130 APPENDIX I. 



be that adopted by Dr. Hirsch, viz., to ascertain by 

 appropriate experiments the time required for 

 registering the passage at the cross-wire of an 

 artificial star moving at a rate similar to that of the 

 real stars, and thus, for the knowledge of the 

 personal equation of two observers, to substitute that 

 of their personal corrections, the difference of which 

 corresponds to their personal equation.* 



As to the theory of the nervous agent, now that 

 we know that this agent moves more than ten times 

 less quickly than sound in air, every attempt to 

 identify it with the electric current as it circulates 

 in a telegraph-wire must appear hopeless, even if a 

 circuit, such as would be necessary for the supposed 

 nerve current to circulate in, were anatomically 

 demonstrated. Thus to the other arguments against 

 this view of the nervous agent that the resistance 

 of the nerve-tubes would be far too great for any 

 battery to send an available current through them 

 that the physiological insulation of the nerve-tubes 

 from each other would be impossible to explain 

 that the effect of ligature or of cutting the nerve 

 and causing its ends to meet again, would be equally 

 obscure to these arguments, unanswerable as they 

 are in themselves, the researches sketched in this 

 lecture have added corroborative evidence of the 

 highest order. What we have termed the nervous 

 agent, if we look upon its very small velocity, in all 

 probability is some internal motion, perhaps even 



* Plantamour et Hirsch, Determination te'le'graphique de 

 la difference de longitude entre les Observatoires de Geneve et 

 de Neuchdtel. Geneve et Bale, 1864. 4, p. 89. 



