OUTLINES OF NATURAL PHILOSOPHY. 



Let ABC (fig. 27.) be the ecliptic; the order of the 

 letters A, B, C, marking the order of the signs; so 

 that if A be the vernal, B is the autumnal equi- 

 nox; AGB a circle perpendicular to the ecliptic; 

 G the pole of the ecliptic ; P the pole of the equa- 

 tor; and APB the equinoxial colure. HG=GK= 

 the obliquity of the ecliptic ; HPK a parallel to 

 the ecliptic passing through the pole of the equa- 

 tor. 



The equator is not represented in this figure ; but 

 the half of it, on the side turned toward the eye, 

 is supposed to be under the ecliptic ; its plane 

 being at right angles to PP. 



The change which the motion <p makes on the pole 

 P, tends to bring it nearer to A. For the diurnal 

 revolution about the axis PD, being in the direc- 

 tion ABC, and the motion about the axis AB be- 

 ing in the direction PG', it will be in the quadrant 

 PA that these motions will be opposed, so as at a 

 certain point P' (and in all the points of the line 

 P'D) to destroy one another. PP' is the arch, of 

 which the tangent has already been shewn to 



bet 



If a great circle be now described from the pole P', 

 it will be the new equator, and the point in which 

 it intersects the ecliptic, will be the new equi- 

 nox. The relation of these small variations to one 



another, 



