142. Sir James Clark’s Ozone Cage (fig. 92), consists of two cylinders of very fine wire gauze, one fitting into the other; the wire gauze being of such a fineness as to permit the free ingress of air, at the same time that it shuts out all light that would act injuriously on the test-paper, which is suspended by a clip or hook attached to the upper part of the inner cylinder.

143. Distribution and Effects of Ozone.—Mr. Glaisher has found that “the amount of ozone at stations of low elevation is small; at stations of high elevation, it is almost always present; and at other and intermediate stations, it is generally so. The presence and amount of ozone would seem to be graduated by the elevation, and to increase from the lowest to the highest ground. The amount of ozone is less in towns than in the open country at the same elevation; and less at inland than at sea-side stations.” It seems to abound most with winds from the sea, and to be most prevalent where the air is considered the purest and most salubrious. This may seem, says Admiral FitzRoy, in The Weather Book, to point to a connection between ozone and chlorine gas, which is in and over sea-water, and which must be brought by any wind that blows from the sea. It prevails more over the ocean and near it than over land, especially land remote from the sea; and, says the Admiral, it affects the gastric juice, improves digestion, and has a tanning effect. Dr. Daubeny, in his Lectures on Climate, writes: “Its presence must have a sensible influence upon the purity of the air, by removing from it fœtid and injurious organic effluvia. It is also quite possible that ozone may play an important part in regulating the functions of the vegetable kingdom likewise; and although it would be premature at present to speculate upon its specific office, yet, for this reason alone, it may be well to note the fact of its frequency, in conjunction with the different phases which vegetation assumes, persuaded that no principle can be generally diffused throughout nature, as appears to be the case, with this, without having some important and appropriate use assigned for it to fulfil.”

144. Registering Ozonometer.—Dr. E. Lancaster has contrived an ozonometer, the object of which is to secure the constant registration of ozone, so that the varying quantities present in the atmosphere may be detected and registered. For this purpose, an inch of ozone paper passes in each hour, by clock-work, beneath an opening in the cover of the instrument.

CHAPTER XVI.

4. In cold weather, if the top of the liquid becomes thick and cloudy, it denotes approaching rain.

5. In warm weather, if small crystals rise in the liquid, which still maintains its clearness, rain may be expected.

6. Sharpness in the points and features of the fern-like structure of the crystals, is a sign of fine weather; but when they begin to break up, and are badly defined, unsettled weather may be expected.

Admiral FitzRoy, in The Weather Book, writes of this instrument as follows:—“Since 1825, we have generally had some of these glasses, as curiosities rather than otherwise; for nothing certain could be made of their variations until lately, when it was fairly demonstrated that if fixed undisturbed in free air, not exposed to radiation, fire, or sun, but in the ordinary light of a well-ventilated room, or, preferably, in the outer air, the chemical mixture in a so-called storm-glass varies in character with the direction of the wind—not its force, specially (though it may so vary in appearance, only from another cause, electrical tension).

“As the atmospheric current veers toward, comes from, or is only approaching from the polar direction, this chemical mixture—if closely, even microscopically watched—is found to grow like fir, yew, fern leaves, or hoar-frost—or like crystallizations.

“As the wind, or great body of air, tends more from the opposite quarter, the lines or spikes—all regular, hard, or crisp features—gradually diminish, till they vanish.

“Before, and in a continued southerly wind, the mixture sinks slowly downward in the vial, till it becomes shapeless, like melting white sugar.

“Before, or during the continuance of a northerly wind (polar current), the crystallizations are beautiful (if the mixture is correct, the glass a fixture, and duly placed); but the least motion of the liquid disturbs them.

“When the main currents meet, and turn toward the west, making easterly winds, stars are more or less numerous, and the liquid dull, or less clear. When, and while they combine by the west, making westerly winds, the liquid is clear, and the crystallization well-defined, without loose stars.

“While any hard or crisp features are visible below, above, or at the top of the liquid (where they form for polar winds), there is plus electricity in the air; a mixture of polar current co-existing in that locality with the opposite, or southerly.

“When nothing but soft, melting, sugary substance is seen, the atmospheric current (feeble or strong as it may be) is southerly with minus electricity, unmixed with, and uninfluenced by, the contrary wind.

