Or Draining. 



49 



continues longer ; and as the fall of rain is usually the consequence 

 of such relative differences of temperature in the atmosphere, this 

 again tends to augment the normal moisture of the climate. Thus 

 it may be inferred that the colder locality has to contend with a 

 double disadvantage — on the one side of a feebler evaporating 

 agency, and on the other of a larger amount of moisture to be 

 evaporated. But be this as it may, there can be no reasonable 

 doubt of an increment of rain when we carry the comparison for- 

 ward to this district ; and I do not hesitate to conclude that if a 

 correction were applied to the difference of summer-heat between 

 it and Bedfordshire with reference to this point alone, that differ- 

 ence would amount, at a very moderate allowance, to 10^ in lieu 

 of 8°. 5. 



But, secondly, observe the remarkable diiterence in even a 

 still more important element for our purpose — that of the 

 duration of summer heat. The figures first quoted give the 

 mean temperature of each separate month ; now, taking the 

 point which is conventionally marked on the scale of the ther- 

 mometer as temperate, namely 55^, and comparing it with these 

 statements, you will perceive that at Bedford it begins to exceed 

 that limit in the month of -May, and does not return below it till 

 October, remaining above it for five months. But how different 

 at Derby ! The mean summer temperature there ranges below 

 the same point throughout every month except July, and in that 

 only passes it by a half degree. 



It thus appears, that between these two places there is a differ- 

 ence of at least 8'. o in amouni, and of four months in duration, of 

 summer heat; and I think you will agree with me that this is 

 not likely to be without a sensible effect upon the subject-matter 

 of draining operations, and that it may afford a clue to some of 

 the puzzling results which we have been striving to understand. 



But it must not be forgotten that even this is not all. We 

 took the case of Derby, not for its own sake, but as our own best, 

 though imperfect, representative in this comparison. Its elevation 

 above the sea, as stated in the foregoing table, is 160 feet ; ours 

 is nearer an average of 750. Let us then suppose Derby gently 

 lifted from its smiling vales of Trent and Derwent, to a height 

 of some 550 feet above them, borne off to the northward more 

 than forty miles, and there lodged upon some ridge or slope at 

 the said elevation — would, or could, its climate remain unchanged? 

 And might we not at once conclude that, instead of a deficiency of 

 8°. 5, or even lO'^ in amount of heat, and of four months in its 

 duration, such a site would exhibit a loss of evaporating power, as 

 represented by summer temperature, of not less than Ti"^ or 15^, 

 compared with the wide, level, and lowland expanse of the east, 

 centre, and south of England ? that the mean would probably in 



VOL. XII. E 



