146 Instructions for Making and Registering 



itself a sufficient indication whether rain has fallen in the night or not. How- 

 eyer, there are usually good reasons for decision on this point from other in- 

 dications. Attention to the amount of dew is very necessary, not only be- 

 cause the meteorological questions involved are of a high degree of interest 

 generally, but because in arid climates the dews are of almost as much im- 

 portance 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 materially. 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 ge- 

 nerally the case in cool moist climates — the latter may be expected in this 

 country. 



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

 are, 



\st, Its average intensity and general direction during the several portions 

 of the day devoted to observation and registry. 



2dly, The hours of the day or night when it commences to blow from a 

 calm, or subsides into one from a breeze. 



3rf/y, The hours at which any remarkable changes of its direction take place. 



Athly, The course which it takes in veering, and the quarter in which it 

 ultimately settles. 



bthly., The usual course of periodical winds, or such as remarkably prevail 

 during certain seasons, with the law of their diurnal progress both as to di- 

 rection 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. 



Sthly^ The existence of Crossing Currents at different heights in the atmo- 

 sphere, as indicated by the course of the clouds in different strata. In observ- 

 ing these, it is advisable to fix the eye by some immoveable object, as some 

 point of a tree or building, the sun, or the moon, other«vise mistakes are apt 

 to arise. 



Tthlt/j The times of setting-in of remarkably hot or cold winds, — the quar- 

 ters from which they come, and their courses, as connected with the progres- 

 sive changes in their temperature. 



8thlp, The connexion of rainy, cloudy, or fair weather, with the quarter 

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



9thly, The usual character of the winds as to moisture on dryness, not as 

 deduced from mere opinion or vague estimation, but from actual observation 

 of the hygrometric state of the atmosphere during their prevalence. 



Among these particulars it will be seen that some are of a nature suscepti- 

 ble of daily observation and registry, while others call for an exercise of the 

 combining and inductive faculty on the observer's part, and cannot be made 

 out otherwise than by continued attention and habitual notice of phenomena 

 with a view to the investigation of their laws. The general impression left 

 upon the mind as to any of the points of this kind above enumerated, by the 

 occurrences of the past month, will therefore be more properly stated, in tlie 

 way of summary remarks at the end of the Monthly Registers, than as en- 

 tries under particular days. 



