244 TRANSACTIO^^S OF THE AMERICAN INSTITUTE. 



"What, now, shall we say of that highest manifestation of animal 

 life, thought-power? Has the upper region called intelligence and 

 reason, any relations to physical force ? This realm has not escaped 

 the searching investigation of modern science ; and although in it 

 investigations are vastly more difficult than in any of the regions 

 thus far considered, yet some results of great value have been obtained, 

 which may help us to a solution of our problem. It is to be observed 

 at the outset that every external manifestation of thought-force is a 

 muscular one, as a word spoken or written, a gesture, or an expression 

 of the face ; and hence this force must be intimately correlated with 

 nerve-force. These manifestations reaching the mind through the 

 avenues of sense, awaken accordant trains of thought only when this 

 muscular evidence is understood. A blank sheet of paper excites no 

 emotion ; even covered with Assyrian cuneiform characters, its 

 alternations of black and white awaken no response in the ordinary 

 brain. It is only when, by a frequent repetition of these impressions, 

 the brain-cell has been educated, that these before meaningless char- 

 acters awaken thought. Is thought, then, simply a cell action which 

 may or may not result in muscular expression — an action which 

 priginates new combinations of truth only, precisely as a calculating 

 machine evolves new combinations of figures ? "Whatever we define 

 thought to be, this feet appears certain, that it is capable of external 

 manifestation by conversion into the actual energy of motion, and 

 only by this conversion. But here the question arises, Can it be 

 manifested inwardly without such a transformation of energy 1 Or, 

 Is the evolution of thought entirely independent of the matter of the 

 brain? Experiments, ingenious and reliable, have answered this 

 question, Tlie importance of the results will, I trust, warrant me 

 in examining the methods employed in these experiments somewhat 

 \n detail. Inasmuch as our methods for measuring minute amounts 

 of electricity are very perfect, and the methods for the conversion of 

 heat into electricity are equally delicate, it has been found tliat 

 smaller differences of temperature may be recognized by converting 

 the heat into electricity, than can be detected thermometrically. 

 The apparatus, first used by Mellon i in 1832,* is very simple, con- 

 sisting first, of a pair of metallic bars like those described in the early 

 pai't of the lecture, for effecting the conversion of tlie heat ; and 

 second, of a delicate galvanometer, for measuring the electricity pro- 

 duced. In the the experiments in question one of tlie bars used was 



♦ Melloni, Ann. Ch. Phys., xlviii, 198. See also >fobili, Bibl. Uuiv., iliv, 335, 1830; Ivii, 1, 1834, 



