329 



tury school, as represented by Poisson. The same conclusion is 

 established by a series of experiments with the previously-described 

 portable torsion electrometer substituted for the absolute electro- 

 meter, leading to results shown in the following Table. 



TABLE II. January 17, 1860. Measurements by portable torsion 

 electrometer of electromotive forces producing sparks across a 

 stratum of air of different thicknesses. 



The series of experiments here tabulated stops at the distance 

 1 8 thousandths of an inch, because it was found that the force in the 

 electrometer corresponding to longer sparks than that, was too strong 

 to be measured with certainty by the portable electrometer, whether 

 from the elasticity of the platinum wire, or from the rigidity of its 

 connexion with the aluminium index being liable to fail when more 

 than 85 or 90 of torsion were applied. So far as it goes, it agrees 

 remarkably well with the other experiments exhibited in Table I., 

 as is shown by the following comparative Table, in which, along 

 with results of actual observation extracted from Table II., are 

 placed results deduced from Table I. by interpolation for the same 

 lengths of spark. 



