246 Laws of Metallic Reflexion, and Mode of 



larization ; that difference being perhaps twice as great as in 

 the case of steel. My own experiments on speculum metal were 

 all made, as has been seen, at incidences greater than 60. 



The experiments of M. de Senarmont do not at all agree 

 with the formulae ; and therefore I have been obliged to analyze 

 his method of observation, and to show that it could not lead to 

 correct results. It is to be regretted that his method was de- 

 fective, as the zeal and assiduity which he has displayed in the 

 inquiry would otherwise have put us in possession of a large 

 collection of valuable data. 



I shall conclude by saying a few words respecting the in- 

 tensity of the light reflected by metals. The formulae for com- 

 puting this intensity have been given in the Transactions of the 

 Academy, in the place already referred to ; but they may be 

 here stated in a form better suited for calculation. If we sup- 

 pose i// and i// to be two angles, such that 



ootan i// = , cotan i// = M^ (o) 



and then take two other angles w, a/, such that 



cos o> = sin 2i// cos x> cos a/ = sin 2$' cos x> (*) 



we shall have 



T = tan iw, r = tan ^o/, (Q) 



where T is the amplitude of the reflected rectilinear vibration, 

 when the incident light is polarized in the plane of incidence, 

 and T is the amplitude of the reflected vibration when the 

 incident light is polarized perpendicularly to that plane ; the 

 amplitude of the incident vibration being in each case supposed 

 to be unity. Hence when common light is incident, if its in- 

 tensity be taken for unity, the intensity I of the reflected light 

 will be given by the formula 



I=\ (tan 2 u + tan 2 >') . (R) 



If with the values of M and x determined by my experi- 



