76 



NATURE 



[May 24, 1894 



with phosphates, potash, and nitrogen. The valuation 

 of unexhauited manurial residues, whether derived 

 directly from manures or from foods, might well receive 

 more attention. 



The book is a genuine effort to treat the subject 

 scientifically, and at the same time in a manner intelligible 

 and interesting to the farmer of good education. We 

 think it has succeeded. E. K. 



LATITUDE BY EX-MERIDIAN ALTITUDE. 

 The "Ex-Meridian " treated as a Problem in Dynamics, 

 Sr'c. By H. B. Goodwin. (London : George Philip 

 and Son, 1894.) 



THE author of this brochure, with a tinge of satire, 

 seems to apologise for its containing nothing about 

 the already exhaustively developed Sumner method. In 

 doing this he alludes to " the too just Aristides." This 

 reminds us of a saying of that practical philosopher, that 

 "the best way to appear just is to be so." The proverb 

 may teach us that the way to obtain dependable results is 

 to have a firm grasp of principles, that the most reliable 

 navigator is one who understands the theory of his 

 problems. 



This remark is apposite, for we can conceive many a 

 "simple sailor" being rather frightened at the title of 

 this pamphlet which will first meet his eye, and we hear 

 him say — " Cannot the seaman continue to navigate his 

 ship without learning dynamics ? " If he has courage to 

 read a little further on, he finds that his belovedly simple 

 " Sun Mer. Alt." connected with such words as " maxi- 

 mum" and "minimum.'' Hitherto he has banished the 

 word " maximum " from his thoughts by avoiding the 

 use of the moon and planets for finding the latitude at 

 their culmination ; considering that the problem — " To 

 find the time when the moon and planets are at their 

 maximum altitudes" to belong to "the gymnasium of the 

 examination room" rather than to "the arena of every- 

 day practical utility." But now he finds that modern 

 ships require this problem to be considered with reference 

 to all the celestial bodies, and that even the sun may be 

 capricious enough not to "dip" at noon, that, in fact, 

 instead of this phenomenon giving a meridian altitude it 

 gives an ex-meridian altitude which has to be reduced to 

 the'meridian. 



There is reason to be thankful for this new feature, 

 because it will attract more attention to the hitherto 

 shamefully neglected method of the ex-meridian among 

 ordinary navigators. That this can be no longer thus 

 relegated is exemplified by Mr. Goodwin, as follows : — 



" In the Standard newspaper of October 23, 1893, it is 

 stated that H..\I.S. ifoya/ Sovereign, flag ship of the 

 Channel Squadron, had arrived at Gibraltar, having 

 made the passage in less than seventy hours. Such a 

 passage as this has ceased to be regarded as pheno- 

 menal, and is looked upon as quite an every-day 

 occurrence. Vox a portion of the voyage a speed of over 

 fifteen knots was maintained, and on board a ship steam- 

 ing ,it this rate nearly due south, at that time of year, the 

 sun would not appear to 'dip' until more than five 

 minutes after noon, and a correction of nearly 45 ' would 

 be necessary to reduce the maximum altitude to the 

 meridian." 



As the ship moves south a fresh horizon comes into 

 view, and the sun will appear to lisc until this shift of the 

 NO. 1282, VOL. 50J 



horizon (the rate of which depends upon the rate of the 

 ship towards the sun) is less than the rate of his motion 

 in altitude. 



There is another reason for being thankful for the sun 

 having to be thus treated at the noon-day observation. 

 It will lead to the moon and planets being no longer 

 avoided for finding the latitude at the time of their 

 culmination. No celestial bodies are more useful for 

 such a purpose, especially at twilight, when a well-defined 

 horizon is frequently available. 



Every practical navigator daily uses the Nautical 

 • Almanac : it would be well if he devoted a short time 

 also to study the " Explanation " at the end of the 

 volume. In explaining" Far. in i liotir'' which occurs 

 on every page I. of the book, it is stated that this " is the 

 variation at noon, and requires to be reduced to midway 

 between noon and the time at which the R A., Dec, or 

 Eq. of time is required " ; in other words, the reduction 

 of the quantities from apparent noon to any other time 

 is a problem in dynamics. The moving body is subject 

 to a uniform acceleration in the direction of its motion, 

 and the space described in a given time is found by 

 multiplying the mean velocity during the time by the given 

 time. The same principle applied to the ex-meridian 

 problem gives the result that the reduction |is equal to 

 the rate of change of altitude per half-minute of time, 

 multiplied by the number of minutes of time from the 

 meridian. 



So far from decrying the rapid methods now so need- 

 ful in practice, the author advocates their further use. 

 He gives a" Method of solving the Ex-meridian Problem 

 practically by the Azimuth Tables," which are, or should 

 be, in the hands of every navigator, and also " Practical 

 Rules for finding Time of Maximum Altitude," and ends 

 with " Application of the Azimuth Tables to other 

 Problems." 



We can heartily recommend this short contribution to 

 the science of nautical astronomy in its application to 

 the practical requirements of modern navigation. 



PERFUMERY. 

 Odorographia : a Natural History of Raw Materials 

 and Drugs used in the Perfume Industry, including the 

 Aromatics used in flavouring. Intended for the use 

 of Grojcers, Manufacturers, and Consumers By J. Ch. 

 Sawer, F. L.S. Second Series. (London : Gurney 

 and Jackson, 1894.) 



THIS book is a continuation of the subject of odour- 

 yielding products treated of by Mr. Sawer in a 

 volume bearing the same title and issued in 1892. 

 Though the present book is a companion volume in 

 every respect to its predecessor, and might well have 

 been designated as the second volume, the author has 

 preferred to call it the second series, thus implying, 

 and indeed distinguishing, the former book as the first 

 series —a little peculiarity which does not in itself affect 

 the value of the work, but which tends to confusion lest 

 the second series might be taken for an extended or 

 enlarged edition of the first ; whereas the term volume 

 would have implied that it is an entirely new book, 

 which is really what the author wishes his readers to 

 understand, as he tells us in the pref.ice to the new 



