542 
MR. HENNESSY’S RESEARCHES IN TERRESTRIAL PHYSICS. 
The value w=147° 30' would make this •1188293, hence this value of n would be a 
little too small. 
2nd. To find p' and From the fourth chapter of the fourth book of the work of 
M DE PoNTECouLANT, it will be perceived that 
Ain 
P 3m^(l + 7 ) cos a’ 
where I represents the mean movement of the equinoxes at the time when h repre- 
sents the apparent obliquity of the ecliptic, and 7 the ratio of the moon’s action on 
the earth compared to that of the sun, n and m being constants, the former depend- 
ing on the earth’s rotation, and the latter on the sun’s mean movement. If the vari- 
ation of h be referred to the plane of the ecliptic in 1800, 
A=23° 27 ' 55", /=50"'363541, 
and also 
w=360°-98561, m=359° 59'-37 ; 
and when m is referred to the same unit of time as n, 
m = 0°-98561. 
Of the three different methods by which 7 can be determined, I select that depend- 
ing on the phenomena of nutation. I do so because it seems that astronomers have 
taken much pains to determine the numerical coefficient which depends on these 
phenomena, and on which the value of 7 depends. If we represent the coefficient of 
nutation by N*, we shall have 
7 N , N 
1+7“"13"-36926’ 5^13"-36926 — N' 
The following values have been deduced for N 
By Robinson . 
By Brinkley . 
By Lindenau . 
By Plana . . 
9*234 
9-25 
8-977 
8-925 
the mean of which is 9"-0965, and therefore 
log (1-1-7)= -4953988 
log m=6-l 125773 
logcos ^=9*9625122 
log 3= -4771213 
7-0476296 
7=2-128951 ; 
log /= 1 - 7021 163 
log 1=2-5637896 
log 4= -6020600 
4-8679659 
7-0476296 
log y =3-8203363 
* PoNTECouLANT, Th^orie, &c., tome iv., Note 3, p. 654. 
