Sessional_Paper_1885-1886 — Page 185

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At Stone Cutters' Island the rim of the rain-gauge is 8 inches in diameter and is placed 2 feet 4 inches above the ground and about 15 feet above Sea Level.

The Monthly Weather Reports are arranged as follows:-

Table I exhibits the hourly readings of the barometer reduced to 32°.0 Fahrenheit, but not to sea level, as measured (at two minutes to the hour named) from the barograms.

Table II exhibits the hourly readings of the temperature of the air round the Observatory as determined by aid of the rotating dry bulb thermometer and the thermograms (at two minutes past the hour named), and also the extreme temperatures during the day.

Table III exhibits the hourly readings of the temperature of evaporation round the observatory as determined by aid of the rotating damp bulb thermometer and the thermograms (at two minutes past the hour named), and also the solar radiation maximum (black bulb) and terrestrial radiation (grass- minimum) temperatures, read at 10 p. and entered for the same day.

The thermometers are rotated round a nearly horizontal axis (which is kept about 4 feet above the ground) the observer generally walking along facing the wind, so that the bulbs describe screws of small pitch. The diameter of the screw described by the damp is larger than that described by the dry bulb.

Table IV exhibits the mean relative humidity in percentage of saturation (the humidity of air saturated with moisture being 100) and mean tension of aqueous vapour present in the air expressed in inches of mercury, for every hour in the day and for every day in the month, calculated by aid of Blanford's tables from the data exhibited in Tables II and III.

Table V exhibits the duration of sun-shine expressed in hours as registered by aid of the sun-shine recorder from half an hour before to half an hour after the hour (true time) named.

Table VI exhibits the amount of rain expressed in inches registered from half an hour before to half an hour after the hour named.

Table VII exhibits, for every hour in the day, the velocity of the wind and its direction in numbers (8=E, 16=S, 24-W, 32-N) as measured from the anemograms. The velocity is the number of miles traversed by the wind, from half an hour before to half an hour after the hour named. The direction is read off at the hour, except when the wind is very light and changeable, when the average direction during the hour is estimated, taking into account the velocity from different quarters. The direction is not noted when the velocity is below 1.5 miles an hour.

Table VIII exhibits, for every hour in the day, the mean velocity of the wind reduced to 4 and also to 2 directions, as well as the mean direction of the wind :

The number of miles traversed by winds from directions 31, 32 and 1 and half the number of miles from 30 and 2 are termed (N). The number of miles from 3, 4 and 5 and half the number of miles from 2 and 6 are termed (NE), etc. We have then :-

N~(N) + (NE) cos 45° + (NW) cos 45°. E=(E)+(NE) cos 45° + (SE) cos 45°.

etc.

which are the components exhibited in this table.

Table IX exhibits the direction (to two points) and force (0-12) of the wind at Victoria Peak, and sea disturbance (0-9) at Cape d'Aguilar.

Table X exhibits the readings of the barometer reduced to 32°.0 Fahrenheit, but not to sea level, and of the thermometers at Victoria Peak.

Table XI exhibits the relative humidity and tension of vapour at 10 a, 4 p. and 10 p. daily at the Observatory and at Victoria Peak.

Table XII exhibits the amount (0-10), name and direction whence coming, of the clouds. Where the names of upper and lower clouds are given, but only one direction, this refers to the lower clouds. Table XIII exhibits the amount of rain measured at 10 a. and entered to preceding day at different stations and the duration of precipitation at the Observatory.

The following Annual Report is arranged as follows:-

Table I exhibits the mean height of the barometer at the Observatory and at the Peak expressed in inches, the latter being the mean of the 10 a., 4 p. and 10 p. observations, and the excess of the hourly values at the Observatory above the mean.

At 4 a. the barometer begins to rise. It is at the time comparatively lower in spring, when the atmosphere is nearly saturated with moisture, than later in the year. It attains its mean height about 6 a., perhaps a little later in spring than in autuinn and winter. At 10 a. the height attains its forenoon