c yn d 
inore than one fingle Minute of Motion (Part of 
which may probably arife from the fmall Uncertainty 
that always attends Agronomical Obfervation) but 
rnoft commonly this Difference was wholly infenfible ; 
fo that by the Help of what I obferved in lyn, 
•I prefume I am able to compute the true Place of 
the Moon with Certainty, within the Compafs of two 
Minutes of her Motion, during this prefent Year 
173 1, and fo for the future. This is the Exadnefs re- 
quifite to determine the Longitude at Sea to twenty 
Leagues under the Equator, and to lefs than fifteen 
Leagues in the Britijh Channel. 
It remains therefore to confider after what Manner 
Obfervations of the Moon may be made atSea with the 
fame Degree of Exaftnefs : But fince our worthy 
Vice-Prefident John Hadley , Efq; (to whom we are 
highly obliged for his having perfeded and brought in- 
to common Ufe the Rejle thing Telefcope ) has been 
pleafed to communicate his mod ingenious Invention 
of an Inftrument for taking the Angles with great 
Certainty by Refleftion, {Vide Jranfaft. N° 42.0.) it 
is more than probable that the fame may be applied to 
taking Angles at Sea with the defired Accuracy. 
II. An Account of the Contrayerva, hy Mr. Wil- 
liam Houftoun, Surgeon in the Service of the 
Honourable South-Sea Company. 
C ONfRH 7 ERVA is a Spanijb Word, fig- 
nifying as much as Herha contra [_V eneria] or an 
Herb againft Poifons. And as there are in all Countries 
Cc 1 different 
