5*6 The Book of the Balance of Wisdom. [October, 
tached a reservoir of water, which, by means of a small 
hole perforated on the bottom of it, emptied itself in twenty- 
four hours. This reservoir, being filled with water, was 
poised by weights attached to the other arm of the lever, 
and, in proportion as the water flowed from it, the arm 
bearing it was lifted, the weights on the other arm slid down, 
and by their distance from the centre of suspension indicated 
the time which had elapsed.” 
Further analysis of the contents of this extraordinary 
work is incompatible with our reader’s patience, and yet 
many points of interest demand at least a passing notice : 
these may, however, be embodied in a summary of the prin- 
cipal propositions contained in this treatise, and the re- 
capitulation may serve to justify in some measure this 
contribution to the early history of chemical physics : — 
1. The “ Book of the Balance of Wisdom ” shows the 
Arabian philosophers of the twelfth century to have 
entertained advanced views regarding attraction. 
They recognised gravity as a force, and attributed to 
it a direction towards the centre of the earth ; they 
also knew that it diminishes with the distance, but 
they erroneously supposed this diminution to be in the 
direCt ratio of the distance and not as its square. 
2. They were acquainted with the connection between the 
weight of the atmosphere and its increasing density, 
since mention is made of the loss of weight of a body 
weighed in a denser atmosphere. 
3. They understood the theory of centre of gravity, and 
applied it to the investigation and construction of 
balance and steelyards. 
4. They made frequent use of the hydrometer, which they 
inherited from antiquity, and possibly they employed 
this instrument as a thermometer for distinguishing 
by variations of density the different temperatures of 
liquids. 
5. They observed the aCtion of capillary attraction. 
6. The)' compiled full and accurate tables of the specific 
gravities of most of the solids and liquids with which 
they were acquainted. 
7. Their system of philosophy was founded on experiment 
and observation. 
In conclusion, we quote the following appropriate remarks 
from M. Khanikoff’s introduction : — 
“ The history of the sciences presents to us an incon- 
testable faCt of deep significance — the re-discovery in modern 
