20S 



Instructions for Making and Registering 



dthh/, The usual character of the winds as to moisture or dryness, 

 not as deduced from mere opinion or vague estimation, but from actual 

 observation of the hygrometric state of the 'atmosphere during their pre- 

 valence. 



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

 ceptible of daily observation and registry, while others call for an exer- 

 cise 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 the way of summary remarks at 

 the end of the Monthly Registers, than as entries under particular days. 



Of the State of the Ski/. — In describing the state of the sky as to 

 clouds, &c. the observer will bear in mind that it is only in that region 

 of the sky which is vertically above him that the true forms and outlines 

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

 tervals between them distinctly seen. As they approach the horizon in 

 any direction, their extent is foreshortened by perspective, their appa- 

 rent magnitude diminished by distance, and their intervals covered in 

 and hidden by their mutual interposition. In estimating therefore the 

 quantity of clouds in the sky, regard must be had to this, and our judg- 

 ment should rather be formed on a view of th'^ region extending from 

 the zenith every way half way down to the horizon, that fr<3m the aspect 

 of the heavens below that limit. It would be better 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 this 

 inferior surface, or the level of the vapour plane, should be estimated. 

 In a mountainous region this is easy, so long as the vapour plane is be- 

 low or not far above the summits of the hills, and in such regions the 

 formation and dissipation of cloud in the neighbourhood of the moun- 

 tain summits, 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, under the in- 

 fluence of a gradually descending temperature, is another point worthy 

 of attention. It frequently happens, that, without any perceptible wind, 

 the sky will suddenly become hazy in some one point, and the haze 

 condensing and spreading, in all directions, without a wind, the whole 

 heaven will become overcast in a remarkably short time. The same 

 thing will sometimes occur nearly at the same hour for many nights in 

 succession. Such phenomena should be noted whenever they occur. 



