W. Harkness—The Solar Parallax. 385 
The value here given for e is that used by pedoely (DTL, 
il, 802). The value of P is that found from the Greenwich 
and Cape of Good Hope observations by Breed (MAS, 1864, 
vol, xxxii, p. 137) and EK. J. Stone (MAS, 1866, vol. xxxiv 6). 
Substituting these values in (16) and (18), the latter equation 
eco 
1 ¥. 
M = £70248 5) — 175-705 (19) 
n connection with oe (18) and OR the reader may 
compare PTL, t. iii, pp. 2 LeVerrier, OPM, t. iv. 
Serret, OPM, v 324: teams, WOb, 1865, App. II, p. 28. 
About 1795 ‘Delambre seems to have determined the moon’s 
mass from the lunar inequality of the earth’s motion. This 
involves the use of equation (14), but as we propose to employ 
that equation for determining the solar parallax, we cannot 
avail ourselves of it for the mass of the moon. 
There is yet another way of determining the moon’s mass ; 
to wit, by comparing the fall of heavy bodies at the surface of 
the earth with the fall of the moon in its orbit. The resulting 
equation will be similar to (8), except that for the masses of the 
sun and earth we must substitute the masses of the earth and 
moon, and instead of 1:000141 sin p we must employ the par- 
ticular value of P which satisfies equation (5) when E+M is 
substituted in it for S+E, and T is taken to be the length of a 
sidereal revolution of the moon, expressed in seconds of mean 
time. ewene these special values of 'T’ and P by T and 
P,, we hay 
E+M 40° 0 
Me ee =) (20) 
IT. ce’ sin (Saar 36 
Of the four methods just described for determining the 
moon’s mass, that depending upon the tides is not sufficiently 
accurate, and that depending upon the lunar inequality of the 
earth’s motion is not available, for our purpose. ‘There re- 
main only the two methods represented ee by equa- 
tions (19) and (20). Let us see what results they give. 
s the luni-solar precession increases continually ‘with the 
time, its value is now known yery accurately. I cae for it 
the sli Seg used by Messrs. Newcomb and Stone (WOb, 
1865, App. IT, p. 28; MNt, 1868, vol. xxviii, p. 43), namely 
50’'878. The constant of nutation is mtch more uncertain. 
The following are some of the best modern values: 
1842, C. A. F. Peters (Num, Con. Nut., p. 37), --------- 9”°223 
1844, C. A. F. Peters ae Ac. Se. St. Petersbourg, 7e 
sér, t. ili, p. 125). 5 oie eee Se be eee ne et 9°216 
Am. Jour. Sor. ge atte Vox. XXII, No, 181.—Novemser, 1881. 
