360 Mr KELLAND, ON THE TRANSMISSION OF LIGHT, &c. 



I have dwelt a long time on this subject, from a wish rather 

 to obtain information on the subject than to communicate it. It is 

 no slight matter of astonishment to me, that a law so elegant as is 

 that which we have been discussing, and one too, the necessity of 

 which (or something analogous) must have been felt at every step 

 which was taken in the development of the Biaxal Theory, has never 

 been mentioned in connexion with this theory, in any writers that I 

 have seen, whilst others apply M. Fresnel's law in its stead without 

 stating their reasons. I do not presume to suppose that it had not 

 been established, my object will be fully attained if I shall have suc- 

 ceeded in exhibiting its importance, and in obtaining for it its proper 

 place in the theory which has been usurped by the no less elegant 

 Theorem of M. Fresnel. 



Note. The figure referred to in (18) is constructed by drawing three rectangular 

 axes Px, Py, Pz, and Px^ , Py^ inclined to these ; PN being the line in which y, s, 

 intersects xy. 



O, R are two points in xz equally distant on opposite sides from Pz. 



The figure of (4) in Supplement, is a broken line AB, BC, CD; as an incident, 

 proceeding and emergent ray of common optics. 



AB is produced to G 



That of (6) is a series of spherical triangles, SRsOT being a large arc, Sz = zT, 

 Rs = sO. 



TPQ, PR, PO, QS, QT all arcs. 



