NAVAL APPARATUS, NEW. 



581 



determining of the distance. Telephonic com- 

 munication is used between the instruments for 

 convenience of adjustment and angling. The 



FIG. 2. POSITION FINDER DIAGRAM. 



accuracy of the range finder is less than one 

 half of 1 per cent, at three thousand yards. 



A mere distance finder does not meet the ne- 

 cessities of a fort, as the men at each gun must 

 know how far the target is from that gun and in 

 what direction, and as it is absolutely necessary 

 to locate and indicate the position not only of 

 one, but of several ships, Lieut. Fiske conceived 

 the idea of the " position finder " as the solu- 

 tion of the problem. One of these instruments 

 is intended to be attached to each group of guns, 

 then these different groups can be concentrated 

 on one ship, or made to fire at different ships, 

 according to the judgment of the commanding 

 officer. In the figure A B represents a line of 

 the defensive work. C, D, E, are guns com- 

 manding the area which includes the position F. 

 The object to be attained is to lay all the guns 

 correctly upon the target, although the persons 

 in charge of the guns may be unable to see the 

 target, and be ignorant of its bearing and dis- 

 tance. G and H are arcs of conducting mate- 

 rial placed symmetrically with respect to a base 

 line, I J. These arcs are located at stations dis- 

 tant from the positions of the guns, and so situ- 

 ated that a view of the area to be protected by 

 the guns will not be cut off from the stations by 

 smoke, points of land, or other obstacles. For 

 this reason it is better that elevated positions 

 should be chosen for the stations. 



K and L are two pivoted telescopes, the free 

 ends of which move over the arcs G and H, and 

 constantly maintain electrical contact therewith. 

 These telescopes may be directed upon the tar- 

 get, which will, therefore, be at the intersection 

 of the two lines of sight of the telescopes. Lo- 

 cated at a station distant both from the guns 

 and from the positions of the arcs G, II , and usu- 

 ally at a place safe from the effects of the ene- 



my's fire, there is established a directing station 

 in which is a chart or map represented by a, b, c, 

 d, and on which are lines drawn to correspond to 

 the parapet of the fort, the base line, etc. K' 

 and L' are pivoted arms similar to the arms K, L, 

 the free ends of which pass over and make con- 

 stant contact with the arcs G' and H'. Extend- 

 ing from the extremities of the arc G' are wires 

 1 and 2, and extending from the pivoted tele- 

 scope K to the pivoted arm K' is a wire 3, which 

 includes a battery ; a galvanometer is also in the 

 circuit. The wires 1, 2, 3, 4, the arcs G, G', the 

 battery, and the galvanometer are connected in 

 circuit in the form of a Wheatstone bridge, and 

 the effect of moving the telescope to the right or 

 left is to increase or decrease the resistance. If 

 the two telescopes be sighted upon the target, 

 and if a third observer moves the arms K' and 

 L', and at the same time watches the galvanome- 

 ters M, M', he will have placed the arms K', L' at 

 precisely the same angles as the telescopes K. L r 

 when both galvanometers show zero reading. 

 Inasmuch as the chart bears a definite propor- 

 tion to the area which includes the position of 

 the target, it follows that if the axes of the arms 

 K', L' be prolonged they will intersect at the posi- 

 tion F', which on the chart would represent the 

 actual position of the target. The latest im- 

 provement in this position indicator, and one 

 which gives less than one third of 1 per cent, 

 error, does away with the chart station and its 

 appendages. The ground over which the bat- 

 teries sweep is delineated on a brass plate, which 

 is fitted inside the tripod of one of the instru- , 

 ments. Over the plate sweeps two pointers, one 



FIG. 3. FISKE POSITION FINDER IN USE. 



of which is moved by the movement of the tele- 

 scope overhead, to w'hich it is parallel, the other 

 pointer is in electrical connection with the second 

 telescope at the other end of the base line. The 

 distance between the pivots of the two telescopes 

 represents the length of the base line, and the 

 pointers the distance from either end of the base 



