[ 922 ] 
ftruction, by making the angle B A C equal to the 
ium or difference of the interval of time, and the 
change in the flrip’s longitude, according as that 
change is made towards the weft, or towards the 
eafl, and then drawing a line from A, not to the 
interfedion of the circles ; but fc, that the portions 
of that line, terminated by each of the circles, may 
be the tangents of arches, whofe difference is half 
the change in the latitude ; which, if made from 
the pole, requires the portion of the line terminated 
at the circle, whofe diameter is D E, to be fhorter 
than the other ; and the contrary is required, when 
the motion of the fir ip is towards the pole. 
For determining the latitude by calculation, if the 
diftance of the fun in the firfb obfervation from the 
zenith of the fecond could be found, this cafe would 
be reduced to the firfl, wherein the fhip is confidered, 
as flationary. And for this purpofe, it has been pro- 
pofed to make an additional obfervation, by an azi- 
muth compafs, of the angle, the fhip’s courfe makes 
with the azimuth of the fun, when the firfl altitude 
is taken; and, perhaps, the fame angle may be found 
with fufficient exadnefs from the latitude in the firfl 
obfervation affirmed, whether from the dead reckon- 
ing, or from the foregoing conflrudion. 
Why I have taken no notice of the calculations ex- 
hibited by the author of the piece here animadverted 
on, as proofs of his method, will readily appear to 
thofe, who fh all caff their eye upon them. 
Scholium. 
The axiom in trigonometry, on which the calcu- 
lations here difeourfed of have been fhewn imme- 
diately 
