ovum ; and to the identity of twins 

 produced from a single ovum which has presumably divided after 

 fertilization. E. B. Poui/roN. 



Oxford. 



A Correction. 



With reference to my communication in last week's Nature, 

 Prof. Oliver Lodge has called our attention to the fact that we 

 had made a mistake in stating that the wave-length of the 

 vibration was 33 centimetres. It is the semi-wave-length that 

 is 33 centimetres ; the wave-length is 66 centimetres, as is 

 evident on consideration of the size of the "vibrator." 



Fred. T. Trouton. 



Temperatute Observations in Rivers. 



The Committee appointed at the Bath meeting of the British 

 Association to investigate seasonal variations of temperature in 

 rivers and streams was able to arrange through local scientific 

 Societies for thirty observers, commencing work in January 

 1889. Of these there are ten in England, ten in Scotland, and 

 ten in Ireland. Each observer is supplied with a specially 

 designed thermometer (costing 2.s. 6d.) which has been com- 

 pared with a standard instrument, and books for recording the 

 observations and full instructions are provided by the Committee. 

 It is desirable to extend the observations to rivers not yet taken 

 up, and I therefore wish to direct the attention of local scientific 

 Societies, of meteorological observers and others interested in 

 similar work, to the opportunity now offered of taking part in a 

 systematic investigation, the preliminary results of which show 

 many interesting features. I shall be pleased to answer any 

 inquiries of intending observers. 



Hugh Robert Mill, _ 

 Secretary Brit. Assoc. Committee. 



Heriot-Watt College, Edinburgh, February 20. 



" Bishop's Ring." 



In your review of the Report of the Krakatab Committee of 

 the Royal Society, it is stated that "Bishop's ring" has quite 

 disappeared. Now this is hardly correct, for although I have 

 not heard of anyone perceiving it in the middle of the day for a 

 long time past, it is still visible about sunrise and sunset, though 

 becoming on the whole gradually fainter. I presume that it is 

 really the same phenomenon. At the time when "Bishop's 

 ring " was most conspicuous in the full day-time, it was always 

 far more so when the sun was rising and setting. 



Sunderland, February 20. T. W. Backhouse. 



Peripatus in Australia. 



Peripatus has been found not only in Queensland and Victoria, 

 but also at CassiHs, in New South Wales, by Mr. A. S. OllifF, 

 of Sydney. The Victorian and New South Wales localities are 

 recorded in a postcript appended to my monograph of the genus 

 as reprinted from vol. iv. of the "Studies from the Morpholo- 

 gical Laboratory of the University of Cambridge." My know- 

 ledge of them is due to Mr. Olliff, who was kind enough to send 

 me his specimen and his description of it (Proc. Linn. Soc. of 



