LABOURS ON THE SOIL. 197 



to the pulverization of stiff soils, which are laid up in a rough state, 

 in order to expose as large a surface as possible to be cooled and 

 frozen during winter, and to be thawed and heated during spring. 

 The retention of moisture by pulverization is an important object of 

 working the soil. All properly cultivated soils hold water like a 

 sponge, while in untilJed soils the rains either never penetrate the sur- 

 face, or they sink into the subsoil and are lost, or are retained by it 

 and prove injurious. Wind, like rain, will communicate heat or ab- 

 stract it from soil, according to its temperature and the rapidity of its 

 motion ; but as in either case it carries off moisture in proportion to 

 its dryness and velocity, it is in general in cold climates much more 

 favourable than hurtful for soils, considered apart from the plants 

 which grow in them. If possible no operation should be performed 

 on the soil excepting when it is in a dry state, and when the weather 

 is also dry. Moist soil cannot be dug without first treading on it, and 

 thus making it into a kind of paste or mortar, which renders it unfit 

 for being pierced by the fibres of plants, and prevents it from 

 being penetrated either by moisture or air ; and water in the form 

 of ice or snow, if dug in, abstracts that heat from the soil which it 

 ought to derive direct from the atmosphere. " A pound of snow 

 (newly fallen) requires an equal weight of water heated to 172 to melt 

 it, and then the dissolved mixture is only of the temperature of 32. 

 Ice requires the water to be a few degrees warmer to produce the same 

 result. When the ice or snow is allowed to remain on the surface, the 

 quantity of heat necessary to reduce it to a fluid state is obtained 

 chiefly from the atmosphere ; but when buried so that the atmospheric 

 heat cannot act directly upon it, the thawing must be very slowly effected 

 by the abstraction of heat from the soil by which the frozen mass is 

 surrounded. Instances have occurred of frozen soil not being com- 

 pletely thawed at midsummer when so buried. 



Digging. The use of the lever and the pick, the former in moving 

 large obstacles, such as stones, and the latter for perforating and raising 

 up hard soils or subsoils, may be considered as preparatory operations 

 for the more perfect pulverization and mixture of the soil by diggiog. 

 Previous to performing this operation, if the surface is uneven, it 

 should be levelled ; but as we are treating of garden digging, we shall 

 suppose that the surface is already in a tit state to be dug. The first 

 step is to fix on those parts of the plot where the operation is to com- 

 mence and finish ; which being done, a trench is to be opened at the 

 former place, and the earth wheeled or carried to the latter. In most 

 gardens where there is to be a regular course of cropping, the com- 

 partments are rectangular, and these are easily divided into smaller 

 figures of the same kind for temporary purposes, the number of which 

 divisions, with a view to digging or trenching, for reasons which will 

 presently appear, must always be even. For example, a piece of 

 ground of a square form, fig. 158, a, >, c, d, may be thrown into two 

 parallelograms, a, f, and , rf, and the soil taken from the trench opened 

 from a to e can be laid down from e to 6, where the operation will be 

 finished. Had the plot been divided into three parallelograms, as in 



