468 STUDIES IN ADVANCED PHYSIOLOGY. 



had with the greatest precision noted the transit just at the 

 moment they saw it in the telescope. These little differ- 

 ences of time were, therefore, due to the differences of time 

 in the nervous systems of the observers, and so it became 

 necessary to find out for each observer the time that he 

 required to record the observation. This was called his 

 personal equation. 



In the field of physiological psychology a great deal of 

 work has been done in determining the reaction time of the 

 various centers. This is the interval between the percep- 

 tion of anything and its interpretation. A multitude of 

 books are available everywhere, and it seems undesirable 

 in this treatise to enter in detail into this field. Interesting, 

 however, .are the points that this reaction time may be 

 shortened by practice, and that the reaction time may in a 

 general way be taken as a physiological index of the 

 individual's education of the sense in question. It is of 

 course understood that the reaction time for complicated 

 psychical processes will be correspondingly longer than for 

 simpler ones, and that they need not necessarily be the 

 same for the different sense organs. The shortest re- 

 action time is possibly that of the eye. The further large 

 field of interesting observations which has to do with the 

 interpretation of sensations and their association in memory 

 must here be referred to the field of physiological psychology 

 in which the advances have in recent years been so great as 

 to rank that science as one of the co-ordinate biological 

 sciences of the day, whose field has, therefore, by the 

 necessities of such an extension been more or less excluded 

 from^purely physiological considerations. 



