CURRENTS AND TENSION IN A MUSCLE-PRISM. 191 



everywhere negative, and the greatest negative tension 

 prevails at the centre of these, and decreases from these 

 points up to where the cross-sections meet the longitu- 

 dinal section. 



2. From this distribution of the tensions it is easy 

 to infer the phenomena which the muscle shows when 

 it is inserted between the pads of the diverting vessels 

 above described, or between the diverting cylinders 

 which represent the feet of the diverting arch. It is 

 evident that no current will result when two points on 

 the equator, or two points on any one of the tension- 

 curves are tested. Nor will any current result when 

 two different points, on either side of the equator, are 

 connected, if these points are equidistant from the 

 equator. Nor will any current result when the two 

 cross-sections are applied to the pads; but, on the con- 

 trary, a current will be observed as soon as any point 

 on the longitudinal section and any one on either of 

 the cross- sections are connected, or when two points 

 on the longitudinal section, situated at unequal dis- 

 tances from the equator, touch the pads ; or. finally, 

 when two points on the same cross-section, or two 

 points, one on each of the two cross-sections, situated 

 at unequal distances from the central point, are con- 

 nected. The strongest current will result when a point 

 on the equator is connected with the central point on 

 one of the cross-sections ; weaker currents are gene- 

 rated when two unsymmetrical points on the longi- 

 tudinal section, or two unsymmetrical points on the 

 cross-section are connected. All these cases are re- 

 presented in fig. 50. The rectangular figure abed 

 represents a section through the muscle-prism ; a b 

 and c d are transverse sections through the longitu- 



