206 FROM NEBULA TO NEBULA 



The mass of the earth is estimated to be about 6,000, 

 000 quadrillions of tons, hence that of the moon, which is 

 about 1-81 as large, is, in round numbers, 74,000 quad- 

 rillions. The question is, how thick would have to be a 

 cable of steel, of the tensile strength of 40 tons to the 

 square inch, in order to equal the gravitational attraction 

 between the earth and the moon when the latter was sup- 

 posedly at the earth's surface, as it must have been in 

 order that it may have been flung off as Darwin describes. 

 Dividing, first, by 40 gives us 1,850 quadrillions of 

 square-inches as the area of the cross-section of the cable. 

 Now, the formula for the area of a circle being ?rr 2 , per- 

 forming the operation gives us the thickness of the cable, 

 in round numbers, as 24,000 miles ! That is to say, Dar- 

 win and all who agree with him (which is to say, all the 

 scientific world, with very few exceptions) gravely assert 

 that by reason of her slow contraction due to cooling the 

 earth acquired so much increased axial velocity as to en- 

 able her to sunder a steel cable more than thrice her own 

 diameter! Did I say sunder That is the wrong word, 

 for the bond of gravitation may be strained, indeed, but 

 not broken. When the moon was hurled, as alleged, to 

 the distance of 4,000 miles from the earth and became a 

 satellite, their mutual attraction was thereby by no means 

 destroyed, but only reduced to 1-4 of what it was before, 

 equaling still the strength of an elastic steel cable 12,000 

 miles in thickness, or 1-J^ times the earth's diameter. 

 From that point on outward, Darwin assumes, by conven- 

 tion, that the momentum of the moon possessed at the in- 

 stant of severance persists undiminished forever, sus- 

 taining her in her orbit automatically; and then he goes 

 on to explain how the gravitational attraction of the 

 ansae, or tidal protuberances of the moon, lift her further 

 and further away by her boot straps, as it were. 



The velocity from infinity, or parabolic velocity, is 

 that which a body falling from infinity would acquire on 

 reaching the cosmic body under consideration. Thus, a 

 cannon-ball falling to the earth from infinity would ac- 

 quire, according to mathematicians, a velocity of 6.9 miles 

 a second. Conversely, in order that any object expelled 



