( »94 ) 
Yet doth it not follow hence, that L^ght demands no time. 
For, alter M. Rower had examined the thing more nearly, he 
fouQidf, that what was not fenfible in two revolutions, became 
very confidcrable in many being taken together, and that , for 
example, forty revolutions obferved on the fide F, might be 
fenfibly (horter, than forty others obferved in any place of the 
Zodiack where Jupiter may be met with ; and that in propor- 
tion of twenty two for the whole interval of tt E, which is the 
double of the interval that is from hence to the Sun. 
The necefiicy of this new Equation of the retardment of 
Light, is eftabliflied by all the obfervations that have been made 
in the R.Jcademy^ and in the Obfervatory^ for the fpace of eight 
years, and it hath been lately confirmed by the Emerfion of the 
firft Satellit obferved at ParU the ^th of November lafl at 
5 a Clock, 35*. 45", at Night, 10 minutes later than it was to be 
expefled, by deducing it from thofe that had been obferved in 
the Month of Mgujl, when the Earth was much nearer to Jupi- 
ter : Which M,Komer had predifled to the faid Academy from 
the beginning of September. 
But to remove all doubt , that this inequality iscaufedby 
the retardment of the Light , hedemonftrates,, that it cannot 
come from any excentricity, or any other caufe of thofe that are 
commonly alledged to explicate the irregularities of the Moon 
and the other Planets ; though he be w^ell aware, that the firft 
Satellit of Jupiter was excentrick, and that, befides, his revo- 
lutions were advanced or retarded according as Jupiter did 
approach to or recede from the Sun, as alfo that the revoluti- 
ons of the primum mobile were unequal ; yet faith hCjthefe three 
laft caufes pf inequality do not hinder the firft from being mani- 
feft. 
