(_Cabinet Cyclopaedia_. Vol. xiv.)
The arrangement of Dr. Lardner's Cyclopaedia, as it becomes more and
more developed, will be proportionally appreciated. Its _system_ is
a marked contrast with the heterogeneous lists of the Family and
National Libraries, which, as books of reference and authority, are
little worth.
The _Cyclopaedia_ plan is to form a series of _Cabinets_ of the
principal departments of human knowledge. Those already commenced are
History, Biography, Natural Philosophy, Geography, and the Useful Arts.
Each of these divisions is to be preceded by a prefatory discourse on
"the objects and advantages" of the branch of knowledge which is treated
of in the series or cabinet. Thus, the work before us is such a volume
for the Cabinet of _Natural Philosophy_; that for History is
promised by Sir James Mackintosh; and that for the Useful Arts, by the
Baron Charles Dupin. The present _Discourse_ is by J.F.W. Herschel,
Esq., A.M. It is divided into three parts:--1. On the general nature and
advantages of the study of Physics. 2. The rules and principles of
Physical Science, with illustrations of their influence, in the history
of its progress. 3. The subdivision of Physics. These parts are divided
into chapters, and these chapters again divided into sectional
illustrations, of which latter there are nearly four hundred. Such an
arrangement can hardly fail to attract the listless reader. The style is
lucid and popular, and the writer's reasonings and bearings are brought
out with much point and vigour. Even a drawing-room reader must be
caught by their attractions, and no better means was probably ever
devised for bringing superficial readers into the way of knowledge, and
setting forth its pleasantness. It has been said that such works as the
present satisfy the reader, and disqualify him for the study of science.
This opinion is hardly worth controverting: since that mind must be weak
indeed which would not be _stimulated_ as well as gratified in this
case; and it is still more improbable that the great truths of science
should at once take root in such a barren soil without any preparation
for their reception.
We conclude with a few specimen extracts. The _how_, the _why_, the
_wherefore_, and the because, of such wonders as they relate to, belong
rather to the treatises themselves.
_Mechanical Power of Coals._
It is well known to modern engineers, that _there is virtue_ in a
bushel of coals properly consumed, to raise seventy millions of pounds
weight a foot high. This is actually the _average_ effect of an
engine at this moment working in Cornwall.
The ascent of Mont Blanc from the Valley of Chamouni is considered, and
with justice, as the most toilsome feat that a strong man can execute in
two days. The combustion of two pounds of coal would place him on the
summit.
_The Wonders of Physics_.
What mere assertion will make any man believe that in one second of
time, in one beat of the pendulum of a clock, a ray of light travels
over 192,000 miles, and would therefore perform the tour of the world
in about the same time that it requires to wink with our eyelids, and
in much less than a swift runner occupies in taking a single stride?
What mortal can be made to believe, without demonstration, that the
sun is almost a million times larger than the earth? and that, although
so remote from us, that a cannon ball shot directly towards it, and
maintaining its full speed, would be twenty years in reaching it, it
yet affects the earth by its attraction in an inappreciable instant of
time?--Who would not ask for demonstration, when told that a gnat's
wing, in its ordinary flight, beats many hundred times in a second? or
that there exist animated and regularly organised beings, many thousands
of whose bodies laid close together would not extend an inch? But what
are these to the astonishing truths which modern optical inquiries have
disclosed, which teach us that every point of a medium through which
a ray of light passes is affected with a succession of periodical
movements, regularly recurring at equal intervals, no less than 500
millions of millions of times in a single second! that it is by such
movements, communicated to the nerves of our eyes, that we see--nay
more, that it is the difference in the frequency of their recurrence
which affects us with the sense of the diversity of colour; that, for
instance, in acquiring the sensation of redness our eyes are affected
482 millions of millions of times; of yellowness, 542 millions of
millions of times; and of violet, 707 millions of millions of times
per second. Do not such things sound more like the ravings of madmen,
than the sober conclusions of people in their waking senses? They are,
nevertheless, conclusions to which any one may most certainly arrive,
who will only be at the trouble of examining the chain of reasoning by
which they have been obtained.
_Extraordinary Property of Shadows_.
An eminent living geometer had proved by calculations, founded on strict
optical principles, that in the _centre of the shadow_ of a small
circular plate of metal, exposed in a dark room to a beam of light
emanating from a _very small brilliant point_, there ought to be no
darkness,--in fact, _no shadow_ at that place; but, on the contrary,
a degree of illumination precisely as bright as if the metal plate were
away. Strange and even impossible as this conclusion may seem, it has
been put to the trial, and found perfectly correct.
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