Jan. 1 1, 1872J 



NATURE 



207 



metal coatings of the band by touching the centre of the 

 charging rod. And for the rest, all that need now be said 

 of the apparatus (this is not all that has to be said, but 

 what remains has to do with a totally different set of ex- 

 periments, and had better be reserved until the time 

 comes for dealing with these experiments) is, that in order 

 to allow of this charging and discharging, the metal sur- 

 face at the back, instead of being insulated all round like 

 the metal surface at the front of the band, is put in com- 

 munication with the earth by bringing it down a little so 

 as to allow it to be clipped by the metal clamp which 

 fixes the band to the stand. 



In the actual experiment with the band, all that has to 



be done is first to charge and then to discharge, watching 

 the index the while. It was anticipated that the band 

 would elongate with the charge, and shorten with the dis- 

 charge, and this is what happens in fact ; for on charging, 

 the index at once moves before the graduated arc in the 

 way which shows that the band elongates in proportion 

 to the charge, and on discharging it suddenly jumps back 

 again to the position it occupied before the charging, these 

 forward and backward movements being through 40' or 

 60°, or even over a still wider range, and not merely through 

 one or two degrees. The band plainly elongates in pro- 

 portion to the charge. The band as plainly shortens in 

 proportion to the discharge, suddenly or gradually, as the 



case may be, suddenly if the charge be augmented until 

 it overleaps the barriers of insulation, or if the discharge be 

 brought about by pushing home the discharging-rod, gradu- 

 ally if the band be charged and then left to discharge itself 

 slowly by keeping back the discharging-rod. And these 

 results are constant, provided only before charging and 

 discharging the weights attached to the band are so ad- 

 justed as to balance without overbalancing the elasticity 

 of the band— a matter which is easily managed with 

 but little patience and practice. 



All, in fact, that was anticipated is fully borne out by 

 the experiment. And thus it may be taken for granted 

 that elongation of the muscular fibre tiiay be caused by 

 the attraction of two opposite charges of electricity 



disposed leyden-jar-wise upon the two surfaces of the 

 sheath of this fibre, and that contraction of this fibre may 

 follow the discharge of these charges ; for what is assumed 

 to happen in this case is nothing more than what does 

 actually happen with the band of india-rubber sheeting 

 under perfectly analogous circumstances. 



But if this be the way in which muscular fibre may be 

 afiected by its natural charge and discharge, how will it be 

 affected by an artificial charge of the same kind t Will 

 this artificial charge — the sheath being still a dielectric — 

 act like the natural charge, the charge imparted to one 

 side of the sheath inducing an equivalent amount of the 

 opposite charge on the other side? Will the artificial charge, 

 presuming it to be larger in amount than the natural 



