SCIENCE 



[N. S. Vol. XLIII, No. 1115 



erals. Just why columbium and tantalum do 

 not find a place here for the same reason is 

 not altogether clear; but of course a limit had 

 to be set. 



Part I. classifies the minerals as follows: 

 (1) silicates; (2) titano-silicates and tita- 

 nates; (3) tantalo-coltunbates ; (4) oxides and 

 carbonates; and (5) phosphates and halides. 

 Such a classification of the one hundred and 

 fifty or more rare-earth minerals, giving the 

 percentages of the chief rare earths present, is 

 useful and has already been adopted by other 

 authors. A valuable addition to this list is the 

 giving of the locality where the minerals are 

 found. 



Part II. discusses adequately and satisfac- 

 torily, on the whole, the chemistry of the ele- 

 ments. A fair amount of attention is given to 

 the separation processes so many and compli- 

 cated in this group. The spectroscopic meth- 

 ods, absorption, spark, arc and cathode lumines- 

 cence, methods themselves of the highest value, 

 are duly emphasized, and Urbain's recent ap- 

 plication of magnetic susceptibility receives its 

 proper consideration. It is of interest to note 

 that the lanthanum test consisting of a blue 

 color when iodine is brought into contact with 

 the hydroxide find a place in the book, al- 

 though no one of whom the reviewer knows has 

 been successful in applying it. 



Part HI. is concerned mainly with an ac- 

 count of the development of the incandescent 

 light industry. This is a most instructive his- 

 tory, and deserves all the space assigned to it, 

 as it has given the main impetus to rare-earth 

 investigation during the past thirty years. 



A feature which commends the book is its 

 international scope. American, English, 

 French and German chemists will find their 

 work fairly represented. 



The book is an important contribution to in- 

 organic chemistry, and should be in the library 

 of every inorganic chemist for study or at 

 least for reference. 



Philip E. Browning 



Relativity and the Electron Theory. By E. 

 Cunningham. Longmans, Green and Com- 

 pany, London. Pp. vii + 96. 



The author has a large work on this sub- 

 ject printed by the Cambridge University 

 Press and now presents a short monograph, 

 from which the more difficult mathematical 

 work is omitted. The result is a book which 

 may be read without serious effort, even by 

 persons not specialists in the theory of rela- 

 tivity or in mathematical physics. The titles 

 of the chapter are: I. Introductory; II. The 

 Origin of the Principle; III. The Eelativity 

 of Space and Time ; IV. The Eelativity of the 

 Electro-magnetic Vectors; V. Mechanics and 

 the Principle of Eelativity; VT. Minkowski's 

 Four-Dimension Vectors; Vii. The New Me- 

 chanics; VIII. Eelativity and an Objective 

 ^ther. Throughout the work emphasis is 

 laid upon the physical foundations of relativ- 

 ity and upon its physical consequences. Some- 

 thing is also said of the philosophical meaning 

 of relativity. 



The natural book with which to compare 

 Cunningham's is Carmichael's Monograph, 

 " The Theory of Eelativity," published by 

 John "Wiley and Sons. The essential element 

 of contrast is that Carmichael proceeds in the 

 Euclidean fashion from definite assumptions 

 or postulates to definite theorems; whereas 

 Cunningham writes in the ordinary style of 

 the physicist. The one lays greater stress on 

 logical foundation, the other upon the phys- 

 ical connections of the theory. So different 

 is the point of view that even though the re- 

 sults overlap to a large extent, any reader of 

 one of the monographs would find much addi- 

 tional interest in reading the other. The 

 change in the concepts of mass and time and 

 space which is suggested by the theory of rela- 

 tivity is so perplexing to many persons that 

 the reading of both these texts wiU be none 

 too much to allay their anxieties. The mathe- 

 matician should begin with Carmichael and 

 the physicist with Cunningham. 



Edwin Bidwell Wilson 



SPECIAL ARTICLES 



THE RELATION OF OSMOTIC PRESSURE AND 

 IMBIBITION IN THE LIVING MUSCLE 



1. A SERIES of independent observations by 

 Nasse, the writer, Overton, Meigs, Beutner, 



