66 OF STIMULUS AND EXERTIOM. SECT. XIL i. 



ception of a difficult fubject. Let twenty very fmall 

 Leyden phials properly coated be hung in a row by 

 fine filk threads at a fmall diftance from each other ; 

 let the internal charge of one phial be pofitive, and 

 of the other negative alternately, if a communica- 

 tion be made from the internal furface of the firft 

 to the external furface of the laft in the row, they 

 will all of them inftantly approach each other, 

 and thus fhorten a line that might connect them 

 like a mufcular fibre. See Botanic Garden, p. i. 

 Canto I. 1. 202, note on Gymnotus. 



The attractions of electricity or of magnetifm do 

 not apply philofophically to the illuftration of the 

 contraction of animal fibres, fince the force of thofe 

 attractions increafes in feme proportion inverfely as 

 the diftance, but in mufcular motion there appears 

 no difference in velocity or ftrength during the be- 

 ginning or end of the contraction, but what may 

 be clearly afcribed to the varying mechanic advan- 

 tage in the approximation of one bone to another. 

 Nor can mufcular motion be affimilated with great- 

 er plaufibility to the attraction of cohefion or elaf- 

 ticity ; for in bending a fteel fpring, as a fmall 

 fword, a lefs force is required to bend it the firft 

 inch than the fecond ; and the fecond than the 

 third; the particles of fteel on the convex fide of 

 the bent fpring endeavouring to reftore themfelves 

 more powerfully the further they are drawn from 

 each other. See Botanic Garden, P. i. addit. 

 Note XVIII. 



I am aware that this may be explained another 

 way, by fuppofing the elalHcity of the fpring to 

 depend more on the compreffion of the particles on 

 the concave fide than on the extenfion of them on 

 the convex fide ; and by fuppofing the elafticity of 

 the elaltic gum to depend more on the refiftance to 

 the lateral ^compreilion of its particles than to the 

 longitudinal extenfion of them. Neverthelefs in 



mufcular 



