405 
i88o.l Analyses of Books . 
It maybe safely said that these additions are decided im- 
provements, and that this second edition will be found a decided 
advance on the foregoing. 
Geodesy. By Colonel A. R. Clarke, C.B., F.R.S. (Clarendon 
Press Series.) London : Macmillan and Co. 
The author commences with a sketch of geodetical surveys from 
Snellins, Picard, and Cassini, down to the operations of Everest 
and Walker in India, of Struve in Russia, and of Maclear at the 
Cape of Good Hope. After two chapters devoted to Spherical 
Trigonometry and the Method of Least Squares, he proceeds to 
the theory of the Earth’s figure. Here it is remarked that, as 
regards the attraaion of mountains, there is little correspondence 
between theory and observation, since the attraaion even of the 
Himalayas is only perceptible at places quite close to them. 
Archdeacon Pratt proposes the theory that the elevations and 
depressions of the earth’s surface have arisen from the mass having 
contraaed unequally in solidifying, and that under mountains 
and plains there is a deficiency of matter approximately equal to 
the mass above the sea-level, whilst below ocean-beds there is an 
excess of matter equal to the deficiency in the ocean as compared 
with an equal volume of rock. On this supposition the amount 
of matter in any vertical column drawn from the surface to a 
level surface below the crust would be approximately the same in 
every part of the earth. We learn that the meridian of the 
greater equatorial diameter passes through Ireland and Portugal, 
cutting off a small bit of the north-west corner of Africa : in the 
opposite hemisphere this meridian cuts the north-east corner of 
Asia, and passes through the southern island of New Zealand. 
The meridian containing the smaller diameter of the earth passes 
through Ceylon on the one side of the earth, and bise(5Is^ North 
America on the other. This position of the axes, it is said, cor- 
responds remarkably with the distribution of land and water on 
the surface of the globe. , . , . , 
In days when such hypotheses as the growth of the earth and 
the secular transfer of the ocean from the southern to the northern 
hemisphere, and vice versa , are brought forward, Col. Clarke’s 
work must be of especial value. 
