2o7 



Now, tlic quantities A and B will be thus composed : The quantity 

 of heat transmitted by the mica bundle and incident on the reflecting 

 surface contains, when the plane of polarization is perpendicular to 



1 p 



the plane of reflection, a portion of heat p -| ~~ polarized +, 



and a portion of heat — ^-^ polarized — ; let these quantities be m 



and n; then w» -j- w = !• Now, let the plane of polarization be 

 turned round 90° ; then the part polarized in the plane of reflection 

 will now be m, and that perpendicular n. So th.it the heat is first 

 composed of a part m reflected according to the law of a in Table I., 

 and a part n reflected according- to the law of b ; and then the con- 

 verse ; so that 



A zz m a + n b 



B^ = w «, + mb,i 



Hence A,^ + B^ = a,^ -\-b^ , as it evidently ought, and 



A,— B, = (m — w) (a, — 6,) 



Hence the differences of the columns in Table II. are in a constant 

 ratio to the differences of tJie columns in Table I. ; and as Table I. 

 may be computed from Fresnel's formulae 



tan'(i — t') J sin'^(i — i') 



tanMi + '') ' sin'^ (i + i') ' 



the agreement or discrepancy will be apparent, and the coeflicient 

 (wt — w) will indicate the polarizing power of the plates. Also, 

 since the sum of the numbers must be the same for both tables, a 

 single comparison would suffice to determine the index of refrac- 

 tion, which must be assumed in computing the first table." 



Monday, \st April. 

 Dr HOPE, V. P., in the Chair. 



The following Donations were presented : — 



Memoirs of the Royal Astronomical Society. Vols. 9 and 10. — 

 By the Society. 



Comptes Rendus Hebdomadaires des Seances de I'Academie des 

 Sciences, 1839. F'" Semestre. No. 9. — By the Academy. 



Transactions of the Society for the Encouragement of Arts, Ma- 

 nufactures, and Commerce. Vol. lii. Part 1. — By the Society. 



