8 Dr. Brewster o?i new Properties of light, &c. 
1 . That mother of pearl polarises light in a manner differ- 
ent from all crystallised bodies, the polarisation having no re- 
ference to any fixed line in the plate. 
2. That mother of pearl polarises light in a manner differ- 
ent from all iincrystallised bodies, the transmitted pencil being 
wholly polarised by a single plate, and in the same manner 
with the reflected pencil. 
3. That if mother of pearl polarises light in virtue of its 
laminated structure, the lamiiice themselves must have the 
property of polarising light in a manner opposite to all other 
bodies. 
I have thus endeavoured to explain, as briefly as possible, 
the various phenomena exhibited by mother of pearl in its 
action upon light. The subject, however, is far from being 
exhausted : it still presents many points of interesting inquiry; 
and if the investigation could be carried on with the aid of 
analogous phenomena, we might confidently look forward to 
some great change in the fundamental principles of physical 
optics.* 
I have the honour to be, Sir, 
your most obedient and humble servant, 
DAVID BREWSTER. 
Edinburgh, February 28th, 1814. 
To the Right Hon. Sir Joseph Banks, Bart. K. B. P. R. S. &c. Sec. &c. 
• Since this paper was written I have made a variety of additional experiments on 
the superficial and communicable colours of Mother of Pearl and other bodies. An 
account of these experiments, and an explanation of the phenomena contained in Sect. 
IV. of the preceding letter, will form the subject of another communication. 
