OBSERVATIONS on TWO ECLIPSES. 245 
In the fecond obfervation was omitted, by inattention, 
‘the inftant of the arrival of the limb of the mcon to the ver- 
tical thread, which however may be calculated by the arri- 
val of the horns to the fame thread, by which CA and CO 
are obtained: By fubtracting S T from thefe, the remain- 
der will be CD and CF, having thefe two lines and the 
femi-diameter of the fun, the angles CS D, CSF, may be 
had, and fubtracting their fum from 180° the remain- 
der will be the angle CS CG, the half of which is the angle 
CSL; from the triangle CSL you may readily obtain 
SL, a fide of this triangle, and of the triangle SLE; from 
thefe at length this laft triangle SLE may be calculated, 
in which are had two angles and one fide, from which 
may be obtained LE the difference of azimuth, and SE 
the apparent difference of altitude of the centers of the 
fun and moon. 
My laft obfervation being more complete, might be 
calculated either from the one or the other method, and 
the paflage to the horizontal thread might even be ufed 
to determine the difference of the altitude of the centers, as 
the motion of thefe planets with refpect to the vertical, 
began to be quicker when this obfervation was made. 
If we are defirous to afcertain the time of the paflage 
of the upper horn of the moon to the vertical thread in the 
firft obfervation, or to know in the fecond obfervation the 
time of the paflage of the limb of the moon by the fame 
thread, they may eafily be calculated by the help of the 
quantities already found. Perhaps it might be ufeful to 
make this calculation, to determine the variation which ought 
to have place in the pofition of the two points obferved, 
Ti relatively 
Si lon vouloit dans la premiere obfervation veriffier Pinftant du paflage de la corne fupe- 
rieure au fil vertical, ou connoitre dans la feconde obfervation l'inftant du paffage du bord 
de la lune au méme fil on pourroit aifement les calculer avec le focours des quantites deja 
connues. I] fera peutetre méme utile de faire ce calcul pour fe mettre en etat de determiner 
la variation quia du avoir lieu dans la pofition des deux points obfervér relativement l’un 2 
Pautre, pendant lefpace de tems ecoulé entre leurs paflages au méme fil. 
Obfervation 
