288 PHYSIOLOGY OF MUSCLES AND NERVES. 



motor nerves of men. INfore tlian this Las been done: 

 the time has been measured which is requisite for an 

 irritant conducted to the brain to be transmuted into 

 consciousness. Such determinations, in addition to 

 their theoretical value, are of practical interest to 

 observing astronomers. In observing the passage of 

 stars on the meridian and comparing the passage seen 

 through the telescope with the audible beats of a 

 second-pendulum, the observer always admits a slight 

 error, dependent on the time which the impressions on 

 the two senses require to reach the stat e of conscious- 

 ness. In two different observers this error is not of 

 exactly the same value ; and in order to render the 

 observations of different astronomers comparable with 

 each other, it is necessary to know the difference 

 between the two cases, the so-called personal equation. 

 In order to refer the observations made by each indi- 

 vidual to the correct time, it is necessary to determine 

 the error which is made by each individual. 



Let us suppose that an observer sitting in complete 

 darkness suddenly sees a spark, and thereupon gives 

 a signal. By a suitable apparatus, both the time at 

 which the spark really appeared and that at which the 

 signal was given are recorded. The difference between 

 the two can be measured, and it is called the physio- 

 logical time for the sense of sight ; the physiological 

 time for the sense of hearing and for that of touch 

 may be determined in the same way. Thus Professor 

 Hirsch, of Neufchatel, found — 



In the case of the sense of sight 0*1974 to 0-2083 sec. 

 „ „ hearing 0*194 „ 



„ „ touch 0*1733 - „ 



When the impression which was to be recorded was 



