320 



Royal Society :— 



Table IV. — January 21, I860. Measurements by portable torsion 

 electrometer of electromotive forces producing sparks across a 

 stratum of air of different thicknesses. 



The difference between the numbers shown in these two Tables 

 and in Table II. above, are probably due in part to true differences 

 in the resistance of the air to electrical disruption ; but variations 

 in the electrometer, which was by no means of perfect construction, 

 may have sensibly influenced the results, especially as regards the 



