[ 5§7 ] 
which were marked with the figures i, 2, 3, &c. 
according to the order of the ftrokes, reckoning up- 
wards from the bottom. The water funk down to 
about the figure o at the new and full moons ; but 
as the water would often fink lower than this by the 
continual undulation, which it has even in the calmed: 
times, and as it was by taking a medium between the 
greateft and lead: heights of the water by the fide of 
the pod: in this undulation that I was to infer the true 
and proper height, I was therefore obliged to have 
the pod: lengthened by a piece at the bottom marked 
with ftrokes as the poft it felf, only with this differ- 
ence, that the figures were fet on from o down- 
wards, as in the poft they were fet from o upwards. . 
The obfervations where the water funk below o were 
reckoned minus with . refpedt to thofe where it rofe 
above o, which were reckoned plus : and a proper 
regard was had to this difference, in inferring the 
true height, in fuch circumftances, from a medium 
between feveral obfervations of the alternate rife and 
fall of the water. 
But here you will perhaps think it incumbent upon 
me to clear my felf from an objection, which at iirft. 
fight may feem to render dubious the whole of my 
experiments. The alternate rife and fall of the water 
is generally fo confiderable that any one would be apt 
to conclude it impodible to find the true height of 
the water to afufficient degree of exa&nefs. In an- 
fwer to this objection I can truly affirm, that I always 
found the mediums of each fuccedive rile and fall to 
agree very nearly together, except in very great fwells; 
from whence I was naturally led to conclude, that, by 
taking the medium of a great number of fuch obfer- 
vations 
