384 



SCIENCE OF GARDENING. 



Part II. 



the upper side (Jig. 374.), unless pro- 

 vision is made for intercepting the water 

 before it comes on the gravel, by a gentle 

 hollow (a), running parallel and close to 

 the road, and communicating in like 

 manner with the drains. 



1966. The durability and comfort of 

 roads and ivalks depend on their power to 

 resist the action of animals walking on 

 them, of machines being rolled over them, 

 of weather, and of vegetation. A dry firm substratum is necessary for all these pur- 

 poses ; and this, as already observed, is to be obtained by draining either in the centre or 

 in the sides, and by a stratum of gravel or fragments of stones ; the largest, in walks, of two 

 or three ounces each, and in garden-roads, of six or eight ounces ; in both cases covered 

 with smaller gravel. For resisting animals, a degree of compactness, solidity, and homo- 

 geneous texture of surface is requisite, according to the weight of the animals and their 

 burdens, and the area of their feet. Thus, supposing a man to weigh seven hundred 

 weight, and to carry a load of two hundred weight, and the area of one of his feet to be 

 twenty-five inches, then the walk or road will require to bear at least forty pounds per 

 square inch, and so on. But an animal not only presses vertically on a walk or road, 

 but his feet (the feet of man singly, and of quadrupeds relatively to each other), 

 acting as levers of the third kind, have a tendency to force up and derange the materials 

 under the point of the foot in the action of walking, in the same way as the lower end of 

 a ladder, when rearing up against a wall, has a tendency to press into and derange that 

 part of the ground which acts as a fulcrum. Hence an additional reason for firmness of 

 surface, and also for using small materials ; for if the end of a ladder, or the extremity of 

 the foot, or any point of pressure, were to exert itself on one end or extremity of a stone, 

 it would act as a weight on the end of a lever ; and, depressing one end and raising the 

 other end, would derange at once the substratum and the surface. During rain, or when 

 the surface of the road was moist, this operation would go on in at least a duplicate ratio. 

 Whatever may be the weight of a four-wheeled carriage or waggon, it presses on the road 

 on four points only, whose united areas seldom exceed one foot ; hence the necessity of 

 firmness, and also of materials reduced to a size, whose areas are less than the separate 

 areas of the four pressing points, in order to prevent derangement from leverage or com- 

 pound action. This subject has been ably illustrated by R. L. Edgeworth, and practi- 

 cally exemplified, to a great and beneficial extent, by J. L. M'Adam (Rules for repairing 

 Roads, &c. 1823), and bids fair to effect an entire change in the system of public road- 

 making followed in this country. (See our Encyc. of Agriculture.) 



1967. To resist weather, the grand object is to get rid of superfluous water ; subterra- 

 neous sources are to be cut off by drains, and surface water is not to be allowed to sink 

 into the road, but the surface gently raised, and rendered and kept, by rolling and conti- 

 nualW obliterating foot or machine marks, so smooth and impervious, as to throw the water 

 entire'ly to the sides. By this means, the effects of frost, heavy carriages, and narrow 

 wheels, is greatly lessened. . 



1968. To resist vegetation, a road must be in constant use ; but firmness is useful even 

 in this point of view, and also the exclusion of vegetable earths from the gravels or other 

 materials used in forming the surface of garden-walks and approach-roads. 



Chap. III. 

 Scientific Processes and Operations. 



1969. Scientific processes and operations include the master-operations of gardening as 

 an art of culture. These operations are all mechanical ; but some depend, for their be- 

 neficial result, on chemical changes, as in the preparation of composts and manures ; 

 others depend on the prevention of chemical changes, as in the preserving and keeping of 

 fruits and roots ; some on imitations of climates, as in the management of hot-houses ; 

 but the o-reater number are dependent on the laws of vegetable life, as in the operations 

 of propagating, rearing, accelerating, and retarding vegetables. Other processes to be 

 treated of are of a mixed nature, and some depend on the laws of animal life, as in the 

 operations for destroying vermin and insects. 



Sect. I. Preparation of fermenting Substances for Hot-beds, Manures, and Composts. 



1970. The fermenting substances used in forming hot-beds are stable litter or dung in a 

 recent or fresh state, tanner's bark, leaves of trees, grass, and the herbaceous parts of 

 plants generally. 



