272 POPULAR LECTURES AND ADDRESSES. 



than the British Association Committee's reductions 

 of tidal observations for several places in different 

 parts of the world allow us to admit to have 

 possibly taken place. The assumption of a fluid 

 interior, which Newcomb suggests, and the flow of 

 a large mass of the fluid " from equatorial regions 

 to a position nearer the axis," is not, from what I 

 have said to you, admissible as a probable ex- 

 planation of the remarkable acceleration of rota- 

 tional velocity which seems to have taken place 

 about 1862 ; but happily it is not necessary. A 

 settlement of 14 centimetres in the equatorial 

 regions, with corresponding rise of 28 centimetres 

 at the poles (which is so slight as to be absolutely 

 undiscoverable in astronomical observatories, and 

 which would involve no change of sea-level 

 absolutely disproved by reductions of tidal obser- 

 vations hitherto made), would suffice. Such 

 settlements must occur from time to time; and a 

 M-ttlemenl of the amount suggested might result 

 from the diminution of centrifugal force due to 

 -150 or 2OO centuries tidal retardation of the earth's 

 i"1a1ional speed. 



