[Trade Journal] Publication: The Electrical Engineer New York, NY, United States |
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LIEUT. FISKE'S NEW RANGE FINDER.
THE importance of being able to determine the exact position and range of an object to be fired at, whether from a fort or war vessel, is too obvious to need further exemplification, and hence a ready means of determining this point is evidently of the utmost practical importance in gunnery. As our readers may be aware, Lieut. Bradley A. Fiske, U. S. Navy, has devoted considerable attention to this subject, and has designed a variety of forms of these instruments. His most recent work in this branch is a range finder which embodies a decidedly novel application of the Wheatstone bridge as a means of measuring the angles, and by means of which ranges or distances can be read directly from a scale.
Broadly considered, Lieut. Fiske's latest method consists in determining a fractional portion of a conductor bearing in length a ratio to the angle included between two lines of sight directed upon a distant object, and simultaneously causing a disturbance in an electrical balance, including the conductor in its circuit, proportional to the resistance of the fractional portion, and observing the difference in potential due to the disturbance. The accompanying diagram, Fig. 2, illustrates the simple and ingenious manner in which this is carried out. We will suppose
Let
In the foregoing formula, the base line It will be plain that when the two telescopes It will of course be obvious, that as the angle between the positions It will be clear that by the method just described the operation of finding the range is reduced to a very easy and rapid process, and at the same time, greatly simplified as regards apparatus. Observers stationed at the two telescopes If, however, the angle
Or, in other words, the observer at the galvanometer may simply multiply the range indication by the sin In the foregoing demonstration, it is assumed that the resistance in the circuit remains constant, that is, remains the same as it is when the two telescopes are parallel to each other, and stand in the positions, It is evident that if the high resistance before mentioned be not put in the battery loop, then the decrease in resistance due to change in position of the telescopes from the middle point of their ares toward the extremities of the arcs may bear a considerable ratio to the resistance of the whole circuit. And as this decrease in resistance will be attended by corresponding increase in current strength, it follows that proportionately greater deflections of the galvanometer will follow for any given angle, But it will be observed that if the telescope, In what has been said above, the resistance of the galvanometer has been neglected, and it has been assumed that the E. M. F. and internal resistance of the battery, and the resistance of the various contacts, remain constant. While this is not theoretically true, Lieut. Fiske finds that by using storage batteries and by making the contacts carefully, no appreciable error is introduced. Careful experiments with this range finder at sea, show that the errors of the instrument are insignificant and the indications absolutely instantaneous. Fig. 1 shows the range finder as actually used on shipboard. The instruments are made of aluminum, bronze and iron, and are left exposed on deck without any protection whatever, except that a cover is placed over the telescope when not in use. The instruments require no care except an occasional cleaning. |

Keywords: | Bradley Fiske : Need Image |

Researcher notes: | |

Supplemental information: | |

Researcher: | Bob Stahr |

Date completed: | June 13, 2011 by: Bob Stahr; |