

RAIN. 



latit tide*, and even on the circumference of the ume parallel, irregular- 

 must produce irregularities in the quantities of rain which fall at 

 different placet; yet the results of observation show that, in proceeding 

 from the equator toward* the north pole, there u in reality a diminution 

 in the mean annual quantities of rain. 



From an average of the observation* nude during fourteen year* 

 (1810 to 1823 inclusive), the mean annual depth of rain on the Malabar 

 coact U 123-5 inches, and the mean annual temperature it 80-4" (Fohr.), 

 but the annual depths of rain are very irregular, and differ considerably. 

 From a mean of observations for seven yean (1817 to 1823 inclusive), 

 the mean annual depth of rain at Bombay was only 85*24 inches. From 

 a mean of observations during seventeen years (1802 to 1818 inclusive), 

 Mr. Dalton makes the mean annual depth of rain at Manchester equal 

 to 33-596 inches, the mean annual temperature being 47-6 ; and here 

 also the annual quantities of rain vary very irregularly. The same 

 meteorologist estimates the average of the annual quantity of rain in 

 England to be 81'3 inches; the greatest quantity, according to the 

 daU he investigated, being at Keswick in Cumberland ( = 67'5 inches), 

 and the least at Upminster in Essex ( = 19-6) ; but it is supposed that 

 this estimate of the mean quantity u higher than the truth, because 

 too many of the observations were made in the maritime counties, 

 where the atmosphere may be expected to be the most humid. 

 According to observations made by members of the British 

 Meteorological Society, collected and discussed by Mr. Olaisher, the 

 quantity of rain that falls annually in the islands of Jersey and 

 Guernsey is about 31 inches ; in the counties of Cornwall and Devon 

 from 30 to 40 inches, or in some places still more; in the Isle of 

 Wight and over the south of England about 30 inches ; about London 

 25 inches; about the town of Bedford and the cities of York and 

 Durham 24 inches; near the east coast 27 inches; 30 inches near the 

 west coast ; and about 27 or 28 inches elsewhere. 



The late J. F. Miller, F.U.S., of the Observatory, Whitehaven, 

 Cumberland, by whom the meteorological phenomena of the English 

 lake district were accurately observed and recorded, (' Phil. Trans.,' 

 1651, &c.) showed that in the valleys of Cumberland and Westmore- 

 land, the usual fall of rain varies from 50 to 100 inches in depth in a 

 year ; and these large quantities increase with the elevation, till the 

 greatest annual depth of rain is attained at the altitude of about 

 1000 feet ; at higher elevations it decreases in amount. He records 

 the very large fall of 38'9 inches in a single month, a quantity exceed- 

 ing the average annual fall of all England. The hamlet of Seathwaitc, 

 in Borrowdale, was until lately considered to be the wettest spot in 

 Great Britain, the rain-fall, in the year 1850, amounting to 

 143-96 inches. But Mr. Miller ascertained that this was greatly 

 exceeded by a new station for observation about a mile and a-half south- 

 west of Seathwaitc, and 580 feet above it, or 980 feet above the sea- 

 level, at the extreme southern termination of the valley, on the 

 shoulder of Sprinkling Fell, or the Stye. In 1850 the rain-fall at this 

 station amounted to 189-49 inches. 



In regions where the trade-winds blow constantly rain seldom falls, and 

 the reason may be, that both the temperature and the currents of air 

 being there nearly uniform, the vapours raised from the ocean are 

 carried about the earth without suffering those partial accumulations 

 by which condensation and precipitation might be produced. But 

 elsewhere the irregular distribution of land and water, the existence of 

 mountain-chains, and even the various capacities of different parts of 

 the earth's surface for absorbing or communicating heat, independently 

 of variations in the electricity of the air, are to be considered aa the 

 most frequent causes of perturbation in the general currents of the 

 atmosphere, and consequently of the fall of rain. 



The dense mists which rest on the ocean near Newfoundland are 

 precipitations caused by inequalities in the temperature of the ocean 

 in the line of the Gulf-itream. In the year 1821, in consequence of 

 very strong winds between the tropics during the summer having 

 caused an extraordinary difference between the levels of the waters in 

 the Gulf of Mexico and those of the Atlantic Ocean, the stream of warm 

 water was found to extend eastward of the Azores ; and it deserves to be 

 remarked that this unusual circumstance was attended, both in France 

 and in England, by a very hot and damp winter, together with an 

 excessive fall of rain. (Sabine, ' Experiment* on the Figure of the 

 Earth,' 1825.) The rains which frequently deluge the tropical islands 

 are in part produced by the volumes of air which are intermingled by 

 the sea and land breezes; and those which fall at the time of the 

 summer solstice in Africa may be ascribed to the immediate precipi- 

 tation of the vapours which flow from the seas to supply the place of 

 the rarefied air above the heated lands ; while the drought which pre- 

 vails in the sandy deserts of that quarter of the earth is partly 

 explained by the level character of those deserts, over which the 

 currents of air may be supposed to flow nearly without interruption. 



