| 3 6 THE POPULAR SCIENCE MONTHLY. 



led to observe infants, as exhibiting emotions with extraordinary force, 

 as well as with a simplicity and an absence of convention which cease 

 with more mature years. Secondly, the insane had to be studied, be- 

 ing liable to the strongest passions, and giving them uncontrolled 

 vent. Dr. Duchenne's ingenious application of photography, repre- 

 senting the effects of galvanism upon the facial muscles of an old man, 

 gave some assistance toward distinguishing varieties of expression. 

 Less aid than was expected was found to be derived from the study of 

 the great masters in painting and sculpture ; beauty in works of art 

 excluding the display of strong facial muscles, and the story of the 

 composition being generally told by accessories skilfully introduced. 

 More important it was to ascertain how far the same expressions and 

 gestures prevail among all races of mankind, especially among those 

 who have associated but little with Europeans. With this view a list 

 of 16 questions was circulated by Mr. Darwin within the last five years, 

 to which 36 answers have been received from missionaries, travellers, 

 and other observers of aboriginal tribes, whose names are appended to 

 Mr. Darwin's introductory remarks. The evidence thus accumulated 

 has been supplemented by the close and keen observation of the author 

 himself through a wide range of animal life. It seemed to him of 

 paramount importance to bestow all the attention possible upon the ex- 

 pression, of the several passions in various animals, not, of course, as de- 

 ciding how far in man certain expressions are characteristic of certain 

 states of mind ; but as affording the safest basis for generalization on the 

 causes or the origin of the various movements of expression. In ob- 

 serving animals we are not so likely to be biassed by our imagination, 

 and we may feel sure that their expressions are not conventional. 



" As the result of his observations, Mr. Darwin has arrived at three 

 principles, which appear to him to account for most of the expressions 

 used by man and the lower animals under the influence of various emo- 

 tions and sensations. The first of these is the principle of serviceable 

 associated habits. Movements which are of service in gratifying some 

 desire, or in relieving some sensation, become by repetition so habitual 

 that they are performed, whether they are of any service or not, when- 

 ever the same desire or sensation is felt, even in a very weak degree. 

 Actions, which were at first performed consciously, become, through 

 habit and association, reflex or automatic the sensory nerve-cells ex- 

 citing the motor nerve-cells, without first communicating with those 

 cells on which our consciousness and volition depend. Starting at the 

 approach of danger, and blinking with the eyelids so as to protect the 

 eyes, become perfectly spontaneous. Reflex actions, too, gained for 

 one purpose, may be modified independently of the will or of habit, so 

 as to serve for some other distinct purpose ; or, they may be developed 

 through natural selection. And they are thus often brought into play 

 in connection with movements expressive of emotion. When move- 

 ments associated through habit with certain mental states are partially 



