Anniversary Address of H.R. H. the late President. 53 



suming that this state of fluidity was the effect of heat, we are led 

 to consider the steps of transition by which the earth has passed into 

 its present state of sohdity, and apparently permanent temperature. 

 After adverting to the analytical investigations of Fourier and Poisson 

 on this subject, the author proceeds to inquire into the results of the 

 laws of refrigeration of heated bodies, which may be conceived to 

 operate in the present case ; namely, refrigeration by ch-culation, 

 which obtains when the fluidity is perfect, and that by conduction, 

 when the particles of the mass, by the diminution of fluidity, no 

 longer retain that mobility among one another which is requisite 

 for their circulation. Thus while, in either case, the superficial 

 parts of the earth would rapidly cool and solidify by the radiation 

 of their heat into sidereal space, forming a crust of small thickness 

 compared with the whole radius of the globe, the internal mass may 

 be in one or other of the three following conditions : — First, it may 

 consist of matter still in a state of fusion, of which both the tem- 

 perature and the fluidity are greatest at the centre, but which has 

 been brought, by the long-continued process of circulation, into a 

 state no longer admitting of this process, and capable, therefore, of 

 cooling only by conduction. Secondly, the earth may consist of 

 an external shell, of a central nucleus, rendered solid by the enor- 

 mous pressure to which it is subjected, and of an intermecUate 

 stratum of matter in a state of fusion. The thickness of the shell, 

 as well as the radius of the solid nucleus, may possibly be small 

 compared with the radius of the earth. The fluidity of the inter- 

 vening mass must necessarily be here, also, considerably more im- 

 perfect than that which would just admit of cooling by circulation. 

 Thirdly, the earth may be solid from tlie surface to the centre. 



The author then shows that the direct investigation of the manner 

 in which the earth has been cooled, assuming its original fluiditj"- 

 from heat, cannot determine the actual condition of its central 

 parts, not from any imperfection in the analytical process, but from 

 the want of the experimental determination of certain values, Avhich 

 it is extremely difficult, if not impossible, accurately to obtain. It 

 has occurred to the author that a more indirect test of the truth of 

 the hypothesis of the central fluidity of the eartli might be found in 

 the delicate but well-defined phenomena of precession and nutation. 

 The investigation of the problems tlius suggested is reserved by the 

 author for the subject of a future memoir. 



Anniversary, Novcniljcr 30, 1838 — The lists of Fellows deceased, 

 and of Fellows admitted since the last Anniversary having been 

 r(!ad, it was stated that the report of the death of K. Z. Mudge, Capt. 

 11. E., noticed at the last Anniversary, has been since found to be 

 eri'oneous. 



The following Address of His Royal Highness the President was 

 read from tlie (jiiair: 



Gentlemen, 

 I CANNOT quit the Chair of the Royal Society, whicli I liave now 

 occu])ie(l during a |)eriod of eight years, witliout availing myself of 

 the opportunity which tlie customary proceedings of the Anniver- 



