R A i air to die requisite do ui heat. i f tiiis construction are be v< ry useful for light- houses, and other places requiring a strong fire, such as lahorati brew-hous* -., smelting -tun.. glass-houses, &c. — Fora more cir- cumstantial account of this patent, we most refer the reader to the 8th vol. of tin- Repertory of Arts and GRAVEL, in agriculture and gardening, is a congeries oi peb- which, it" mixed with stilt' loam, make excellent and durable gravel-walks. For this pur loltora should bfl laid with lime-rubbish, large flints, or any other hard substance, to the depth ul" six. or eight inches, in order to preveui any weeds from shooting through the surface. Over this stratum, the gravel is to he strewed six. or cigiit inches thick, and somewhat sloping, that all the larger stones nun roll oft to tl t sides. The next operation is that iking, when the larg< stones are to be removed, and the walks carefully rolled in everj direction, especially during or alter hard showers : thus they will bind, and become very firm. The most proper gravel for walks, is that which abounds with smooth round pebbles; for tl when mixed with a small po tion of loam, are not so liable to be turned up by the feet in walking, as those of a rough and irregular shape. Gkavellv Lands or Soils arc stub as abound with gravel or sand, which easily admit both heat and moisture. They receive but little benefit from the latter, if there be ■j. loose bed at the bottom, because it easily evaporates G R A • stratum be firm, fijfr instance, clay or stone, " ted, so a ; to chill the soil and render it unfruitful. The best method of counteracting this in- conv( nience, is to manure such land with chalk, which is slightly to be plough* -1 in, that il ma . sink too deep into the ground. A; gravel constitutes the i material of our roads, and thus be- cot tes an article of considerable importance, we shall briefly men- tion a method, by which gravel or stone may be discovered wit boring. It simply consists in ob- serving, whether the Common or granulata.,1 ,. (which see) grows on any spot where a bed oi grai : suspected to lie : far, it that plant be discov< r< 1, it w ill s< i e as a guide to surveyors or other-,, w • with a certainty of finding the object of their search. Wc state this fact on the authority of Mr. T. Walfokd, in the 2.3 th vol. ui Annals of Agriculture, where an accurate representation of the Saxi- frage is given. — For a method oi ring land from stone or grav i I, we refer the reader to the article Stqn e. GRAVEL, in 1* dieiue, is a disorder affecting chiefly the blad- der and ureters ; it is occasioned by a sandy or gritty suhstam e which collects in those parts, prociuees considerable pain, and at length obstructs the due secyetion and excretion of the urine. Although the gravel is generally considered as the forerumier of the cu Lulus, or stone, vet wc are con- vinced from experience, that they are distinct, diseases ; and that those patients who are afflicted with the former, are generally exempt from die ihiigcvi of the latter. Persons
