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clay and lialf sand. This is meant of the two earths perfectlypure. Such a mixture of sand and clay is sometimes called brick-earth.
The most eligible situation for making these experiments, shouldthe Board of Agriculture think them expedient, is between threeto six miles from London ; or, if nearer could not be procured,eight or ten. Nearer than three miles the air of the atmosphereis contaminated, so as to make great variation in the growth ofplants; * it would be inconvenient to the members, at a greaterdistance than from six to eight, or ten at the farthest, to pay thefrequent attention to the course of the experiments that, would bedesirable. It should also be at as great a distance as such a fieldCan be conveniently procured from any village, and particularlya populous one, so that it may not be infested with sparrows, andthat it may be out of the way of the curiosity of idle people.
Dr Fordyce thinks an acre of ground would be sufficient to be-gin these experiments upon. It would be necessary to take offthe whole of the present soil, as far down as it is at all alteredby former cultivation; and it would require another acre to laythis soil upon; so that similar experiments might be carried on atthe same time upon the earth already cultivated, either by naturalor artificial means. These two acres might be in the middle of anenclosed field, perhaps of about five acres, in order that experi-ments might not be influenced in any way by enclosing hedges.The other part of the ground might be employed in any other ex-periment that might occur to the Board, such as the difference be-tween dibbling, drilling, and broadcast; different successions ofcrops, &c. ; so that it would not be thrown aw ay'. He conceivesa command of water necessary; and if a small stream should runthrough the field, it would be much more eligible, not only for theconvenience of the experiments themselves, but also for showingthe advantages of irrigation, and the best method of employingit. At the same time, the field itself should either be naturallydry, or perfectly drained.
The furface of the ground from which the soil had been totallycarried off, should be made into divisions; all of which should beperfectly flat, and should also have a path between them sufficientto afford an easy passage, without hurting the crops, which maybe feet.
The following crops might be cultivated.
Of the Gramina which bear farinaceous Seeds.
1st division. One bearing very heavy seeds in proportion totheir bulk, which Dr Fordyce thinks ought to be wheat.
* As a proof that the air of large towns is not favourable to vegetation, atleast to the bringing of plants to perfection, it may be observed, that very fewplants will bear flowers in London , still fewer fruit, as may be seen in all thepublic gardens. Them are some, such as the yellow rose, that will not flowerwithin three or fyur miles of London . The great crops in the vicinity of that<ity, arises from the facility with which manure can be procured.