[ 207 ] 
to the great obfcurity which follows, might not fee 
the fatellite at all. As the opening is gradually 
contra&ed, the fatellite feems to grow lefs. The 
obferver fometimes lofes fight of it for a moment.;, 
but, if he continues to look attentively, he fees it 
again. The real difappearance is only to be con- 
cluded, when, upon fixing with fteady eyes, for about 
half a minute, on the place it occupied, it is feen no 
more ; for if one perfifted to obferve it much longer, 
it might happen, that it might be feen to glimmer a,t 
times, and immediately difappear. I have always 
made it a rule, to confider the debilitation of the light, 
in this degree, as adtual difparition, and it is necef- 
fary, that obfervers fhould agree upon this point, in 
order that their different eflimations may be confiftent. , 
Thefe fits, of momentary glimmering and extinction, 
are undoubtedly owing to the motion of the particles 
of the atmofphere. In the cleared: weather, there are 
always particles of vapour floating in it, in vaft 
abundance j according as thefe particles place them-- 
felves . 
fois qu’on diminue l’ouverture, on voit diminuer le fatellite: 
quelquefois on croit ne le plus voir, mais, apres y avoir fait at- 
tention, on le revoit: il faut le juger difparu, quand on ne l’ap- 
per^oit plus, apres avoir confidere, avec des yeux bien repofes, 
pendant une demie minute environ, la place qu’il occupe : car, 
fi on s’attachait a le confiderer plus longrems, il pourrait arriver^. 
qu’on le revit, par moment, paraitre, comme par eclairs, & difpa- 
raitre aufiitot. Je l’ai toujours juge difparu, quand il a ete reduit a . 
cet etat d’aftaibliflement ; il eftefientiel de convenir dececi, afin 
que les mefutes fe rapportent. Ces variations font dues, fans 
doute, au mouvement de i’atmofphere. Il y a toujours, dans les - 
mo men* 
