Note 20 — PART I FROM DUSK TO DAYLIGHT (continued 4)

The equation we have to verify is

gR² = 4π²r³ ,

T²

with the data that r, the moon's distance, is 60 times R, the earth's radius, which is 3,963 miles; while T, the time taken to complete the moon's orbit, is 27 days, 13 hours, 18 minutes, 37 seconds. Hence, suppose we calculate out g, the intensity of terrestrial gravity, from the above equation, we get

g = 4π² × (60)³ = 39·92 × 216000 × 3963 miles = 32·92 feet-per-second per second,

T² (27 days, 13 hours, &c.)²

which is not far wrong.