"I don't know about that," was the Captain's reply, "but I do know that this formula is wonderfully come at."
"Now, Ardan, listen a moment," said Barbican, "and you will see what sense there is in all these letters."
"I listen," sighed Ardan with the resignation of a martyr.
"d is the distance from the centre of the Earth to the centre of the Moon, for it is from the centres that we must calculate the attractions."
"That I comprehend."
"r is the radius of the Earth."
"That I comprehend."
"m is the mass or volume of the Earth; m prime that of the Moon. We must take the mass of the two attracting bodies into consideration, since attraction is in direct proportion to their masses."
"That I comprehend."
"g is the gravity or the velocity acquired at the end of a second by a body falling towards the centre of the Earth. Clear?"