from calling this a strict consideration of the subject, I own I should call it the loosest, and most erroneous way possible, of considering it. It is the calculating the velocity of a falling body in vacuo, and persisting in it, that it would be the same through whatever resisting mediums it might fall. This was not Newton's mode of philosophizing. Very few general propositions are just in application to a particular subject. The moon is not kept in her orbit round the earth, nor the earth in her orbit round the sun, by a force that varies merely in the inverse ratio of the squares of the distances. To make the general theory just in application to the revolutions of these bodies, it was necessary to calculate accurately, the disturbing force of the sun upon the moon, and of the moon upon the earth; and till these disturbing forces were properly estimated, actual observations on the motions of these bodies, would have