“Repeated trials with a delicate galvanometer, applied to measure electric tension in the air, have proved these facts, which are now found useful for aiding, with the barometer and thermometer, in forecasting weather.

“Temperature affects the mixture much, but not solely; as many comparisons of winter with summer changes of temperature have fully proved.

“A confused appearance of the mixture, with flaky spots, or stars, in motion, and less clearness of the liquid, indicates south-easterly wind, probably strong to a gale.

“Clearness of the liquid, with more or less perfect crystallizations, accompanies a combination, or a contest, of the main currents, by the west, and very remarkable these differences are,—the results of these air currents acting on each other from eastward, or from an entirely opposite direction, the west.

“The glass should be wiped clean now and then,—and once or twice a year the mixture should be disturbed, by inverting and gently shaking the glass vial.”

146. Leslie’s Differential Thermometer.—A glass tube having a large bulb at each extremity, and bent twice at right angles, as represented in figure 93, containing strong sulphuric acid tinged with carmine, and supported at the centre by a wooden stand, constitutes the differential thermometer as invented by Professor Leslie. The instrument is designed to exhibit and measure small differences of temperature. Each leg of the instrument is usually from three to six inches long, and the balls are about four inches apart. The calibre of the legs is about ¹⁄50 inch, not more; the other part of the tube may be wider. The tube is filled with the liquid, the bulbs contain air. When both bulbs are heated alike, each scale indicates zero. The scale is divided so that the space between the freezing and the boiling-points of water is equal to 1,000 parts. When one bulb is heated more than the other, the difference of temperature is delicately shown by the descent of the coloured fluid from the heated ball. It is uninfluenced by changes in the temperature of the atmosphere; hence it is admirably adapted for experiments of radiant heat. The theory of the instrument is that gases expand equally for uniform increments of heat.

147. Rumford’s Differential Thermometer differs from that just described in simply containing only a small bubble of liquid, which lies in the centre of the tube, when both bulbs are similarly influenced. The bulbs and other parts of the tube contain air. When one bulb is more heated than the other, the bubble moves towards the one less heated; and the scale attached to the horizontal part of the tube affords a measurement of the difference of temperature.

148. Glaisher’s Thermometer Stand.—The thermometer stand consists of a horizontal board as a base, of a vertical board projecting upwards from one edge of the horizontal one, and of two parallel inclined boards, separated from each other by blocks of three inches in thickness, connected at the top with the vertical, and at the bottom with the horizontal board, and the air passes freely about and between them all. To the top of the inclined boards is connected a small projecting roof to prevent the rain falling on the bulbs of the instrument, which are carried on the face of the vertical board, with their bulbs projecting below it, so that the air plays freely on the bulbs from all sides. The whole frame revolves on an upright post firmly fixed to the ground, as shown in the engraving, fig. 94; and in use, the inclined side is always turned towards the sun.

149. Thermometer Screen, for use at Sea.—This screen, or shade, was designed by Admiral FitzRoy, and has been in use for several years on board H.M. vessels and many merchant-ships. It is about twenty-four inches long by twelve wide and eight deep; having lattice-work sides, door, and bottom; with perforation also at top, so contrived that the air has free access to the interior, while the direct rays of the sun, rain, and sea spray are effectually excluded from the thermometers mounted inside. There is ample space for two thermometers placed side by side on brackets, at least three inches from each other or any part of the exterior of the screen. One thermometer should be fitted up as a “wet bulb” (see p. 105). A small vessel of water can easily be fixed inside the screen so as to retain its position and contents under the usual motions of the ship; and by means of a piece of cotton-wick, or muslin rag tied round the bulb of the thermometer and trailing into the cup of water, keep the bulb constantly moist.

Self-registering thermometers should be protected by a similar screen. It has been found that thermometric observations made at sea are not valuable for scientific purposes unless the instruments have been duly protected by such a screen.

150. Anemoscope, or Portable Wind Vane for travellers, with compass, bar needle, &c., shows the direct course of the wind to half a point of the compass.

