October 20, 1904] 



NA TURB 



599 



Dr. Rendle has devoted much time to the Monocoty- 

 ledons, so that it is with special interest that one turns 

 to this part of the book. As might be expected, one 

 finds here a valuable exposition of the morphology 

 both of vegetative and reproductive organs, with a 

 succinct account of all such doubtful and subtle ques- 

 tions as the morphology of the flower of Orchidaces, 

 or the value of the vegetative body of the Lemnacese. 

 .'\ noticeable feature is the inclusion of so many facts 

 concerned with the vegetative part of the plant. The 

 various devices manifested by plants during germin- 

 ation, a subject in which the writer has made special 

 investigations, receive very full treatment, and 

 numerous anatomical details are mentioned ; but 

 perhaps more striking is the value which is attached to 

 vegetative characters for the purpose of splitting the 

 orders up into tribes. Thus in the Aroideas anatomical 

 structure and the leaf-nervature are considered by 

 Engler to be the best distinguishing characters ; in 

 the Liliaceae the vegetativ:; habit is important; and 

 Pfilzer makes use of several vegetative characters in 

 separating the sections of the Orchidacese. It has 

 already been pointed out that in the enumer- 

 ation of the genera of the Gymnosperms it would be 

 useful to have more details for comparing one with 

 another, and the same applies to the latter part of the 

 book, where geographical distribution is fully given 

 to the exclusion of critical data. One misses, too, 

 those broad generalisations, which serve as landmarks 

 or guide-posts, until the last chapter — a most im- 

 portant one — in which the writer gives a general 

 review of the important characters and relationships of 

 the series and orders of the Monocotyledons. The 

 author has had some difificulties with his illustrations, 

 and the blocks prepared for the book, which on the 

 whole have reproduced clearly, but are too crowded, 

 suffer by comparison with the illustrations found in 

 other descriptive works ; otherwise the book forms a 

 worthy and valuable addition to the standard series 

 which is being issued by the Cambridge University 

 Press, and will certainly be of very great use to 

 students of botany. 



A. TEXT-BOOK OF NAVIGATION. 



Modern Navigation. By W. Hall, R.N. Pp. viii + 



378. (London : W. B. Clive, 1904.) Price 6s. 6d. 



THIS is a valuable text-book on navigation at a 

 very moderate price. Its small size and general 

 handiness are a great feature compared with other 

 works on the subject. The proofs throughout the book 

 arc graphically explained so far as possible, and are 

 easily intelligible to people with a limited knowledge 

 of mathematics; the figures and illustrations are good, 

 numerous examples are given throughout, and the 

 answers are tabulated at the end of the book. The 

 extracts from the " Nautical Almanac " necessary for 

 working any of the examples are also given. 



An excellent feature in the book is the great stress 



laid on navigation by " Sumner " or " position lines," 



which are the foundation of the present practice of 



navigation. Without a clear understanding of position 



NO. 1825, VOL. 70] 



lines it is impossible to comprehend the importance of 

 the errors in position due to working with approximate 

 data, such as finding longitude with D.R. latitude 

 and vice versa. These and other errors are thoroughly 

 and clearly explained by the author ; in many previous 

 works these errors have been either neglected 

 altogether or passed over without explanation of the 

 methods used in compiling the tables given for their 

 correction. 



The method of obtaining position by combining posi- 

 tion lines derived from a chronometer sight and from 

 an ex-meridian is rendered complete by the plan 

 given of calculating the final result by factors as 

 opposed to plotting it. It is brief and accurate, and 

 will be welcomed by those who have experienced the 

 difficulties of plotting results in small ships in bad 

 weather. A very short and accurate method of 

 obtaining these results by the " nautical slide rule " 

 is also given. The slide rule was Mr. Hall's invention, 

 and is useful for ex-meridians and other computations. 



The treatment of the short equal altitude as a 

 dynamical problem tends to simplify the work, and 

 renders it easier of comprehension. The chapter on 

 the " new navigation " is much in advance of any 

 previous discussion of this method ; the explanation is 

 clear and the work straightforward, and the figures 

 required for the computation are reduced. An 

 accurate means of obtaining the final result by calcu- 

 lation instead of plotting is also added to this method. 

 Mr. Hall's treatment of the " new navigation " should 

 greatly assist to popularise this valuable means of 

 navigating, which is applicable to any heavenly body 

 at any azimuth. 



The investigation of errors due to inaccuracies in 

 time and altitude is satisfactory, and many interesting 

 problems in theoretical navigation are fully explained. 

 A valuable feature in the book is the shortening of 

 computation by using five places of logarithms and 

 in some cases only four places. The chapter on tides 

 is very simply and effectively written, and supplies a 

 want much felt by seafaring men. 



In a book where so much is good, it is a pity more 

 stress has not been laid on the utility of twilight stars 

 for position ; the author refers to displacement of the 

 horizon due to abnormal refraction, &c., as a cause of 

 errors in position, but does not mention the best fix 

 that can be obtained in the twenty-four hours at sea. 

 Ex-meridians of stars north and south for latitude, and 

 chronometers of east and west stars for longitude, the 

 mean of the north and south stars for latitude and of 

 the east and west stars for longitude, obviate the 

 effects of displacement of the horizon, and the fix is 

 not dependent on run between observations except to 

 the extent of a few minutes. This fix is specially 

 valuable to men-of-war, which, owing to manoeuvres, 

 are seldom long on a steady course, thereby causing 

 the run between observations, taken at an interval of 

 two or three hours, often to be inaccurate. The system 

 of notation used throughout the book and the extensive 

 use of Greek letters are likely to confuse men already 

 practising their profession afloat and used to calling 

 things by their old names ; it will consequently not 

 commend itself to them. Possibly young students 



