U4I 



METEOROLOGY. 



which rain is most prevalent, U subject to much vnria- 



,t countries. Throughout Central K' 

 are most r ; but in Southern 



a the Mile of winter rains/ 



iy i.< subject to copious wiutor rains ; whilst in 



Sweden they are almost entirely wanting. Sweden, in 



fact, although placed to near the sea, has 



a climate altoj," ' prevalent in continental 



:i The reason why Norway is subject to winter 



ruins, ami Sweden is deprived of tho same, hinges upon 



\;. lanation already made, that western winds (which 



predominate in Scandinavia during winter; lose their 



lire in passing over the Scandinavian range. Al- 



h summer rains are in many places rare, yet when 



iln-y nro generally more copious than rains at 



any other i>eriod. 



il.iin which falls in summer at different places, taking 

 the rain which falls on a winter's day at the correspond- 

 ing place as unity is in, 



land 1-07 



Western France .... 1 03 

 Central France .... 1 ">7 



lany 176 



1'etersburg . . . . 2 '17 

 From which Matt-incut it appears that the prevalence of 

 summer rain increase* towards the cast. 



PeeutiaritittcfBai*-Walr, PtMh-faQing rain-water, 

 collected far from towns or other sources of local con- 

 tamination, is very nearly pure ; nevertheless, modern 

 chemical observation has succeeded in discoverin 

 presence of many substances, in small quantities. Nitric 

 acid and nitrate of ammonia are by no means unusual 

 constituents ; and iodine has been frequently recognised. 

 As regards the sources of these and other extraneous 

 In-dii-s, much Rtill remains to be discovered. Nitric acid 

 is most probably formed in the atmosphere by the 

 agency of electricity ; aud the ammonia may be referable 

 MIS from decomposing matters on the earth's 

 surface. Many of the extraneous bodies, especially salts, 

 are unquestionably due to the action of winds upon 

 finely-divided ocean spray. 



icert of Fishes, Stoiies, <tc. Instances are on record 

 of whole shoals of fishes, and numerous collections of 

 other animals also stones, <tc. being cast on the earth 

 by showers. At one time these phenomena were regarded 

 riously, and referred to occult causes. At present 

 they are deprived of their mystery, and referred to the 

 previous elevation of the. fishes, etc., by aerial currents, 

 whirlwinds, and water-spouts. 



SNOW. If tho temperature of a cloud should fall at 

 any time to 32 F., or lower, instead of rain the result 

 is snow. Much that is beautiful and beneficent is seen 

 in this divided form of frozen water. In our own tem- 

 j>orat clime we do not comprehend, except by reflection, 

 the true value of snow in the economy of nature. Its 

 fall amongr-t us is uncertain and exceptional ; wo know 

 not when it is to come, or how long it is to remain. We 

 therefore make no provision for it regard it as a con- 

 dition to be tolerated regret that it interferes with our 

 locomotion that it impedes our railway trains, and wets 

 our feet, and wish it away. Nevertheless, even in these 

 isles, the farmer, from experience, is not insensible to the 

 value of snow. He says it keeps his winter crops warm ; 

 and the thoughtless passer-by, wrapped in his own self- 

 conceit, l.iu /li-i at lnin for making a statement so appa- 

 rently grotesque. The philosopher, however, who is 

 aware of tho low heat-conducting power of snow, and 

 who can appreciate tho evil consequences of frost on 

 vegetation, indorses the farmer's statement. 



If we would desire to recognise tho full benefits of 

 snow, we must direct our attention to northern climes 

 M-d.-ii. l:\issU, and Canada. There, the advent of 

 snow is looked forward to as a blessing ; and when it 

 come*, tho period of its duration admits of being pre- 

 dicted with tolerable accuracy. No sooner is the ground 

 rtil with i- MI"*, than wheeled carriages, 



which but yesterday were rtick the axli-treo in 



mud and wot, are put aside, and sledges suppled in their 

 Market-places, which, before the snow liad fallen, 



were naked am! unworthy, now teem with good 

 brought from li'i miU-t away. Snow hiw, all at 



laid down a far -stretching track, over which tho 

 lo almost with tlu ease an 1 velocity of a rail- 

 \\.iv train. 



I-' n-in of Snow -Flukes. In certain conditions of tem- 

 perature snow falls as a pulvcriil-.ut body ; in other 

 diii. IIM as a flaky MnorphoM m iss ; but if very dry snow 

 be microscopically examined before it hat 1> -n br 

 up, indications of crystalline structure will bo reoog- 

 n:-iV.e. - illine snow-flakes attain 



such large dim 'iisions, that they are quite evident to tho 

 naked eye. Tin- crystalline forms thus developed are 

 numerous, but they are all referable to one crystalline 

 system, the rbombonedrie o: 



..f which is, that cryst. .ils bel .uiging to it have throe 



axes crossing each other at tho angle of ,-rees, 



aud one axis at right angle* to thoso. Scoresby, who hai 



minutely examined these snow-flakes describes rive priu- 



Fig. 61. 



oipal forms of snow-crystals: 1st, crystals having the 

 form of thin plates, which are the most abundant ; 2nd, 

 surfaces or spherical nuclei, with ramifying branches in 

 dill'crcnt planes ; ">rd, tine points, or six-sided pri- 

 4th, six-sided pyramids. The latter form is the least 

 frequent of all. The above diagram (Fig. 51) represents 

 the principal crystalline varieties of snow-flakes. 



The Siiow-Liiie. Inasmuch as tho upper regions of the 

 atmosphere arc intensely cold, there is an elevat.o.i for 

 every latitude at which atmospheric moisture is ch:r 

 into snow. This elevation corresponds with what is 

 termed the snow-line. At the equator, the snow -Hue is 

 elevated from 12,000 to 15,000 feet above the sea-level. 

 As we proceed towards the north, the elevation of the 

 snow-line will evidently be lower. Snow does not fall on 

 level ground in Europe, farther south than Central Italy; 

 but in Asia and America tho region extends nearer to 

 the equator. Through Florence, passes the isothermal 

 line of o'J F. , aud it may be regarded as the southern 

 limit of the region, in which snow falls on level places. 

 Snow does not usually fall at the time of maximum cold; 

 some meteorologists say it never doon but this is an 

 error. After snow has fallen, the weather generally in- 

 creases in severity. We are usually in the habit of 

 assuming that the total quantity of snow which falls, in- 

 creases as we roach either pole an assumption, how- 

 ver, which is only correct within certain limits. Thus, 

 taking the northern hemisphere, for instance, the fall of 

 snow increases from the isothermal of 5'J 3 F., to the 

 isothermal of 41 F., which latter cuts the town of 

 Pronthcim, in Norway. Passing still further north, the 

 quantity of snow goes on diminishing, evidently because, 

 in the polar regions, tho temperature of the air is too 

 cold to retain much moisture, and atmospheric moisture 

 must necessarily bo the antecedent to either rain or snow. 

 The atmospheric condition during the fall of snow, may 

 vary from the limits of almost complete tranquillity, to 

 the other extreme of most violent perturbations. In 

 i Germany, and other countries having a corresponding 

 latitude, the fall of snow is usually tranquil, ex 

 during the mouths of February and March. In high 

 latitudes, snow usually occurs during violent tempost- 

 gusts, almost equal, sometimes, to the West Indian 

 hurricane, or tho Chinese typhoon. In Nor.-. 



frequent, also m Kamtschatka ; in which 

 latter region they are called jrurga. They :un verr 

 thunder-storms, as is completely proved by the int 



'al condition of the atmosphere. On mountainous 

 elevations, snow-storms are commonly prevalent, irre- 

 spective of latitude. 



