Chap. 2. PHILOSOPHICAL DISCOVERIES. 25*

the earth, is able to make her descend in one minute through15^ Parisian feet. This power increases as the approaches tothe earth : in order to fee what its force would be at the sur-face of the earth, let us suppose her to descend so low in herorbit as, at her least distance, to pass by the surface of theearth. She would then come sixty times nearer to the centreof the earth, and move with a velocity sixty times greater,that the areas, described by a line drawn from her to thatcentre in equal times, might still continue equal. The moontherefore passing by the surface of the earth, at her lowest dis-tance, would describe an arc in one second of time (which isthe sixtieth part of a minute) equal to that which she de-scribes in a minute at her present mean distance, and wouldfall as much below the tangent at the beginning of that arcin a second, as she falls from the tangent at her mean distance ina minute ; that is, she would fall near the surface of the earth15-^ Parijian feet in one second of time. Now this is exactlythe fame space through which all heavy bodies are found byexperience to descend by their gravity, near the surface of theearth, as we observed above. The moon, therefore, would.descend at the surface of the earth with the fame velocity, andevery way in the fame manner, as heavy bodies fall towardsthe earth ; and the power which acts upon the moon, agreeingin direction and force with the gravity of heavy bodies, andacting incessantly every moment, as their gravity does, theymust be of the fame kind, and proceed from the fame cause.

1 2. The computation may be made also after this manner :the mean distance of the moon from the earth being sixty timesthe distance of heavy bodies at the surface from its centre, andher gravity increasing in proportion as the square of her distancefrom the centre of the earth decreases, her gravity would be60x60 times greater near the surface os the earth than at her

present