102 



SCIENCE. 



[N. S. Vol. XXI. No. 525. 



one of the examples he informs the more care- 

 ful reader that a large class of equations are 

 excluded from consideration. This is, indeed, 

 necessary, as otherwise the reasoning of §172 

 may become illusory by the vanishing of 

 [(.), a], as simple examples will show. But 

 even with this restriction it must be shown or 

 assumed that this expression does not vanish. 



Another point which wo believe has not been 

 suiRciently emphasized relates to the ecjuality 

 or inc'ciiiality of rational functions of the roots. 

 I low often in Galois's theory do we have to 

 decide whether a rational function of the roots 

 has or has not been changed or altered by a set 

 of substitutions. The only explanation of this 

 fundamental and delicate matter we have 

 found is in a footnote on page 124. 



Would it not be well to restrict the term 

 general equation to one whose group is the 

 symmetric group? The author follows well- 

 established usage in calling a general equation 

 one whose coefficients are independent vari- 

 ables. Because algebraicists thought a cen- 

 tury ago that these equations represented the 

 general case is no reason to perpetuate a term 

 which is sure to produce confusion in the 

 mind of the beginner. Apropos of these equa- 

 tions we must express our regret that the 

 author has allowed the demonstration given in 

 § 158 to pass muster; it is a demonstration 

 which does not demonstrate. 



James Pierpoxt. 



Yale Uxivehsity. / 



La contagion mentale. Dr. A. Vigouroux et 

 Dr. P. JuQUELiER. Paris, 1905. Pp. 250. 

 This is one of the volumes in the French 

 Bihliotheque intrrnationale de psijchologie <>x- 

 perimentale, normal et pathologique. Mental 

 contagion is the name here given to what is 

 generally known as imitation in the narrow 

 sense, i. e., unconscious imitation. The proc- 

 ess is unconscious on the part of both the imi- 

 tator and the person imitated. Thus contagion 

 excludes voluntary imitation and personal sug- 

 gestion. The first half of the book deals with 

 normal contagion and the second half with 

 abnormal. 



A.ssuming that the reflex arc is the funda- 

 mental type of neural action, and that the 



impulse may enter a given sensori-motor 

 circuit from any sense and at any point in 

 tlie circuit, we may trace a physiological ex- 

 planation for all the contagious acts, e. g., 

 yawning, laughing, crying, coughing, dancing, 

 nuirching, etc. Then, on the theory that every 

 emotion tends to express itself in muscular ad- 

 justment, that this adjustment may be trans- 

 mitted by contagion, and that a given emo- 

 tional expression creates the emotion, the same 

 explanation accounts for the contagion of 

 emotional states e. g., fear in a panic, anger 

 in a revolution, the soldier's adoration of 

 Napoleon, the schools of art and the havocs 

 of intellectual bias. 1'he same principle may 

 also be extended to ideas because all ideas a;e 

 more or less fused with feeling, e. g., belief, 

 scientific theory, dogma. The idea is con- 

 tagious in proportion to the feeling present. 

 Good analytic and genetic accounts run 

 parallel to this mode of explanation, and 

 special emphasis i.s laid on the social cond'- 

 tions and significance of mental contagion. 

 The second part of the book cons'sts largely 

 of citation and classification of cases. The 

 less nornuil the individual or the group, the 

 more liable to contagion. Like tl:e microbe, 

 tlie mental contagion may be either beneficent 

 or )ioxious. 



A practical lesson from this book is pre- 

 e ainent : mental contagion is preventable. If 

 insanity and crime are contagious, that prin- 

 ciple should be recognized in our penal and 

 corrective institutions; and society may take 

 steps to prevent epidemics of fanaticism and 

 crime. To-day science is interested in the 

 physical microbes of disease; in the near 

 future there will be a similar interest in the 

 facts of mental contagion. 



C. E. Seashore. 



University of Iowa. 



KCIESTII'IC JOURNALS AND ARTICLES. 



The American Jonrnal of Science for Jan- 

 uary contains the following articles : ' Sub- 

 marine Great Canyon of the Hudson River,' 

 by J. W. Spencer; 'Radioactivity of Under- 

 ground Air,' by 11. M. Dadourian; 'Types of 

 Limb-Structure in the Triassic Ichthyosauria,' 



