A View of Sir Isaac Newton's PhilosophyPemberton, Henry
Science
A View of Sir Isaac Newton's Philosophy
Pemberton, Henry
Newton, Isaac, 1642-1727. Principia
39. IN like manner, while the moon is passing from L on the other side
the plane A G C H, the node shall advance forward, as long as the moon
is between the point L and the next quarter; but afterwards it shall
recede, till the moon come to pass the plane A G C H again in the point
V, between B and A: and because the time between the moon’s passing
from L to the next quarter is less, than the time between that quarter
and the moon’s coming to the point V, the node shall have more receded
than advanced; so that the point V will be nearer to A, than L is to C.
So also the inclination of the orbit, when the moon is in V, will be
greater, than when the moon was at L; for this inclination increases
all the time the moon is between L and the next quarter; it decreases
only while the moon is passing from this quarter to the mid way between
the two nodes, and from thence increases again during the whole passage
through the other half of the way to the next node.
40. THUS we have traced the moon from her node in the quarter, and
shewn, that at every period of the moon the nodes will have receded,
and thereby will have approached toward a conjunction with the sun.
But this conjunction will be much forwarded by the visible motion of
the sun itself. In the last scheme the sun will appear to move from
S toward W. Suppose it appeared to have moved from S to W, while the
moon’s node has receded from B to V, then drawing the line W T X,
the arch V X will represent the distance of the line drawn between
the nodes from the sun, when the moon is in V; whereas the arch B A
represented that distance, when the moon was in B. This visible motion
of the sun is much greater, than that of the node; for the sun appears
to revolve quite round each year, and the node is near 19 years in
making one revolution. We have also seen, that when the node was in
the quadrature, the inclination of the moon’s orbit decreased, till
the moon came to the conjunction, or opposition, according to which
node it set out from; but that afterwards it again increased, till it
became at the next node rather greater than at the former. When the
node is once removed from the quarter nearer to a conjunction with the
sun, the inclination of the moon’s orbit, when the moon comes into the
node, is more sensibly greater, than it was in the node preceding; the
inclination of the orbit by this means more and more increasing till
the node comes into conjunction with the sun; at which time it has
been shewn above, that the sun has no power to change the plane of the
moon’s motion; and consequently has no effect either on the nodes, or
on the inclination of the orbit.
Public-domain text, read in full here on John Shaqi.
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