148 



SCIENCE 



[N. S. Vol. XLIX. No. 1258 



If we do not care to eliminate the goldeui'od 

 from the national flower contest because of 

 thoughtfulness for our friends and neighbors 

 who suffer from its existence, let us do so 

 merely from the eificiency standpoint, both in- 

 dividual and state. Horace Gunthorp 

 Washburn College, 

 TOPEKA, Kans. 



SCIENTIFIC BOOKS 



The Theory of Relativiiy of Motion. By 



E. 0. ToLMAN. University of California 



Press, ix -|- 225 pp. 



This book, which the author calls an intro- 

 duction to the theory of relativity, is very 

 attractive in style, sufficiently accurate, and 

 covers the subject rather thoroug'hly. After a 

 brief sketch of the historical development and 

 statement of the postulates on which Einstein 

 founded the theory, there is a very interesting 

 chapter containing " elementary deductions " 

 of some of the most striking results. This 

 chapter makes it possible for students of 

 physics to get a fairly definite idea of the 

 subject without the rather perplexing mathe- 

 matics in which it is usually hidden. Un- 

 fortunately the author finds it necessary to 

 state that observers moving relatively to each 

 other would find the same measurements per- 

 pendicular to the line of motion because they 

 could make a direct comparison of their meter 

 sticks when the motion brings such meter 

 sticks into juxtaposition. There is nothing in 

 the previous discussion that shows why this ap- 

 plies when the meter sticks are iJerpendicular 

 to the line of motion and not when they are 

 parallel to it. 



A reader interested in the formal develop- 

 ment would perhaps turn first to the chapter 

 on the Lorentz transformations for, as Poin- 

 care pointed out, these constitute the real 

 essence of relativity. Most writers have some 

 difficulty in logically deducing these from 

 Einstein's postulates, the reason apparently 

 being that it can not be done. The author 

 avoids this difficulty by showing that the trans- 

 formations do satisfy the postulates without 

 attempting the impossible converse. 



The applications cover the dynamics of a 

 system of particles, elastic bodies, thermo- 

 dynamic systems, and electromagnetic theory. 

 In a chapter on the chaotic motion of a system 

 of particles there is given what amounts to 

 statistical mechanics in the form required by 

 the principle of relativit.y. The last chapter 

 is an introduction to the four-dimensional 

 vector analysis used by Wilson and Lewis. 

 This will be welcomed by many readers who 

 have struggled with the original. The book 

 does not enter into the extended relativity pro- 

 posed by Einstein in connection with his 

 speculations on gravitation. H. B. Phillips 



SPECIAL ARTICLES 



ON EXPLAINING MENDELIAN PHENOMENA 



So many devices have been invented for 

 representing the possible combinations of the 

 various factors in Mendelian inheritance that 

 one comes to entertain a suspicion that other 

 folk have their troubles also in the presenta- 

 tion of this subject to beginners. The follow- 

 ing suggestion is offered as having helped in 

 serious cases. The beginning student of hered- 

 ity is dealing with unfamiliar terms and, un- 

 less considerable laboratory work has rendered 

 him no longer a beginner, he is considering 

 unfamiliar processes. In his quicksand of 

 strangeness he is glad to find a firmament of 

 familiarity and he, therefore, welcomes a 

 process of reasoning or of routine that he has 

 employed before. Practically every high school 

 graduate has had at least a year of algebra 

 and has learned by rote the square of a -|- Z). 

 Whether or not he remembers that a- -\- '2ah -j- 6^ 

 represents all the possible combinations of the 

 two factors, he is in a position to be reminded 

 of that fact and. to take the first short step 

 into the unfamiliar. If a and h represent 

 the two types of gametes produced by the 

 heterozygous parents Fj, then a^ -j- 2o6 -|- 6^ 

 represents all possible progeny in the F, gen- 

 eration. Factors of second power represent 

 pure strains because the determiner is the 

 same from both parents. Conversely factors 

 of the first power represent heterozygotes or 

 the luiion of unlike determiners. 