151. Evaporating Dish, or Gauge (fig. 95), for showing the amount of evaporation from the earth’s surface. This gauge consists of a brass vessel, the area or evaporating surface of which is accurately determined; and also a glass cylindrical measure, graduated into inches, tenths, and hundredths of inches. In use, the evaporating gauge is nearly filled with water, the quantity having been previously measured by means of the glass cylinder; it is then placed out of doors, freely exposed to the action of the atmosphere; after exposure, the water is again measured, and the difference between the first and second measurement shows the amount of evaporation that has taken place. If rain has fallen during the exposure of the gauge, the quantity collected by it must be deducted from the measured quantity; the amount is shown by the quantity of rain collected in the rain gauge. The wire cage round the gauge is to prevent animals, birds, &c., from drinking the water.

152. Dr. Babington’s Atmidometer, or instrument for measuring the evaporation from water, ice or snow, consists of an oblong hollow bulb of glass or copper, beneath which and communicating with it by a contracted neck is a second globular bulb, duly weighted with mercury or shot. The upper bulb is surmounted by a small glass or metal stem, having a scale graduated to grains and half-grains; on the top of which is fixed horizontally a shallow metal pan. The bulbs are immersed in a vessel of water having a circular hole in the cover through which the stem rises. Distilled water is then gradually poured into the pan above, until the zero of the stem sinks to a level with the cover of the vessel. Thus adjusted, as the water in the pan evaporates, the stem ascends, and the amount of evaporation is indicated in grains. This instrument affords a means of measuring evaporation from ice or snow. An adjustment for temperature is necessary.

153. Cloud Reflector.—At the International Exhibition 1862, Mr. J. T. Goddard exhibited a cloud mirror, for ascertaining the direction in which the clouds are moving.

The mirror is laid on a horizontal support near a window, and fastened so that the point marked north may coincide with the south point of the horizon,—the several points will consequently be reversed. The edge of a conspicuous cloud is brought to the centre of the mirror, and the observer keeps perfectly still until it passes off at the margin, where the true point of the horizon from which the clouds are coming can be read off.

154. Sunshine Recorder.—Mr. Goddard also exhibited an instrument which he calls by this name. It works by letting the sun’s rays pass through a narrow slit, and fall on photographic paper wound round a barrel moved by clock-work; the paper being changed daily, and the photographic impression developed and fixed in the usual manner.[19]

155. SET OF PORTABLE INSTRUMENTS.

In a small box, 8 in. by 8 in. by 4 in., a complete set of meteorological instruments have been packed. The lid of the box, by an ingenious arrangement, is made to take off and hang up; on it are permanently fixed for observation, a maximum and minimum, and a pair of dry and wet bulb thermometers. The interior of the box contains a maximum thermometer in vacuo for solar radiation, and a minimum for terrestrial purposes, one of Negretti and Zambra’s small pocket aneroid barometers, pedometer for measuring distances, pocket compass, clinometer, and lastly a rain gauge. This latter instrument consists of an accurately turned brass ring having an india rubber body fastened to it to receive the rain, which is measured off by a small graduated glass, also contained in the box. Gentlemen travelling will find this compact observatory all that can be desired for meteorological observations.

156. IMPLEMENTS.

The practical meteorologist will find the following articles very useful, if not necessary. They scarcely require description; an enumeration will therefore suffice:—Weather Diagrams, or prepared printed and ruled forms, whereon to exhibit graphically the readings of the various instruments to render their indications useful in foretelling weather, &c.;—Meteorological Registers, or Record Books, for recording all observations, and the deductions;—Cloud Pictures, by which the clouds can be readily referred to their particular classification, very necessary to the inexperienced and learners;—Cyclone Glasses, or Horns, outline Maps with Wind-markers, are also useful, especially in forecasting weather.

157. HYDROMETER.

A simple kind of hydrometer is very much used at sea, as “a sea-water test;” and as the observations are usually recorded in a meteorological register or the ship’s log-book, it may not be altogether out of place to give a description of it here.

It is constructed of glass. If made of brass, the corrosive action of salt-water soon renders the instrument erroneous in its indications. The shapes usually given to the instruments are shown in figs. 96 and 97. A globular bulb is blown, and partly filled with mercury or small shot, to make the instrument float steadily in a vertical position. From the neck of the bulb the glass is expanded into an oval or a cylindrical shape, to give the instrument sufficient volume for flotation; finally, it is tapered off to a narrow upright stem which encloses an ivory scale, and is closed at the top. The divisions on the scale read downward, so as to measure the length of the stem which stands above the surface of any liquid in which the hydrometer is floated. The denser the fluid, the higher will the instrument rise; the rarer, the lower it will sink.

