r 268 ] 
“ [ale, quod cry [l alii gaudent figitra nitri, quodque 
“ omncs gencrcntur in cavo : Hi (viz,, cry ft alii) quo 
“ magis Jim) lice s, eo magis puri & pellucidi : Hmc 
“ mtro origmem debent , quemadmodum gemma ifta , 
“ qua / njmaticam nitri figur am exhibent." 
As Nitre may be reafonabiy conjefrured to give the 
ordinary and general hexagonal Figure to Cryftals, it 
may be as juftly inferred, that when they depart from 
this Uniformity, it isowing to fomc mineral, earthy, 
or metallic Mixture, fome heterogeneous Salt, which 
impedes the Nitre in its fhooring, and turns it into 
trigonal, cubical, conic, or other unufual Figures. 
Sect. y. 
Of their Size. 
The next thing to be confidered, is the Caufe to 
which the different Size in which thefe Bodies do ap- 
pear may be owing, Some Cryftals are faid to be 
a Cubit high : Livia Augufta dedicated one in the 
Capitol of fifty Pounds Weight (1 9) 5 and Dr. Ifaac 
Lawfon, late Phyfician to the Army in Flanders , 
informed me, that he faw a Cryftal in a foreign 
Mine, with irs Edges well preferved, which lie be- 
lieved might weigh about 200 Pounds. Dr. Wood- 
ward reckons, among his Cornifo Diamonds, a fingle 
Column or Shoot very large, if it be three Inches in 
Length, and one Inch and half in Diameter near the 
Bafe. The largeft 1 have yet feen in Cornwall weighs 
fomewhat more than three Pounds, is about ten Inches 
in 
(19) Tlbiy , lib. 37. c. 2. Sir Hans Sloane has one Block of Cryf- 
ral which weighs between 40 and 50 Pounds, and another about 20, 
quite clear and regular. C. M. 
(20) Catal. 158./. 98. 