From April to October, the winds blowing from the south-west 

 towards the count of Malabar are accompanied by heavy rams, and the 

 circumstance may be accounted for by the vapours of the ocean lieiiuf 

 brought from a warm region to one which is less so, and consequently 

 becoming there condensed and precipitated. On the other band, the 

 prevailing wind* on the coast of Peru, being from the south and south- 

 west, come from a cold to a warmer region ; consequently a diminution 

 <if the degree of saturation must there take puce, and the vajwurs 

 i uncondensed; accordingly it is found that rain seldom falls on 



that coast The clouds which overhang the coast of Malabar din inn 

 the monsoon above mentioned are arrested by the chain of the (Jhaute, 

 and while it rains on the western side the fair season is enjoyed on th. 

 coast of Coromandel. Again, the currents of air which pass over ! 

 in crossing the chain of the Andes, where the temperature is lower, 

 become condensed by the cold, and the rain is then- |<iv. imitated in 

 abundance. The vapours which come from the Atlantic Ocean, and 

 lss over the south-western counties of England, must be more abundant 

 than those which arrive there from the continent of Europe ; and from 

 observations made at Penzance, the rains which accompany the westerly 

 winds at that place exceed those produced by the easterly winds in il/. 

 ratio of about three to one. 



In tropical regions, the quantities of rain which fall in different 

 months of the some year are very unequal : at Bombay, the mean 

 monthly ilqith in June was found to be 24 inches, and in t>. 

 r_'i inches. In temperate climates the quantities differ much less, 

 but more rain falls during .the second half-year than during the 



In the article CLIMATK (vol. ii.,col. 972) the local distribution of 

 rain has been treated at some length, and the rainless regions of tli.- 

 earth particularly distinguished. An attribute of the l.ct 

 unnoticed, may now be pointed out : this is, the different condition of 

 oxidisable and readily soluble substances in them from that charac- 

 terising the same class of bodies in those countries which are ordinarily 

 subject to rain, and in which, consequently, the earth, even in us 

 depths, has been from time to time drenched with water during the 

 present period of its physical history. Mr. Frederick Field, 1 

 chemist, who, during his residence for some years on the western -M.- 

 of South America, was actively engaged in the examination 

 mineral products, remarks that, " In the northern part of Chili, where 

 little or no rain falls, and the mines have only been recently worked, 

 [and their contents, therefore, not long exposed to the action 

 atmosphere,] many minerals in a highly oxidised state are found, which 

 have been preserved untouched from the absence of any solvent. 

 Arsenic is obtained sometimes as arsenious acid, and sulphur as sul- 

 phuric acid, in combination with the oxides of iron and copper. In 

 1'eru, even crystals of native sulphate of silver have been observed." 

 (' Quart. Joum. of Chem. Soc.,' vol. xii, April, 1859.) In ordinary 

 rainy countries, for the reason above stated, these substances are of 

 rare occurrence, under occasionally favourable circumstances only. 



In general the lowest stratum of ah- about the earth contains the 

 greatest quantity of aqueous vapour ; and hence it might be expected 

 that more rain should fall on low level plains than in elevated countries. 

 The contrary, however, is the fact : and this may be accounted for by 

 the variety of currents among mountains, and by clouds resting 

 frequently on the summits of hills without descending to the plains. 

 While the average annual depth of rain at Keswick is 67'5 inches, in 

 the interior of the country and on the sea-coast it is but 25 inches : 

 and while the average depth on the St. Bernard is 63-13 inches, that 

 at Paris is 20 inches only. Yet, from the observations of Dr. 

 Heberden, Mr. Luke Howard, and M. Arago, it appears that the depth 

 of rain on the level of the ground is greater than at the top of a 

 building. The first of these philosophers found that the annual depth 

 at the top of Westminster Abbey was 12-099 inches, while at a lower 

 level, on the top of a house in the neighbourhood, it was 1S-139 i 

 and on the ground, in the garden of the house, it was 22*608 inches. 

 M. Arago observed, from observations during twelve years, that on the 

 terrace of the Observatory at Paris the annual depth was 50'471 centi- 

 metres (19'88 inches), while in the court of that building, which is 

 28 metres (30 yards) lower, the annual depth was 50*371 centimetres 

 22-21 inches). 



On this subject we are now able to add some precise informa- 

 tion derived from modern research. In 1833 was conimm 

 to the British Association for the advancement of Science, a ' Report 

 of Experiments on the Quantities of Hain Falling at dilln.m 

 Elevations above the surface of the ground at York, undertaken 

 at the request of the Association,', by William Gray, jun., and 

 John (now Professor) Phillips ; to which remarks on their result 

 added by the latter; and the whole published in the 'Third Report ' 

 of the Association, pp. 401-412. These ex , u ere mode at three 



stations; the summit of York Minster, at the height of 241 feet 104 

 inches above the river Ouse, which is nearly level with high water in 

 the H umber ; the roof of the Yorkshire Museum, at the height 

 feet 8 inches, and at the distance of 1100 feet from the Minster; and 

 in the Museum grounds, at the height of 29. feet, and distance of 1 ".!' 

 feet from the Museum ; the second and third stations were nearly 

 equidistant from the Minster. These points embraced in a remarkable 

 manner the desired conditions of gradation of altitude, openings of 

 sky, and contiguity of position. The results for twelve months, 

 exclusive of snow, were, in the order of altitudes, as follows :1,V715 



. 20*182, 23*785. On these results Mr. Phillips remark 

 arranging them in relation to mean temperature and the season of t h.- 

 year, that the diminution of the quantity of rain received at dill'ncnt 

 heights above the ground, as compared with that received on the. 

 ground, is very accurately represented by a simple formula involving 

 one constant, namely, the square root of the height of the station 

 above the ground, and one variable coefficient. He then examines Dr. 

 Heberden 's results at Westminster, noticed above, and finds that it is 

 probable that they obey the game constant relation to la i 



