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LVIII. A treat if e on the preceffion of the equi- 
noxes r, and in general on the motion of the 
nodes , and the alteration of the inclina- 
tion of the orbit of a planet to the ecliptic . 
Infcnbed to the gentlemen of the Royal 
Society, by M, De St. Jaques Silvabelle. 
Tranjlated jrom the French M. S. by J. Bevis, M. D. 
Introduction. 
Read March 
12, 1752. 
I F the earth were perfedtly fpherical, the 
adtion of the fun on all the parts which 
compofe it, would not produce any effedt to make it 
turn round its centre ; becaufe the moment, which 
would be produced on one fide, would be always 
counterbalanced by an equal moment on the oppofite 
fide of the centre. 
It would be the fame, if the earth were a fpheroid 
flatted at the poles, and the fun was always in the 
equator, or in the ninetieth degree of declination : 
But in every other degree of declination its adtion on 
the excefs of matter about the equator has a tendency 
to make the equator approach towards the fun’s place, 
or to diminifh the angle of the fun’s declination, by 
making the earth’s axis to turn round its centre in the 
plane of the circle of the fun’s declination. 
The earth has then, at every inflant, two motions 
of rotation ; one about the axe of the equator, called 
ilfo the earth’s axe 5 and this is the diurnal motion, 
C c c which 
