Dec. 30, 1881.] 



KNOWLEDGE 



173 



MAGMINE OF^IENCE 



PLAlNirSf ORBED -£XACTUfjDE$CRIBH>, 



LONDON: FRIDAY, DECEMBER 30, 1881. 



Contexts of No. 9. 



PAGE. 



CultiTatrd Fields. By E. W. Pre- 



TOjt, Ph.D 173 



Babylonitui Sun-'Worsliip 174 



Brain Troubles.— Part UI 175 



Intelligence in Animals 177 



The Planet S»UTa—{IUuttraUS) ... 178 

 The Magic Wheel— (/Uii»(ra/<ii) ...179 



Primary Colonrs 179 



Bight-Uandedness. Bj James Shaw ISO 



Barth Tremors .^. 181 



Breathin?. Br Dr. J. Mortmier 



Granville ...: 182 



Man's Proper Food 182 



jCallao "Painter" 182 



PAOK. 



Colours of Animals 183 



ScientiHc Ghosts 183 



CoRKSSPONDBKCE : — The Primary 

 Colours— Hed at the Blue End of 

 the Spectrum— The Moon's Rota- 

 tion — Four Fours, Singular Nume- 

 rical Eelation, &c 181 



Queries 1*8 



Replies to Queries 189 



Notes on Art and Science 189 



Our Chess Column 190 



Our Whist Column 190 



Out Mathematical Column 191 



Answers to Correspondents 192 



CULTIVATED FIELDS. 



By E. W. Peevost, Ph.D. 



IN a former number (No. V.) of Knowledge, the forma- 

 tion of the soil of a field was described as succinctly 

 as possible, and it was then shown how a certain class of 

 rock was caused to j-ield a loam tit for the gro^rth of plants. 

 It is now proposed to continue the subject, and to point 

 out how, by the present methods of cultivation, soil can be 

 brought into a higher condition of fertility than it would 

 Otherwise possess, if left only to the action of the weather. 



It is generally found that there exists below the surface 

 soil a layer of earth of a chai-acter somewhat different to 

 that of the upper layer. This has Ijeen termed the svhsoil, 

 and we shall see later on that its composition may exert a 

 considerable influence on the fertility of the surface soil. 

 The methods of cultivation which we propose to consider 

 (as also the reasons why they are employed), are draining, 

 ploughing, and manuring. If water be poured upon some 

 clay soil, placed in a suitable vessel, it will be noticed that 

 some of it will pass through the soil, and that the rest will 

 be retained ; but, depending on the class of soil under ex- 

 amination, the amount of water retained will be greater or 

 less, a clay soil retaining much, a sandy soU but little ; 

 this property of holding liack some of the water which 

 falls upon soil has been termed the retentive power, and it 

 exerts a very great influence on tlie luxuriance of crops, 

 for when a soil remains wet, its temperature cannot rise 

 as high as if it were dry, and is consequently " cold." 

 Such a '■ cold " land militates against the germination of 

 seeds. On the other hand, if the retentive power is low, 

 then the land dries quickly after a fall of rain, and the 

 plants run the risk of being scorched by the heat of the 

 sun. Now, it may occur that a soil is not naturally reten- 

 tive of water to any great extent, yet an excess of water 

 may be observed incapable of passing away from the sur- 

 face ; the cause of this stagnation may be found, on exami- 

 nation of the under-lying portion of the land, to arise from 

 a bed of clay that will not admit of the downward passage 

 of the water. This or another arrangement of the deeper 

 portions of a field has given rise to the modem system 

 of draining, which by causing the removal of the excess 



of water, and its more even distribution through the soil, 

 permits of the entrance of air into its pores, whereby de- 

 coinposition of the insoluble minerals is occasioned, and 

 of a higher temperature being attained. Nor are these 

 the sole advantages, but an excess of soluble saUue matter, 

 injurious to plants, such as stagnant water will deposit, 

 is deviated, and the roots of plants are enabled to seek for 

 their food at a greater depth than they otherwise could. 

 Apart from these considerations affecting the well-being of 

 the crops, there is also the great gain to the cultivator, in 

 that the labour of tilling a soil sodden with water is far 

 greater than when the land is fairly dry. The various 

 methods in use for breaking up the surface of a field that 

 pass under the name of tUlage operations produce effects 

 both physical and chemical ; for by ploughing, the condition 

 of the soil is improved, the soil being rendered less com- 

 pact, dried from superfluous moisture, and exposed to the 

 decomposing action of the air, whereby as before stated, 

 solution of the minerals is facilitated. This decomposi- 

 tion has, however, been in progress but more slowly 

 all the year round, and some of its products have 

 been carried deep down by the rain ; these the plough 

 brings to the surface, thus adding to the stores requisite 

 for the future crop. Sometimes, when the ploughing is 

 carried too deep, the results are far from satisfactory, the 

 land becoming for a short time less fertile than previously. 

 When such an event as this happens, we may be nearly 

 certain that the sub-oxide of iron has been brought to the 

 surface, where it must remain until it becomes peroxide by 

 exposure to the air, and after that the land may resume 

 its original condition of fertility. Hence it is desirable on 

 all accounts to allow a newly-ploughed field to remain 

 untouched for some time, and the more so if the ploughing 

 has been deep. It appears, then, that ploughing is in 

 some measure supplementary to draining, and vice versd, 

 as without draining, a hea\'j' wet soU can only be imper- 

 fectly ploughed ; or, rather, the advantages following on 

 plougliing are but in part gained. 



By the removal of a heavy crop off" a field, a consider- 

 able quantity of mineral matter is lost to the soil, which 

 cannot be replaced under natural conditions in amount 

 suflicient to produce a heavy crop in the succeeding sea- 

 son ; to get rid of this difficulty it is customary to apply 

 manure to the exliausted field, manures being substances 

 which either of themselves supply food, or else by their 

 action on the soil cause it to yield an increased quantity of 

 available plant-food — at the same time improving its 

 character. It would occupy far too much space to describe 

 the properties, itc, of all the manures in use, so that we 

 will confine our attention to two which are well known to 

 the general public, namely, lime, and farm-yard manure. 

 In the first of these two we have an example of a sub- 

 stance used not so much as a food — for, as a rule, all soils 

 contain a sufficiency of lime for the plants — but as an agent 

 whereby the stores in the soil are rendered accessible ; but 

 before being able to appreciate wholly the virtues of lime, 

 we must call to mind what are the chief substances which 

 are of value, and which are likely to be affected by the 

 presence of such a manure ; these substances are potash in 

 combination with silica and alumina, and nitrogen con- 

 tained in the organic matter or humus. 



Lime may be applied as caustic or quick-lime, and as slaked 

 lime (quick-lime to which water has been added), but as 

 regards the action of either of these forms, there is no 

 absolute difference, but only one of degi-ee, in that quick 

 lime is more energetic in its action than slaked lime ; but 

 to counterbalance the deficiency in energy of the latter, it is 

 more capable of even distribution through the soU, by reason 

 of its fine state of division. Rank and luxuriant herbage 



