If, however, the bodies were all moving in the same sense as the Earth, i.e. direct, the ratios would be:—
| Parabolic Speed | Speed of Short Period Comets | Speed of Actual Short-Period Period Comets about Jupiter | |
|---|---|---|---|
| Sunrise | 2.4 | 3.5 | 3.3 |
| Sunset | 1.0 | 1.0 | 1.0 |
As the actual number encountered is between 2 and 3 to 1, we see that the greater part must be travelling in the same sense as the Earth, since they come indifferently at all altitudes from the plane of her orbit.
2
Densities of the Planets
The densities of the principal planets, so far as we can determine them at present, the density of water being unity, are:—
| Mercury | 3.65 | |
| Venus | 5.36 | |
| Earth | 5.53 | |
| Moon | 3.32 | |
| Mars | 3.93 | |
| ——— | mean 4.36 | |
| Jupiter | 1.33 | |
| Saturn | 0.72 | |
| Uranus | 1.22 | |
| Neptune | 1.11 | |
| ——— | mean 1.09 | |
| Sun | 1.38 |
The second decimal place is not to be considered as anything but an indication.
3
Variation in Spectroscopic Shift