the heavens. This was
followed by a third paper on August 31st, giving a rather completer
discussion, and arriving at the conclusion that the planet should be
recognisable from its disc. This again is an important point. We remember
that in the discovery of Uranus it needed considerable skill on the part
of Sir William Herschel to detect the disc, to see in fact any difference
between it and surrounding stars; and that other observers, even when
their attention had been called to the planet, found it difficult to see
this difference. It might be expected, therefore, that with a planet twice
as far away (as had been assumed for the new planet) the disc would be
practically unrecognisable, and as we shall presently see, this assumption
was made in some searches for the planet which had been commenced even
before the publication of this third paper. Le Verrier's courageous
announcement, which he deduced from a consideration of the mass of the
planet, that the disc should be recognisable, led immediately to the
discovery of the suspected body. He wrote to a German astronomer, Dr.
Galle (still, I am glad to say, alive and well, though now a very old
man), telling him the spot in the heavens to search, and stating that he
might expect to detect the planet by its appearance in this way; and the
same night Dr. Galle, by comparing a star map with the heavens, found the
planet.

[Sidenote: Adams' work publicly announced.]

To two points to which I have specially called attention in this brief
summary--namely, the preliminary assumption that the planet would be,
according to Bode's Law, twice as far away as Uranus; secondly, the
confident assertion that it would have a visible disc--I will ask you to
add, thirdly, that it was found by the aid of a star map, for this map
played an important part in the further history to which we shall now
proceed. It may naturally be supposed that the announcement of the finding
of a planet in this way, the calculation of its place from a belief in the
universal action of the great Law of Gravitation, the direction to an
eminent observer to look in that place for a particular thing, and his
immediate success,--this extraordinary combination of circumstances caused
a profound sensation throughout not only the astronomical, but the whole
world; and this sensation was greatly enhanced by the rumour which had
begun to gather strength that, but for some unfortunate circumstances, the
discovery might h