This is an instrument to be attached to carriages for showing the distances over which the wheels pass. As improved, it is the invention of Wm. Grayson, of Henly-on-Thames, England, who recently took out a patent fol the same, which has been published in'the last number which we have received of "Newton's London Journal." As we have had many enquiries about these instruments, we know that this article will interest many of our readers. This invention consists of an arrangement of apparatus denominated an " odometer oi road-measurer," to be attached to a street cab, or other vehicle, for the purpose of denoting the length of way passed over by the running-wheels. The apparatus is composed of a train of wheelwdrk, with two.dials and indexes, to indicate the distance travelled. It is mounted on a metal plate and enclosed in a box which is affixed to some convenient part of the carriage, in such a manner that one dial may be seen from, the outside thereof; so that, | previous to entering thecarriage, the passen-I ger may examine the dial, and have the "index placed at zero. The other dial must be inspected from the inside of the carriage, and is intended for the use of the proprietor, to serve as a check upon the driver, who will be accountable for the distance travelled, as indicated or marked lipon this dial, after due allowance for back carriage. The train of wheels whereby the indexes are actuated is set in motion by a pin, stud, or cam, on the nave of one of the running-wheels; this pin. stud, or cam, is, at every revolution of the wheel, brought against the lower end of the pendent lever, which it iorces back; and the upper end of the lever is thereby made to act upon a ratchet-wheel, which forms part of the mechanism of the odometer. ' Kgures 1 and 2 exhibit the improved odo-fflfet or road-measuring apparatus which forms the subject ofthis invention. This instrument is applied to the upper part of the body of a street. cab or other vehicle, in a suitable position above the axletree; arid from it depends a lever, x, the lower end of which is acted upon by a pin, stud, or cam, on the nave of the running-wheel. As the wheel rotates, the pin will be brought against and caused to force back the lever, by which means, a tooth at the upper end of the lever will drive round the. ratchet-wheel, c, one tooth; as will he understood on examining fig. 1, which represents a back view of the instrument. In this view is shown the wheelwork at the back of the plate, d, on which all the counting mechanism is mounted. The diali!, represented in this figure, is inspected from the inside, of the carriage, and, being enclosed within a box, cannot be tampered with by the driver; Figure 2 represents a front view of the plate, rf,—thepassen-ger's dial,/, being removed, and its position only indicated by the dotted'circle,/, in order that the parts .beneath may be more clearly seen. Figure 3 exhibits the passenger's dial, /, detached. The lever, -J, turns on a pin or centre mounted in the bridge-piece, g, on the back of the plate, d, as shown in figure 1.— Its upper end bears, against a stop, h, and is kept in its proper- position by a spring, i.— The ratchet-wheel is prevented by the spring-cli'ckjj, from moving more than one toothat a time. On the axle of the ratchet-wheel, at the opposite side ot the plate, d, is a pinion, k, with 10 teeth, which gears into a cogwheel, I. with 100 teeth. On the axle of this wheel, I, is another, pinion, m, of 10 teeth, which gears into a wheel, n, of 100 teeth ;v and on'the shaft ol this wheel, n, is mounted a hollow shaft, that carries the index of the passenger-dial,/, which, as will be seen by referring to figure 3, indicates quarters of miles, half miles, and miles, to the number of ten. For the purpose of indicating a larger number of miles, thepatenteehasadapted to the back of the dial, /a magic or jumping index, consisting of a small dial with tens printed thereon, which is connected to a jump-wheel, o, (fig. 2J behind the dial,/, shown by dots in fig. 3. On the hollow shaft which carries the index, is mounted a pin or stud, p, which, at every rotation of the wheel, , acts on the wheel, o, and jumps it one tooth, —thereby indicating that ten miles have been hollow shaft (which is mounted on ihe shaft of the wheel, n, and is carried round thereby by friction of contact) may be moved round by the finger, when required to bring it back to zero, without deranging the other mechanism ; and, before a passenger enters a vehicle, he shouW see that the driver sets the index at zero ; so that, at the end oi his journey, he may, by a (ample inspection ot the dial, at once ascertain the distance he has travelled. In order ftiat the proprietor may be protected from fraud, his index, which is inside the carriage, will continue to count and indicate the total distance travelled during the several journeys throughout the day. The proprietor's index, as well as the passenger's index, is worked by meansof the toothed wheel, ; but an intermediate wheel, g, of an equal number of teeth, communicates motion from the wheel, , to the index, which indicates, on the dial, e, the total distance travelled. This dial, e, is also provided with a magic or jumping index, to indicate the tens; bufy as the jumping index is precisely similar in construction and operation to that connected with the passenger's index, and already described, it will not be necessary to-enter further into detail in reference thereto. The proprietor's dial and index are kept under lock and key. The apparatus and train -of wheelwork, above shown and described, are intended for a vehicle of which the running-wheels measure 13 feet in circumference; and,' for this purpose, the ratehet-wheel is made with 44 teeth, which is obtained by dividing 528 (the number of feet in the 10th part of a mile) by 12, the circumference'of therunning wheel, which muslin passing over "a tenth of a mile, revolve 44 times. It will therefore be evident that, if a running-wheel ofany other iimensions is employed, thenumber ofteeth in the ratehet-wheel must be varied; forin-stnce,supposirig the running-wheel measures rally 11 feet, then, by dividing 538 by 11, we liave 40-Whicli gives the number of teeth for bhe ratchet-wheel,—all the other parts remaining the same.