( 4M ) 
Tides his Knowledge in the Theory and Pradice of 
Navigation, was the better qualified to make Trial of 
it. in regard he had fometimes accompanied me in 
my Experiment on the Canal in St. James's Park, and 
in the River Thames. As he was then going a Voyage, 
i intreated him to ad impartially with me, and to 
lo|e no Opportunity in letting me know how far, and 
with what Certainty, my Invention might be depend- 
ed on. Agreeable to my Requeft, he wrote twice to 
me on this Occafion : Hi< firft Letter was dated at 
Nantes the 20th of October 1724, and the following 
is an Extrad of it, viz. 
“ According to my Promife, I am to acquaint you, 
“ that I have had as favourable an Opportunity as I 
“ could have wilh’d for, to try your Marine-Surveyor ■, 
“ for Tome Part of my Voyage being from St. George's 
“ Channel to the Bay of Bifcay, I pafs’d clofe to the 
“ Land's-End of England, with a moderate Gale of 
“ Wind at North, our Courfe S. by E. When I had the 
“ Land’s-End Eaft of me about 3 Miles, I began to 
“ reckon, and the next Morning, when Ufiant bore 
“ Weft, about 7 Miles Diftance, the Surveyor had 
“ made juft 37 Leagues. Thefe two noted Headlands, 
“ which are very near under the fame Meridian, dif- 
“ #er in Latitude about 33 or 34 Leagues. As for 
“ the Tides, we crofs’d them, having in this Run two 
“ Floods and two Ebb; * and as the Wind blew crofs 
“ the Channel, one Tide was no more influenced by 
“ it than the other, nor could the Current be any 
“ Impediment to the Trial. Now as to our having 
« 3 or 4 Leagues more than the true Diftance, the 
“ Reafon is very plain, fince it cannot be expeded 
“ but that a Ship before the Wind will deviate from 
« her true Courfe, fometimes one Way, fometimes 
« another, in her Taws and Sheers. Of this all Sea- 
“ men 
