thenthefe animals in it live longeft,and move very briskly^ 
whereas on the contrary the Melt being not full ripe, we 
mud wich force prefs it om of the Fifh , and then tis diffi* 
cult to fee thefe Animalcules alive. 
Theory of thm Variatton of the}Aag^ 
netical C O UFASS.h Mr. Ed. 
Udky Feilmofthe % S. 
T^He Variation of tWe Convpafs (by which I mean th^- 
defleflion ofthe Magnetical Needle from the true 
Meridian j is of that great concernnneut in the Art of Na- 
vigation ; that the neglect thereof , does litde kfs than 
render ufelefs one of the nobleft Inventions mankind ever 
yet attained to. And for this caafe all Ships of Confe" 
quence (efpecially thofe bound beyond the Equator ) cai;- 
ry with them Inftruments on purpofe to obferve this Vari- 
ation: that fo thecourfeflearedby the Compafs, maybe 
reduced to the true courfe in refpeft of the Meridian . 
Now altho the great utility that a perfefb knowledge of 
the Theory of the Magnetical diredion would afford to 
mankind in general ,^ and efpecially to thofe concerned in 
Sea affairs > feem a fufficient incitement to all Philofophlcul 
andMathematical heads,to take under ferious confideration 
thefeveral Phnomena ^znd to endeavour to reconcile them 
