416 Rev. B. Powell's Remarks on Mr. Barton's Reply. 



his views with extraneous considerations, he would give the 

 scientific world a perspicuous and systematic development of 

 them, so as fairly to contrast the explanation of the facts which 

 his theory affords with that resulting from the other theories. 

 PerharJs^ it may not be altogether uninteresting to the reader 

 to see at one view how the rival theories at present apply. 

 I subjoin, therefore, a synoptic sketch, which I believe to be 

 perfectly impartial ; indeed, 1 have given every advantage to 

 the corpuscular theory. It would be interesting if Mr. Bar- 

 ton would add a third column, giving a similar view of his 

 own theory. 



Phenomena. 



Reflection 



Ditto at boundary of \ 



transparent medium J 

 Refraction (light ho- \ 



mogeneous) J 



Dispersion 



Absorption 



Colours of thin plates"! 

 (in general) J 



Central spot. 



Airy's modification ... 



Thick plates 



Coloured fringes of 

 apertures and sha- 

 dows in simple cases 



in more complex 



cases 



Stripes in mixed light 



Shifting by interposed 1 

 plate J 



Colours of gratings... 

 Double refraction 



Corpuscular 

 Explanation. 



Perfect .. 

 Imperfect. 



Perfect ... 



Imperfect 



f Perfect "\ 



< (with subsidiary > 

 L theory of fits).. .J 



{ 



rerrecc 



*1 C Imperfect ...."I C 



> < (with subsidiary )> J 

 J Ltheory of inflection) J L 



Polarization. 



Connexion with dou-\ 

 ble refraction J 



Law of tangents 



Interferences of po-\ 

 larized light J 



Polarized rings 



None 

 None 



None 



None .. 

 Perfect. 



{ 



, Imperfect .... 



(with subsidiary 

 theory of polarity) 



None 

 None 

 None 



.... Imperfect "J 



(with subsidiary I 

 theory of move- [ 

 able polarization) J 



Undulatory 

 Explanation. 



Perfect. 

 Perfect. 



Perfect. 



Imperfect. 



(PCauchy.) 

 Imperfect. 



Perfect. 



Perfect. 

 (Imperfect according 



to Mr. Potter.) 



Perfect. 



Perfect. 



Perfect 



(Imperfect according 



to Mr. Barton.) 



None. 



...... Perfect. 



f Perfect. 



< (Imperfect according 

 L to Mr. Potter.) 



Perfect. 



Perfect. 



Perfect. 



(with subsidiary theory 

 of transverse vibra- 

 tions.) 

 Perfect. 



Perfect. 

 Perfect. 



Perfect. 



