4-1 



GRASS LAND 



GRAVITATION. 



471 



fancied analogy with the animal muscle, which U invigorated by 

 occajuun.il inaction. 



Hut setting aside theory, it is well known that land which baa been 

 some yean in gran is improved in fertility. The convertible system 

 of htubandry take* advantage of this fact ; and all iU art consist* in 

 reproducing a good mature without Ion of time, after having reaped the 

 benefit of the fertility imparted to the land during three or (our yean 

 when it was in grau. Good pasture is very profitable ; so are good 

 crops : by making the one subservient to the other, the fanner who 

 adopts the convertible system U enabled to pay higher rente, and still 

 have a better profit than those who adhere to a simple rotation of 

 annual crops. 



When an arable field is sown with the seeds of grasses and other 

 plants which give herbage tor cattle, it U called an artificial meadow, 

 and the various plant* which are raised are all called artificial grasses, 

 although many of them have no botanical title to the name of grass, 

 such as clover, saintfoin, lucern, and many others, which produce the 

 best pastures and the finest hay. 



In laying down a field to grass for a very few years the mode of 

 proceeding is somewhat different from that which is recommended 

 tor producing a permanent pasture. Clover in this case is always 

 principal plant, both the red and the white; these with annual 

 or perennial rye grass are sown with a crop of corn in spring, and 

 begin to show themselves before harvest. The grasses are often 

 mown the first year after they are sown, on account of the abundance 

 and value of the red clover, but the best farmers recommend the 

 depasturing them with sheep, to strengthen the roots and increase 

 the bulk. Various circumstances, such as a greater demand fur 

 clover hay, or for fat cattle, may make mowing or feeding most 

 profitable ; but when there is not a decided advantage in making 

 hay, feeding should always be preferred. At all events the great 

 object of the farmer should be to have his land in good heart and 

 tilth, and free from weeds, when the grass is sown. If his gross 

 is good, he is certain of good crops after it with little trouble or 

 manure. 



The seeds usually sown on an acre, when the land is laid down 

 to gross, are as follows : Ked clover, 12 Ib. ; white, 6 Ib. ; trefoil, 41b. ; 

 rib grass, 2 Ib. ; and 2 pecks of Pocey's rye grass. Sometimes cock- 

 foot grass (Daclylu glomerata) and cow gross (Trifolium medium) ore 

 added. This is for a field intended to remain four or five years in 

 grass. 



The introduction of artificial meadows, in districts where the soil 

 seemed not well adapted for pasture, has greatly increased the number 

 of cattle and sheep reared and fattened, and has caused greater atten- 

 tion to be paid to the means of improving the breeds of both. Thus 

 a double advantage has arisen : the public is benefited by an increased 

 supply, and the farmer is rewarded by an additional source of profit. 



In the neighbourhood of large towns there are many meadows, 

 which, without being irrigated, are mown every year, and only fed 

 between hay harvest and the next spring. These require frequent 

 manuring to keep them in heart, and with this assistance they produce 

 great crops of hay every year. The management of this gross land is 

 well understood in Middlesex. Sometimes the meadows are manured 

 with stable dung which has been laid in a heap for some time, and 

 been turned over to rot it equally. This is put on soon after the hay 

 is cut, and the rains of July wash the dung into the ground ; but if a 

 very dry and hot summer follows, little benefit is produced by the 

 dung, which is dried up, and most of the juices evaporated. A better 

 method is to make a compost with earth and dung, and, where it can 

 be easily obtained, with chalk, or the old mortar of buildings pulled 

 down. The best earth is that which contains most vegetable matter ; 

 and as many of these meadows are on a stiff clay soil, which requires 

 to be kept dry by open drains and water furrows, the soil dug out of 

 these and carted to a corner of the meadow makes an excellent founda- 

 tion for the compost. It is sometimes useful to plough furrows at 

 intervals to take off the superfluous surface-water in winter ; the earth 

 thus raised by the plough is excellent to mix in the compost ; having 

 been turned over with 'dung, sweepings of streets, or any other manure, 

 so as to form a uniform mass, it is spread over the land in winter ; and 

 in spring a bush-borrow is drawn over the meadow, and it is rolled 

 with a heavy roller. All this compost is soon washed into the 

 ground, and invigorates the roots of the grass. It is better to put 

 on a slight coating of this compost every year than to give a greater 

 portion of manure every three or four years, as is the practice of some 

 farmers. When grass land is let to a tenant, it requires some attention, 

 and particular conditions in the lease, to prevent the meadows bcinf 

 deteriorated by continual mowing without sufficient manuring, which 

 might be the case near the expiration of the lease. It is very common 

 to insist, by a clause, on a cart-load of stable dung being bought for 

 every load of hay which U made and not consumed on the premises. 