The indications depend upon the hydrostatic principle, that floating bodies displace a quantity of the fluid which sustains them equal to their own weight. According, therefore, as the specific gravities of fluids differ from each other, so will vary the quantities of the fluids displaced by the same body when floated successively in each.

The specific gravity of distilled water, at the temperature of 62° F, being taken as unity, the depth to which the instrument sinks when gently immersed in such water is the zero of the scale. The graduations extend from 0 to 40; the latter being the mark which will be level with the surface when the instrument is placed in water, the specific gravity of which is 1·040. In recording observations, the last two figures only—being the figures on the scale—are written down. Sea-water usually ranges from 1·020 to 1·036.

A small tin, copper, or glass cylinder is useful for containing the water to be tested. It should be wider than the hydrometer, and always filled to the brim. If fitted to a stand, which is supported by gimbals, it will be very convenient. Water in a bucket, basin, or other wide vessel, acquires motion at sea, and the eye cannot be brought low enough (on account of the edges) to read off the scale accurately.

Errors of observation may occur with the hydrometer, if it be put into water without being clean, or without being carefully wiped. The instrument is extremely accurate if correctly used. It should be kept free from contact with the sides of the vessel; and all dust, smears, or greasiness, should be scrupulously avoided, by carefully wiping it with a clean cloth before and after use.

Whenever the temperature of the water tested differs from 62°, a correction to the reading is necessary, for the expansion or contraction of the glass, as well as the water itself, in order to reduce all observations to one generally adopted standard.

Negretti and Zambra’s hydrometer, with thermometer in the stem, shows the density and temperature in one instrument.

For the following Tables we are indebted to the kindness of Admiral FitzRoy:—

Table for reducing observations made with a Brass Hydrometer, assuming the linear expansion of brass to be 0·000009555 for 1° F. The correction is additive for all temperatures above 62°, and subtractive for temperatures below 62°.

Table for reducing observations made with a Glass Hydrometer, assuming the linear expansion of glass to be 0·00000463 for 1° F. The correction is additive for temperatures above 62°, and subtractive for temperatures below 62°.

158. NEWMAN’S SELF-REGISTERING TIDE-GAUGE.

At places where the phenomena of the tides are of much maritime importance, a continuous series of observations upon the rise and fall, and times of change, is essentially necessary as a basis for the construction of good tide tables; and as such observations should also be accompanied with the registration of atmospheric phenomena, we have no hesitation in inserting a description of an accurate self-registering tide-gauge.

The tide-gauge, as shown in the illustration, consists of a cylinder, A, which is made to revolve on its axis once in twenty-four hours by the action of the clock, B. A chain, to which is attached the float, D, passes over the wheel, C, and on the axis of this wheel, C (in about the middle of it) is a small toothed wheel, placed so as to be in contact with a larger toothed wheel carrying a cylinder, E, over which passes another smaller chain. This chain, passing along the upper surface of the cylinder, A, and round a second cylinder, F, at its further end, is acted on by a spring so as to be kept in a constant state of tension. In the middle of this chain a small tube is fixed for carrying a pencil, which, being gently pressed down by means of a small weight on the top of it, performs the duty of marking on paper placed round the cylinder the progress of the rise or fall of the tide as the cylinder revolves, and as it is drawn by the chain forward or backward by the rise or fall of the float. The paper is prepared with lines equidistant from each other, to correspond with the hours of the clock, crossed by others showing the number of feet of rise and fall.

The cylinder while in action revolves from left to right to a spectator facing the clock, and the pencil is carried horizontally along the top of the cylinder; and the large wheel being made to revolve by the rise and fall of the float, turns the wheel with the small cylinder, E, attached to it. If the tide is falling, the small chain is wound round the cylinder, E, and the pencil is drawn towards the large wheel; but if the tide is rising, the small chain is wound on to the cylinder, F, by means of the spring contained in it, which constantly keeps it in a state of tension. Thus, by means of the rise and fall of the tide, a lateral progress is given to the pencil, while the cylinder is made to revolve on its axis by the clock, so that a line is traced on the paper showing the exact state of the tide continuously, without further attention than is necessary to change the paper once every day, and to keep the pencil carefully pointed; or a metallic pencil may be used, which will require little, if any, attention.

