beyond. Which is the true scientific attitude, to
be alive to them all, or to concentrate attention upon one?

But we are perhaps wandering too far from the main theme. It is easy to do
so in reviewing this extraordinary piece of history, for at almost every
point new possibilities are suggested.

[Illustration:

III--U. J. LE VERRIER.
(_From a print in the possession of the Royal Astronomical Society._)]

[Illustration:

IV--J. G. GALLE.
WHO FIRST SAW THE PLANET NEPTUNE]

[Sidenote: Airy receives Le Verrier's memoir.]

We must return, however, to Airy's "account." We reached the point where
he had written to Adams (on November 5, 1845), asking his question about
the radius vector, and received no reply; and there the matter remained,
so far as he was concerned, until the following June, when Le Verrier's
memoir reached him; and we will let him give his own version of the
result.

"This memoir reached me about the 23rd or 24th of June. I cannot
sufficiently express the feeling of delight and satisfaction which I
received from it. The place which it assigned to the disturbing
planet was the same, to one degree, as that given by Mr. Adams'
calculations, which I had perused seven months earlier. To this time
I had considered that there was still room for doubt of the accuracy
of Mr. Adams' investigations; for I think that the results of
algebraic and numerical computations, so long and so complicated as
those of an inverse problem of perturbations, are liable to many
risks of error in the details of the process: I know that there are
important numerical errors in the _Mecanique Celeste_ of Laplace; in
the _Theorie de la Lune_ of Plana; above all, in Bouvard's first
tables of _Jupiter_ and _Saturn_; and to express it in a word, I have
always considered the correctness of a distant mathematical result to
be a subject rather of moral than of mathematical evidence. But now I
felt no doubt of the accuracy of both calculations, as applied to the
perturbation in longitude. I was, however, still desirous, as before,
of learning whether the perturbation in radius vector was fully
explained. I therefore addressed to M. Le Verrier the following
letter:--

No. 13.--G. B. AIRY _to_ M. LE VERRIER.

"'Royal Observatory, Greenwich, _1846, June 26_.

[Sidenote: He puts the "radius-vector" question to Le