794 



SCIENCE 



[N. S. Vol. XLI. No. 1065 



And so it is with this report. It is filled 

 with mathematics in which elliptic functions, 

 long a favorite study of Sir Greorge's, plays an 

 important role; but the reader is continually 

 running across such homely illustrations as 

 those a teacher might use in the classroom — 

 the illustrations of bicycle wheels, stepladders, 

 clock hands, reflections in a mirror, plumb 

 lines, balancing on a knife edge, tops, chil- 

 dren's hoops, race wheels, motor cars, the 

 motor omnibus, spinning cards through the 

 air. Whitehead torpedoes, the monorail car- 

 riage, and the like — just the sort of things 

 that those who have used the problems in the 

 author's calculus have delighted to find for 

 interesting a class. 



The report is divided into nine chapters. 

 Chapter I. relates to steady gyroscopic mo- 

 tion, with applications to the problem of the 

 precession of the equinox and to the gyro- 

 scope as a stabilizer. Chapter II. continues 

 the applications of the gyroscope, in partic- 

 ular with reference to ships, the Brennan 

 monorail carriage and the Bessemer saloon. 

 Chapter III. relates to the general unsteady 

 motion of the gyroscope, and to the figures 

 resulting therefrom — for example, to the 

 rosette curve described by Klein. Chapter IV. 

 deals with the geometrical representation of 

 the motion of a top, and in particular with 

 the work of Darboux. Chapter V. treats of 

 the algebraic cases of top motion, and in par- 

 ticular of the section problems, a subject con- 

 tinued in Chapter VI. Chapter VII. relates 

 to the spherical pendulum and related topics. 

 Chapter VIII. to such topics as the gyroscope 

 on a whirling arm, and Chapter 15. to the 

 dynamical problems of steady motion and 

 small oscillation. 



It is not intended in this brief review to do 

 more than call attention to the general nature 

 of the work. The practical value of the sub- 

 ject has come to be recognized in this war as 

 never before, and it is well that we have in one 

 place the body of theory which students of the 

 subject would otherwise have to search for in 

 many pamphlets, books and periodicals. The 

 report lays no claim to any important dis- 

 covery, but it may fairly claim to bring to- 

 gether in convenient form the mathematical 



theory of the gyroscope as far as it has been 

 developed up to the present time. 



David Eugene Smith 



Teachers College, '; 



Columbia University 



Monographs on Biochemistry. Soil Condi- 

 tions and Plant Growth. By Edward J. 

 EussELL, D.Sc. (Lond.), Director of the 

 Eothamsted Experimental Station, Har- 

 penden; with diagrams. New Edition. 

 Longmans, Green and Co., 1915. Pp. 150. 

 This is the third edition called for within 

 three years of the best book on the soil which 

 has yet been written. A new chapter has been 

 added on " The Relationship between the 

 Mieroorganic Population of the Soil and the 

 Growth of Plants." A number of minor 

 changes and a few of considerable importance 

 have been made in the original text, usually 

 because of recognition of literature non- 

 existent when the text was prepared originally. 

 The versatility of Dr. Eussell is astonishing 

 and the wealth of his information is prodigi- 

 ous. And yet he has told his story in some 

 lYO pages without an undue crowding. In fact 

 the book has " charm " and is easily read. 

 The professional chemist, physicist and bac- 

 teriologist will find it a mine of information 

 most interestingly woven together, but with 

 frequent references to original authorities. 

 And at the same time the layman can get a 

 purview of the complex system involved in 

 plant production in an understandable story. 

 Not only is the book the best in its field rela- 

 tively, but it is very good absolutely. But it 

 is not ideal, and probably most of the experts 

 will feel that its accents should be altered 

 and even that some of the statements should 

 not have been made as they are. Eor instance, 

 the reviewer should prefer to see the relation 

 between moisture content and the measurable 

 physical properties of the soil given more 

 prominence; and the dynamic as contrasted 

 with the static properties of the soil developed 

 more definitely. One is left with a too hazy 

 idea of the colloidal properties of clay and their 

 importance to the soil, and the purely hypo- 

 thetical calcium bicarbonate is called upon 

 rather frequently to explain things without 



