[ 542 ] 
“Upon the whole, it Teems to me, that an inftrument, 
made as above dcTcribed, is capable of meaTuring the 
way of a fhip at Tea, when its velocity does not ex- 
ceed f lea miles an hour, to a degree of exadtnefs ex- 
ceeding the log. It therefore may be ufeful in the 
menfuration of the velocities of tides, currents, &c. 
and alfo in meafuring diftances at Tea in taking fur- 
veys of coafts, harbours, c '3c. Thus far it Teems 
capable of performing, upon the fuppofition, that it 
cannot be brought to a greater degree of perfection. 
But this 1 am very far from fuppohng : On the con- 
trary, I do not defpair, that it may be brought to an- 
fwer the end of meafuring the way of a ihip at fea 
univerfally ; and, for that reafon, it may not be amils 
to put down a few hints, concerning the caufe and cure 
of the error* above-mentioned, for the fake of thofe, 
who may hereafter be inclined to profecute thefe en- 
quiries*. 
It appears then from the preceding obferva' ions, 
that the rotation of the plate is coididerably retarded 
in the quickeft motions of the fhip ; and Teniibly fo, 
in all velocities exceeding y miles an hour. 1 his 
may proceed, firft, from the friction of the machine 
increaiing in a greater proportion than the power to 
turn it round. Secondly, From the water's being \ ut 
in motion by the fhip, To as to follow it in the Tame 
* Upon communicating thefe experiments and obfervations to 
my ingenious friend Mr. William Rufi'el, he gave me an account 
of a machine, that he had made trial of in a voyage, fome years 
fince, from the Levant, fo nearly agreeing with the above-deferibed, 
that one would have imagined we had been of each other’s council 
in ddigning them. 
di- 