 Sometimes the tenant is bound to feed the land in alb-mate years ; bul 

 if horses or heavy cattle should be taken in, especially in spring am 

 mi. they may do more harm by tlicir treading, when tlio groum 

 is soft, than would have been done by inking off a crop of hay. Win i 

 the |rr.j.r.. i ; ',f meadows resides near them, he often finds it most 

 profitable to keep them in band, and sell the crop when it i fit to be 

 mown. In that caae he must I* careful to manure them sufficiently 

 or his profits will soon diminish rapidly. The grazing of cattle has 



enerally been a more profitable occupation than simply tilling the 

 and. The capital required is considerable, but the current expenses 

 are not great. The grazier U not subject to such total failures as the 

 armor of arable land is in his crops. With a little experience and 

 irudence, he can always reckon on a certain return. An acre of good 

 [razing land, worth 40. rent, U supposed to produce 200 Ib. of meat in 

 he year. If this is worth 8rf. a pound, the gross produce is U. per 

 acre. The expenses will not exceed 10. per acre, so that here is a net 

 irofit of 2/. 10. per acre with little or no risk ; few arable farms will 

 iverage this net profit. By uniting the raising of corn and the grazing 

 of cattle and sheep, the greatest profit is probably obtained, and this U 

 the great argument in favour of the convertible system of husbandry. 



The value of pasture land, and of some of the sown grasses, espe- 

 cially the Italian rye-gross, under irrigation and under the application 

 of sewage-manure, will be considered hereafter. [IRRIGATION.] 



GRAVE. [AcoT.] 



GRAVER. [ENORAVWO.] 



GRAVITATION. SECTION I. On the KvUt for calculating Attrac- 

 tion, or the Lair of Oravit 



(1.) The principle upon which the motions of the earth, moon, and 

 planets are calculated is this : Every particle of matter attract* every 

 Jther particle. That is, if there were a single body alone, and at rest, 

 then, if a second body were brought near it, the first body would 

 Immediately begin to move towards the second body. Just in the 

 same manner, if n needle is at rest on a table, and if a magnet is brought 

 . the needle immediately begins to move towards the magnet, 

 and we say that the magnet attracts the needle. But magnetic 

 attraction belongs only to certain bodies : whereas the attraction of 

 which we speak here belongs to all bodies of every kind : metals, 

 earths, fluids, and even the air and gases are equally subject to its 

 influence. 



(2.) The most remarkable experiments which prove that bodies 

 attract each other are a set of experiments made at the end of the last 

 century by Mr. Cavendish. Small leaden balls were supported on the 

 ends of a rod which was suspended at the middle by a slender wire ; 

 and when large leaden balls were brought near to them, it was found 

 that the wire was immediately twisted by the motion of the balls. 

 But the result* of this experiment ore striking, principally because they 

 are unusual; the ordinary force of gravity serves quite as well to prove 

 the existence of some such power. For when we consider that the 

 earth is round, and that, on all parts of it, bodies, as soon as they are 

 at liberty, fall in directions perpendicular to its surface, (and therefore 

 fall in opposite directions at the places which are diametrically opposite,) 

 we ore compelled to allow that there is a force such as we call attrac- 

 tion, either directed to the centre of the earth, or produced by a great 

 number of small forces, directed to all the different particles composing 

 the earth. The peculiar value of Cavendish's experiment consists in 

 showing that there is o small force directed to every different partiulo 

 of the earth. 



(3.) But it is necessary to state distinctly the rules by which 

 this attraction is regulated, and by which it may be calculated ; or (as 

 it is technically colled) tine law of yraritation. Before we can do this, 

 we must determine which of the effects of attraction we choose to take 

 as its measure. For there are two distinct effects : one U the prtstnre 

 which it produces upon any obstacle that keeps the body at rest ; the 

 other is the tpace through ichich it drawl tlie body in a certain time, if 

 the obstacle is removed and the body set at liberty. Thus, to take 

 the ordinary force of gravity as on instance : we might measure it by 

 the pressure which is produced on the hand by a lump of lead held in 

 the hand ; or we might measure it by the number of inches through 

 which the lump of lead would fall in a second of time after the hand is 

 opened (as the pressure and fall are both occasioned by gravity). But 

 there is this difference between the two measures : if we adopted the 

 first, since a great lump of lead weighs more than a small one, we 

 should find a different measure by the use of every different piece of 

 ead ; whereas, if we adopt the second, since it is well established by 

 careful and accurate experiments that large and small lumps of lead, 

 stones, and even feathers, fall through the same number of inches in a 

 second of time, (when the resistance of the air, Ac., is removed,) we 

 shall get the same measure for gravity, whatever body we suppose 

 subject to its influence. The consistence and simplicity of the measure 

 thus obtained incline us to adopt it in every other case ; and thus we 

 shall say, Attraction i measured by the tpacc through ichich, it dram a 

 laxlii in one second of time after He body is ixl at liberty. 



(4.) Whenever we speak, therefore, of calculating attraction, it must 

 be understood to mean calculating the number of inches, or feet, 



i which the attraction draws a body in one second of time. 

 (5.) Now the first rule is this : " The attraction of one body u|*>n 

 ;i,..tli. r l.-i'ly does not depend on the man of the body which is 

 attracted, but is the same whatever be the mass of the body so 

 attracted, if the distances are the same." 



(6.) Thus Jupiter attracts the sun, and Jupiter attract* the earth 

 also ; but though the sun's mass is three hundred thousand times as 

 great as the earth's, yet the attraction of Jupiter on the sun is exactly 

 equal to his attraction on the earth, when the sun and the earth are 

 equally distant from Jupiter. In other wordo, (the attraction being 

 measured in conformity with the definition above,) when the sun and 

 the earth are at equal distances from Jupiter, the attraction of Jupiter 



