N THE CURRENTS OF THE ATLANTIC. 403 



in any order or regularity. The most remarkable of these 

 groups is that of the years 1809-1817, comprising no fewer than 

 nine years in which the temperature was below the mean. The 

 average price of wheat in these years was 95.$. the quarter, the 

 ordinary average being 70s. ; while in the years 1811 and 1812, 

 it reached 122s. The total deficiency of summer temperature in 

 these nine years amounted to twenty-three degrees. 



I need not remind you of the incidental confirmation of this 

 law of groups, in the account which we have in Grenesis of the 

 seven years of famine, following seven years of abundance, in Egypt 

 and Syria. Our own recent experience at home has instructed us, 

 that years of deficient harvest come in succession. But I wish 

 particularly to point out, that this recurrence of bad years by no 

 means justifies the conclusion which some have drawn from it 

 namely, that our climate has changed, or was changing, for the 

 worse. On the contrary, we learn from observation that such 

 unpropitious years are not likely to occur more frequently than 

 three or four in succession ; and that they will probably be suc- 

 ceeded, at some future time, by three or four years of an opposite 

 character. 



Now when these years of low summer temperature are ex- 

 amined, with reference to the price of wheat, it is found that they 

 are, with few exceptions, years of scarcity and high prices. A de- 

 ficiency of temperature, amounting only to 2, is most injurious to 

 the wheat harvest in England ; while a deficiency of 3 is almost 

 destructive. The reverse is the case when the summer tempera- 

 ture exceeds the average by the same amounts. 



This result is of considerable importance. The lowest summer 

 temperature at which wheat can be successfully cultivated in Eng- 

 land, is only 2 below the mean ; and, as the mean summer tem- 

 perature of England is 60, it follows that the minimum for wheat 

 is 58. This minimum, however, is not absolute. It varies a 

 little with the soil, and other circumstances ; and thus it is, that 

 we find the culture of wheat in Scotland extended as far as Inver- 

 ness, where the mean summer temperature is only 57. 



Now taking this lower limit as the most favourable, let us see 

 what we are to learn from it in Ireland. In this island, the mean 

 temperature of the three Bummer months is 58 ; and, accordingly, 

 for places about the centre of Ireland, a deficiency of a */;///' tl^ir,-.- 

 of summer temperature brings us to the very limit of wheat culti- 



