160 Scientific Intelligence. 
There is, however, another side of the subject, which must, I 
think, attract notice, or at least criticism, and this is the applica- 
bility of the results of analysis to the history of the earth and of 
the other planets. 
We know that no solids are either perfectly rigid or perfectly 
elastic, and that no fluids are devoid of internal friction, and there- 
fore the tides raised in any planet, whether consisting of oceanic 
tides or of a bodily distortion of the planet, must be subject to 
2 ae From this it follows that the dynamic cal ioe cate tae 
and satellite, ah becutioiors earth and moon are use 
The effect of tidal friction upon the pave pete and inclination 
of the lunar orbit here affords the principal topic. The obliquity 
efo 
solety on December 19, 1878, and 5 ae tikas will appear in the Phil- 
osophical senecsar he for 1879. 
Pp t paper completes (as far as I now see) the main in- 
aa a for the case of the earth and moon, — therefore it is 
now possible to bring the various results to a focu 
appears then, that when we trace backwa rd in time the 
the moon always opposite the same face of the earth, or moving 
very slowly relatively to the earth’s surface ; the whole system 
rotating in from two to four hours, about an ‘axis inclined to the 
normal to the ecliptic at an angle of 11° 45’, or somewhat less; 
and the moon moving in a circular — the plane of which is 
est period of ber Station of a fluid mass of the same mean density 
as the earth, which is consistent with an ellipsoidal form of equi- 
librium, is two hours twenty-four minutes; and that if the eon 
were to revolve about the éarth with this periodic time, the s 
faces of the two bodies would be almost in contact with one ee 
