510 Notices of Memoirs — M. Delaunay 



round along with the globe itself, the whole revolving together just 

 as if the liquid had been frozen, and along with its envelope formed 

 one entirely solid body. 



Let us return to the terrestrial globe, and let us admit with the 

 geologists that it is composed of a liquid mass covered by a thin 

 solid crust. If the disturbing actions which produce the precession 

 and nutation did not exist, the entire globe, both the solid envelope 

 and its enclosed liquid, would revolve together as one, round the 

 poles whose direction would remain constant in space. 



Even if it is advanced, that at some particular epoch a difference 

 might have existed between the rate of movement of the crust and 

 of the liquid interior, the resulting friction must gradually have 

 destroyed this difference and brought about a conformity in the 

 motion of both parts. 



The disturbing forces which give rise to the precession and nuta- 

 tion act upon the solid crust and tend to make it revolve round an 

 axis, which deviates more and more from the direction of the axis 

 round which it at first rotated ; the rotary motion imparted to the 

 solid crust by these actions is one of extreme slowness, and has to 

 unite itself with the movement of rotation which it already possesses. 



The question then is, whether the internal liquid mass participates 

 in this additional movement, or is the solid crust alone affected by it 

 without immediately carrying the liquid along with it. In my 

 opinion there cannot be the least doubt as to what the reply must 

 be, for the additional motion due to the before-mentioned causes is 

 of such slowness that the fluid mass which constitutes the interior of 

 the globe must follow along with the crust which confines it, exactly 

 as if the whole formed one solid mass throughout. 



The pressure to which the liquid mass which we suppose to exist 

 in the interior of the earth is subjected to, is so enormous, that we 

 cannot even form an idea of the influence which it may exert on the 

 degree of viscidity of the fluid in question. But even if the fluid 

 matter is present under conditions identical with those of the liquids 

 which we see around us, this would suffice to cause the results to be 

 such as we have already explained. 



At the same time that I was perfectly convinced of the correctness 

 of these views, I resolved nevertheless to confirm them by direct 

 experiment. At my request, therefore, M. Champagneur, attached 

 to the Philosophical Laboratory of the Sorbonne, has arranged a 

 simple and complete experimental demonstration which removes 

 every possible doubt on the subject. 



I content myself at present with merely alluding to this experi- 

 ment, as I leave it to that gentleman to make the Academy acquainted 

 with its details. 



After the preceding observations, it appears to me impossible to 

 admit that the effect of the disturbing forces, to which the precession 

 and nutation are due, only extend over a portion of the terrestrial 

 globe : the entire mass, on the contrary, must be influenced by these 

 disturbing forces, whatever may be the supposed magnitude of its 

 fluid interior, and consequently it follows that the phenomena of 



