[ 6 02 ] 
don a$ formerly famous for glafs-houfes, adds im- 
mediately afterwards, Siquidem etiam fpecula excogi- 
t aver at ( 3 ). But then it is to be obferved, that be- 
fore the application of quickfilver in the conftruCting 
of thefe glafles (which, I prefume, is of no great an- 
tiquity), the reflection of images by fuch fpecula muff 
have been effected by their being befmeared behind , 
or tinged thro ’ with fome dark colour, efpecially 
black, which would obftruCt the refraction of the 
rays of light (q). Upon thefe hypothefes (fuppofing 
the tincture to be given after fufion) the lamina be- 
fore us may be allowed to be capable of anfwering 
the purpofe here afligned. 
It may further be fuggefted, that plates of this 
kind might be intended to be wrought into lens’s, or 
convex glaffes, either for burning, or magnifying ob- 
jects placed in their focus. But this defignation can- 
not be fupported by proper vouchers from antiquity. 
On the contrary, we are informed, that the ancients 
ufed either Jpecula (j) of metal, or balls (6) of glafs 
for 
(3) Plin. Nat. Hilt. lib. xxxvi. c. 26. §. 66. 
(4) Pliny mentions a kind of glafs or jet called obfidianum : — 
nigerrimi coloris , aliquando et tranfiucidi , craffiore vifu , atque in 
fpeculis parietumpro imagine umbras reddente. Nat. Hilt. lib. xxxvi. 
c. 26. §. 67. 
And that the practice of ftaining glafs was known in his time, 
appears from what he fays concerning the obfidianum mentioned 
above: — Fit et genere tintturcc — tot urn fubens vitrum , atque non 
tranfucidum. Ibid. 
(5) Panciroll. Rer. Mem. p. 288. 
(6) Thefe glafs balls had fometimes water within them: Cum 
additd aqua vitreet piles foie adverjo in tantum exxandefcant , ut vefies 
ixurant, Plin. lib. xxxvi. c. 22. §. 45. 
lnvenio 
