BAIN.] 



METEOROLOGY. 



1143 



And again, as in Fig. 50, it is demonstrated that the 

 observer at A will see clouds which are quite invisible 

 to another observer at B. 



RAIN. When, from any cause, cloud- vesicles aggregate 



into drops, and these drops fall, the result is rain. Some 



M ago, Mr. Green, the aeronaut, stated that rain only 



fell when the cloud producing it was covered by another 



lloating directly over it This seems to be confirmed by 



Mr. Glaisher, during his balloon asceutsof 18C2-'G3. Still, 



the phenomenon of rain without clouds is well attested. 



Fig. 50. 



amount of r.uu \MncU i.\lU i-i ii:i/.nu;,.'d by A 

 jiluviametor, or rain-gauge. The principles on which 

 'nunent is founded are of the simplest kind. If, 

 for example, a cup or basin, of known cubic capacity 

 and known orifice, be exposed go that it may receive the 

 fallen drops of rain, the cup or basin would be a rough 

 rain-gauge. Were it not that tho collected water thus 

 exposed would be continually evaporating, thus ap- 

 parently diminishing the total fall of rain, no better rain- 

 gauge need be desired ; but in practice it is necessary to 

 provide against such evaporation ; and it is usually ac- 

 complished by forming nn instrument of such construc- 

 tion, that one part may be destined to collect the fallen 

 rain, and another part to diminish, within the smallest 

 limits, tlic amount of evaporation. In expressing the 

 amount of rain which falls at any particular spot, it is 

 necessary to express the height also at which the obser- 

 vation is made. The annual fall of rain increases as land 

 acquires elevation ; nevertheless, at one and the same 

 place, the amount of rain decreases with elevation, for 

 the reason that each drop of rain throughout its descent 

 goes on collecting moisture, and becomes larger. Dalton 

 appears to have been the first to notice this fact. He 

 proved, on comparing two sets of observations one set 

 made at the base, tho other at the summit, of a high 

 tower that the amount of rain at the top to that at 

 the bottom was as two to three. Similar observations 

 made at the Paris Observatory have led to similar re- 

 sults. This variation between the amount of rain at 

 different elevations in one locality, is the more consider- 

 able as the point of aerial saturation is more nearly at- 

 tained ; for which reason, it is less in summer than in 

 winter. The heaviest rains usually occur in the tropics, 

 and during the hot season. There the fall of rain is 

 ions, sometimes amounting to an inch per hour ; 

 nay, Humbpldt has related, that in South America, no 

 less than five inches of rain fell in one hour. In these J 

 islands, we can hardly say that any one season m< 

 the designation of the rainy season ; but in tropical re- 

 gions, except the belt of calm-*, and in the sub-tropical 

 . the separation between the dry and rainy seasons 

 is well marked. In the continental i">i lions of the tor- 

 rid <nu, the rainy season sets in when the summer heat 

 attains its maximum, and continues during four or five 

 months, the atmosphere being clear and bright ti 

 out the nBUUUng portion of the year. Near the equator 

 there are two wet seasons, sometimes separated from 

 each other by a totally rainless period ; but at other time* 



demarcated only by periods of maximum and minimum 

 fall of rain. Dutch Guiana furnishes the well-known 

 illustration of a country having two well-marked rainy 

 seasons ; one, and that the chief, commences in April, 

 and lasts till June ; the other, or minor rainy season, 

 commencing in the middle of December, lasts till the 

 middle of February. The drops of tropical rain attain 

 a magnitude never seen in the tamer showers of these 

 northern regions ; their weight is so considerable, and 

 the force with which they descend so great, that their 

 splash or stroke leaves a smarting sensation on the 

 skin. The region situated between the influence 

 of the two trade winds, and commonly known as 

 the region of calms, is devoid of periodic rains, 

 although the fall of rain there is frequent and 

 heavy. 



H'linlesa Portions of the Earth. There are somo 

 localities in which rain never occurs : for example, 

 K_;vpt, the Desert of Sahara, .the table-lands of 

 Persia and Mongolia, the rocky flat of Arabia 

 Petraa, Arc. Bain is generally the most abundant 

 near mountain ranges ; but there are exceptions, 

 one of the most remarkable of which is presented 

 by the part of Spain south of the Sierra Nevada. 



Condition of Europe with regard to .Ruin. 

 Europe, considered in relation to the prevalence 

 of rain, admits of beingdivided into three districts 

 the South European, the Middle European, and the 

 Swedish. In Portugal, and the larger portion of 

 it hern and central Spain, there is an almost 

 il absence of rain during summer; but north 

 o/ tLe Pyrenees, rain occurs at variable times through- 

 out the whole year. All the portions of Europe, 

 north of the Alps and Pyrenees, are subject to the 

 Middle European and the Swedish pluvial conditions. 

 The characteristic of the Middle European climate, aa 

 regards rain, is, that the latter chiefly occurs during 

 westerly winds ; whereas the Swedish climate is charac- 

 terised by the prevalence of rain during both easterly 

 winds and westerly winds, which bring rain to the whole 

 of Central Europe, and deluge our isles with wet, leaving 

 the bulk of their moisture by the mountainous Scandi- 

 navian range, which separates Norway from Sweden. 

 St. Petersburg and Moscow cannot be said to belong 

 either to the Central or Northern European climate ; 

 these places lie on the confines of both ; hence neither 

 westerly nor easterly winds are there prevalent. In 

 England, the maximum number of rainy days through- 

 Out the year occurs in Cornwall and Devonshire ; passing 

 thence east into Central Europe, the total number of 

 rainy days per annum continually declines. If we as- 

 sume the annual amount of rain which falls at St. 

 Petersburg to be nearly three, the corresponding annual 

 amount for the West of England will be 2'1 ;* in Cen- 

 tral England, 1'4; in Central Germany, 1'2. This 

 statement assumes an average of some special localities 

 to have been taken into consideration : special places 

 present many deviations. In describing any place as 

 subject to rain, or rainy, distinction must be made be- 

 tween the actual quantity of rain per annum which falls, 

 and the total average number of rainy days. Under- 

 standing by the latter term every day on which rain, 

 much or little, falls, the number of rainy days increases 

 in Europe from south to north. The mean average for 

 Southern Europe may be taken as 120, in Central 

 Europe as 146, and in Northern Europe as 180. The 

 following statement indicates the total number of rainy 

 days per aunum for a few places specifically named : 



Buda 312 Ratisbon .... 115 



Warsaw .... 138 Rotterdam. ... 137 



Germany, average of 150 Paris 100 



Carlsiuho .... 174 Poictiers .... 99 



Tagernsee . . . . 170 St. Petersburg . . 108 



Munich 149 Moscow 205 



Stuttgardt .... 12? 



Annual Distribution of Bain. The time of year at 



The position of our Western Coasts, in reference to the Gulf Stream, 

 WUKU wuhci them, must be borne in iuM.Lu. 



