nuity
in experimentation are as striking as ever. He tried the effect of
having a polished metal as one of the surfaces limiting the thin plate
of air. Observing the so-called "blue bow" of NEWTON at the limit of
total reflection in a prism, he was led to the discovery of its
complement, the "red bow" by refraction. Here he thought he had found
the solution of his problem, and attributed the rings to the reflection
of the light which passed through in the red bow. Though mistaken, he
had presented to the world of science two experiments which have since
played very prominent parts in the undulatory theory of light, namely,
the rings formed upon polished metal, and the bands produced by a thin
plate near the critical angle.

As in his later researches upon the nature of radiant heat, he was wrong
in his conclusions, and perhaps with less excuse. His experiments were
skilfully devised and most ingenious. His philosophizing was distinctly
faulty. We can see not only that he was wrong, but exactly where he
began to go wrong. Yet these papers are full of interest to the
physicist, and by no means deserve the neglect into which they have
fallen.

_Researches on the Dimensions of the Stars._

HERSCHEL examined a number of bright stars, using extremely high
magnifying powers, in order to determine whether the stars have sensible
dimensions. In a good telescope stars present round and pretty uniformly
illuminated disks. If these disks really represent the angular diameter
of the stars, they should admit of magnifying, like other objects; but,
instead of this, HERSCHEL found that they appeared smaller as the
telescopic power was increased. He accordingly called the disk of light
seen in the telescope a spurious disk. This singular phenomenon gave its
discoverer a ready criterion for determining whether a small bright body
has an appreciable size, or only impresses the sense of sight by virtue
of its intrinsic brightness. If the first were the case, the apparent
size would increase with increased magnifying power, while, if the
angular dimensions were inappreciable, the apparent size would, on the
contrary, diminish with additional magnifying. An occasion for using
this criterion came in the first years of this century, with the
discovery of three small planets having orbits lying between those of
_Mars_ and _Jupiter_. HERSCHEL gave the name _Asteroids_ to these
bodies. As the appropriateness of this term had b