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tinued until 1822, when the planet’s rate of progress was 
retarded, and this has continued to the present time. It was 
felt that according to the law of planetary disturbance, the 
gravitating action of Jupiter and Saturn not being sufficient to 
explain the perturbations, it was probable that a mass of matter 
exterior to our known system was the exciting cause. In this 
state of the question the following problem became the subject 
of investigation to Mr. Adams, in England, and M. Leverrier, 
in France, unknown to one another: — “ Given the disturbances 
to find the orbit, and place in that orbit, of the disturbing planet." 
These geometers arrived at conclusions differing from each 
other only 3° 19'; and M. Leverrier having announced to 
Dr. Galle, of the Royal Observatory of Berlin, the position in 
which a new planet, — the disturbing cause, — should be found 
according to his calculation ', on the very night of the daj on 
which the letter was received the astronomer of Berlin dis- 
covered the planet Neptune in a point of space differing only 
47' from the mean of the two calculations. The planet Nep- 
tune, like the old planet Saturn, is surrounded by a ring. 
Allow me for one moment to direct attention to some expei i- 
ments by Plateau on the condition of bodies relieved from the 
influence of gravitation, which appear to show that the remark- 
able phenomena of these two planets, with their luminous rings, 
are due to the influence of motion exerted under peculiar con- 
ditions. If oil is dropped upon water it swims ; if upon 
alcohol it sinks ; but if we make a careful combination of 
water and alcohol we obtain a fluid of the same specific gravity 
as the oil, and the globule of oil will swim in the very centre of 
the fluid, a perfect sphere. If into a properly arranged glass 
box we pass a fine wire through the sphere of oil, and by means 
of a handle cause it to revolve slowly, the sphere becomes an 
oblate spheroid ; by increasing the motion we flatten it still 
more, until at a certain rate of revolution it becomes a disc, 
when a ring of oil is thrown off from the central globule, and 
although separated by intervening water, it revolves at precisely 
the same rate. It is not a little interesting thus to find 
mechanical science affording us the means of explaining the 
grander phenomena of creation. 
