tion in every part of intertropical Western Africa, especially just before and after the rainy seasons.

Howard gives three simple and distinct forms and four intermediate or compound forms or modifications.

PRINCIPAL FORMS.

1. Cirrus consists of filaments, either parallel, flexuous, or diverging, which, by association, form a slender network or woolly hair expansion. They possess the least density, and are very high in the atmosphere, higher than all the other clouds, being more than ten miles. It is regarded as prognostic of wind, and is vulgarly called "mares' tails."

2. Cumulus.-Hemispherical or conical heaps, increasing from an horizontal base resembling a mountain; its structure is exceedingly dense, and may be considered as the "cloud of day," and moves with the current next the earth. Some have compared the cumuli with bales of cotton.

3. Stratus.-A widely-extended, continuous, horizontal sheet, increasing from below upwards, forming often at sunset, and is the lowest of the clouds, having its inferior edge resting on the earth or water. It has a mean degree of density, persistent during night, and disappearing at sunrise.

INTERMEDIATE AND COMPOUND MODIFICATIONS.

1. Cirro-cumulus. - Small, roundish, well-defined masses, in close horizontal arrangement or contact, most frequent during the warm and dry weather. The sky in this condition. is said to be fleecy.

2. Cirro-stratus.-Horizontal or slightly inclined strata or masses, attenuated towards a part or the whole of their circumference, more compact than the cirri, bent downwards or undulated, apparently composed of a number of thin clouds at the zenith, at the horizon, or a long narrow band. This cloud is. almost always followed by a lowering of temperature by wind and rain. This modification exhibits frequently the phenomena

Definition.

Ozonometer.

Mode of preparation.

known as the solar and lunar halo, of parhelia, mock-suns, paraselena, and mock-moons.

3. Cumulo-stratus. The cirro-stratus blended with the cumulus, and either appearing intermixed with the heaps of the latter or superadding a wide-spread structure to its base. The distinct cumulo-stratus indicates the approach of thunderstorms; the indistinct is principally observed in the intervals of showers, rain, snow, or hail.

4. Cumulo-cirro-stratus vel Nimbus.-The rain-cloud. It is a horizontal sheet above which the cirrus spreads, while the cumulus enters it laterally and from beneath. It forms a system of clouds from which rain is falling.

Clouds are masses of visible vapour, or visible collections of minute globules of water in suspension in the atmosphere, placed at considerable distance above the earth's surface; the. ordinary height is sometimes less than a mile, and, according to Professor Leslie, they can never rise beyond two miles above the line of perpetual congelation. Their formation is the result of admixture in the higher regions of the atmospheric strata of air of different degrees of saturation and temperature. OZONOMETER.

The observations were made from papers covered with a composition of iodide of potassium and starch, and exposed to the air.

This ozone paper is easily made by saturating strips of bibulous paper in a mixture made "by boiling one drachm of white starch in an ounce of distilled water for three minutes, in which are to be dissolved, when cold, twelve grains of chemically pure iodide of potassium."

When the paper is exposed to the atmosphere it is turned brown, and when immersed in water, yellow-the degree of intensity of discoloration indicates the amount of ozone. The principle of action is that the ozone oxidises the iodide of potassium, and so disengages the iodine free, which attacks and combines with the starch, forming a coloured compoundthe iodide of starch. The estimation is expressed in numbers,

one being the smallest quantity, and 10 the highest degree of

intensity.

There are both physical and chemical objections in the objections in estimation of ozone, from the following circumstances:*

1. Other substances, such as nitric acid formed during electric storms, act on iodide of potassium as ozone; air containing 00005 of its volume of this acid-coloured starch and iodide. paper.

2. The reaction is effected by light, wind, humidity, and temperature, by expelling the free iodine.

3. Two chemical objections have been made: "Supposing that iodine is set free by ozone, a portion of it is at once changed by additional ozone into iodozone." This substance in ordinary temperature is very volatile, and, in contact with water, is changed into free iodine and iodic acid.

