3S4 Instructions for Making and Reyistering 



dryness, not as deduced from mere opinion or vague estimation, 

 but from actual obsiirvation of the hygroraetic slate of the 

 atmosphere during their prevalence. 



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

 nntuie su.scej)tibie oF daily obseivation and registry, while 

 others call tor an exercise of the combining and inductive 

 faculiy on the observer's part, and cannot be made out other- 

 wise than by continued attention and habitual notice of 

 phsenomena with a view to the investigation of their laws. 

 The general impression left upon tlie mind as to any of the 

 points of this kind above enumerated, by tlie occurrences of the 

 past month, will tlicrefore be more properly stated, in the way 

 of summary remarks at the end of the MonthU' Kegisiers, than 

 as entries under particular days. 



Of the state of the Shy- 



In describing the state of the sky as to clouds, &c. the ob- 

 server will bear in mind tbat it is only in that region of rhe sky 

 wliich is vertically above liim that the true forms and outlines 

 of the clouds are exhibited, and the area they cover, as well as 

 the intervals between them distinctly seen. As they approach 

 the horizon in any direclion, tlieir extent is foreshortened by 

 perspective, their apparent magnitude diminished by distance, 

 and their intervals covered in and hidden by their mutual inter- 

 position. In estimating therefore tlie quantity of clouds in tlie 

 sky, regard must be had to this, and our judgment should 

 ratlier be formed on a view of the region extending from the 

 zenith everyway half way down to the horizon, than from the 

 aspect of the heavens below that limit. It would be belter to 

 notice both, and state, separately, the proportions in which 

 each are covered, and the quarter of the horizon towards which 

 the chief masses in the lower region lie. 



The general aspect of Clouds, as classed under the heads 

 Cumulus, Cirrus, Stratus, &c. should be noticed, and especially 

 the height of their inferior surfaces, or the level of the vnpour 

 pl'ine, should be estimated. In a mountainous region this is 

 easy, so long as the vapour plane is below or not far above the 

 summits of the hills, and in such regions the foimation and 

 dissipation of cloud in the neighbourhood of the mountain sum- 

 mits, under the influence of certain winds, form a subject of 

 study of a highly curious and interesting nature. 



The formation of Clouds at night, during calm weather, 

 tinder tiie influence of a gradually descending temperature, is 

 auothcr point worthy of attention. It frequently happens, that, 

 ■without any perceptible wind, the sky will suddenly become 

 ha/.f in some one point, and the haze condensing and spreading, 



