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SPIRIT OF DISCOVERY

HYDROSTATICS AND PNEUMATICS

(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:

Generally the rising of the mercury indicates the approach of fair weather; the falling of it shows the approach of foul weather.

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.

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.

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.

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.

REFLECTION

It is better to reflect ourselves, than to suffer others to reflect for us. A philosopher has a system; he views things according to his theory; he is unavoidably partial; and, like Lucian’s painter, he paints his one-eyed princes in profile.

STATUE OF PETER THE GREAT

This superb work of modern art stands in one of the finest squares of St. Petersburgh, and of Europe, according to Sir Robert Ker Porter. It was erected by command of the Empress Catherine, and, like all her projects, bears the stamp of greatness. The name of the artist is Falconet: “he was a Frenchman; but,” adds Sir R.K.P. “this statue, for genius and exquisite execution, would have done honour to the best sculptors of any nation. A most sublime conception is displayed in the design. The allegory is finely imagined; and had he not sacrificed the result of the whole to the prominence of his group, the grand and united effect of the statue and its pedestal striking at once upon the eye, would have been unequalled in the works of man. A mass of granite, of a size at present most immense, but formerly most astonishing, is the pedestal. A steep acclivity, like that of a rugged mountain, carries the eye to its summit, which looks down on the opposite side to a descent nearly perpendicular. The figure of the hero is on horseback, supposed to have attained the object of his ambition, by surmounting all the apparent impossibilities which so arduous an enterprise presented. The victorious animal is proudly rearing on the highest point of the rock, whilst his imperial master stretches forth his mighty arm, as the father and protector of his country. A serpent, in attempting to impede his course, is trampled on by the feet of the horse, and writhing in all the agonies of expiring nature. The Emperor is seated on the skin of a bear; and habited in a tunic, or sort of toga which forms the drapery behind. His left hand guides the reins; his right is advanced straight forward on the same side of the horse’s neck. The head of the statue is crowned with a laurel wreath.” It was formed from a bust of Peter, modelled by a young French damsel. The contour of the face expresses the most powerful command, and exalted, boundless, expansion of thought. “The horse, says Sir Robert, is not to be surpassed. To all the beauties of the ancient form, it unites the easy grace of nature with a fire which pervades every line; and gives such a life to the statue, that as you gaze you expect to see it leap from the pinnacle into the air. The difficulty of keeping so great a mass of weighty metal in so volant an attitude, has been admirably overcome by the artist. The sweep of the tail, with the hinder parts of the horse, are interwoven with the curvatures of the expiring snake; and together compose a sufficient counterpoise to the figure and forepart of the animal.”⁶

Our representation of this masterpiece of art is copied from a Russian medallion presented to our ingenious artist, Mr. W.H. Brooke, by M. Francia.