Our moon perturbs at first sight nothing, and accordingly its mass is not even yet known with exactness.
"Pioneers of Science"
Oliver Lodge
But now it may be asked, surely the moon perturbs the earth, swinging it round their common centre of gravity, and really describing its own orbit about this point instead of about the earth's centre?
"Pioneers of Science"
Oliver Lodge
It was not an exact ellipse, of course: none of the planets describe exact ellipses-each perturbs all the rest, and these small perturbations must be taken into account, those of Jupiter and Saturn being by far the most important.
"Pioneers of Science"
Oliver Lodge