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310 



METEOROLOGY. 



[Sect. IX. 



Sec 



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courses, as connected with the progressive chancres in 

 their tcinperature. 



8thly. The connexion of rainy, cloudy, or f^iir weather 

 with the qnarter from which the wind blows, or has 

 blown for some time previously. 



Several of these points of inquiry have especial refer- 

 ence to land winds, and can only be duly studied in port 

 or during residences on shore. In cruises along shore, 

 or on arrival or depnrture, observe how far the influence 

 of the land extends, and by what gradations the character 

 of the winds changes from terrestrial to oceanic, especially 

 with reference to the difference between the hours when 

 the sun is above and when belov/ the horizon. 



Clouds and Fogs.~ThQ dissipation of cloud under the 

 apparent influence of the full moon is a point to which 

 attention has lately been called ; the state of the sky on 

 the days and nights of the full moon, and those imme- 

 diately preceding and following it, should be noted with a 

 view to confirming or renting this connexion. Hourly 

 observations, commencing before sunset, of the relative 

 proportion of clear and clouded sky would be desirable. 



The height of the vapour plane is a datum of impor- 

 tance, especially in tropical regions. At sea it is not easy 

 o determine ; but when near a mountainous coast, where 

 the clouds repose at definite levels on the hills, many 

 opportunities may occur to ascertain it with precision. 

 The lower level of unmelted snow may in such localities 

 also be made a subject o+' inquiry. The average height 

 of the vapour plane at sea under the equator is a mete- 

 orological element of much interest. Opportunities cf 

 determining it by measuring the apparent altitude of the 





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