112 APPENDIX I. 



of an indicator, the velocity ot tne nervous agent 

 was found by Professor Helinholtz to be 27-25 

 metres (89*4 feet) in one second, which agrees very 

 well with the figure formerly obtained by M. 

 Pouillet's method.* It is hardly necessary to 

 mention that the difference s a s m corresponds to 

 the time spent by the nervous agent in travelling 

 from A to the termination of the nerve-tubes in the 

 muscle. 



Different "kinds of Myographion proposed ; descrip- 

 tion of the Apparatus used by the speaker on the present 

 occasion. The myographion, as it was originally 

 designed by Professor Helmholtz, is a rather com- 

 plicated and expensive apparatus. Various modifi- 

 cations have been proposed in order to simplify it. 

 For the clockwork moving the cylinder, Thiry has 

 substituted a reaction-engine moved by air, like that 

 in M. Foucault's apparatus for comparing the 

 velocity of light in air and in water. The rotation 

 of the cylinder in this myographion is uniform, and 

 its rate is ascertained by the pitch of a siren connected 

 with it.f Harless and Professor Fick altogether 

 abandoned the rotating scheme, which, in fact, 

 involves great and, perhaps, unnecessary difficulties, 

 and for the rotating cylinder substituted a glass 

 plate moving in its own plane. Harless allowed the 

 plate to drop in an apparatus constructed upon the 

 principle of Atwood's machine, and thus obtained an 

 uniform velocity, which could easily be determined 



* Job. Muller's Archiv, u. s. w., 1852. S. 199. 

 t Henle und Pfeuffer, Zeitschrift filr rationelle Medicin, 

 3. B., B. xxi., 1864, S. 300. 



