| On the Law of Rotation of the Primary Planets. 395 
\ Il. That the mass, distance and time of rotation of the origi- 
| nal planet between Mars and Jupiter, as determined by the law 
in question, are inadmissible. ‘A 
ILL. at the values of the rotation constant for Mars, Jupiter 
and Saturn are not identical ; an 
Finally, that the law is incompatible with certain analogies 
found to exist between the different members of our planetary 
system. If design in this paper briefly to review these objections 
in order. The first has the greatest appearance of plausibility, 
and is therefore entitled to special consideration. 
The time of rotation of Uranus, according to my analogy, is 
saa Rats ne eT el al oe 
this period as inadmissible. His first objection is stated as follows: 
“ Laplace, in the Mec. Cel., vol. iv, , Says, ‘the time of 
rotation of Uranus is not probably much less than that of Jupiter 
or Saturn,’ and in the last edition of Herschel’s Astronomy, page 
648, the time of rotation is given at 9h. 30m. ?” 
To this I reply, that Uranus’s time of rotation has never been 
measured. Consequently if the first objection is different from 
the second it has no other foundation than mere conjecture. 
The second objection is based on Madler’s determmation of 
the planet’s polar compression. But can its rotary velocity be dex 
duced from its figure? Exclusive of Uranus, the oblateness of 
only four members of our system has been measured: viz., the 
arth, Mars, Jupiter and Saturn. ‘The figure of Saturn, it 1s 
well known, is not that of a regular spheroid. It was observed 
by Sir William Herschel that “the flattening of the poles did 
not seem to begin till near a very high latitude, so that the real 
figure of the planet resembled a square, or rather a parallelogram 
with the corners rounded off deeply, but not so much as to bring 
it to a spheroid.” ‘lhe proportion of the disc, as given by Her- 
hel is 
Diameter of the greatest curvature, . 36 
Equatorial diameter, - 5 a 
Polar diameter, : ‘ 
| _. "This figure, it is evident, could not have been produced sim- 
_ ply by the centrifugal force due to the planet’s rotation. _ Again, 
the oblateness of Mars is, according to Arago, eight times, or ac- 
i een times greater than that of the fig- 
_et’s: polar compression indicates a rotation-per! 
irs Herschel’s measurement, less than six hours ; and — 
ween the two, about seven hours. The true period, there- 
- e hat inferred from the shape of the planet in 
rtion as my estimate of Uranus’ period 
about 34 hours. Professor Loomis, on several accounts, regards - 
