428 THE CANADIAN NATURALIST. [Dec. 



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 expressson 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 

 alterations of black and white awaken no response in the ordinary 

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

 pressions, the brain-cell has been educated, that these before 

 meaningless characters awaken thought. Is thought, then, simply 

 a cell-action which may or may not result in muscular expression, 

 — an action which originates new combinations of truth only, 

 precisely as a calculating machine evolves new combinations of 

 figures ? Whatever we define thought to be, this fact 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? Or is the evolution of 

 thought entirely independant of the matter of the brain ? Expe- 

 rimeots, ingenious and reliable, have answered this question. The 

 importance of the results will, I trust, warrant me in examining 

 the methods employed in these experiments somewhat in 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 that 

 smaller difi'erences of temperature may be recognized by convert- 

 ing the heat into electricity, than can be detected thermometri- 

 cally. The apparatus first used by Melloni in 1832,^- is very 

 simple, consisting first, of a pair of metallic bars like those de- 

 scribed in the early part of the lecture, for effecting the conversion 

 of the heat ; and second, of a delicate galvanometer, far measuring 

 the electricity produced. In the experiments in question one of 

 the bars used was made of bismuth, the other of an alloy of 

 antimony and zinc.^^ Preliminary trials having shown that any 

 change of temperature within the skull was soonest manifested 

 externally in that depression which exists just above the occipital 



