I! 
planets, which cannot be the result of chance and which 
demand an explanation. Kant and Laplace propounded 
the nebular hypothesis, according to which the solar 
system originated as a vast globular mass of hot rotating 
gas, from which as it cooled and contracted, rings were 
separated at its equator. The rings afterwards con- 
densed into planets. The present condition and 
appearance of Jupiter may be taken as representing a 
stage through which our Earth passed ages ago. As 
the earth condensed in cooling, her rate of rotation 
would have increased according to the principle of the 
“conservation of the moment of momentum.” Prof. G. 
H. Darwin’s calculations of the earth’s rotation were 
alluded to, and his theory of the tidal evolution 
of the earth-moon system explained. The earth, it was 
pointed out, was solid, as is shown by certain phenomena 
of the tides; by the velocity of propagation of earthquake 
vibrations ; and, lately, by a study of latitude variations. 
There is reason to think, nevertheless, that she has ad- 
justed her figure as her rotation has slowed. 
The objects of the science of Geodesy and the term 
“geoid” were explained. The work of the ordnance 
survey under Colonel Clarke and the dimensions of the 
earth as given by him were alluded to. The “Clarke's 
Spheroid”” was said to have a polar diameter of 7,900 
miles and an equatorial diameter of 7,927 miles. It was 
pointed out that, according to Professor G. H. Darwin, 
the future of the earth-moon system will be that the day 
and month will become equal. The slowing of all 
motions by tidal and other friction and the equalisation 
of all temperatures are in accordance with the inexorable 
law of “dissipation of energy.” The end of all things 
will be a state of absolute rest at a uniform temperature, 
