Geognosy of the Cape of Good Hope. ^89 
In short, the mountains and hills of the peninsula of the. Cape 
€)f Good Hope, are to be considered as variously aggregated 
compounds of quartz, felspar, and mica, and the whole as the 
result of one nearly simultaneous process of crystallisation. 
This view affords a plausible explanation of all the varieties of 
aggregation, structure, position, and transitions, observed in the 
rocks of this part of Africa. 
Aet. XI. — Historical Account of the Discoveries respecting 
the Double Refraction and Polarisation of Light. Com- 
municated by the Author. 
The subject of the Double Refraction and Polarisation of 
Light, though one of the most important and interesting bran- 
ches of human knowledge, has scarcely, if at all, attracted the 
attention of English readers. Our chemists and mineralogists 
have neglected to avail themselves of the lights which it offers to 
throw upon their respective sciences : Our popular lecturers on 
Experimental Philosophy have not been aware of the fine ex- 
periments and brilliant exhibitions with which it can so libe- 
rally supply them ; and the greater number of our learned Pro- 
fessors have not yet found leisure to admit it into their course 
of physical science. This inattention to an inquiry possessing so 
many claims upon our notice, can have arisen only from an opinion 
which we believe has too generally prevailed, that the subject of 
double refraction and polarisation is not susceptible of popular 
explanation ; and from an erroneous notion, propagated by in- 
dividuals whose pursuits have becjn eclipsed in the splendour 
of a new science, that it consists only of insulated facts and ex- 
travagant assumptions. 
One of the principal objects of the present series of papers is 
to correct these absurd misapprehensions ; and we have no doubt 
that we shall be able to render the subject intelligible to such of 
our readers as have but a very slender portion either of physical 
or mathematical knowledge ; and to convince those whose attain- 
ments are of a higher order, that almost all the phenomena of 
double refraction and polarisation, intricate and capricious as 
they appear to be, have been brought under the dominion of 
general laws, and can be calculated with as much accuracy as 
