HERSCHEL, more particularly because his claims as a discoverer seem to
have been strangely overlooked by historians of the development of
physical science. He, before any other investigator, showed that radiant
heat is refracted according to the laws governing the refraction of
light by transparent media; that a portion of the radiation from the sun
is incapable of exciting the sensation of vision, and that this portion
is the less refrangible; that the different colors of the spectrum
possess very unequal heating powers, which are not proportional to their
luminosity; that substances differ very greatly in their power of
transmitting radiant heat, and that this power does not depend solely
upon their color; and that the property of diffusing heat is possessed
to a varying degree by different bodies, independently of their color.
Nor should we neglect to emphasize, in this connection, the importance
of his measurements of the intensity of the heat and light in the
different portions of the solar spectrum. It is the more necessary to
state HERSCHEL'S claims clearly, as his work has been neglected by those
who should first have done him justice. In his "History of Physics,"
POGGENDORFF has no reference to HERSCHEL. In the collected works of
VERDET, long bibliographical notes are appended to each chapter, with
the intention of exhibiting the progress and order of discovery. But all
of HERSCHEL'S work is overlooked, or indexed under the name of his son.
One little reference in the text alone shows that his very name was not
unknown. Even in the great work of HELMHOLTZ on physiological optics,
HERSCHEL'S labors are not taken account of.

It is easy to account for this seemingly strange neglect. HERSCHEL is
known to this generation only as an astronomer. A study of his memoirs
will show that his physical work alone should give him a very high rank
indeed, and I trust that the brief summaries, which alone can be given
here, will have made this plain.

* * * * *

We may conclude from the time expended, the elaborate nature of the
experiments involved, and the character of the papers devoted to their
consideration, that the portion of HERSCHEL'S researches in physics
which interested him to the greatest degree, was the investigation of
the optical phenomena known as NEWTON'S rings. In 1792 he obtained the
two object-glasses of HUYGHENS, which were in the possession of the
Royal Society, for the p