100 APPENDIX I. 



if the difference of time resulting therefrom for the 

 perception of messages conveyed by the two senses 

 were large enough to become apparent, as is the case 

 when we see the flash of the gun before hearing its 

 report. Now we cannot well distinguish intervals of 

 time smaller than one-tenth of a second at the most ; 

 so that within that limit any irregularity in the 

 working of our organs of sense may occur, from any 

 cause whatever hence from a delay of the messages 

 in the nerves without our becoming aware of it. 



The problem thus suggests itself, to ascertain 

 whether any perceptible time is required for the 

 transmission of volition and sensation through the 

 nerves, and if so, what is the rate of propagation of 

 the nervous agent. 



Historical Remarks. This problem is by no 

 means a new one ; for a hundred and fifty years it 

 has engaged the attention of physiologists, and many 

 an adventurous hypothesis has been broached in order 

 to approach to at least a pretence of a solution. 



One of the early latro-mathematicians preposter- 

 ously conceived that the velocity of the nervous 

 agent ought to bear the same proportion to that of 

 the blood in the aorta as the width of the aorta to 

 that of the nerve-tubes, and he thus inferred the 

 velocity of the former to be one hundred and twenty 

 millions of miles in one second, rather more than 

 six hundred times the velocity of light.* 



Haller himself tried, in reading the 2Eneid aloud, 

 how many letters he could pronounce in one minute. 



* Haller, Elementa Physiologix Corporis liumani. Tom. iv. 

 Lausann, 1762. 4 C . P. 372. 



