318 SCIENCE Ot" AGRICULTURE. Part II. 



of 55 J in less than a quarter of an hour it was found to have gained the temperature of the 

 room. The soils in all these experiments were placed in ^mall tin-plate trays two inches 

 square, and half an inch in depth ; and the temperature ascertained by a delicate thermo- 

 meter. Thus the temperature of the surface, when bare and exposed to the rays of the 

 sun, affords at least one indication of the degrees of its fertility ; and the thermometer 

 may be sometimes a useful instrument to the purchaser or improver of lands." 



2109. The moisture in the soil and sub-soil materially affects its temperature, and pre- 

 vents, as in the case of constantly saturated aquatic soils, their ever attaining to any great 

 degree either of heat or cold. The same observation will apply to moist peaty soils, or 

 peat-bogs. 



2110. Chemical agency of soils. Besides these uses of soils, which may be considered 

 mechanical, there is, Sir H. Davy observes, another agency between soils and organisable 

 matters, which may be regarded as chemical in its nature. The earths, and even the 

 earthy carbonates, have a certain degree of chemical attraction for many of the princi- 

 ples of vegetable and animal substances. This is easily exemplified in the instance of 

 alumina and oil ; if an acid solution of alumina be mixed with a solution of soap, which 

 consists of oily matter and potassa, the oil and the alumina will unite and form a white 

 powder, which will sink to the bottom of the fluid. The extract from decomposing 

 vegetable matter, when boiled with pipe-clay or chalk, forms a combination by which the 

 vegetable matter is rendered more difficult of decomposition and of solution. Pure 

 silicia and siliceous sands have little action of this kind ; and the soils which contain the 

 most alumina and carbonate of lime, are those which act with the greatest chemical energy 

 in preserving manures. Such soils merit the appellation, which is commonly given to 

 them, of rich soils ; for the vegetable nourishment is long preserved in them, unless 

 taken up by the organs of plants. Siliceous sands, on the contrary, deserve the term 

 hungry, which is commonly applied to them ; for the vegetable and animal matters they 

 contain, not being attracted by the earthy constituent parts of the soil, are more liable to 

 be decomposed by the action of the atmosphere, or carried off from them by water. In 

 most of the black and brown rich vegetable moulds, the earths seem to be in combination 

 with a peculiar extractive matter, afforded during the decomposition of vegetables ; this is 

 slowly taken up or attracted from the earths by water, and appears to constitute a prime 

 cause of the fertility of the soil. 



2111. Thus all soils are useful to plants, as affording them a fixed abode and a range 

 for their roots to spread in search of food ; but some are much more so than others, as 

 better adapted by their constituent parts, climate, inclination of surface and sub-soil 

 attracting and supplying food. 



Sect. V. Of the Improvement of Soils. 



2112. Soils may be rendered more ft for answering the purposes of vegetation by pul- 

 verisation, by consolidation, by exposure to the atmosphere, by an alteration of their 

 constitutent parts, by changing their condition in respect to water, by changing their 

 position in respect to atmospherical influence, and by a change in the kinds of plants 

 cultivated. All these improvements are independently of the application of manures. 



SuBSECT. 1. Pulverisation. 



2113. The mechanical division of the parts of soils is a very obvious improvement, and 

 applicable to all in proportion to their adhesive texture. Even a free siliceous soil will, 

 if left untouched, become too compact for the proper admission of air, rain, and heat, 

 and for the free growth of the fibres ; and strong upland clays, not sumbitted to the 

 plough or the spade, will, in a few years, be found in the possession of fibrous-rooted 

 perennial grasses, which form a clothing on their surface, or strong tap-rooted trees, as 

 the oak, which force their way through the interior of the mass. Annuals and ramen- 

 taceous-rooted herbaceous plants cannot penetrate into such soils. 



21 14. The first object of pulverisation is to give scope to the roots of vegetables, for with- 

 out abundance of roots no plant will become vigorous, whatever may be the richness of 

 the soil in which it is placed. The fibres of the roots, as we have seen (1512.), take up 

 the extract of the soil by intro-susception ; the quantity taken up, therefore, will not 

 depend alone on the quantity in the soil, but on the number of absorbing fibres. The 

 more the soil is pulverised, the more these fibres are increased, the more extract is ab- 

 sorbed, and the more vigorous does the plant become. Pulverisation, therefore, is not 

 only advantageous previous to planting or sowing, but also during tlie progress of vege- 

 tation, when applied in the intervals between the plants. In this last case it operates also in 

 the way of pruning, and by cutting off or shortening the extending fibres, causes them to 

 branch out numerous others, by which the mouths or pores of tlie plants are greatly in- 

 creased, and such food as is in the soil has the better chance of being sought after, and 

 taken up by them. TuU and Du Hamel relate various experiments which decidedly 

 prove that, cceteris paribus, the multiplication of the fibres is as the inter-pulverisation ; 



