(_Cabinet Cyclopædia_, vol. xvii.)
This volume is in every respect worthy of standing beside the luminous
_Discourse on the Study of Natural Philosophy_, by Mr. Herschel. It is
just in the method that we wish to see all branches of science treated,
and it is the only means of rendering such knowledge familiar; and this
has only to be known to become popular. We understood this to be the aim
of the _Cabinet Cyclopædia_ at its outset, and the scientific volumes
already published are an earnest of the Editor's zeal and success. The
best method of illustrating this recommendation, is to seize from the
volume a few familiar effects whose causes are imperfectly understood, and
thus to show how closely the spread of science is identified with
civilization and the common comforts of social life:--
_Deceptive appearance of Waves_
If we observe the waves continually approaching the shore, we must be
convinced that this apparent motion is not one in which the water has any
share: for were it so, the waters of the sea would soon be heaped upon the
shores, and would inundate the adjacent country; but so far from the
waters partaking of the apparent motion of the waves in approaching the
shore, this motion of the waves continues, even when the waters are
retiring. If we observe a flat strand when the tide is ebbing, we shall
still find the waves moving towards the shore.
_Ornamental Fountain Clocks._
It is the same cause (that which produces the deceptive appearance of a
progressive motion in the waves of the sea) which makes a revolving
cork-screw, held in a fixed position, seem to be advancing in that
direction in which it would actually advance if the worm were passing
through a cork. That point which is nearest to the eye, and which
corresponds to the crest of the wave in the former example, continually
occupies a different point of the worm, and continually advances towards
its extremity.--This property has lately been prettily applied in
ornamental clocks. A piece of glass, twisted so that its surface acquires
a ridge in the form of a screw, is inserted in the mouth of some figure
designed to represent a fountain. One end of the glass is attached to the
axle of a wheel, which the clock-work keeps in a state of constant
rotation, and the other end is concealed in a vessel, designed to
represent a reservoir or basin. The continual rotation of the twisted
glass produces the appearance of a progressive motion, as already
explained, and a stream of water continually appears to flow from the
fountain into the basin.
_Facility of Swimming._
The lighter the body is in relation to its magnitude, the more easily will
it float, and a greater proportion of the head will remain above the
surface. As the weight of the human body does not always bear the same
proportion to its bulk, the skill of the swimmer is not always to be
estimated by his success; some of the constituent parts of the human body
are heavier, while others are lighter, bulk for bulk, than water. Those
persons in whom the quantity of the latter bear a greater proportion to
the former, will swim with a proportionate facility.
_Common Mistake in Cooling Wine._
When ice is used to cool wine, it will be ineffectual if it be applied, as
is frequently the case, only to the bottom of the bottle; in that case,
the only part of the wine which will be cooled is that part nearest the
bottom. As the application of ice to the top of the bottle establishes two
currents, upwards and downwards, the liquid will undergo an effect in some
degree similar to that which would be produced by shaking the bottle. If
there be any deposit in the bottom whose weight, bulk for bulk, nearly
equals that of the wine, such deposit will be mixed through the liquid as
effectually as if it had been shaken. In such cases, therefore, the wine
should be transferred into a clean bottle before it is cooled.
_Why Cream collects on the surface of Milk._
There are numerous familiar effects which are manifestations of the
principle now explained. When a vessel of milk is allowed to remain a
certain time at rest, it is observed that a stratum of fluid will collect
at the surface, differing in many qualities from that upon which it rests.
This is called _cream_; and the property by which it ascends to the
surface is its relative levity; it is composed of the lightest particles
of the milk, which are in the first instance mixed generally in the fluid;
but which, when the liquid is allowed to rest, gradually arise through it,
and settle at the surface.
_Directions engraved upon the Common Weather Glasses absurd._
The barometer has been called a _weather glass_. Rules are attempted to be
established, by which, from the height of the mercury, the coming state of
the weather may be predicted, and we accordingly find the words "Rain,"
"Fair," "Changeable," "Frost," &c., engraved on the scale attached to
common domestic barometers, as if, when the mercury stands at the height
marked by these words, the weather is always subject to the vicissitudes
expressed by them. These marks are, however, entitled to no attention; and
it is only surprising to find their use continued in the present times,
when knowledge is so widely diffused. They are, in fact, to be ranked
scarcely above the _vox stellarum_, or astrological almanac.
Two barometers, one near the level of the River Thames, and the other on
the heights of Hampstead, will differ by half an inch; the latter being
always half an inch lower than the former. If the words, therefore,
engraved upon the plates are to be relied on, similar changes of weather
could never happen at these two situations. But what is even more absurd,
such a scale would inform us that the weather at the foot of a high
building, such as St. Paul's, must always be different from the weather at
the top of it.
It is observed that the changes of weather are indicated, not by the
actual height of the mercury, but by its _change_ of height. One of the
most general, though not absolutely invariable, rules is, that when the
mercury is very low, and therefore the atmosphere very light, high winds
and storms may be expected.
The following rules may generally be relied upon, at least to a certain
extent:
1. _Generally_ the rising of the mercury indicates the approach of fair
weather; the falling of it shows the approach of foul weather.
2. In sultry weather the fall of the mercury indicates coming thunder. In
winter, the rise of the mercury indicates frost. In frost, its fall
indicates thaw; and its rise indicates snow.
3. Whatever change of weather suddenly follows a change in the barometer,
may be expected to last but a short time. Thus, if fair weather follow
immediately the rise of the mercury, there will be very little of it; and,
in the same way if foul weather follow the fall of the mercury, it will
last but a short time.
4. If fair weather continue for several days, during which the mercury
continually falls, a long continuance of foul weather will probably ensue;
and again, if foul weather continue for several days, while the mercury
continually rises, it long succession of fair weather will probably
succeed.
5. A fluctuating and unsettled state in the mercurial column indicates
changeable weather.
The domestic barometer would become a much more useful instrument, if,
instead of the words usually engraved on the plate, a short list of the
best established rules, such as the above, accompanied it, which might be
either engraved on the plate, or printed on a card. It would be right,
however, to express the rules only with that degree of probability which
observation of past phenomena has justified. There is no rule respecting
these effects which will hold good with perfect certainty in every case.
This volume, we should add, is by Dr. Lardner, the editor of the
_Cyclopædia_, and is a good model for his collaborateurs.
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