3 o8 THE POPULAR SCIENCE MONTHLY. 



a visit." I have translated as literally as possible Mosso's words 

 those unfamiliar with Italian should remember that words like " vene- 

 ration " and " master," when rendered literally, convey a more fervid 

 feeling in English than is expressed by the original. "We reproduce 

 the tracing referred to ; the upper line is drawn by the pen, and its 

 descent corresponds to the diminution of the volume of Mosso's right 

 forearm ; A marks the point when Professor Ludwig entered. The 

 lower line records the time, each notch corresponding to an interval 

 of five seconds. The diminution of volume was equal to about six 



Fig. 2. Curve traced by the Plethysmograph, showing the diminution of size in the fore- 

 arm, produced by the emotions caused by Ludwig's entrance at A. 



cubic centimetres. This effect was not due to any strong emotion of 

 fear or anxiety, but merely to the affectionate respect which Professor 

 Ludwig's genial manners win from his pupils. The same experiment 

 was tried upon Dr. Pagliani, with the same result. 



Cerebral activity, like all the emotions, is reflected by the vascular 

 system. To test this, the person experimented upon was given some 

 simple arithmetical problem to solve ; this was chosen because it could 

 be solved without the person's speaking, which would have necessitated 

 a change in the respiration, and so have modified the circulation. Fig. 

 3 shows the effect of calculating 245 X 15. The lines as before. This 

 experiment was made upon Dr. Frey, and testifies to the great effect 

 of a comparatively light and brief mental labor. It appeared that the 



245X15 



Fig. 3. Curve traced by the Plethysmography, showing the diminution of size in the fore- 

 arm of Dr. Frey, produced by his calculating 245 x 15. 



more complicated the sum to be solved the longer and greater was the 

 contraction of the arm. The response of the circulation is very ready 

 and marked, and, in persons of excitable temperaments, strong effects 

 are produced from such very slight causes that it is sometimes difficult 

 to make any experiments upon them. 



There is undoubtedly a relation between the intensity of the emo- 



