336
Table VI. exhibits the mean rain-fall. The hourly values for January and February are the means of 4 years only. It shows also the hourly intensity, which is greatest about noon, and least about midnight, while the rainfall itself is a maximum shortly after sunrise and a minimum about sunset. Most rain falls in June and least in November. The proportion of rain at the Peak to that at the Observatory is as follows:-January, 1.687, February, 1.322, March, 0.998, April, 1.135, May, 1.125, June, 1.174, July, 1.161, August, 1.192, September, 0.843, October, 0.920, November, 1,507, December, 1.244, Year, 1.141. There falls on an average more rain on top of the Peak, but in September and October, while the rain is chiefly collected during typhoons, there appears to fall less on top of the leak.
Table VII. exhibits the number of hours during portion of which rain was registered. This was six or seven times larger in July than in November. Rain falls more frequently at sunrise than at sunset particularly in summer. The values for the two first months are means of 4 years only.
Table VIII. exhibits the mean wind-velocity. This is greatest in spring when the trade-wind and the easterly monsoon co-operate, and least in August when the southerly monsoon is blowing. At the Peak the wind blows nearly as strong during summer as during winter. The wind is strongest about 1 p.m., and least shortly after sunset. This causes during the hottest months of the year a secondary maximum of temperature shortly after sunset, which is particularly well marked during cloudy weather. In winter, at times when the North-east trade-wind blows strongly, its force is often greatest at night, or during the early morning hours. The diurnal variation for January and February is the mean of four years only.
Table IX. exhibits the mean. wind direction. This veers from ENE in November to S in August and veers daily from the hour of minimum till the hour of maximum temperature. The daily variation is greatest in summer when the wind is light. The diurnal variation for January and February is the mean of four years only.
Table X. exhibits the four yearly means and velocity of winds from different quarters.
(1885-1888 inclusive) of total annual amount, duration
Three quarters of it comes from E and NE.
Table XI. shows that fogs are common in March and occur also during typhoons in August and September. Electric phenomena prevail in August. Unusual visibility of distant objects prevails when the air is frequently cleared from dust by heavy rain in July. Dew is common in August, when also halos and coronas are most frequent. Rainbows- are comparatively rare in hot countries, where the rain is so heavy and the sun usually too high in the sky.
Table XII. shows cumulus to be the cominon cloud in China. Cirrus is most frequent during typhoons and Cumulo-stratus during the hottest part of the year.
Table XIII. shows the amount of clouds. That is greatest in March and least in December. On an average there are more clouds at sunrise than about midnight. But looking at the different seasons, it is seen that in summer the amount is greatest in the afternoon and least about midnight, while in winter the amount is greatest during the early morning hours and least in the afternoon.
Table XIV. exhibits monthly extremes registered at the Observatory. The extreme temperatures are derived from 4 years only (1885-1888). The wind velocity in January and February is derived from the same 4 years. The minimum temperature on grass for July and August is derived from four years (1884-1887) only, and also the solar radiation (1885-1888). The range of vapour tension is seen to be enormous. The daily maximum of rain was exceeded in 1889 when there fell 27.080 inches of rain between 7.30 a. on the 29th May and the same time on the 30th.
Table XV. exhibits the same data for the Peak. The solar and terrestrial radiation extremes are derived from 4 years only (1885-1888). It will be remarked that the minimum thermometer exposed an inch above the grass registered below freezing point. That never occurs at sea-level in Hongkong, but a little farther inland, as at Canton, frost is not unknown.
Table XVI. exhibits various data. The barometric tide is large in winter (when the air is dry) and small in summer (when it is damp). The mean diurnal variability of temperature—the mean of the differences of temperature of each day and the next-is greatest in winter. This as well as the mean maxima and minima temperatures at the Observatory are the means of four years only (1885-1888). The number of days on which at least 0.01 inch of rain fell at the Observatory was a minimum in November and a maximum in June and July. The hourly intensity of rain is greatest in July, and least in February. The directions whence clouds in different levels come together with the wind directions given in Table IX. prove the direction of the wind to veer on ascending in the atmosphere. The height of the lower clouds is least in April and greatest in November.
Table XVII. exhibits the average results of the radiation thermometers and the diurnal range of temperature. The rate at which the temperature falls on ascending in the atmosphere is least in March, when the relative humidity is great and the clouds are low, and greatest in June. The solar radiation at the Observatory is the mean of 4 years (1885-1888) and also for January at the Peak. The diurnal range of temperature at the Observatory is the mean of the same four
years.