viii 



INTRODUCTION. 



On the distribution of Temperatures. A study of the iso- 

 therms of English winters and the distribution of corresponding 

 barometrical pressures, show that low temps, are due to radiation. 

 The isotherms of 30° and 20° usually run very nearly parallel to 

 the coast, while those of lower temps, are generally surrounding 

 isolated "patches" or "spots" which are included within the 

 former. A comparison of such positions with the physical features 

 of the land clearly shows how the form of these isolated areas cor- 

 respond with the more elevated tracts. Thus a "spot" appeared 

 on Dec. 3rd, 4th and 11th, 1879, immediately South of Edinburgh 

 with temps., 0°, -10°, and 10°, respectively, over the high land 

 between Lammermuir and Cheviot hills. It occurred again in the 

 winter of 1880-81. As an example of a "patch " may be mentioned 

 one on Jan. 14th, 1881, extending from Chester to Milford Haven 

 and to Berks. This includes the high land of Wales, bounded on 

 the East by the Clen and Lickey Hills, and corresponds with the 

 Cotswold hills and the table land which extends Eastwards. 



The close correspondence of higher isotherms (20° and 30°) with 

 the coast line points to the ameliorating influence of the proximity 

 to the sea, as vapour tends to arrest radiant heat ; whereas it more 

 readily escapes from land, where the temp, of the air is correspond- 

 ingly lowered by radiation. Thus, the more inland and elevated 

 regions are, other things being equal, more subject to low temps, 

 than maritime. 



When, however, we investigate the causes of locally low temps., in 

 contradistinction to those of more extended areas, we find the con- 

 verse to hold true ; that is to say, the temp, in a valley will be often 

 many degrees colder than that on the adjacent land, say from 100 

 to 200 ft. higher. Gilbert White was the first person who noticed 

 this fact in the severe winter of 1784, when his thermometer fell to 

 -1° on Dec. 10th ; whereas at Newton at an elevation of " two 

 hundred feet or more," it only fell to 17°; and as a consequence he 

 says, " All my Laurustines, Bays, Ilexes, Arbutuses, Cypresses, and 

 even my Portugal Laurels, and what occasions more regret, my fine 

 sloping Laurel hedge were scorf ched up ; while at Newton the same 

 trees have not lost a leaf." Numerous instances are recorded in the 

 following reports, and M. Duchartre records similar facts in France.* 



* Jovrnal de la Soc. Nat. et cent. d y Horticulture de Fr. f 3 Ser. Tom. ii. (Nov. 

 1880), p. 678; Tom. iii. F6v. 1881. p. 89. 



