Modern machinists have long recognized the importance of knowing, as precisely as possible, what a machine is doing, while in motion, without waiting for ultimate results. The engineer must have his steam gage to inform him at all times the quantity of operative pressure in the boiler, and the applications of the dynamometer are made with the sole view to determine the motive power of machinery at the time of application. Various contrivances have come into use for indicating the speed, that is to say, the number of revolutions performed within a given time, in the running of machinery. But a1! hitherto employed may be resolved into mere “ counters “ of revolutions. A time-piece must be consulted both at the beginning and conclusion ofthe counting process, or nothing is ascertained as to the running rate. Prior to the invention which we are about to explain to our readers, nothing was ever patented in this country which proposed to indicate of itself, at all times, the running rate of machinery while in motion, so that, whenever glanced at, it would inform the observer how fast the machine was then running. The invention referred to was patented through the Scientific American Patent Agency Nov. 26,1867, to Mr. Edward A. Lewis, of St. Charles, Mo. It is about the size of an ordinary clock-it may be larger or smaller, according to taste—and may be connected with any running machinery either by immediate contact or in a remote part of the buildings occupied. It has two dials, placed similarly to those on calendar slocks ; one an ordinary time dial, with clock movement, and the other for indicating the running speed of the machinery. Its operative principle consists in a continually repeated division of time into minute periods-say of one to three seconds each— with corresponding divisions of the running movement of the machinery. The rate of speed in each of these divisions is shown on the dial by an index pointing to figures expressing, for standing machinery, the number of revolutions per minute ; for locomotive engines, the number of miles per hour. Thus, the fractional period being three seconds—if a wheel makes exactly three revolutions in that time, the index will point to the figures “ 60 “ on the dial, showing sixty revolutions per minute—and will stay at those figures so long as the machinery continues to run at the same rate. The index does not move at all except when the speed is changed. Then it will move to the proper point, whether faster or slower, and there remain until another alteration is made in the speed. When the machinery stops the index recedes to “ 0." The mechanism by which these results is attained may be comprehended by a reference to the accompanying engraving. A is a volute cam, or eccentric, which is caused to rotate from left to right by connection with the running machinery through the crank shaft, B. This connection is, however, so controlled by the clock movement above, that the cam moves only three seconds at a time, when it stops and returns quickly to its starting position. At C is a projecting pin in the rack bar, D, which rests on the periphery of the cam, and is thus caused to rise as the cam revolves from left to right, operating the pinion, E, which carries the' index on the dial. Now it is obvious that the faster the machinery is running the higher the rack, D,. will rise in the period of three seconds, and vice versa. When the three-sscond movement is accomplished, the rack and pinion are held in position by a.ratchet arrangement not shown in the engraving, while the cam returns to its starting point and makes another like fawtific Mtmitm, revolution. If the speed continues the same as in the preceding three seconds, the index will of course remain pointing at the same figures. If the speed be increasing, the index will be pushed further along. If it be decreasing, the release of the ratchet hold on the pinion, E, at the instant of the termination of the cam's three-second movement, permits the index to recede until the pin, C, again rests on the periphery ofthe cam, by which the diminished speed is indicated on the dial. Thus the index will always remain stationary, until there is a change in the speed of the machinery. But the performances of this ingenious instrument do not stop with the mere indications of speed. It also records it; so that one may know at any time afterward the exact speed that was being made at any previous minute. The cylinder, F, [by connection with the clock movement, is caused to re- yolve once per hour, winding upon itselfa strip of paper from the spool, G. This paper is ruled with horizontal and perpendicular lines, similarly to that used on the steam indicator. A pencil, H, is fixed in the rack-bar, D; this marks the passing paper higher or lower as the speed is greater or less for the time being. The perpendicular lines indicate the minutes of time, while the horizontal ones represent the velocity. As placed in the engraving, the pencil mark would indicate a speed of ten miles' per hour of the locomotive (supposing that to be its application) for as many minutes as there are perpendicular lines over which it passes.. When the locomotive stops, the pencil will descend to the lowest horizontal line, and will there make its continuous mark, reporting the exact duration of the stoppage. This registering apparatus is so arranged that it may be locked up within the instrument, and made inaccessible to any one but the key holder. The paper may be replaced jaily or oftener. Railroad officers may thus have in their possession an exact history, as to speed and stoppages, of the movements of every train upon their road. The dial represented in the engraving is the one ^signed for use on locomotives. For standing machinery thojftgures run up to 120, or higher if required. An instrument of this kind is to mechanics what double- entry book-keeping is to business, a means whereby work may be done understandingly and accurately. By its use all machinery designed to be controlled by personal supervision may be made to perform its work with great uniformity, and, its speed regulated with great accuracy. As a legal evidence, in case of collisions on railways, or other accidents, its record would be of great value. Locomotive engineers are often placed in very unplelUlant circumstances, by the testimony of persons incompetent to judge of the rate at which a train is moving at the time an accident occurs. This record would not only serve to protect them from such injustice, but would also keep them in check from exceeding the proper rate in crossing bridges,-trestles, etc,, since not only the rate at which they were running, but the precise time at which they were running it, could be accurately determined. This instrument will prove an important addition to the means now in the hands of mechanical engineers, for the estimation of the performance of machines. Further information may be obtained of the inventor, Edward A. Lewis, St. Charles. Mo.
This article was originally published with the title "The Velocimeter–A New Aid in Mechanics"