March 30, 1899J 



NA TURE 



509 



An Elementary Text-hook of Botany. By Sydney H. 



Vines, M.A., D.Sc, F.R.S. With 397 illustrations. 



Pp. 611. (London: Swan Sonnenschein and Co., 



Ltd., 1S98.) 

 Prof. A'ines's '• Students' Text-book of Botany," or at 

 least the first half of it, was reviewed in Nature for 

 October 25, 1894. This book is now widely known, and, 

 as a well-ordered repertory of facts for the advanced 

 student, is probably unrivalled. 



The present work, as we are told in the preface, was 

 " undertaken to meet a demand which appeared to exist 

 for a less bulky and expensive volume." While the 

 reduction in cost is considerable, the diminution in bulk 

 is not so very great ; the number of pages is about 600, 

 as compared with about 800 in the larger work. The 

 new text-book has also been somewhat simplified, by 

 the omission of "certain difficult and still debatable 

 topics, such as, for instance, the details of nuclear 

 division, or the alternation of generations in the 

 Thallophyta." 



The book, however, subject to these omissions and 

 abridgments, is the same, and for the most part verbally 

 the same, as the original work. It is obvious that an 

 elementary text-book, in the sense of a first introduction 

 to the science, cannot be prepared on this principle. 

 Such an introduction requires to be thought out as a 

 whole, from the point of view of the beginner's needs. 

 Prof. X'ines's new publication is only to be called elemen- 

 tary relatively to its predecessor. It remains essentially 

 what it was before its abridgment — a book for con- 

 sultation and reference on the part of those who have 

 already gained some considerable knowledge of the sub- 

 ject. For this purpose we have no doubt that the book, 

 in its new form, will prove of great value to readers who 

 require sound information on all parts of the science, 

 but who do not need quite so much detail as the larger 

 text-book contains. 



It should be added that the present work has been 

 brought "up to date," and takes account of the chief 

 advances in the science which have been made since the 

 publication of the "Students' Text-book." 



The Prineiplcs of Agrieulture : a Text-hook for Schools 



and Rural Societies. Edited by L. H. Bailey. Pp. 



XV -F 300. (New York : the Macmillan Company. 



London : Macmillan and Co., Ltd., 1898.) 

 This is a work written by eight of the professors and 

 teachers of Cornell University. It attempts within the 

 limits of a small volume to give an elementary popular 

 account of the principles of agriculture. The task is 

 made the more difficult as the subject is not limited to 

 the discussion of the conditions necessary for the growth 

 of field crops, but includes fruit culture, and a long sec- 

 tion on animal physiology and nutrition. It follows, 

 consequently, that a great deal is left out that we should 

 have expected to find. An attempt is made to reduce 

 the necessary deficiencies of the book by frequently 

 referring the reader to other books treating the subject 

 more fully. 



In the earlier part of the volume there is much excel- 

 lent teaching in vigorous language as to the primary 

 necessity of a good physical condition of the soil. " The 

 fanner should give attention to the texture of his soil 

 before he worries about its richness. The conditions 

 must first be made fit or comfortable for the growing of 

 plants ; then the stimulus of special or high feeding may 

 be applied." ..." By superior tillage you can expand one 

 acre into eight, or by neglectful management eight acres 

 can be reduced to one." . . . "Success in modern agricul- 

 ture depends more on the size of the farmer than on the 

 size of the farm." 



The book includes not a few misstatements, the result, 

 probably, of hasty writing for uncritical readers. 



R. W. 



NO. 1535, VOL. 59] 



LKT'lEliS '10 IBE KUllUU. 



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 op NATtJRE. 

 No notice is taken of anonymous commiinications.'\ 



Experiment to Illustrate the Zeeman Effect. 



An interesting dynamical illustration of the Zeenian effect 

 may be made by fixing a gyroscope so that its axis of rotation is 

 the line of suspension of a pendulum bar so suspended as to be 

 capable of vibrating in any plane. When the gyroscope is 

 rotating the plane of vibration of the pendulum rotates with a 

 precessional motion, and when the pendulum is caused to 

 vibrate in a circular path its rate of description of its orbit 

 depends on its direction of rotation round its orbit. The 

 analogy to the Zeeman effect would make the rotation of the 

 gyroscope correspond to the imposed magnetic force and the 

 motion of the pendulum to that of the electrons. The explan- 

 ation of the motion by the properties of a gyroscope is pretty 

 obvious. It may be a matter for further consideration whether 

 there are analogies between the length of the pendulum and its 

 precession when descrilnng elliptic orbits and the Zeeman 

 effects : the ordinary elliptic precession corresponding to such a 

 phenomenon as the double sodium line. 



Geo. Fras. FitzGerald. 



Trinity College, Dublin, March 24. 



The Colour of Sea Water. 



As Mr. Threlfall, in his letter to Nature of March 16, seems 

 to have fallen into an error regarding the explanation of the 

 colour of sea water, given by me in the paper referred to in his 

 letter, perhaps I may be allowed to make a few remarks on the 

 subject. He says my explanation is based on the principle that 

 sea H'ater is a blue liquid, and that the green tint often seen in 

 sea water is due to the presence of yellow particles. Now, 

 while it is pointed out in the paper referred to that yellow 

 particles will make a blue water appear greenish, yet it is 

 nowhere stated that yellow particles are the exclusive cause of 

 greenness in sea waters. VVhat may have caused Mr. Threlfall 

 to make this overlook, may be the fact that only an abstract of 

 the paper was published, and the different points, therefore, not 

 fully explained. Still, I think there is enough in the abstract 

 to show that greenness in sea water was recognised to be due 

 in some cases to other causes than the one referred to in Mr. 

 Threlfall's letter. 



At the beginning of the paper referred to, experiments are 

 described showing that the water of the Mediterranean is a blue 

 transparent medium full of solid floating particles, and that it 

 is "these solid particles that determine the brilliancy, and the 

 selective absorption of the water determines its colour." It is 

 then shown that the colour of the particles will have an influence 

 on the appearance of the water ; that if the particles be yellow the 

 blue water will appear green, as anyone can observe on looking 

 at the Mediterranean water where it overlies a yellow sand bed. 

 After describing experiments made on the waters in the Italian 

 and Swiss lakes, the paper goes on to the consideration of the 

 experiments made on sea water on the west coast of Scotland, 

 from which I quote the following: — "The water was here 

 found to be much greener than any previously examined. A 

 large quantity of the water was filtered, when it was found that 

 most of the suspended particles were fine grains of sand. From 

 this it is concluded that the greenness of our northern seas is 

 in part due to the reflecting particles being yellow, and the 

 reflected light, therefore, deficient in the more refrangible rays. 

 These yellow sand particles not only explain /ar^ r^/the green- 

 ness of our northern se.as, but they also explain their compar- 

 ative darkness and deadness, the yellow sand particles reflecting 

 so little light. The importance, however, of even these bad 

 reflectors was very evident during the time the observations 

 were being made. It was noticed that the water was much 

 more brilliantly green during and immediately after an inshore 

 wind, and when the filter showed the water to have a good deal 

 of sand in suspension, than after a calm, when many of the 

 particles had settled out. Some water collected about a mile 

 seaward from Ballantrae was examined in a glass tube 7i "'• 

 long, and was found to be of a blue-green colour. " 



