18 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



idea of the characteristic vegetation of other regions, humid and dry, and 

 of the results obtained in arid districts by means of irrigation. 



From measurements which have been made of the hourly falls of rain 

 as recorded by self-registering gauges it is possible to find out what are 

 the most rainy hours of the day in many places. The most rainy hours 

 are in the morning, somewhere near 6 a.m., and there are indications 

 of a second maximum in the afternoon, the driest part of the day being 

 about noon. The quantity of rain measured in each hour is also greatest 

 in the morning, except at Kew, at which place the afternoon hours get 

 the largest falls. 



I have already mentioned the limitations of the part played by the 

 meteorologist in dealing with the supply of water, and pointed out that it 

 is the botanical physicist who has to deal with the effect of the supply upon 

 plant life. But there is one important point bearing upon those effects 

 to which I should like to call attention, and that is the relation which 

 Dr. Shaw, the director of the Meteorological Office, has found to exist 

 between the amount of rainfall in the autumn and the yield of wheat in 

 the succeeding harvest ; and he has deduced a formula by which he can 

 calculate the probable character of the ensuing harvest from the amount 

 of rainfall, and he finds that the calculated amounts for the same district 

 compared with the actual yield per acre each year are remarkably similar. 



1 have not the time left to say anything about snow T or hail, except to 

 mention that the first is formed of minute particles of frozen vapour in 

 hexagonal crystals, adhering to one another and forming flakes of beauti- 

 ful form. It only falls in cold weather, whilst hail, on the other hand, 

 seldom falls in winter but generally in the hot weather, and frequently 

 in connection with thunderstorms. The cause of the formation of hail is 

 not very well known, but it is most probably due to the sudden chilling of 

 vapour which has already been condensed into water and which by a 

 sudden further fall of temperature becomes frozen into pellets of ice. It 

 is not necessary to remind a gathering of horticulturists that sometimes 

 hailstorms may be productive of much damage to crops and to gardens. 



I said just now that we in this country are much favoured in the 

 matter of rain. At times, however, we get more than we appreciate, and 

 those who dwell by the sides of rivers have sometimes ample reason for 

 an appearance of ingratitude. A rainfall of less than about 18 inches 

 per annum is probably too small for the requirements of agriculture 

 without the aid of irrigation, and an excessive rainfall is doubtless less 

 hurtful to vegetation than a deficient one. 



But occasionally long-continued wet weather combined with modern 

 methods of draining land leads to heavy Hoods, the rivers receiving more 

 water than they can readily carry away, and it is quite easy to understand 

 how dwellers by their banks should fail to consider rain an unmixed blessing. 



During one Hood, in 181)4, the gauging at Teddington Lock showed 

 that the quantity of water which passed over the weir in one day was 

 lifteen times tho normal quantity, and amounted to twenty thousand one 

 hundred and thirty-five and a quarter million gallons. Well, that is a 

 quantity which the mind ennnot grasp. But 1 have calculated that if the 

 entire surface of Middlesex were enclosed with a wall H feet high the 

 excess of water passing over the weir in that one day would have sufficed 



