ave often seen technicalities which must
operate as a wet blanket on the enthusiasm of the reader; and break up
the charm which the subject had hitherto created. Upon this principle,
treatise upon treatise has been published without effecting the primary
object. The matter of Dr. Arnott's work, however, appears to us to be in
strict accordance with its title--elementary; but it is accompanied with
a variety of explanations of familiar facts on philosophical principles,
which possess attractions of a most amusive character.

The present portion of Dr. Arnott's work comprehends the subjects of
_Light_ and _Heat_, which admit of more familiar illustration than any
other branches of Natural Philosophy. Of this advantage the author has
fully availed himself in a variety of familiar exemplars, which, to
speak seriously are brought home to our very firesides. A few of these
facts will form a recreative page or two for another MIRROR: in the
meantime we quote a few illustrative observations on the most
interesting exhibitions of the day:--

"Common paintings and prints may be considered as parts of a panoramic
representation, showing as much of that general field of view which
always surrounds a spectator, as can be seen by the eye turned in one
direction, and looking through a window or other opening. The pleasure
from contemplating these is much increased by using a lens. There is
such a lens fitted up in the shops, with the title of _optical pillar
machine_, or _diagonal mirror_, and the print to be viewed is laid upon
a table beyond the stand of the lens, and its reflection in a mirror
supported diagonally over it, is viewed through the lens. The illusion
is rendered more complete in such a case by having a box to receive the
painting on its bottom, and where the lens and mirror, fixed in a
smaller box above, are made to slide up and down in their place to allow
of readily adjusting the focal distance. This box used in a reverse way
becomes a perfect camera obscura. The common show-stalls seen in the
streets are boxes made somewhat on this principle, but without the
mirror; and although the drawings or prints in them are generally very
coarse, they are not uninteresting. To children whose eyes are not yet
very critical, some of these show boxes afford an exceeding great
treat."

_Cosmoramas and Dioramas._

"A still more perfect contrivance of the same kind has been exhibited
for some time in London and Paris under the t