Mr Marshall on the Ver?ial Winds'. 



Art. VI. — On the probable came of the North-East Winds 

 which occur in the Spring in most parts of Great Britain. 

 By Mr Samuel Marshall. Communicated by the Au- 

 thor in a Letter to the Editor. 



Phe winds of the torrid zone mostly blow in the same direc- 

 tion, or in opposite directions in stated periods, but this is not 

 the case in the temperate zones. Here the direction of the 

 wind perpetually varies, and " as fickle as the wind"" is prover- 

 bial in this country. The evident irregularity of the winds 

 has long perplexed philosophers to assign an adequate cause 

 for such variations, and perhaps little more can be advanced 

 to this day than the very general conclusion, that " partial 

 changes of temperature are the chief general causes of all 

 winds.''^ 



In the torrid zone, whilst the barometer seldom varies but 

 in a trifling degree in the temperate zone, it is not less fickle 

 than the wind. This indication of a loss of weight in the at- 

 mosphere can arise only from a local diminution of elasticity 

 in this fluid. 



On this general ground, therefore, I conceive may be ex- 

 plained the cause of the only periodical wind which we have 

 in this island, I mean that from the north-east, which prevails 

 generally from about the middle of April to the 7th or 8th of 

 May, and sometimes longer; as for instance in the present 

 year it prevailed- till the 18th, which is later by several days 

 than is generally the case. 



In Sweden and Norway the face of the country is covered 

 with snow to the middle of May or longer. This frozen co- 

 vering, which has been formed during winter, grows gradually 

 shallower to the 15th or 16th of May, or until the sun has ac- 

 quired 17° or 18° of north declination; while, on the other 

 hand, the valleys and mountains of England have received an 

 accession of temperature of 24° or 25°. On this account, 

 when the temperature of Sweden and Norway is cooled down 

 by snow of 32°, that of Britain is 24° or 25° higher than that 

 of the preceding countries. Because, while tbe ground is co- 

 vered with snow, the rays of the sun are incapable of heating 



