Sessional_Paper_1886-1887 — Page 279

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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. These observations are generally made every hour during the day and as often as possible during the night.

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.

The

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. 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.

The mean diurnal range in the different months came out as follows: January, 0.111, February, 0.118, March, 0.094, April, 0.087, May, 0.086, June, 0.069, July, 0.067, August, 0.073, September, 0.082, October, 0.091, November, 0.112, December, 0.110. The average range was 0.092 or 0.004 larger than in the two previous years. The mean tension of aqueous vapour was smaller this year than during the previous years, and both these circumstances were no doubt due to the scarcity of rain. The height of the rock on which the look-out at Victoria Peak is placed has been calculated from the mean of the barometric observations made in 1886 to be 1812 feet, and from the mean of all those made during the past three years to be 1813 feet, adopting for the first year the temperatures observed in Stevenson's screen reduced to the true air-temperature, which were as follows: January 1884, 61°.5, February, 56°.7, March, 610.5, April, 660.5, May, 730.4, June, 78°.7, July, 81°.5, August, 81.3, September, 80%.4, October, 76°.6, November, 67°.2, December, 59°.9. Year, 1884, 70°.4.

Table II exhibits the mean temperature in degrees Fahrenheit at the Observatory and at the Peak, the latter being the mean of the 10 a., 10 p., maximum and minimum temperatures, and the excess of the hourly values at the Observatory above the mean. The hottest part of the day is between 1p. and