the number of days in the year of each planet bears a definite proportion to this line; and as this line depends on the masses of the planets, a definite relation is asserted between the day of each planet and its mass. As this holds through all the solar system, it is maintained that the law clearly points to some common origin for the rotation of the planets, and that the hypothesis of an original rotating nebulous mass furnishes such a common origin.
It is very much to be doubted, whether astronomers will be disposed to accept of this as an established law. The reason is obvious. The data on which the law is founded are very uncertain in many cases. The masses and periods of rotation of various planets are merely conjectural, and such numbers are assumed as will suit the theory; and the law, even in the most favourable cases, does not pretend to anything like absolute accuracy.[1]The nebular hypothesis, then, can only derive very doubtful support from Kirkwood's law.
In directing the eye to the heavens, it is at once obvious, that the background from which the stars appear to shine is not uniform. There are brighter patches, which are distinguishable from the general
- ↑ The discordance for the various planets is indicated by the following numbers:— 928, 961, 1275, 3138, 833, 985, 3614. If the law held strictly, there should be no difference in these numbers; and therefore the least compared with the greatest indicates the maximum amount of error, which is obviously far too great.
