and
p = GMm/d².
(2)
By division
| Δ = | 3M | · | w | . |
| 4πRd² | p |
If then we can arrange to observe w/p we obtain Δ, the mean density of the earth.
But the same observations give us G also. For, putting m = w/g in (2), we get
| G = | d² | · | p | · g. |
| M | w |
In the second mode of attack the pull p between two artificially prepared measured masses M1, M2 is determined when they are a distance d apart, and since p = G·M1M2/d² we get at once G = pd²/M1M2. But we can also deduce Δ. For putting w = mg in (1) we get
| Δ = ¾ | g | · | 1 | . |
| G | πR |