$56 Mr B. Martin's Experiments on Island Crystal. 
body but Island crystal refracts a ray of light, both from and 
towards the perpendicular, in the same medium. — With Iceland 
crystal only, can you construct a microscope or telescope, with 
a double focus. — ’Tis by Iceland crystal we are taught how little 
we know of the nature of light, and the mutual action between 
it and common matter. — ’Tis by Iceland crystal we learn how 
much remains to complete a competent theory of optics ; and 
how small a portion of that curious science depends upon the 
laws of refraction in glass. — In short, by means of Iceland crys- 
tal, it seems very probable, that posterity will have laid open to 
them a much more extensive and perfect view of the field of Na- 
ture, than we, with all our boasted improvements, at present en- 
joy. And whatever others may think of this substance, I es- 
teem it the greatest curiosity of Nature, and pregnant with fu- 
ture systems of philosophical science. And, if my leisure hours, 
amusements, and experiments on this important subject, may be 
an excitement to others for further researches therein, I shall 
have all the honour and satisfaction that any author can wish 
for, as a reward for his trouble *.”■ 
Art. V. — Observations on a New Genus of Plants , belong- 
ing to the Natural Order Gastromyci. By Robert Kaye 
Greville, Esq. F. It. S. E. & M. W. S., &c. 
IP roeessor Link has, in the third volume of the Memoirs 
of the Society of Friends of Natural History of Berlin, distri- 
buted the fungi into four natural orders, retaining as true 
Fungi a comparatively small number of genera. In that high- 
ly meritorious essay, the celebrated Professor has done more to- 
wards a rational arrangement of the obscure plants of this diffi- 
cult department of botany than perhaps any other author. 
His third natural order, Gastromyci, is composed of those 
fungoid plants which have their sporules contained within one or 
more coverings ; a principal section of which order, is formed of 
those genera whose sporules are intermixed with a mass of fila- 
* We have been indebted for the originals of these two scarce essays to Mr 
William Jones, optician, London.— Ed. 
