WAYWISER

, an instrument for measuring the road, or distance travelled; called also PERAMBULATOR, and Pedometer. See these two articles.

Mr. Lovell Edgworth communicated to the Society of Arts, &c, an account of a Way-wiser of his invention; for which he obtained a silver medal. This machine consists of a nave, formed of two round flat pieces of wood, 1 inch thick and 8 inches in diameter. In each of the pieces there are cut eleven grooves, 5/8 of an inch wide, and 3/8 deep; and when the two pieces are screwed together, they enclose eleven spokes, forming a wheel of spokes, without a rim: the circumference of the wheel is exactly one pole; and the instrument may be easily taken to pieces, and put up in a small compass. On each of the spokes there is driven a ferril, to prevent them from wearing out; and in the centre of the nave, there is a square hole to receive an axle. Into this hole is inserted an iron or brass rod, which has the thread of a very fine screw worked upon it from one end to the other; upon this screw hangs a nut which, as the rod turns round with the wheel, advances towards the nave of the wheel or recedes from it. The nut does this, because it is prevented from turning round with the axle, by having its centre of gravity placed at some distance below the rod, so as always to hang perpendicularly like a plummet. Two sides of this screw are filed away flat, and have figures engraved upon them, to shew by the progressive motion of the nut, how many circumvolutions of the wheel and its axle have been made: on one side the divisions of miles, furlongs, and poles are in a direct order, and on the other side the same divisions are placed in a retrograde order.

If the person who uses this machine places it at his right hand side, holding the axle loosely in his hands, and walks forward, the wheel will revolve, and the nut advance from the extremity of the rod towards the nave of the wheel. When two miles have been measured, it will have come close to the wheel. But to continue this measurement, nothing more is necessary than to place the wheel at the left hand of the operator; and the nut will, as he continues the course, recede from the axletree, till another space of two miles is measured.

It appears from the construction of this machine, that it operates like circular compasses; and does not, like the common wheel Way-wiser, measure the surface of every stone and molehill, &c, but passes over most of the obstacles it meets with, and measures the chords only, instead of the arcs of any curved surfaces upon which it rolls.