_Dr. Arnott's Elements of Physics._
Vol. ii. Part I.
We are warm friends to the diffusion of knowledge, and accordingly
receive the present portion of Dr. Arnott's work with much satisfaction.
We believe the sale of the first volume to have been almost
unprecedentedly rapid, (a _fourth_ edition being called for within two
years) in comparison with the usual slow sale of _scientific_ works.
This success may easily be traced. The title of the work is not
extraordinarily inviting, illustration, not embellishment, is attempted
in a few outline diagrams, and the only external inducement to read, is
a plain, legible type, to suit all sights. Looking further, we find the
great cause in the manner as well as the matter of the volume, which is
throughout a text-book of _plain-spoken philosophy_, or as the author
says in his title-page, "independently of technical mathematics." Again,
in his introductory chapter on "Imponderable Substances," he says, "To
understand the subjects as far as men yet usefully understand them, and
sufficiently for a vast number of most useful purposes, it is only
necessary to classify important phenomena, so that their nature and
resemblances may be clearly perceived." The main error of most people
who write on philosophical subjects, or the stumbling-block of all
students, has been that of the writer presuming too much upon the
cultivated understanding of his reader. Thus, in the midst of very
familiar explanations we have 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 title of _Cosmorama_ (from
Greek words signifying _views_ of the _world_, because of the great
variety of views.) Pictures of moderate size are placed beyond what have
the appearance of common windows, but of which the panes are really
large convex lenses fitted to correct the errors of appearance which the
nearness of the pictures would else produce. Then by farther using
various subordinate contrivances, calculated to aid and heighten the
effects, even shrewd judges have been led to suppose the small pictures
behind the glasses to be very large pictures, while all others have let
their eyes dwell upon them with admiration, as magical realizations of
the natural scenes and objects. Because this contrivance is cheap and
simple, many persons affect to despise it; but they do not thereby show
their wisdom; for to have made so perfect a representation of objects,
is one of the most sublime triumphs of art, whether we regard the
pictures drawn in such true perspective and colouring, or the lenses
which assist the eye in examining them.
"It has already been stated, that the effect of such glasses in looking
at near pictures, is obtainable in a considerable degree without a
glass, by making the pictures very large and placing them at a
corresponding distance. The rule of proportion in such a case is, that a
picture of one foot square at one foot distance from the eye, appears as
large as a picture of sixty feet square at sixty feet distance. The
exhibition called the Diorama is merely a large painting prepared in
accordance with the principle now explained. In principle it has no
advantage over the cosmorama or the show box, to compensate for the
great expense incurred, but that many persons may stand before it at a
time, all very near the true point of sight, and deriving the pleasure
of sympathy in their admiration of it, while no slight motion of the
spectator can make the eye lose its point of view."
_The Colosseum._
"A round building of prodigious magnitude has lately been erected in the
Regent's Park, in London, on the walls of which is painted a
representation of London and the country around, as seen from the cross
on the top of St. Paul's Cathedral. The scene taken altogether is
unquestionably one of the most extraordinary which the whole world
affords, and this representation combines the advantages of the circular
view of the panorama, the size and distance of the great diorama, and of
the details being so minutely painted, that distant objects may be
examined by a telescope or opera-glass.
"From what has now been said, it may be understood, that for the purpose
of representing still-nature, or mere momentary states of objects in
motion, a picture truly drawn, truly coloured, and which is either very
large to correct the divergence of light and convergence of visual axes,
or if small, as viewed through a glass, would affect the retina exactly
as the realities. But the desideratum still remained of being able to
paint motion. Now this too has been recently accomplished, and in many
cases with singular felicity, by making the picture transparent, and
throwing lights and shadows upon it from behind. In the exhibitions of
the diorama and cosmorama there have been represented with admirable
truth and beauty such phenomena as--the sun-beams occasionally
interrupted by passing clouds, and occasionally darting through the
windows of a cathedral and illuminating the objects in its venerable
interior--the rising and disappearing of mist over a beautiful
landscape, runningwater, as for instance the cascades among the sublime
precipices of Mount St. Gothard in Switzerland;--and most surprising of
all, a fire or conflagration. In the cosmorama of Regent-street, the
great fire of Edinburgh was admirably represented:--first that fine city
was seen sleeping in darkness while the fire began, then the
conflagration grew and lighted up the sky, and soon at short intervals,
as the wind increased, or as roofs fell in, there were bursts of flame
towering to heaven, and vividly reflected from every wall or spire which
caught the direct light--then the clouds of smoke were seen rising in
rapid succession and sailing northward upon the wind, until they
disappeared in the womb of distant darkness. No one can have viewed that
appalling scene with indifference, and the impression left by the
representation, on those who knew the city, can scarcely have been
weaker than that left on those who saw the reality. The mechanism for
producing such effects is very simple; but spectators, that they may
fully enjoy them, need not particularly inquire about it."
Even for the present we cannot omit mention of the delight with which we
have read several of the more playful portions of the present work; we
allude to such passages as the Influence of Heat on Animated Beings, in
which Dr. Arnott has really blended the pencil of the artist with the
pen of the philosopher, and thus produced many sketches of extreme
picturesque beauty.
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