Some portion of the iodine, originally set free, being either volatilised or oxidised, never acts on the starch. Another error might be occasioned by the ozone itself acting on the starch.

The observations were made alone in countries along the sea coast, where it is supposed to be always abundantly produced ; as it is found in large quantities on mountains and elevated localities; over lands covered with luxurious vegetation; over water, and on the sea coast.

its estima

tion.

WEATHER. Generally speaking, the term weather includes Definition of. the condition of the atmosphere which relates to the temperature-humidity, winds, pressure, &c.; but in the following observations I have confined it to the number of wet and dry days.

Barometer. The barometer was first invented by Evangel- Barometer. ista Torricelli, and is so termed from Bagas, weight, and μergov, measure. It is a very important instrument in meteorological observations, but unfortunately my register has been very limited, from an accident which destroyed my instrument.

*Parke's Practical Hygiene. Beitrage zur Ozonometrie, von Dr V. Maach.

Rules for

observation

We subjoin the following from Dr Pickford's Hygiene, as the rules laid down by Dr Halley, John Patrick, M. Cotte, and others, for our guidance in the use of the barometer as a weather-glass. We are, at the same time, to remember that the changes in the weather indicated by the barometer may occur in the upper part only, not extending to or being observable at the earth's surface; that sometimes variations produced by changes in the atmosphere of an adjoining district, and not from changes of wind or weather in the district of observation in the weight of the atmosphere over any given district, may arise :

1. Indications of approaching changes of weather, and especially of the direction and force of winds, depend less on the absolute height of the mercury in the tube than on its falling and rising.

2. A height of 30 inches at the level of the sea is more indicative of settled weather and steady winds than any other height.

3. The barometer is said to be falling when the mercury in the tube is sinking, at which time its upper surface is almost always concave or hollow; the barometer is said to be rising when the mercurial column is lengthening, and its upper surface is convex or rounded.

4. The rising of the mercury presages, in general, fair, and its falling, foul weather, as rain, snow, high winds, and storms.

5. Below 30 inches the probability of rain is in an increased proportion with equal decrements of the mercurial column; above 30 inches the probabilities of fine weather are in a diminishing proportion with equal increments.

6. In calm weather, when the air is inclined to rain, the mercury is commonly low.

7. It sinks lowest in very great winds, though these be unattended with rain.

8. In very hot weather the falling of the mercury forebodes thunder.

9. In winter the rising presages frost; and in frosty weather, if the mercury, which is generally high, fall three or four tenths

of an inch, a thaw will certainly follow; but in a continued frost, if the mercury rise, it will certainly snow.

10. A rapid rise of the barometer indicates the approach of unsettled weather; a slow rise, the reverse.

11. A considerable and rapid fall is a sign of stormy weather, though of short duration, and is usually accompanied with rain.

12. A sudden rise in the barometer during a storm indicates that the worst is over.

13. The greatest depressions of the barometer are accompanied by rain and gales from the south and south-west; the greatest elevations by the north-west, north, and north-east winds.

14. Although the barometer almost always falls with the southerly and rises with a northerly wind, the reverse sometimes occurs, in which case the southerly wind will be dry, and the weather fine, whilst the northerly wind will be wet and violent.

15. When the barometer sinks considerably, high winds, rain, or snow will follow; the wind will be from the northward if the thermometer is low for the season, from the southward if the thermometer is high.

16. If, when the wind is from any point between north-west and north-east, the barometer fall and the thermometer rise, the wind will shift to the south.

17. If, when the wind is from any point between east and south-west, the barometer fall, an increasing gale from that quarter will ensue, which will be of shorter or longer duration according as the fall is rapid or slow.

18. Sudden falls of the barometer, with the wind from west, are frequently followed by violent storms from north-west or north, during which the mercury will rise to its former height.

19. If a gale set in from the east or south-east, and the wind veer by the south, the barometer will continue falling until the wind becomes south-west, when a comparative lull may occur, after which the gale will be renewed, and the veering of the