( hs ) 
dis tentativjs ac parum Geometricis innixos. Lie au- 
tern fentiat Leftor ^quus qualia in dcftrina Tridis a me 
pr^ftita fint, vellem Librum pr^didtum perlegat, ac 
cum noftris conferat ^ ne in his edeadis, aftum agere, 
Crambehq^ re-codam apponere videar. Quant os aucem' 
preheat ufus in Aftrcnomicis Lemma hoc noftrum 
alia data occafione commonftrabitur. 
IV. An aJvertifement necefary for all Naviga- 
tors bound up the Channel oj England 
F'^Or feveral years laft paft it ha^s been obferved, that 
many Ships bound up the Channel, have by mi- 
ftake fallen to the Northward of Scilly^ and run up 
the Brijlol Chduftel or Severn Sea^ not without great 
danger, and the lofs of many of them. The reafon of 
it is, without difpute, from the Change of the Variati- 
on of the Compaft.and the Latitude of the Lizard and 
Scilly laid down too far Northerly by near 5 Leagues^ 
For from undoubted obfervation the Lizard lies in 49*=* 
55', the middle of Scilly due Weft therefrom, and the 
South part thereof neareft 49^ . 50'. whereas in moft 
Charts and Books of Navigation they are laid down 
to the Northward oSjo^ : and in fomefuU 50° . 10, 
Nor was this without a good effeft as long as the Va- 
riation continued Eafterly, as it was when the Charts 
were made. But fince it is become confiderably Wefter- 
ly, ('as it has been ever fince the year 165 7 J and is at 
prefent about 7 i degrees ^ all fliips ftanding in, 
out of the Ocean, Eaft by Compals, go two thirds of 
a po nt to the Norrhward of their true Courfe, and in 
every eighty Miles chey fail, alter their Latitude about 
tea 
