1837.] 



Meteorological Observations. 



207 



slight rain of one day, if left unregistered, will be entirely lost by eva- 

 poration in the next — nay, that slight and transient showers may never 

 enter it, being evaporated fn>m it as they fall. The effect of copious 

 dew, too, must be separated from that of rain, so that the mere registry 

 of the contents of the gauge is not of itself a sufficient indication whe- 

 ther rain has fallen in the night or not. However, there are usually 

 good reasons for decision on this point from other indications. Atten- 

 tion to the amount of dew is very necessary, not only because the meteo- 

 rological questions involved are of a high degree of interest generally, 

 but because in arid climates the dews are of almost as much importance 

 to the maintenance of vegetation as the rain. 



In stating the quantity of rain daily received in the gauge, the height 

 of the receiver above the soil should be mentioned, experience having 

 shown that the quantities of rain which actually fall on a given area on 

 the ground, and at a very moderate height above it, often differ materi- 

 ally. In some localities and circumstances, the rain-drops receive 

 accession from the air as they descend, in others they undergo partial 

 evaporation. The former is generally the case in cool moist climates — 

 the latter may be expected in this countiy. 



Of the Wind.— The, points most important to remark respecting the 

 wind, are, 



1st, Its average intensity and general direction during the several 

 portions of the day devoted to observation and registry. 



'Idly, The hours of the day or night when it commences to blow from 

 a calm, or subsides into one from a breeze. 



3dly, The hours at which any remarkable changes of its direction 

 take place. 



4thly, The course which it takes in veering, and the quarter in which 

 it ultimately settles. 



5thly, The usual course of periodical winds, or such as remarkably 

 prevail during certain seasons, with the law of their diurnal progress 

 both as to direction and intensity — at what hours and by what degrees 

 they commence, attain their maximum, and subside, and through what 

 points of the compass they run in so doing. 



tithly, The existence of Crossing Currents at different heights in the 

 atmosphere, as indicated by the course of the clouds in different strata. 

 In observing these, it is advisable to fix the eye by some immoveable ob- 

 ject, as some point of a tree or building, the sun, or the moon, otherwise 

 mistakes are apt to arise. 



Ithly, The times of setting-in of remarkably hot or cold winds,— the 

 quarters from which they come, and their courses, as connected with 

 the progressive changes in their temperature. 



Sihly, The connexion of rainy, cloudy, or fair weather, with the quar- 

 ter from which the wind blows or has blown, for some time previous. 



