788 The Outline of Science 



year. If the track is more northerly than usual, and passes to the 

 north of Scotland, the year will be brighter, drier, and warmer 

 than normal, because our Islands will then lie more under the 

 influence of the Atlantic high pressure system, but if the cyclone- 

 track lies more southerly than is its wont we shall have duller, 

 colder, and wetter weather than usual. 



And very often an abnormal season is followed by one of 

 opposite abnormality. The amazing summer of 1911 with its 

 halcyon days was followed by the dull cold summer of 1912; while 

 the very cold December of 1879 over Europe was succeeded by 

 the mild December of 1880; in central Europe the difference of 

 temperature between these two months was over 20 F. It may 

 therefore be said that the chief characteristic of our weather is 

 rapid variability rather than slow periodic change. 



Weather Lore 



A good deal of traditional weather lore is familiar to most 

 people, and part of it, at all events, has some scientific basis. There 

 are certain cloud developments, such as those associated with a 

 depression, and which have been already described, that are really 

 accurate guides to coming changes of weather, and there are many 

 reliable maxims in use by sailors, as for instance: 



If the wind backs against the sun, 

 Trust it not, for back it will run, 



a saying that is quite justified by the behaviour of the wind before 

 a coming cyclone. Such proverbs are based on experience and are 

 capable of scientific explanation. Another adage that "a rainbow 

 in the morning is the shepherd's warning" is also accurate, for it 

 implies that if showers are falling as early as morning-time they 

 are likely to continue most of the day ; and this is very likely to be 

 the case, for the rising air currents that form the shower-clouds are 

 not usually effective enough to cause showers until the afternoon. 

 Therefore, if showers are already falling in the forenoon, they are 



