1883.] on Weather Knoidedge in 1883. 327 



various portious of these islands are variously circumstanced as 

 regards proximity to the sea, and as to the mountainous or flat 

 character of their surface, an attemjDt has been made to group the 

 counties together into a series of districts, the boundaries of which are 

 determined by the general character of the agriculture most developed 

 within them. Thus the western districts are mainly grass producing, 

 while the eastern are corn producing. 



This division is necessarily more or less of an arbitrary nature, 

 as the separation between a grazing and an arable region is not a 

 hard and fast line, and of course a driving shower does not cease to 

 fall on crossing a county boundary. But supposing a forecast is 

 drawn up for any one district, it is necessarily limited by the 

 exigencies of telegraphy to a very few words, and it is simply 

 impossible to frame it so as to be correct for the whole of the 

 district. If there is a range of hills crossing the country, the wind 

 which produces rain on the weather slope of the ridge brings dry 

 weather to its lee side. This is a consequence of the well-known 

 principle, that air forced to rise over an obstacle like a hill, is cooled 

 at the rate of about 1° F. for every 300 feet, and is also expanded 

 by the pressure on it being reduced. Both of these actions reduce its 

 capacity for containing moisture in the state of vapour, and rain is 

 produced as the air ascends. Once it has crossed the ridge the 

 reverse action takes place, the air is heated and compressed by 

 descent. It thus becomes capable of containing more moisture, and 

 is felt as a warm and dry wind. 



To give an instance of this action on a somewhat large scale, I 

 may cite the district of Elgin and Nairnshire, on the south coast of 

 the Moray Firth. This comparatively flat area is bounded on the 

 south and south-east by the Grampians, and on the west by the hills 

 of Inverness-shire and Eoss-shire, and all the air from the south and 

 west has had to travel up a series of successiTC hill sides on its 

 passage from the Atlantic. The result is, that the region I have 

 named has a rainfall not more than one half that of the upper valleys 

 of the Grampians, and yet it is situated in the same district for fore- 

 casting. Such is the exceptionally dry character of this strip of 

 coast, that one summer a friend of mine who has a fishing on the 

 Spey told me that for some weeks w^hile the river was in spate, 

 showing that rain fell on the hills, and the fishermen out in the Firth 

 had rain almost every night, not a drop fell at Nairn 



My hearers will therefore perceive that the same wording will 

 not suit a whole district, unless it be judiciously phrased so as to 

 bear more than one interpretation. 



The figures which I give in Table I. are obtained in a very 

 general way ; the forecast for the district is tested by as many reports 

 from that district as are available. This mode, therefore, gives a 

 iiigher figure for correctness than would be obtained by testing them 

 for a single place. 



The second series of figures, in Table II. however, are obtained by 