A good self-registering tide-gauge is a valuable and important acquisition wherever tidal observations are required, and the only perfectly efficient instrument of this kind is that invented by the late Mr. John Newman, of Regent Street, London. It is now in action in several parts of the world, silently and faithfully performing its duty, requiring no other kind of attention than that of a few minutes daily, and thus admitting the employment of the person on any other service whose duty it would otherwise have been to have registered the tide. It has done much by its faithful records in contributing to the construction of good tide tables for many places; for those unavoidable defects dependent on merely watching the surface on a divided scale are set aside by it, all erroneous conclusions excluded, and a true delineation of Nature’s own making is preserved by it for the theorist.

ADDENDA.

1. French barometers are graduated to millimetres. An English inch is equal to 25·39954 millimetres. Hence, 30 inches on the English barometer scales correspond to 762 millimetres on the French barometer scales. Conversions from one scale to another can be effected by the following formulæ:—

Of course, a table of equivalent values should be drawn up and employed, when a large number of observations are to be converted from one scale to the other.

2. In Germany, barometers are sometimes graduated with old French inches and lines,—the vernier generally indicating the tenth of a line.

Old French Lineal Measure.

“The Germans indicate inches by putting two accents after the number; lines, by putting three accents; 27″ 3′″·85, means 27 inches 3 lines 85 hundredths of a line; more frequently, they give the height in lines, and the preceding number becomes 327′″·85.”—Kaemtz.

3. Rule for finding Diameter of Bore of a Barometer Tube.

“If the maker has not taken care to measure the interior diameter directly, it may be deduced from the exterior diameter. The exterior diameter is first measured by calipers, and, by deducting from this diameter 0·1 of an inch for tubes from ·3 to ·5 of an inch in external diameter, we have an approximation to the interior diameter of the tube.”—Kaemtz.

4. Wind Scales.

5. Letters to Denote the State of the Weather.

A letter repeated denotes much, as r r, heavy rain; f f, dense fog; and a figure attached denotes duration in hours, as 14 r, 14 hours rain.

By the combination of these letters, all the ordinary phenomena of the weather may be recorded with certainty and brevity.

Examples.—b c, blue sky with less proportion of cloud. 2 r r l l t, heavy rain for two hours, with much lightning, and some thunder.

The above methods of recording the force of wind and state of weather were originally proposed by Admiral Sir Francis Beaufort. They are now in general use at sea, and by many observers on land.

6. Table of Expansion by Heat from 32° to 212° F.

7. Table of Specific Gravity of Bodies at 32° F. except water, which is taken at 39°·4.

Weight of a cubic foot of water, at the temperature of comparison, 62·425 lbs. avoirdupois.

The pound avoirdupois contains 7,000 grains.

Air is 813·67 times lighter than water.

The linear expansions are the mean values of the results of various experimentalists. The specific gravities are as given in Professor Rankine’s Applied Mechanics.

8. Important Temperatures. Under the circumstances of—

9. TABLE OF METEOROLOGICAL ELEMENTS, FORMING EXPONENTS OF THE CLIMATE OF LONDON.

In the above Table, columns 1 to 10 are results obtained at the Royal Observatory, Greenwich, by J. Glaisher, Esq., F.R.S. The data contained in columns 2 and 10, are deduced from observations extending over the years 1841 to 1855 inclusive, and are copied from Edward Hughes’ Third Reading Book; the other columns are results of observations made during the twenty years ending 1861. The rest of the information is from Luke Howard’s Climate of London.

These valuable data indicate the characteristics of the weather in each month in the suburbs of London, and will be found tolerably accurate as indications of weather, and serviceable as standards for comparisons of observed results, at most places in England.

STANDARD WORKS ON METEOROLOGY

SUPPLIED BY NEGRETTI & ZAMBRA.

