376 W. Harkness-—The Solar Parallax. 
v' =the geocentric longitude of the moon. 
p =the equatorial radius of the earth, 
p, =radius of the ear oy at latitude gp. 
yp er rable’ latitu 
W=the luni-solar ocoeesion: 
O =the constant of nutation. 
In citing authorities the following abbreviations will be used: 
MAc =Memoires de l Académie odes des Sciences. ely 
HAc =Histoire de Académie Royale des Sciences. Par 
CRH =Comptes Rendus ey eae des séances de P Acadé- 
es Sciences. 
PTr =Philosophical Niiicaodii of the Royal Society of London. 
ANn =Astronomische Nachrichten 
MAS =Memoires of the Royal Astronomical Society. London 
MNt =Monthly Notices of the Royal Astronomical Society, 
London 
OPM = Annales de Observatoire Impérial de Paris. Mémoir 
BeumeerE sony and Meteorological Observations Coe. a 
he United States Naval acne pat Washington. 
PTL =Théore du Mouvement de la Lune, par Jean Plana. 
rin, 1832. 3 vols. 4to. 
DTL iheons du Mouvement de a Lune, par Ch, nope ; 
Paris, 1860-1867. 2 vols. 4 
Every known method of ee the solar parallax be- 
longs to one or other of the following classes, namely: 
I. Trigonometrical methods. 
Il. Gravitational methods. 
IIL. Photo-tachymetrical methods. 
We will consider them in their order. 
Trigonometrical Methods. 
Observations of Mars, when in opposition to the sun, and at 
its least distance from the earth, constitute one of the oldest 
planet is observed on or near he pare Ni at two stations, 
situated respectively in the northern and southern hemispheres ; 
or it is observed soon after rising, and just before setting, at a 
single station. The first method will be termed the meridian 
method; the second, the diurnal method. In the meridian 
method the observations may be made either with a transit 
circle, or with a micrometer attached to an equatorial telescope. 
In the diurnal method they nes oe made either with an equa- 
torial telescope, or with a heliom 
The values of the solar pack peat from some of the 
most — attempts by the meridian method are as fol- 
lows 
