( S97 ) 
Art. XXVII. — Proceedings of the Wernerian Natural History 
Society. (Continued from p. 184.) 
Augusts. 1820.- — M R SivRiGHT communicated to the Society 
a short account of a series of experiments he had made on the 
teak wood, (in confirmation of those; previously made by Dr 
Wollaston,) from which it appears, that it contains a considerable 
quantity of silica, specimens of which he laid on the table. He 
intimated his intention of examining other hard and heavy 
woods, with the view of discovering their constituent parts and 
other properties. — See p. 413. 
The Society adjourned till November. 
Art. 111. ^Proceedings of the Cambridge Philosophical 
Society. 
As the following abstract of two interesting papers, read by 
Mr Her schel, before the Cambridge Philosophical Society, did 
not reach us till after that part of our number was printed, 
we avail ourselves of the present opportunity of laying it before 
our readers. 
April 17. — A paper by J. F. W. Herschel, Esq. was read, 
On the rotation impressed on the planes of Polarization the 
rays of Light by plates of rock-crystal^ as connected with cer-- 
tain peculiarities m its crystalline form^ S^c. <^c. 
In this paper the author has entered into an examination of 
that peculiar variety of crystallization in quartz, to which Hauy 
has given the name Plagledral. The peculiar faces which cha- 
racterise this variety, are situated unsymmetrically with respect 
to the axis of the primitive rhomboid, and in the same crystal 
uniformly appear to lean as it were in one and the same direc- 
tion around the adjacent summit, while in different crystals 
these directions differ. Mr Herschel has found, that the direc- 
tion of these faces, in all such crystals as he has been able to pro- 
cure, is the same with that in which a plate cut from them at 
right angles to the axis, turns about the plane of polarization 
of a ray transmitted along the axis. From this invariable cor- 
respondence, he concludes, that the forces which produce the 
VOL. III. NO. 6. OCTOBER 18S0. D d 
