120 Mr. Rennie’s account of experiments 
also been made by Mariotte, Varignon, Perronet, Ramus, 
Rondelet, Gauthey, Navier, Aubry and Texier de Nor- 
beck, as also at the Ecole Polytechnique, under the direction 
of M. Prony. With such authorities before us, it might be 
deemed presumption in me, to offer you a communication on 
a subject which had been previously treated of by so many 
able men. But whoever has had occasion to investigate the 
principles upon which any edifice is constructed, where the 
combination of its parts are more the result of uncertain rules 
than sound principle, will soon find how scanty is our know- 
ledge on a subject so highly important. The desire of 
obtaining some approximation, which could only be accom- 
plished by repeated trials on the substances themselves, in- 
duced me to undertake the following experiments ; for which 
purpose I ordered an apparatus to be prepared, of which the 
two annexed plates [[Plates VI. and VII.] are representations. 
Description of the Apparatus. 
A bar of the best English iron, about 10 feet long, was 
selected and formed into a lever (whose fulcrum is denoted 
by f). The hole was accurately bored, and the pin turned, 
which suffered it to move freely. The standard (A) was 
firmly secured by the nut (c) to a strong bed plate of cast 
iron, made firm to the ground. The lever was accurately 
divided in its lower edge, which was made straight in a line 
with the fulcrum. A point, or division (D), was selected, at 
5 inches from the fulcrum, at which place was let in a piece 
of hardened steel. The lever was balanced by the balance 
weight (E), and in this state it was ready for operation. But 
in order to keep it as level as possible, a hole was drilled 
