788 MR J. Y. BUCHANAN ON THE 



values for each month, with the maximum hourly rainfall during the thirteen years for each 

 hour. Table XII. contains the diurnal variation of the monthly mean hourly values. 



On studying these Tables we note the following facts : — 



In continuous foggy weather there is always some precipitation measured, and it is 

 usually very abundant. There is only one spell of foggy weather in which no 

 precipitation was registered, and that was in January 1897. In continuous clear (not 

 necessarily cloudless) weather it may be said that it never rains at all. The only ex- 

 ception which could be taken to this might be the cases of June and August. In June, 

 in the 2895 selected hours, the total amount of rain measured was 1*243 ins., giving an 

 average of one-hundredth of an inch in twenty-four hours. In August, in the 971 

 selected hours, 0'72 in. fell, giving an average of 0*018 in. per twenty-four hours. The 

 rainless character of continuous clear weather is well shown in Table IX., in which the 

 total amount of rain which fell in eaeh month in each year during clear weather is given. 

 There are only five occasions in the course of the thirteen years when more than one- 

 tenth of an inch of rain fell during the clear weather of any one month, and the chief 

 of these are 0-685 in. in August 1890, and 0*298 and 0*774 in. in June of 1887 and 1893 

 respectively. Two-thirds of the whole rain fell in these five months, the remaining 

 third is distributed over forty months, and 111 months out of the total of 156 have 

 none at all. 



If we now turn to Table X., drawn in the same form for foggy weather, we see a 

 very different state of things. As already pointed out, there is only one spell of foggy 

 weather where no rain or precipitation has been measured. The smallest mean daily 

 rainfall in foggy weather is 0'590 in. in April. The highest daily mean is 1*286 in. 

 in September, and next to it comes February with 1*270 in., and October with 1*163 

 in. April, May, June, July, and August are all under the mean for the year, which 

 is 0*998 in., or almost exactly one inch. When it is remembered that in foggy weather 

 the air is alwa} 7 s saturated, and besides that it has disseminated through it particles of 

 water, which form the fog, on which the vapour can immediately and without resistance 

 condense, and that in summer there is a much larger percentage of water vapour 

 present in the atmosphere than is found in winter, it appears somewhat remarkable that 

 the summer rainfall per foggy day should be so much lower than that of winter. When 

 we turn to the maximum rainfall of any foggy day in each month during the thirteen 

 years, we find these same months below the average again. The absolute maximum for 

 the thirteen years falls on the 3rd October 1890, when 7*287 ins. fell in the twenty-four 

 hours; the next highest value, 6*668 ins., falls on 6th February 1894, and the 

 maximum rainfall on a foggy day is above five inches in December, January, and 

 March. The greatest fall in one hour occurred between fifteen and sixteen hours on 

 ]4th January 1890, when 0*850 in. fell. 



The following short table puts together concisely the results of the rainfall 

 measurements in the two kinds of weather, and shows clearly the great contrast 

 between them in this respect : — 



