286 ANNUAL OF SCIENTIFIC DISCOVERY. 



thus developed and the work performed by the muscle during its 

 contraction has been studied ; and it has been shown that the law 

 of the conversion of heat into mechanical work, which has been 

 so firmly established for physics, is equally applicable to living 

 beings ; that in these latter, as in our machines, a given amount of 

 chemical action produces less heat when mechanical work is done 

 than when it is not, a portion of the heat being, in the former 

 case, expended in performing the work. 



But the relation between brain-work and heat still remains un- 

 decided, no light having as yet been thrown upon this subject. 



The object of the investigation related in this article was to de- 

 termine the effect of different mental states upon the temperature 

 of the head, this being the first step toward the elucidation of the 

 problem in question. For this purpose thermo-electric apparatus 

 of a very delicate description, and arranged with special reference 

 to the experiments in view, was employed. 



The experiments now to be given were all made upon myself, 

 and have extended over the space of a year. They are, however, 

 but a part of those which have been made in that time, many hav- 

 ing been withheld for further examination. 



The object of the first series of investigations was to study the 

 temperature of the head, while sitting quietly by myself, with no 

 special mental occupation. 



Under these circumstances, it was found that while the tempera- 

 ture of the head was in some instances quite steady, in others it 

 was very variable, rising and falling often with great rapidity. 

 The variations were slight, not amounting, as a rule, to more 

 than a hundredth of a degree of Centigrade; but still they were 

 very marked, if some other portion of the bodj^ was taken as a 

 standard of comparison ; thus the temperature of the leg or arm 

 varied, if at all, within much narrower limits. 



What the exact cause of these irregularities was, could not be 

 determined with certainty ; but the conclusion arrived at from a 

 great many observations was, that this variability of temperature 

 was connected with certain conditions of the mind. It was found 

 that, in those cases in which the temperature was steady, the mind 

 was, as a rule, in a more or less torpid state, such as persons are 

 apt to fall into after a hearty meal ; while in the cases in which 

 variability of temperature existed the mental condition was one 

 of much greater activity. The effect of a transition from the 

 former to the latter condition was frequently shown, under the 

 following circumstances : — 



It often happened, when the mind was in the state of inactivity 

 mentioned, that one or more persons would enter the room in 

 which the observer was seated, and a short conversation ensued. 

 The subjects of conversation were of no particular interest, and 

 required no reflection ; but, nevertheless, in a few moments the 

 temperature, which had previously been steady, would begin to 

 vary, rising and falling, but with a general upward tendency. 



This change was not due to the muscular exertion of talking, 

 for it manifested itself when the observer took no part in the con- 

 versation, — merely listening to the words of others, and saying 



