IRRIGATION. 



particle? of arable lands, be fprcad over the bottom of the 

 valley, to an extent proportioned to the height of the bank, 

 and its own flatnefs : a valve or flood-gate being fixed in 

 the bed of the rivulet to let off the waters, when the ivliole 

 of their foulnefl'es were depofited : thus gaining a principal 

 advantage over natural flooding ; in which the grofler par- 

 ticles only are let full ; the finer, and perhaps moil valuable 

 efcaping to the river, and thence to tlie fea, before they be 

 precipitated or let fall upon the land." It is conceived 

 that on thefe principles, it is evident, fome of the meadow- 

 lands of the midland dillrids have formerly been flooded ; 

 and that it is not probable, that fo evident a method of im- 

 jwoving meadow-lands fliould have been confined to a par- 

 ticular dillria ; but may have been common to other parts 

 of theilland. And it is further Hated by the fame writer, 

 that the ancient method of meliorating grafs-lands, by the 

 means of jla^nant water, could no longer prevail, than until 

 the fuperior effefts of running water, on fuch lands, were 

 difcovered and afcertained. And that this important dif- 

 eovery muft have been made by o/^Jlrviilion, on the compa- 

 rative cfFefts of running and ftauding water, in the natuial 

 and artificial flooding fpoken of above ; and muft have been 

 afcertained by a long courfc o( experience : as it is not likely 

 that req/in fliould have had any (liare in ftriking out the 

 modern method of improving grafj-lands by running water. 

 For even now, when the reality of the improvement appears 

 to be fully eftab'ilhed, there fcems to be no full or fatisfac- 

 tory /l)eyv to account for it : th:)ngh many of th,; efi^efts 

 thus produced have lately been more clearly explained and 

 better underllood, as will be feen below. The -warmth, 

 communicated by running water to the grafs it flows over, 

 is one great reafon adduced for the good efFeft of running 

 water on this fort of land. But even after this difeovery 

 was made, and the effeft fully eftabU.'hed, it would be fome 

 length of time before the art arrived at its prefent high 

 degree of perfeftion. As it may, in its prefent ftate, be 

 fafely deemed the mofl; ufeful and fcientific operation, that 

 has entered into the common praftice of hufbandry. And 

 the memory of the inventor, or inventors, deferves the higheil 

 praife and admiration. 



It has likewife been remarked, that the great degree 

 of verdure and luxuriance wliich almnil immediately iuc- 

 ceeds the occafional covering of grafs-lands with water, 

 fufficiently demonftrates the power which it poffefles in pro- 

 moting vegetation : and that it is a means of fertility that 

 has been employed for ages in more warm climates, with the 

 moll beneficial confequences in increafing the quantity of 

 vegetable produce. But tliat although it has been long in 

 ufe in other countries, and of late more particularly attended 

 to in this, the principle on which it produces its effefts are 

 not yet fully explained. 



In confidering manure as the nourifhment or food of plants, 

 fome of the properties of water, that may be beneficial in 

 the vegetable economy v/hen abforbcd or taken up by the 

 fibroui roots of plants, have been mentioned ; and there are 

 other ways in which it may be advantageous in forwarding 

 the growth of grafs herbage when applied over the furface. 

 It is conceived that in climates where the heat is confiderable, 

 it may be of much utility, not only by keeping the fine 

 fibrouo roots of the grafs or other plants in a moiil patulous 

 ftate, the mod proper for tlie purpofes of abforption, but 

 in fuch a temperature or ihite of heat, from the cooling 

 effeil produced by the conftant evaporation that is taking 

 place near the furface of the ground, as is the moll fuitaljle 

 for their healthy and vigorous growth. It is probably in 

 this way that garden plants are principally benefited by the 

 appiication of water in ihe hot fummer feafons in our own 



climate ; as when the waterings are not conftantly kept up 

 injury rather than good is moftly experienced. But that 

 another and more beneficial way in which grafs produce 

 may be immediately increafed, and the fertility of the lands 

 more permanently improved in this country by the floating 

 or covering them with water, is from the waters of the 

 rivers or brooks that are turned upon them, containing, 

 either in the fl:ate of folution or diffufion, a variety of dif- 

 ferent forts of enriching materials which they gradually and 

 evenly depofit upon the furface while they reft upon or flowly 

 flow over it. This muft, it is imagined, be the cafe in all 

 thofe inftances where the rivers or ftreamlcts cither ar i in, 

 or in their courfe flow through or over beds of chalk, marie, 

 or other calcareous ftrata ; as in their pali'age they become 

 higbly impregnated with the fine particles of thefe different 

 fubitances. And where they are fed by the fmall runlets 

 which receive the waters that proceed from the higher and 

 more elevated lands, they muft often, efpecially after heavy 

 rain, be loaded with a large proportion of fine rich ma- 

 terials of the animal, vegetable, or other kinds, which they 

 depofit in a regular manner in their tardy trickhng courfe 

 over the furfaces of the fields below. 



It wou'd appear that waters thus impregnated produce 

 the moft beneficial effecls, particularly when not in flood, 

 ui on the lands that are the neareft to the fources whence 

 they become principally impregnated with their fertilizing 

 piinciples ; as when they have flowed to fome diftance they 

 liiive, in a great meafure, depofited and let fall fuch enrich- 

 ing fubftances, and are become too pure for affording ad- 

 vantage in the way of depofition. It is only in the time of 

 fliods that they can produce much utility in this way at any 

 great diftance. It was found by an able philofophical 

 writer, Dr. Darwin, that the water of the Derwent, though 

 it flows for fevcral milts near Matlock, through calcareous 

 ftrata, contained no impregnation of this fort on its reaching 

 Derby, although the fprings in that neighbourhood had a 

 la!"ge proportion of it in their compofition. And the fame 

 author has ingenioufly fuggefted another mode in which 

 water may prove ferviceable in floating grounds in this cli- 

 mate, which is that already ftatcd of protefting the grafs or 

 other plants from the too fevere effecls of cold diu'ing the 

 winter, or early fpring feafon. In this view it is obferved, 

 that the water of ilrong fprings, which in this country have 

 conftantly the temperature of forty-eight degrees of Fah- 

 renheit's thermometer, is to be prefen-ed to that of rivers, 

 where it can be procured in a fufficient proportion, as the 

 degree of cold in thefe is in the fame ratio with that of the 

 atmofphcre, till it declines to the freezing point, or that of 

 thirty-two. Though bot:h, when fpread out, forming a thin 

 fhcet of ice on the furface of the laud, are beneficial in de- 

 fending the roots of the grafs plants from too intenfe de- 

 grecs of cold, and of thus preferving them in a more healthy 

 condition ; and it is added, that thofe of fome forts of 

 grafles are fuppofed even to vegetate beneath the ice, as the 

 rein-deer mofs in Siberia moftly vegetates beneath the fnow, 

 in a degree of heat of about forty, which is the medium be- 

 tween that of the inferior furface of the diffolving fnow, or 

 that of thirty-two, and that of the common heat of the in- 

 ternal parts of the earth, vrhich is forty-eight ; and in this 

 manner the grafs produce in this cold country be confidcr- 

 ably increafed, fo as, under proper management, to nearly 

 double the ufual annual quantity under other circumftances. 

 In further illuftration of thefe principles it may be ob- 

 ferved, that the water iffuing from fprings wheie they 

 abound with particles of gravel, or a flaty, mouldering kind 

 of rock, containing a large proportion of calcareous earth, 

 are known from experience to be better adapted to the pur- 



pofe 