THE WEATHER BOOK:
A MANUAL OF PRACTICAL METEOROLOGY.
By Vice-Admiral FitzRoy, F.R.S., M.I.F., &c.
Price, £0 15 6

THE LAW OF STORMS,
By H. W. Dove, F.R.S.
Translated by R. H. Scott, M.A.
Price, £0 10 6

L. F. KÆMTZ’S “COMPLETE COURSE OF METEOROLOGY,”
Translated by C. V. Walker, Esq.
Price, £0 12 6

PRACTICAL METEOROLOGY,
By John Drew, Ph.D., F.R.A.S.
Price, £0 5 0

HYGROMETRICAL TABLES,
Adapted to the use of the Wet and Dry Bulb Thermometer,
By James Glaisher, Esq., F.R.S.
Price, £0 2 6

TABLES OF THE CORRECTIONS FOR TEMPERATURES,
To reduce observations to the 32° Fahrenheit, for Barometers with brass scales
extending from the cistern to the top of the mercurial column,
By James Glaisher, Esq., F.R.S.
Price, £0 1 0

TABLE OF THE DIURNAL RANGE OF THE BAROMETER,
By James Glaisher, Esq., F.R.S.
Price, £0 0 6

TABLES FOR CALCULATION OF HEIGHTS FROM OBSERVATIONS
ON THE BOILING-POINT OF WATER,
Adapted to the use of Negretti and Zambra’s Boiling-point Apparatus.
Price, £0 1 0

A THERMOMETRICAL TABLE,
ON THE SCALES OF FAHRENHEIT, REAUMUR, AND CENTIGRADE,
By Alfred S. Taylor, Esq., M.D., &c.
Price, in Sheet, with explanatory Pamphlet, £0 1 6

METEOROLOGICAL TABLES,
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of Heights by the Barometer and Boiling-point Thermometer, &c.
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Price, £0 2 6

BAROMETER MANUAL,
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NEGRETTI & ZAMBRA’S
PATENT RECORDING AND DEEP-SEA THERMOMETER.[20]

This Thermometer differs from all other Registering or Recording Thermometers in the following important particulars:—

I. The Thermometer contains only Mercury without any admixture of Alcohol or other fluid.

II. It has no indices or springs, and its indications are by the column of Mercury only.

III. It can be carried in any position, and cannot possibly be put out of order except by actual breakage of the instrument.

And lastly, it will indicate and record the exact temperature at any hour of the day or night, or the exact temperature at any depth of the sea, irrespective of either warm or cold currents, or stratum through which the Thermometer may have to pass in its descent or ascent, this last very special quality renders this Thermometer superior for deep-sea temperatures to any others; for those now being used in the “Challenger” sounding expedition are liable to give erroneous indications owing to their indices slipping, and otherwise getting deranged—(This was proved by Messrs. Negretti and Zambra at a Meeting of the British Meteorological Society,) and under certain conditions of temperature it is not possible by the old Thermometers to obtain true temperatures at certain depths which might be required. Annexed is a copy of a report to the Admiralty from Captain G. S. Nares, of H.M.S. “Challenger,” dated Melbourne, March 25th, 1874, which we have taken from Nature, July 30th, 1874, proving the assertion.

“In the report to the Admiralty of Capt. G. S. Nares, of H.M.S. Challenger dated Melbourne, March 25, 1874, Capt. Nares, speaking of the temperature of the ocean, especially near the pack edge of the ice, says:—‘At a short distance from the pack, the surface water rose to 32°, but at a depth of 40 fathoms we always found the temperature to be 29°; this continued to 300 fathoms, the depth in which most of the icebergs float, after which there is a stratum of slightly warmer water of 33° or 34°. As the thermometers had to pass through these two belts of water before reaching the bottom, the indices registered those temperatures, and it was impossible to obtain the exact temperature of the bottom whilst near the ice, but the observations made in lower latitudes show that it is about 31°. More exact results could not have been obtained even had Mr. Siemens’s apparatus been on board.’ It seems to us that the difficulty mentioned is one which would certainly have been surmounted by Messrs. Negretti and Zambra’s new Recording Thermometers, a description of which appeared in Nature, vol. ix. p. 387; this being exactly one of the cases to which this instrument is peculiarly adapted. We believe the inventors and makers have greatly improved their Thermometer since our description appeared, and no doubt means will be taken by the Admiralty to transmit one to the Challenger.”