Stones, in general, are defined to be hard, solid bodies, which are neither soluble in water, nor malleable. They are formed in the progress of time, within the bowels of the earth, by the gradual accretion of earthy particles ; which, by different combinations, acquire various degrees of hardness.
Stones have, by mineralogists, been divided into numerous clashes, according to their respective consistence, colour, form, and other properties: but, as we state the most valuable kinds and species of these fossils, in alphabetical order, we shall in this place only remark, that the practice of indiscriminately collecting stones from land, is productive of great disadvantage, because it tends to diminish its fertility. (See also vol. i. p. 95.) There are, however, certain situations abounding with stones, that might be usefully employed in repairing roads : - the usual mode of gathering them by hand, or separating them from the soil by means of an iron or wooden riddle, being equally troublesome and expensive, we have procured the following cut, of a machine for clearing land from stones, and also for sifting sand or gravel: it was invented by Peter Francis Ponti, an ingenious Italian mechanic, on whom the Patriotic Society of Milan conferred a premium of 16 scudi, and a silver medal.
b, b, are two cross pieces, fixed to the inner surface of the feet; and which contribute to strengthen the machine, and to keep it steady. They are made to project in the form of handles, for the greater convenience of transporting the implement to different places, two men being thus enabled to carry it with ease.
k, is a continuation of the iron axis, e, so as to form the handle of the basket; and, on turning it round, the basket moves in a circular direction: the axis is fixed to the bottom of the receiver by a cross of iron, f, or, such axis may be made to pass through the basket, and be so firmly attached to its inner surface, as to support its rotary motion.
The receiver described by the letters i, m, h; i, m, h; consists a thick wooden bottom, to which are fastened (by means of nails re-presented by black dots) the iron bars, of which all its sides are composed. These bars extend in an oblique direction to the bottom; so that the diameter of the outer periphery, h, h, is double to that of the bottom : they are equal in length to the diameter h, h; at which part they are fastened to a strong iron hoop.
The original basket delineated in our figure, is nearly two Paris feet in diameter; and all the other parts are constructed accordingly: size of the machine may, however, be enlarged, or diminished, as occasion requires. But, as the spaces between such bars would be disproportionaliy wide, in case the latter were throughout of an equal size, or breadth, these are made somewhat round towards the letters i, i; becoming gradually broader as they approach to h, h ; so that the spaces between the bars do not increase in proportion to the width of the basket.
Lastly, in case such bars be not sufficiently strong, they may be supported by fixing another iron hoop round them, at m m. And, if this machine be designed to sift sand or gravel, as well as to clear land from stones, a sieve of iron wire may be fastened around it; and the interstices of which may be enlarged or diminished, according to circumstances.
In employing this machine, it must be placed at one end of the field; two men, furnished with spades, should place themselves in the front, and throw the earth dug up into the basket, which may be turned round by a bay, or any other person. The soil and stones strike against the wooden bottom, and fail upon the bars, bring whirled round by the rotary motion of the iver. During such revolution, the sand, small stones, and earth, fall through the interstices of the bars on the ground, while such as are larger will be thrown to a cer- tain distance from the basket into a trench, made for their reception. When the labourers are so far advanced that they cannot, without difficulty, supply the basket, it will be necessary to spread the sifted parts regularly on the surface, and to remove the machine by means of the handles b, b, so as to be exactly over the stones already separated. Thus, the work may be continued in a similar progression, till the land be properly cleared.
The most favourable time for this agricultural labour, will be during temperate weather; when the ground is neither so moist as to adhere between the interstices, and consequently to diminish the utility of the machine; nor so dry and dusty as to be troublesome to the labourers. In such seasons, stony land may be greatly improved ; as the stones will be buried in those i to which the roots of annual plants do not extend ; and in which neither trees nor shrubs will prosper.