Pedometer, or Podometer, a contrivance for measuring distances, which is usually constructed in the form of a watch, and consists of several wheels with teeth, that are arranged in the same plane, and correspond with each other. Such instruments are either fastened by means of a string, chain, etc. to the knee of a person, or to the wheel of a carriage; and advance one notch at every step, or each revolution of the wheel: so that the number being marked on a dial-plate, the traveller is enabled to compute his progress by the number of his steps, or to measure accurately the distance between certain places. Some of these machines are contrived so as to mark both the time, and distance ; by combining within the same case, the mechanism of a watch, so that they may be conveniently worn in the pocket.

The utility of pedometers for the purpose of surveying land being obvious, various instruments of tins description have been constructed by ingenious mechanics, in order to facilitate the practice of geometry. Among these, Mr. Edgeworth's late contrivance deserves to be first mentioned, on account of its great simplicity ; but, as it is calculated only for level grounds, and is apt to be deranged by hilly or irregular surfaces, we decline to enter into any detail.

A pedometer, upon a new plan, was a few years since contrived by Mr. W. Fkaser, mathematical instrument-maker, of New bond-street. It is stated to be perfectly correct, and not liable to be out of order. The wheel-work is constructed on the scale of 1000 paces to a mile; and, as it winds itself up, while in motion, being adjusted to pockets of all sizes, it is attended with no trouble to the wearer. It is provided with a compass, by rneans of which the traveller is enabled to ascertain the different directions which he takes on his excursion; while he learns the accurate distance which he has walked. Hence it recommends itself to those invalids, who are obliged to take a certain degree of exercise within doors; as they may thus measure the thousandth part of a mile.

Another machine, which deserves more immediate attention, is the pedometer invented by Mr. Lewin Tugwell, of Beverstone, in the county of Gloucester, and which, is represented in the following Cut:

A, The stock of the pedometer.

B, B, B, etc. Twelve spokes; one end of which is fastened by means of a screw to the outward ring, or periphery of the wheel, while the other is inserted in the stock.

C, The periphery, which is an iron ring 16 1/2 feet, or one pole in circumference; and which is divided into 25 equal parts, corresponding to the Jinks of Gunter's chain for land measuring, &:c.

D, D, D, etc. Are twelve small plates, representing the separate spokes, and each of which includes two links of the chain above-mentioned ; the tweleth spoke being divided at its foot, for comprehending the 25th link.

E, An iron axis being a screw with 320 circumvolutions, each of which is marked separately on an engraved index on one of its sides: and, in order to apply thiss pairt of the machine, it is screwed firmly into the stock of the wheel, with which it revolves when in motion.

F, A style, or alidade, being an expanding screw-nut, that embraces the axis, along which it screws, as the latter revolves with the wheel; and, as each revolution describes an exact longitudinal pole (four of which are computed to a chain), the style being pendent, and moving towards its proper figure, denotes the length of ground passed ; as it is divided into chains and poles on the index of the axis E, and into links on the periphery C.

G, is a small adjusting screw ; which being turned, the style may be removed to the beginning of the index, alter the given line, in surveying or measuring land, has been ascertained in chains, poles, etc.

H, represents a cross, or square, with sights, for determining perpendiculars in land-measuring. It is Suspended at its ends on the axis, whence it may be occasionally detached by a simple touch of the finger and thumb, when in use. farther, this cross prevents the style from being revolved with the axis by any accident. As the 320 divisions marked on the index of the axis E, describe a mile, the style F, after having passed over them, will stop : and, as it will now move round with the axis, it Will carry with it the standard ; which will strike on the wrist of the operator, and thus prevent him from proceeding to any farther distance, till he withdraws his hand from between such standard and the axis. Having received this hint, he turns the screw G; puts the style F bark to the bottom of the index, and continues the revolution of the machine, till he has completed his course.

Mr. Tugwell's contrivance is particularly calculated to prevent error in measuring land; as one person may thus survey with greater accuracy and expedition, than by the use of the chain alone. Besides, no fraud can possibly be committed by labourers, in measuring task-work; a circumstance of the utmost importance to agriculturists.

The last contrivance, we have been requested to mention, is that of Mr. Ralph Gout, of Bunhill-row, London ; whose new pedro-meticral patent-watch differs from the instrument invented by Mr. Fraser, in this essential circumstance, that the former is connected with a time-piece, while the latter is combined With a compass. Those who live in the metropolis, or visit places, the situation of which is known to the traveller, will perhaps give the preference to Mr. Gout's capped metal watch with a pedometer, which he manufactures by subscription lor 15l. 15s. (or the pedometer alone, for 81. 9s.) :—on the other hand, we conceive, persons residing in the country, especially sportsmen, who are generally provided with a watch, on their excursions, will probably find Mr. Fraser's pedometer, on account of its compass, the more useful instrument.