628 Mr. mann’s Treatife 
inftant of the beginning of its motion, to let go the pen- 
dulum at the fame moment, and to count its vibrations 
till the inftant that the boat ftruck with an accelerated 
force againft the fore end of the canal. As to the weight 
of eight ounces fufpended at the end of the cord, and 
which ferved as a moving force to draw the boat along 
the canal, it was juft as much as fufficed to -counter- 
balance the cord, and to put the boat in motion ; lefs 
weight than that would do neither : therefore I was 
obliged to ufe fo much, notwithftanding the confiderably 
accelerated motion it gave to the boat. 
This is the whole mechanifm of the inftruments I 
ufed for the experiments in queftion, and fuch were the 
precautions I judged it neceffary to ufe for making them 
with fcrupulous exadtnefs. 
In the following table, which confifts of twelve co- 
lumns, the firft of them contains the different depths of 
water at which theexperiments were made; the ten follow- 
ing ones contain ten different experiments made at each 
depth of water in the canal; and the twelfth or laft co- 
lumn is the reduction of the ten others to a mean pro- 
portional or mean refult of the whole, which is in feconds 
,of time. 
Table 
