sunrise . . . . . . . . 8.0
sunset . . . . . . . . 1.0
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 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:—
|
|
The second decimal place is not to be considered as anything but an indication.
3
Variation in Spectroscopic Shift
In the case of a body reflecting light, the shift differs from that for a body emitting it. If the planet be on the