I 588 ] 
\ ations, I fhould obtain the true height of the water 
to a confiderable degree of exa&nefs. I therefore 
generally made 40 or 50 obfervations, and fometimes 
more than 100, if the rife and fall of the water 
feemed very irregular. And that fuch a method of 
procedure renders the obfervations very confident with 
themfelves appears from infpedting of them : for 
about the times of high and low tide, when the 
u atei is flationary for a long while together, different 
obfervations give the fame altitude with a very little 
difference; and where the water is rifing or falling at 
the faffed, the obfervations will diew a lenlible rife or 
fall in the fpace of a very few minutes. 
In order to find if a fenfible difference could arife 
from any peculiar difference in different people’s man- 
ner of judging of the altitude of the water, I defired 
Mr. Charles Mafon, to whom we are indebted for a 
mod excellent obfervation of the tranfit of Venus at 
the Cape of Good Hope, to obferve the water at the 
fame time I did, and in the refult of trials made at 
different times we feldom differed more than _L. of 
one of the divifions of the pod, and never _y h % °that 
is never fo much as half an inch. I cannot on this 
occafion omit doing Mr. Mafon the judice to acknow- 
ledge the advantage I received from his frequent afi- 
fidance in making of thefe obfervations, which it was 
in a manner impodible for one to have compleated 
alone, on account of the almod condant attendance 
they required, and my living at fome didance from 
thewater fide. 
The following example of my method of making 
thefe obfervations may ferve to give an idea of the 
whole. When the water funk I took its altitude on 
the 
