afford a grateful food to mankind. They also greatly tend to fertilize the soils through which they flow; and the Mud, that subsides at the bottom, as well as the weeds which vegetate on their banks, form a valuable fertilizing Manure. But, though rivers are thus beneficial to vegetation, they are easily swoln by sudden torrents, so that their banks burst, or overflow, and occasion irreparable injury. To prevent such dangerous accidents, it has been recommended to widen the courses, or passages of rivers, where they are narrow, or where the velocity of the current is otherwise obstructed: by this simple expedient, the sudden inundations of contiguous ground will be prevented; and the numerous flocks, &c. that in low situations are apt to be carried away, will be completely secured.
River-water is much softer, and better adapted to economical purposes, than that obtained from springs: for, though all rivers originate from the latter, yet, by the rapidity of their current, and their successive exposure to the sun and air, the earthy and metallic salts which they contain, are mostly decomposed; the acid is evolved; and the grosser or feculent particles are in a great measure precipitated. River-water, however, is more pure and salubrious, after having passed through gravelly or sandy soils, than if it flow over muddy or clayey beds; or glide through forests, or populous villages and towns, where it becomes impregnated with numerous impure vegetable and animal substances. In this turbid state, it is improper for domestic uses, and especially unfit for culinary supply; but, if it be suffered to subside, and be afterwards boiled and filtred, such water will become sufficiently clear and potable.—See also Alum, (vol. i. p. 37); Filtration; and Water.
ROACH, or Cyprinus rutilus, L. a well-known British fish, found in ponds, and still, deep rivers: its body is broad, though thin; the back much elevated, and sharply ridged; the scales are large and deciduous.
Roaches are gregarious fish, remarkably prolific, and active; but seldom attain to any considerable size. They are caught in a manner similar to Dace, and are much esteemed for their delicacy.
ROAD, an open way, or public thoroughfare, which forms a communication between two distant places.
Roads being frequently disfigured, and otherwise injured by the deep ruts which are necessarily made by the continual passing and re-passing of narrow wheel-carriages; various machines have been contrived, with a view to facilitate the repairing of highways, and to fill up such excavations.—From these, we shall first communicate the Road-Harrow, invented by Mr. Harriott, to whom the Society for the Encouragement of Arts, &c. in 1789, voted a reward of ten guineas.—As this machine may not only be employed with great advantage, by the surveyors of public roads, but will also be found very serviceable in repairing and improving the private ways, or avenues, belonging to manors, we have annexed the following representation:
