1295 
The equation (6) has in the course of time been used for the 
determination of u, of 7, and of ¢. It is, however, doubtful whether 
the accuracy, needed to derive a real correction to our present know- 
ledge of any of these constants, could be attained even by a series of 
observations such as is proposed by E. W. Brown in his address to 
the British Association in Australia. It certainly should determine the 
parallax within a fraction of + 0”.Ol to be of real value. To make 
this possible the selenocentric coordinates, especially the radius-vector 
of the Crater Mésting A, or any other feature of the lunar surface 
which is used for the determination, must be accurately known. 
The determinations of the height of Mösting A over the mean 
radius are: 
HAYN *) + °2".2 = '0".6 effect on &’ . . . 0".087 
STRATTON’) + 3.00.7 a Sel pe Sic EE 
The difference between the two determinations makes a difference 
in the parallax larger than the uncertainty due to any of the con- 
stants 7,,:°9,, u Or €. 
Our eonelusion is thus that the value (8) of the lunar parallax 
is more accurate than any that can at present be derived by direct 
observations. 
Geodesy. — “On 1sostasy, the Moments of Inertia, and the Com- 
pression of the Earth’. By Prof. W. pr Srrrer. 
1. The hypothesis of isostasy is strictly speaking a compound ot 
two hypotheses, -viz. : 
A. Up to a certain distance from the centre the constitution of 
the earth is in agreement with the theory of Crarraur; i, e. the 
equipotential surfaces are surfaces of equal density, and the density 
never increases*) from the centre outwards. | Apart from this con- 
dition it may vary in any manner, even discontinuously.| The last 
1) Selenographische Koordinaten. ILI. (1907). Abh. der K. Siichs. Ges. der Wiss. 
Band XXX. page 74. 
2) Memoirs of the R. A. S. Vol. LIX, Part IV, page 276. 
dL 
8) Strictly speaking it is not necessary that always Tb <0. It is sufficient if, for 
) 
b b 
dà . d& 
all valaesvof b, §8* —— d3< 0, ands} 8° « —_dp<0. 
dp d3 
0 0 
