74 Rainfall, Natural Drainage, 



Mean 

 of 14 Years. 

 Years. Inches. Inches. 



1829—1835. Mean rainfall 24-3 



1836—184:2 

 1843—1849 

 1850—1856 

 1857—1863 



t-3 \ o 



24-1 S 

 23-8 ( 

 23-7 } 



4-7 

 24'G 



24- 



It will be observed that the means of the fourteen years, taken 

 at intervals of seven years, are singularly regular, decreasing 

 each period without exception, though by a small amount. As 

 the years 1864 and 1865 have been particularly dry, it is evident 

 that no alteration in the way of increase of the averages can l)e 

 looked for at present. 



I do not think it can be necessary to carry the tabulation of 

 the Greenwich rainfall any further. It seems to me fully proved 

 that there has been during the past fifty years a diminution in 

 the quantity of rain, at least in the south-east of England, and 

 in the neighbourhood of the metropolis. I think also it is proved 

 that this diminution has been on the whole gradual ; wet years, 

 as usual, alternating with dry years, but the wet years not gene- 

 rally so wet, and the dry years generally drier as time has 

 advanced. The form of the curve, though extremely zigzag, 

 seems to indicate this, and the calculations of averages extending 

 over several years unquestionablv points to this as the general 

 rule. The period of fifty years, though not very considerable, is 

 sufficient both to yield an average and also to justify a deduction, 

 especially when this deduction is in conformity with the observa- 

 tions both personal and recorded of those who have paid attention 

 to the subject. The locality is also not unfavourably placed. 



It is important to observe that this difference in the rainfall 

 corresponds with, and is accompanied by, an apparent change 

 both in the mean temperature and the distribution of the tem- 

 perature in England. Mr. Glaisher has established the fact that, 

 within the last hundred years the mean annual temperature has 

 risen 2° Fahr. During that time the winter months have become 

 much warmer in proportion, and the summer months not cooler. 

 Thus the January temperature has increased as much as 3°. 

 Such an alteration alone inay be regarded as sufficient to produce 

 a change of climate in many important respects, both in the 

 rainfall and in the fitness of England now for the favourable 

 production of many plants not before grown. The increased 

 temperature would naturally tend to diminish the rainfall, other 

 things remaining the same. 



