to the Undulatory Theory of Light, 

 The following are the results : 



443 



I have not thought it necessary to follow out these results 

 through so long a series of incidences as Mr. Potter has done ; 

 but for the purpose of the results here aimed at, I have no 

 doubt these comparisons will be deemed sufficient. Here 

 again my resulting ratios differ most widely from those of 

 Mr. Potter ; yet they will be found to give (for the case of 

 perpendicular incidence) an agreement with theory, which is 

 fully as exact as can be expected from experiments of this na- 

 ture. The ratio from the undulatory theory as calculated by Mr. 

 Potter, being in this case 18*36, by my experiments it is 20'6. 



Another set of experiments, conducted and calculated pre- 

 cisely in the same way, gave me very similar results for a sur- 

 face of glass of antimony. 



For perpendicular incidence the undulatory theory gives the 

 ratio 13*33. 



I have made other experiments with several substances, 

 which I will not now detail, as my principal object is answered 

 if I can draw attention to these results, so as to induce any 

 one sufficiently versed in the subject to investigate the source 

 of error, which somewhere and somehow has certainly crept 

 in, to give rise to the remarkable discrepancy between my re- 

 sults and those of Mr. Potter. Our data of observation, it 

 will be seen, agree in a singularly close manner, and the tri- 

 fling errors of observation are such as can in no way account 



3 L2 



