55 



The rain-fall was occassionally measured at shorter intervals than 

 24 hours, when it was excessive in amount. Thus, 1-82 inches of the 

 heavy rain-fall of September 27th, 1863, was collected in 12 hours. On 

 September 20th, 1866, 1.24 inches fell in 12 hours. On October 6th, 

 1874, there fell also in 12 hours 1.89 inches. During a thunder-storm 

 on May 20th, 1865, there fell 0.55 inches in twenty minutes. 



The average number of rainy days during the year is (for 15 years) 

 185, or rather more than every other day. By a rainy day is meant a 

 day on which not less than ■— of an inch of rain is collected. In the 

 year 1871 there were only 167 wet days, whilst in 1872 there were 209. 

 These were the two extreme years both as to amount and frequency of 

 rain fall. 



Evaporation. 



It would be very interesting to be able to say how much of the rain 

 which falls in our neighbourhood passes off by evaporation, and how 

 much percolates through the soil or flows off in streams and rivers. 



I made some attempt to ascertain the first of these points, but 

 without much success, owing chiefly to want of time to devote to it. 



The usual form of Evaporating Gauge, or "Evapometer," is a circular 

 shallow metallic vessel. Into this a known quantity of water is placed, 

 and the whole is kept freely exposed to the air. 



It is evident that in summer, the water contained in a vessel of this 

 kind will become unduly heated by the rays of the sun, and consequently 

 too great an amount of evaporation will take place from it : a metallic 

 vessel being a much better conductor of heat than any kind of soil. 



Isaac Fletcher, Esq., F.R.S., of Tam^Bank, has pubHshed in "British 

 Rainfall, 1869," p. 39, the result of his experiments on evaporation, 

 carried on for six years, in a copper vessel ; from which it appears that 

 the evaporation exceeds the rain-fall. This may be quite correct under 

 the given conditions, but it cannot be of any practical or scientific value 

 as a guide to the amount of evaporation that goes on from the surface of 

 the soil or of water. 



In my attempts to elucidate this matter, I adopted a suggestion of 

 Mr. G. J. Symons, and endeavoured to ascertain the evaporation which 



