iS;6.] 
503 
The Book of the Balance of Wisdom. 
Abu-r-Raihan. 
Modern Authorities. 
Copper .... 
. . 870 
878 
Brass 
• • 8-57 
8-58 
Iron 
• • 774 
779 
Tin 
7*31 
7*29 
Sapphire. . . 
• • 3‘97 
3*99 
Oriental Ruby . 
• • 3'58 
3*90 
Ruby 
• • 3'85 
3*5 2 
Emerald .... 
• • 275 
273 
Pearl ..... 
£’69 
275 
Lapis Lazuli . . 
. . 2*60 
2*90 
Cornelian . . . 
• . 2-56 
2‘6i 
Amber (?)... 
• . 2*53 
ro8 (?) 
Rock crystal . 
. . 270 
2-58 
In the third leCture of the “ Book of the Balance of 
Wisdom” al-Khazini describes a form of specific gravity flask 
which he calls the “ conical instrument of Abu-r-Raihan ” 
and to whom he apparently ascribes the invention. A mere 
inspection of the accompanying cut, a fac-simile of that in 
the original manuscript, together with the explanations (also 
from the original), suffices to show its nature and the method 
of using it. The author remarks that “the instrument is 
Fig. i. 
a, Neck of the instrument. b. Perforation. c. Tube in the form of a water- 
pipe. d. Handle of the instrument. e. Mouth of the instrument. /. Place of 
the pan (of the balance). 
very difficult to manage, since very often the water remains 
suspended in the lateral tube, dropping from it little by little 
into the scale of the balance.” This passage shows that 
Abu-r-Raihan had noticed capillary attraction ; it is also 
certain that he understood that the size of the neck of the 
instrument affeCted the delicacy of the determinations, for 
he says he would have it “ made narrower than the little 
finger but for the difficulty of removing through a smaller 
tube the bodies immersed in the water.” 
