4 
ARTIFICIAL PRECIOUS STONES—HEATON. 219 
and also of deciding whether an alleged gem is genuine or imitation 
with ease and certainty. 
The scientific examination and identification of gems in this 
manner is a matter of the greatest interest, but it would take far too 
much time to discuss it in detail, and it is quite unnecessary to do 
so, because it has already been brought before the society most 
exhaustively by our chairman, Dr. Miers.t. I propose, therefore, 
merely to remind you of the main points by means of the accom- 
panying summary (Table I). 
TaBLe 1.—Properties influencing the value of precious stones and used as means of 
identification. 
Color. 
Cleavage. 
Structure Lamination. 
Inclusions. 
Refractive power [refractometer]. 
Double refraction [polariscope]. 
Optical properties ; Pleochroism [dichroscope]. 
Dispersion. 
Absorption spectrum [spectroscope]. 
Hardness [hardness points]. 
Durability 23s ooo [rowne 
Chemical composition. 
Specific gravity. 
Thermal conductivity. 
eatron sa. iss ashe: 
X rays. 
Additional means of a 
In order to bring this matter up to date in the records of the 
society, however, I must refer briefly to one or two particulars in 
which advance has been made since the time of these lectures. 
The most*important properties of a precious stone are those 
depending upon its refractive powers. Until recently the accurate 
determination of the refractive index of a stone was a matter involvy- 
ing the use of complicated and expensive instruments, and a matter for 
the skilled mineralogist rather than the practical jeweler. It is 
true that at the time Dr. Miers published his lectures there existed 
an instrument known as the reflectometer, but the determination 
of the refractive index with this was a matter of some difficulty 
even in skilled hands, and its value for commercial purposes was 
very small. Since that time, however, thanks to the ingenuity 
of Dr. Herbert Smith, this instrument has been improved out of all 
recognition, and in its place we have the Herbert Smith refractom- 
eter (pl. 1, fig. 1), by means of which anyone of normal common 
sense can determine the refractive index of a stone in a few seconds 
without even removing it from its setting, and which, with a little 
1 Cantor Lectures on Precious Stones, April, 1896. 
