140 



SCIENCE 



[N. S. Vol. XXXIX. No. 995 



mendation of the committee above mentioned 

 should not be accepted, for it is opposed to 

 the established rules of priority. 



F. W. Clarke 



THE CYTOLOGIOAL TIME OF MUTATION IN TOBACCO 



In the current volume of Science, p. 35, 

 Hayes and Beinhart after describing the 

 origin of a many-leaved variety of Cuban to- 

 bacco by mutation say : 



This mutation must have taken place after fer- 

 tilization, i. e., after the union of the male and 

 female reproductive cells. If the mutation had 

 taken place in either the male or female cell be- 

 fore fertilization, the mutant would have been a 

 first generation hybrid, and would have given a 

 variable progeny the following season. 



Is it not equally probable that the mutation 

 occurred in an egg-cell which then developed 

 without fertilization? Parthenogenesis is 

 known to occur in tobacco, and mutation in 

 a growing or immature germ-cell seems in- 

 herently more probable than in a fully formed 

 and fertilized one. Perhaps the behavior of 

 the additional mutants obtained in 1913 will 

 throw light on the matter. 



W. E. Castle 



BussET Institution, 

 January 2, 1913 



SCIENTIFIC BOOKS 



Analytical Mechanics. By Haroutune M. 

 Dadourian, M.A., Ph.D., Instructor of 

 Physics in the Sheffield Scientific School of 

 Tale University. D. Van Nostrand Com- 

 pany. Price $3.00. 



In his preface, the author states that his 

 " work is based upon a course of lectures and 

 recitations which the author has given, during 

 the last few years, to the junior class of the 

 Electrical Engineering Department of the Shef- 

 field Scientific School." We expect this book 

 to contain, therefore, several topics of special 

 interest to students of electricity. We find a 

 chapter devoted to " Fields of Force and New- 

 tonian Potential," one to " Periodic Motion," 

 one to " Energy " and one to " Work." But, as 

 the author states, " In order to make the book 



suitable for the purposes of more than one 

 class of students more special topics are dis- 

 cussed than any one class will probably take 

 up. But these are so arranged as to permit 

 the omission of one or more without break- 

 ing the logical continuity of the subject." 



The author himself is a physicist, and per- 

 haps he intends this book to be suitable for 

 classes in physics. The book seems to be 

 written from the standpoint of the physicist 

 rather than from the standpoint of the engineer. 

 If this book is intended for the students of 

 civil and mechanical engineering, then it must 

 be said it has no advantage over the number 

 of books already in the field. I doubt if it is 

 even as suitable. 



Judging from the recent discussions con- 

 cerning the teaching of mathematics and 

 mechanics, it seems that the successful book has 

 not yet been written. Possibly the book every- 

 body is looking for must be written on a new 

 plan. To say that an author deviates from 

 the generally acknowledged plan need not be a 

 criticism of his book. Dr. Dadourian makes 

 his volume unique in several ways, but I 

 doubt if it will stand the test. 



In the first place, he seems to avoid the 

 graphical treatment. The modern tendency 

 seems to be to emphasize this phase of the 

 subject. 



The question of " units " is always a source 

 of contention between the physicist and the 

 engineer. The absolute system of units is 

 certainly the most logical. To the engineer, 

 however, it is not a question of logic, but of 

 adaptability. 



Another departure from the usual mode of 

 procedure in modern elementary text-books in 

 mechanics is the extent to which he makes use 

 of " vector addition." The first chapter is 

 devoted to the subject of the " addition and 

 resolution of vectors." On page 10 he gives 

 the analytical expression for the resultant of 

 any number of vectors, and the resolution of a 

 vector into its three rectangular components. 

 This section is made the basis of his whole 

 book so far as the composition and resolution 

 of vector quantities (forces, moments, couples, 

 etc.) are concerned. All he needs to say is, 



