very Small Portions of Time. 325 



from the great toe arrives about ^th of a second later than from 

 the ear or the face. If from the measured sum of the single 

 intervals be subtracted that which belongs to the conduction in 

 the sensitive and motor nerves, and also the time, determined by 

 other experiments, during which the muscle puts itself in motion, 

 the remainder is the time which passes while the brain is trans- 

 ferring the intelligence received through the sensitive nerves to 

 the motor ones. 



Other experiments on man which corresponded to those on 

 the frog, inasmuch as the motor nerves were directly excited, 

 have up to the present time given no exact results, but they 

 suggest other interesting relations connected with the subject. 

 It is possible, for example, to cause the muscles of the fore-arm 

 to contract exactly like those of the frog by means of very feeble 

 electric shocks imparted to the nerves through the skin. In 

 this case both hand and fingers are contracted ; and it is shown 

 that these motions are totally independent of the influence of the 

 will, because the will, informed of the shocks by the sensible 

 nerves, cannot exert itself sufficiently soon upon the muscles. 

 Such a series of experiments, in which the hand fell back very 

 speedily, and when the very object sought was to retain it in the 

 bent position which it was caused to assume through the con- 

 tractions produced by the electric shocks, failed totally, because 

 the influence of the will first reached the muscle after the hand 

 had fallen back again, and simply raised it a second time. 



If we reflect on what has been said at the commencement of 

 this discourse regarding the inaccuracy of our impressions of 

 time, we see that the differences of time in the nervous impres- 

 sions, which we are accustomed to regard as simultaneous, lie near 

 the limits of our capability of perception, and that finer differ- 

 ences cannot be appreciated simply because the nerves cannot 

 operate more quickly. We are taught by astronomy, that on 

 account of the time taken to propagate light, we now see what 

 has occurred in the spaces of the fixed stars years ago ; that, 

 owing to the time required for the transmission of sound, we 

 hear after we see, is a matter of daily experience. Happily the 

 distances are short which have to be traversed by our sensuous 

 perceptions before they reach the brain, otherwise our self-con- 

 sciousness would lag far behind the present, and even behind 

 the perceptions of sound ; happily, therefore, the distances are 

 so short that we do not observe their influence, and are therefore 

 unprejudiced in our practical interest. With an ordinary whale the 

 case is perhaps more dubious ; for in all probability the animal 

 does not feel a wound near its tail until a second after it has 

 been inflicted, and requires another second to send the command 

 to the tail to defend itself. 



