1819.] Royal Academy of Sciences. 217 



theorems and the most important consequences. The title of 

 the first paper is : " On the Rotation of the Earth." 



From the time of Hipparchus to the present, the length of the 

 day has not changed the hundredth part of a second. The axis 

 of the earth's rotation is thus as invariable in relation to its 

 surface as the quickness of the rotation; the axis always answer- 

 ing to the same points of the earth, the most exact observations 

 have not discovered any change in the geographical latitude 

 of places. A century ago, Cassini endeavoured to demonstrate 

 this truth, but he did not dare to affirm it absolutely. He only 

 simply stated, that if any variation of the height of the pole 

 existed, it must be extremely small. At present it may be 

 asserted for a certainty, that the earth moves uniformly round an 

 invariable axis. 



It is known that all solid bodies have three principal rectangu- 

 lar axes, around which they can revolve in an uniform manner, 

 the axis of rotation remaining at rest. Is this very remarkable 

 property common to bodies which, like the earth, are surrounded 

 by a fluid 1 The actions of the sun and moon influence the figure 

 of the sea, which, by these means, varies incessantly. Among 

 the powers which produce the phenomena of the tides, some are 

 variable ; but as these are beyond comparison much less 

 than the centrifugal force, the alteration which they produce in 

 the permanent figure of the earth is insensible. A small agita- 

 tion in an ocean of quicksilver, if it were to be substituted for 

 our present seas, would be sufficient to spread it over the terres- 

 trial continent. This well-known inferiority of the density of the 

 sea is the consequence of the original fluidity of the earth ; for 

 at that time the heaviest strata were enabled to settle nearest the 

 centre. Theoretical considerations unite with the experiments 

 made upon the pendulum to show that, in oil probability, it was 

 a very violent heat which rendered all the parts of the earth 

 originally liquid. 



" The laws of mechanics and of gravity are, therefore, suffi- 

 cient to give a firm state of equilibrium to the sea, which is but 

 very slightly altered by celestial attractions. Its gravity, which 

 constantly tends to bring it back to a state of equilibrium, and 

 its specific gravity less than that of the earth, both necessary 

 consequences of these laws, are the true causes which maintain 

 it in its limits, and hinder it from spreading itself over the land, 

 which is a necessary condition towards the preservation of organ- 

 ized beings. The necessity of this condition may appear to be 

 a sufficient reason for its existence, but these kinds of explana- 

 tion ought to be banished from natural philosophy, as they 

 would infallibly hinder its progress. The phenomena ought to 

 be confined as much as possible to the laws of nature, and when 

 lliis object cannot be obtained, we ought to stop ; always recol- 

 lecting that the true progress of philosophy consists in proceed- 



