256
Then began the most appalling thunderstorm within my own experience, or that, I venture to believe, of the majority of the residents in the Colony. For hours flash succeeded flash in rapid succession, and the roll of the thunder was almost uninterrupted, while the rain descended in nasses.
Several buildings were struck by lightning, and six ccolies were killed in a matshed at the Peak. The dam- age to the structure, in the case of the buildings which I have had an opportunity of inspecting, was singularly slight. The storm raged with greatest intensity between the hours of 1 and 5 A.M. of the 30th. The rain that fell during that morning is so exceptional that I give below the result in detail.
inches.
hundredths. 1
Hour ending 12.30 a.M.,
1.30
#
2.30
3.30
77
4.40
>>
5.80
00 00 00 1-O
84
.80
30
20
4 hours 11.90
40
3 hours 9".60
00
6.30
62
91
፡፡
Total in 7 hours,....
16
16
5. After 6 A.M. the storm abated, but rain continued to fall until about 5 P.M., when it ceased. The total rain which fell during the storm from 3 A.M. of the 29th to 5 P.M. of the 30th, a period of 38 hours, was 33.11 inches, and of this quantity the very remarkable fall of 27,44 inches occurred in the 24 hours ending 6.30 A.M. of the 30th (nearly twenty seven and a half inches).
6. Before proceeding further it may be interesting to add that the total rainfall recorded for May was 48.84 inches, and for the six months ended 30th of June 75.45 inches. Comparing this with the records of the five years ending 1888, I find that the annual average is 84.84 inches, of which an average of 35.6 inches fell in the first half of the year, while the maximum monthly fall during these five years was 31.36 inches (in June 1885). It therefore follows that the rainfall of the past half year very nearly equals the average annual rainfall, and is more than double the quantity that fell in the corresponding period in former years, while the quantity that fell in May was one-third greater than that of any previous mouth, during these five years.
7. I have dwelt somewhat at length on this remarkable down-pour because, so far as I am able to ascertain from the limited records accessible to me here, the aggregate rainfall during this storm is without precedent in the case of any storm of equal duration, and it is specially noteworthy that the fall during certain hours, and the maximum for 24 hours, appear (if I may be permitted the expression) to break the record. My authorities are two standard works on Hydraulics, but the data are necessarily imperfect as they do not extend to a later date than 1875. I would call attention however to this very interesting and important subject of enquiry, in the hope that my imperfect comparison may be supplemented (and corrected if necessary) by those who may have leisure for investigation, and access to more recent records. The practical importance of the subject is manifest, since we must depend on the accuracy of the meteorological returns for guidance in designing works of drainage and water supply.
8. I should add that the observations were made at the Observatory at Kowloon, two miles north of the centre of the Victoria rainfall area. It is I think probable that the results may be safely assumed as indicating approximately the rainfall on the main island, but it would be well to bear in mind that the proximity of the steep mountain slopes to the City, render it possible, judging by the records of analogous sites, that the rainfall in the City and on the mountain slopes above, was greater, rather than less, than the rainfall at Kowloon.
9. For the purpose of comparison I will now quote some exceptional rainfalls recorded in other countries. At Nottingham on 13th of August, 1857, 5 inches fell in about 5 hours. During my residence in Cyprus (December, 1880) a flood, disastrous to life and property, occurred at Limassol, where a fall of 5 inches was registered (nearly the whole falling in 4 hours). It is noteworthy that at Kowloon more than double this quantity fell in the same space of time. I can find no record elsewhere of a maximum hourly fall equal to that at Kowloon, viz., 3.4 inches, although it appears that the maximum on 30th May was slightly exceeded by an observation made at the Kowloon Observatory in July, 1886, when 3.48 inches was registered in one hour. Those who carefully observed the storm will, I think, agree with me, that when at its height, the down-pour was not constant for any consi- derable consecutive period, but that for short periods it was exceptionally severe, so that if the fall could have been measured for a limited period of say a quarter, or half an hour, I have little doubt that the result would have been at the rate of fully four inches per hour. In designing works in which it is necessary to provide for a maximum fall, it would in my opinion be unsafe, in the light of recent experience, to calculate on a smaller fall than four inches per hour.