-542 Scientific Proceedings, Royal Dublin Society. 



the otlier. Of this event we know that it is of a kind that arises 

 only in living brains and in them only while the man is either 

 awake or dreaming. We also know that it is of a kind that lasts 

 for a considerable time when it does occur, viz. throughout the 

 duration of the perception or other thought in the mind. 



This last consideration is very significant. The event in the 

 brain with which human perception or any other human thought 

 is associated must be one which can last while the thought lasts, 

 i. e. for a time immensely long when compared with the original 

 molecular events that are going on. The event may, for example, 

 be such an event as a strain consequent on a stress, whether 

 dynamical or electro-magnetic, acting on some part of the brain ; 

 or it may be of the nature of a forced vibration or current. These 

 are events which would continue in existence so long as the stress is 

 applied, and will cease when the stress is removed : they fulfil the 

 requisite time conditions. Another event which would fulfil the 

 time conditions is an undulation — dynamical, electro-magnetic, or 

 of any other kind. The waves that make up an undulation may 

 continue in it but a short time, some passing ofi while others come 

 on, and the motions or stresses of which each wave consists may be 

 such as succeed each other with extreme rapidity, while all the time 

 the undulation viewed as a whole continues as much unchanged 

 as a human thought does while it lasts. Hence an event of this 

 kind may, so far as its relation to time is concerned, be that event 

 in the brain which is intimately associated with human thought. 

 Possibly the event we are in search of may be found among the 

 processes of metabolism whereby nutrient matter brought by the 

 blood becomes part of the brain ; or more probably among those 

 processes in which matter that had formed part of the brain sepa- 

 rates and is swept away either by the blood or lymphatic vessels. 

 Events of this kind, including every interference with those here 

 specified, and the many other events which like them may be de- 

 scribed as stream effects, are marked by the peculiarity that a vast 

 number of molecules are concerned in them in such a way that 

 different molecules successively take up the running. All such 

 events fulfil the necessary condition of continuing temporarily in 

 existence, as each of our thoughts does, for a time which may be 

 immensely long compared with the fundamental events within or 

 between the molecules, or in the interfused Eether. It must, how- 



