METEOROLOGY. 



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remaining duration of total darkness after twilight and moonlight, 

 can scarcely exceed three months in the year. The interval towards 

 the close of astronomic or common twilight corresponds to what is 

 commonly termed, in the country, "early candle-light," when the 

 glimmering landscape fades on the sight and the stars hegin to be 

 visible. The end of civil twilight marks the time at which some city 

 corporations in Europe are said to have made regulations for ligliting 

 the street lamps. 



In conclusion, without entering into further details, the connexion 

 of solar heat and light has enabled us to exhibit, by the same formulae 

 and curves, the intensities of bo*li in common. Indeed, so close is 

 the analogy that even the monthly height of the mercurial column, 

 which shows the temperature, indicates generally the average intensity 

 of sunlight in that locality. 



Half days, or Semi-Diurnal Arcs, in the Northern Hemisphere. 



Increase of the Half Day at Sunrise, or Sunset, by Refraction. 



